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Old 02-10-2013, 23:39   #76
Any Cal.
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Quote:
Originally Posted by TDC20 View Post
Shadow, I think that is absolutely a possibility. I would think that a locking block would break while the barrel was smacking it traveling back towards the shooter in recoil. If that is the case, then the broken locking block would allow the barrel+slide to remain locked longer than necessary. This would cause the normal locked dwell time to increase, not decrease, so that would actually make a KB less likely on that round. On the next round, if it chambered for firing, the barrel+slide might not be fully locked in the normal forward position, reducing the travel of the locked slide+barrel. For a typical handloaded hot 180 XTP at 1200fps, if the normal unlocking travel were reduced from .210" to .070", that would most definitely cause a KB! See explanation below....

Physics: It's not just a good idea, it's the law!

OK, I've been wanting to do this for some time now, but never sat down and took the time to do it. But what I've done is to create a spreadsheet to do some calculations on barrel-slide lock time, pressure, slide velocity, etc. Based on a realistic velocity for firing a 180XTP from a G29, and some assumptions that I've made below, I've checked my numbers a couple of different ways, and I'm 99% sure they're OK. It took a while to figure out how to work the math using the English (pounds, feet, etc.) system. The SI system (MKS) is so much simpler!

Assumptions:
- Glock 29
- Barrel weight (weighed) 4.0 Oz. (0.25lb)
- Slide weight (weighed) 15.6 Oz. (0.975lb)
- Slide + barrel (locked) 19.6 oz. (1.225 lbs)
- 180gr. XTP fired at 1200fps plus 10gr. of powder(hot, don't try this without working up)
- Slide travel before barrel unlocks from slide (measured) 0.210"
- Spring force 17lbs
- Linear acceleration ***
- Distance bullet traverses barrel 3.145" (measured from where a 180 XTP would be positioned in the 3.77" barrel in chamber when shot is fired)
- Conservation of momentum, M1*V1 = M2*V2, where "1" is bullet and "2" is barrel + slide
- Neglecting slide friction and small amount of momentum transferred to the shooter in the first 500 us of shot initiation (time it takes to get the bullet out the bore).
- Neglecting force of "jet effect" of combustion gasses leaving the barrel after the bullet has cleared the muzzle.

*** The assumption of linear acceleration here is totally bogus, but it does fit within the use of the conservation of momentum equation. The problem with figuring actual time-based acceleration is having a precise pressure curve, then knowing what the force of barrel friction + bullet obturation is. This is still going to require some assumptions, because you can't precisely measure the time vs. pressure curve with load cells. A properly calibrated piezo could (could meaning "properly calibrated" and applied) get you very close. However, we can precisely determine what the velocity of the bullet is when it leaves the barrel, so that is what the spreadsheet is based on. The best method, IMO, would be to attach an accelerometer to the slide. Then you would know exactly how the slide velocity changes as the bullet traverses the barrel.

So what I did in my spreadsheet is to calculate, based on linear acceleration (assumption is a constant force is applied the bullet and powder mass to move them down the barrel). The counter-force to this acceleration must be an equal and opposite force applied by the system of the locked barrel-slide combo and the recoil spring. The resulting force in both directions turns out to be appx. 2320 lbs., and the bullet would leave the barrel appx. 437 microseconds after this force was applied.

In order for unlock to occur while gas pressure was still in the barrel (i.e., bullet has not left the barrel), the slide-barrel combo would have to travel the 0.210" backwards into the unlock point (locking block) faster than the bullet can traverse the barrel. Applying 2303 lbs of force to the 1.225 lb mass of the barrel + slide, the time it would take to reach the unlock point under 2303 lbs of force (subtracting the 17lb spring force) would be 761 microseconds. If I assume that the opposing forces are terminated as the bullet leaves the barrel at 437 us (neglecting gas jet effect), then my numbers for momentum are exactly balanced.

Here's some interesting observations from this exercise:
- Calculated slide velocity is 26.4 fps
- Changing the spring from 17lbs to 22lbs only changes slide velocity by 0.06 fps. (note that a 22lb spring will decelerate the slide motion much more quickly than a 17lb spring, that's really the only benefit to extra spring force)
- Reducing the slide mass by one ounce increases the slide velocity by 1.42 fps.
- Increasing spring force is not going to significantly delay unlock time. Completely removing the spring in this system makes almost zero difference in unlock time. No spring at all would not cause a KB.
- Mass is critical to control slide velocity, but it takes a huge reduction in slide mass for unlock to occur early. The normal barrel + mass of 19.6 Oz, all other factors held the same, would have to be reduced to appx. 6.5 Oz for KB to occur (assuming this "normal ammo" pressure)
- Slide travel to unlock is critical. In this case, all other things held equal, KB would occur if the distance was shortened from 0.210 to about 0.070" (could the KB round have fired somewhat out of battery/incomplete lock-up?)

I tried all kinds of practical changes to the system to induce an unlock condition, and I couldnt, even at 100,000 psi. Of course, I did make some assumptions on pressure-time curve, and neglected the "jet-effect" of gasses continuing to exert force on the barrel-slide combo.

So, I'm not claiming to be a gun expert, and I certainly could have made errors in my assumptions, especially with the linear acceleration, but it seems to me that the system is designed to never unlock under practical conditions, regardless of the chamber pressure.

OK, flame proof suit is on, fire away!
Oh Awesome!

1911 Tuner always said that a recoil spring made no difference in the recoil operated system of a 1911 and by extension, a Glock. I have been waiting a very long time for someone who knows the formulas to run out the problem.

Thank you.
Thank you.
Thank you.
Thank you.
Thank you.

I don't have any reason to flame you, similar specs have been mentioned by other people in other times. Having some kind of numbers specific to a Glock does help to make ideas that were somewhat unbounded considerably more concrete.

Thanks again.

Last edited by Any Cal.; 02-11-2013 at 00:01..
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Old 02-11-2013, 05:52   #77
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Originally Posted by Any Cal. View Post
Oh Awesome!

1911 Tuner always said that a recoil spring made no difference in the recoil operated system of a 1911 and by extension, a Glock. I have been waiting a very long time for someone who knows the formulas to run out the problem.
Thank you.
Thank you.
Thank you.
Thank you.
Thank you.
Quote:
Originally Posted by TDC20 View Post
...
Assumptions:
...
- Slide travel before barrel unlocks from slide (measured) 0.210"
- Spring force 17lbs
...
- Changing the spring from 17lbs to 22lbs only changes slide velocity by 0.06 fps. (note that a 22lb spring will decelerate the slide motion much more quickly than a 17lb spring...
Any Cal, I think what TDC20 is sayin is that:

(1) "Changing the spring from 17lbs to 22lbs only changes slide velocity by 0.06 fps" during the first 0.210-inches of slide travel, but

(2) "a 22lb spring will decelerate the slide motion much more quickly than a 17lb spring" after that.

So, the strength of the recoil spring makes a big difference in the process, but just not in the first 1/5th of an inch in rearward travel of the slide.

Last edited by MarineHawk; 02-11-2013 at 06:01..
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Old 02-11-2013, 08:33   #78
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Remember that the spring's force = 0.5 * k * square(distance) plus mfg rated force.

So at zero distance, it is just 17 lbs or 23lbs, not much against the explosion. But as distance increases, force goes up by half of the distance squared. That goes up by the law of exponential squared. for practical purpose of early unlock, assumption of mfg rating and linear behavior is close enough.

Now, turn to the issue of "nearly" in battery, a strong spring would regenerate enough velocity and force from recoil, to slam it into full battery a little more authoritatively. Right?

Causes for short of full battery that I've seen are:
- Too long OAL.
- dirty gun, too much friction or impeding of slide action (case sliding into extractor not smooth)
- primer not fully seated.

I'm sure there's more, like improper dimension barrels. But in my experience, all of my current 10mm barrels, KKM and SLake, impart no dent on the frames. I did sell another mfgr's barrel because it wasn't reliable in slide action.


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Old 02-11-2013, 08:55   #79
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I applaud the sensible application of physics that has been used here. It's been a few years since my last physics class, but from what I can remember the math looks sound. We have to remember (and TDC20 recognized this himself) that we are making a lot of assumptions when trying to deal with this problem.

That said, how do we explain the extreme velocity spread that many have reported when shooting high powered ammo with the stock spring that is significantly reduced when switching to an aftermarket 22+ pound spring?

If it is true that running an aftermarket spring greatly reduces velocity spreads when shooting high powered ammo, then we could reasonably infer that the barrel is staying locked up for a longer period of time before unlocking.

That would then lead us to ask how this could happen, in spite of the mathematical evidence we have been shown to the contrary? I would postulate that either: (1) there are significant variables that we are not accounting for; or (2) there are variables that have not been correctly represented.

A big problem that I can see is that while we're talking about a 17lb stock spring vs. 22+ lb. aftermarket spring we do not know all of the important specifications of these springs. Are these the true spring weights? Are there overall length differences between these springs? What is the actual amount of force being placed on the slide while at rest (pre-load)?

I don't have an answer these questions, but I do think that in light of some evidence we have that contradicts our current mathematical findings maybe we need to take a deeper look before concluding that different springs do not significantly alter lockup time/characteristics.
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Old 02-11-2013, 11:22   #80
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I should have been a bit more clear. I wasn't saying that a recoil spring didn't do ANYTHING, but that it didn't do anything significant as far as increasing lockup. I realize that the extra poundage will do something at some point, and didn't mean to say otherwise.

The main point Tuner hammered on was that it was a slide return spring, and its main function was to return the slide to battery, and keep it in battery during normal usage. You will see this in the gamer's guns when they run too light a spring with a normal or heavy striker spring, and pulling the trigger pulls the gun out of battery.

---------------

I think the idea of velocity swings changing with recoil spring is a myth, regardless of the fact that the guy from Buffalo Bore really believes it. So far I have seen two cases where it should have shown itself, and it didn't do so in either case. What would be needed is someone who understood statistics AND internal ballistics to run some tests that would actually show something, rather than some nearly random guy claiming it works that way.
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Old 02-11-2013, 14:54   #81
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Originally Posted by ModGlock17 View Post
Remember that the spring's force = 0.5 * k * square(distance) plus mfg rated force.

So at zero distance, it is just 17 lbs or 23lbs, not much against the explosion. But as distance increases, force goes up by half of the distance squared. That goes up by the law of exponential squared. for practical purpose of early unlock, assumption of mfg rating and linear behavior is close enough.

Now, turn to the issue of "nearly" in battery, a strong spring would regenerate enough velocity and force from recoil, to slam it into full battery a little more authoritatively. Right?

Causes for short of full battery that I've seen are:
- Too long OAL.
- dirty gun, too much friction or impeding of slide action (case sliding into extractor not smooth)
- primer not fully seated.

I'm sure there's more, like improper dimension barrels. But in my experience, all of my current 10mm barrels, KKM and SLake, impart no dent on the frames. I did sell another mfgr's barrel because it wasn't reliable in slide action.


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Spring specs seem to vary, but in general the rated weight in Glock springs is the spring force at full compression, not the installed length.
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Old 02-11-2013, 16:01   #82
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Originally Posted by Any Cal. View Post
Spring specs seem to vary, but in general the rated weight in Glock springs is the spring force at full compression, not the installed length.
Then it is far less than 17lbs or 23lbs at full battery. And it would be a bit more involved to understand the actual force at full battery on a stock spring vs. a replacement spring (perhaps even a variable or torsional spring). Such data never got quoted to compare and we replace them at will.
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Old 02-11-2013, 17:03   #83
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so answer me this... I don't understand all the timing stuff of unlocking the slide etc.. but is it better to have a heavier spring with hotter loads or a stock spring okay? I have some 165 underwood ammo... should I get a heavier spring in my G29 before i shoot them?
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Old 02-11-2013, 19:10   #84
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cablecutter, I changed to the Wolff Gun Springs, non-captive two piece recoil rod with 21 lb dual spring set, this has worked very well for all the loads I've run thru mine to date. Many loads matching Underwod's line up. also switching to a 40S&W, 357Sig or 9x25Dillon conversion barrels no problem cycling the any of them using this RSA.

Do you need the heavier springs maybe not, but if you see the slide over running the ammo during feeding you may want to consider the extra power springs.
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Old 02-11-2013, 21:52   #85
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Thanks for the reply shadow! You are always good at answering my questions!


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Old 02-11-2013, 22:36   #86
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The extra power spring will reduce the time available for ammo to feed, as it increases slide speed on the return. The stock spring comes back fast, and goes forward slowly, allowing the ammo to rise in the mag. If you are 'overrunning' the ammo in the mag, it is because the extra power recoil spring. You can see the difference in slow mo quite easily.
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Old 02-11-2013, 22:57   #87
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Originally Posted by Any Cal. View Post
The extra power spring will reduce the time available for ammo to feed, as it increases slide speed on the return. The stock spring comes back fast, and goes forward slowly, allowing the ammo to rise in the mag. If you are 'overrunning' the ammo in the mag, it is because the extra power recoil spring. You can see the difference in slow mo quite easily.
That is exactly the problem I've had with heavier spring weights and hot ammo. Nose-up FTFs. No such problems with the factory spring.
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Old 02-12-2013, 01:37   #88
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Originally Posted by ModGlock17 View Post
Remember that the spring's force = 0.5 * k * square(distance) plus mfg rated force.
Yes, you are correct, it's called Hooke's law. I ignored it for this calculation due to the small amount of distance the slide has to travel, so the spring force remains relatively unchanged.

Quote:
Originally Posted by ModGlock17 View Post
Now, turn to the issue of "nearly" in battery, a strong spring would regenerate enough velocity and force from recoil, to slam it into full battery a little more authoritatively. Right?
This would seem to be true, especially if the slide were to travel full length in recoil (which I believe it has to for reliable cycling). Upon slide return to battery, beginning at the physical slide stop, the heavier weight spring is going to accelerate the slide faster than a lighter weight spring, so the final velocity of the slide when it reaches full battery will be higher. I'm not sure how important this is, but it would seem that if there were any friction/dirt/ammo tolerance issues impeding full lock up, that a heavier spring would certainly help overcome that.

The other benefit to the heavier spring, and the one that applies most to those of us who shoot hot ammo, is that the slide velocity will be lower when the slide reaches the physical stop at the end of recoil. This means less battering of your frame.

I admit, I used to believe that the heavier spring helped maintain lock up, but I no longer believe that. I'm more inclined to believe the numbers.

Quote:
Originally Posted by Any Cal.
Spring specs seem to vary, but in general the rated weight in Glock springs is the spring force at full compression, not the installed length.
I checked my G29 with the stock spring, and this is true. It only takes about 5.5lbs of force to start the slide moving from full battery, but about 19lbs of force just before the slide hits the slide stop limits. I also checked my G20 with a Wolff 22lb spring, and it too starts to move from full battery around 5.5lbs, with right at 22lbs near the stop limit. I don't have a very good way to measure this, I used a baby scale that measures to the nearest 0.1 ounce. But it was repeatable.

So, my initial assumption was incorrect that the slide and barrel were working against a 17-22lb opposing force. It's more like 5-7lbs of force. Fortunately, it makes so little difference since it's working against an accelerating force of 2320 lbs, that for practical purposes, it can be ignored. So it doesn't affect the original numbers. But for the non-believers, this also disproves any possible benefit that an extra weight spring might have on lock up timing. There just isn't that much difference in spring force between a 17 and 22 lb spring in that first .210" of travel.
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Old 02-12-2013, 02:04   #89
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That said, how do we explain the extreme velocity spread that many have reported when shooting high powered ammo with the stock spring that is significantly reduced when switching to an aftermarket 22+ pound spring?

If it is true that running an aftermarket spring greatly reduces velocity spreads when shooting high powered ammo, then we could reasonably infer that the barrel is staying locked up for a longer period of time before unlocking.

That would then lead us to ask how this could happen, in spite of the mathematical evidence we have been shown to the contrary? I would postulate that either: (1) there are significant variables that we are not accounting for; or (2) there are variables that have not been correctly represented.
RMM, I can't give any explanation as to why this is true. The bullet should be out of the barrel before any significant difference in spring weight plays into it. In any case, the mass of the slide and barrel should create almost 400 times more resisting force due to acceleration from the initial recoil force than the spring does.

I have done most of my load work with a G20 and 22lb spring, so maybe next time I'm at the range with my chrono, I'll try the stock 17 lb spring and see how the data compares. Was the data all taken on the same day with the same ammo, with every powder charge hand weighed, consistent reloading technique with attention to details, and measured over the same chrono?

The other thing I can't explain is that some people have insisted that they get glock smiles with lighter springs and not with heavier springs, using the same ammo. If that's true then there is something definitely wrong with my basic assumptions. We probably need some time to see whether all of this holds water or not. I'm pretty sure it will.
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Old 02-12-2013, 02:10   #90
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The extra power spring will reduce the time available for ammo to feed, as it increases slide speed on the return. The stock spring comes back fast, and goes forward slowly, allowing the ammo to rise in the mag. If you are 'overrunning' the ammo in the mag, it is because the extra power recoil spring. You can see the difference in slow mo quite easily.
AnyCal, if you have a link to a slow mo video of this phenomenon, please send it to me or post it. I'm very interested in seeing this.

Also, has anyone ever tried to keep the action closed on a Glock during firing by applying pressure to the back of the slide? I seem to remember someone mentioning this on GT, that you could keep the slide locked simply by pressing your thumb against the back of the slide. I'm calling BS on this, unless someone can say that they actually did it. I think your thumb would be broken or very sore if you tried it.
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Old 02-12-2013, 10:36   #91
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I appreciate all of the great comments and thoughts in this thread.

TDC20, I hope that you didn't misunderstand my intentions. I am not trying to be argumentative, I was simply offering an alternative theory/explanation. Thank you for putting in so much work into this. Being from a scientific background, I am also inclined to "believe the numbers". However, experience has taught me that sometimes there are things that just don't work quite the way we think they do. This may be one of those cases. If the results we're seeing don't match up with the numbers, then we're missing something. The problem is, I'm not sure that we have established yet whether or not changing recoil springs really affects velocity spreads, or increases brass smileys. Unfortunately I am relying heavily on others' anecdotal experiences, not on concrete, reproducible data.

In order to make a valid comparison, we need to do some experiments with the same gun, same shooter, same ammo, on the same day. We need to limit our changes to the recoil spring only and eliminate all of the other variables.

Unfortunately at the moment I am locked away in a law school library and don't have access to a chronograph so I won't be of much help.
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Old 02-12-2013, 15:48   #92
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on the lighter side...

Wow...a lot of thought has gone into this discussion....very deep and intelligent thinking...

Now for levity....I swear, on my hand where the injury is, my right hand which rested on the frame right where the mag release blew out....there is a reverse imprint in purple...dried blood under the skin(which will disappear as the healing progresses) of Made in Austria....blasted/burned into my skin!!!!

No need for a picture....I can barely make it out in bright light...but it is there!!!! Somehow the blast used the letters as a focal point....

Now, let the physics slide rule folks figure this one out!!!

Nah....nevermind. Just happy to be able to have some fun with this!!!!!


ed
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Old 02-12-2013, 15:50   #93
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Now for levity....I swear, on my hand where the injury is, my right hand which rested on the frame right where the mag release blew out....there is a reverse imprint in purple...dried blood under the skin(which will disappear as the healing progresses) of Made in Austria....blasted/burned into my skin!!!!

No need for a picture....I can barely make it out in bright light...but it is there!!!! Somehow the blast used the letters as a focal point....
HAHAHA!!! Wow... i mean, that is funny. HA!
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Old 02-12-2013, 16:12   #94
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AnyCal, if you have a link to a slow mo video of this phenomenon, please send it to me or post it. I'm very interested in seeing this.

Also, has anyone ever tried to keep the action closed on a Glock during firing by applying pressure to the back of the slide? I seem to remember someone mentioning this on GT, that you could keep the slide locked simply by pressing your thumb against the back of the slide. I'm calling BS on this, unless someone can say that they actually did it. I think your thumb would be broken or very sore if you tried it.


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Old 02-12-2013, 17:07   #95
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Big difference between 1911 and Glocks! Although both are blow back designs, drag from hammer and hammer spring to lock up with swing link as compared to surfaces and angles to bring the barrel an slides in to lockup...inother words slighly different setups!
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Old 02-12-2013, 18:25   #96
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Big difference between 1911 and Glocks! Although both are blow back designs, drag from hammer and hammer spring to lock up with swing link as compared to surfaces and angles to bring the barrel an slides in to lockup...inother words slighly different setups!
There is very little difference between 1911s and Glocks in their operation. Neither are blow back designs, they are both a short recoil operated design. The locking block on the Glock works exactly like the barrel link in the 1911,(disengages the barrel from slide), and the barrel hood on the Glock works exactly like the barrel lugs on the 1911,(locks slide to barrel).

The Glock doesn't have a hammer, but it doesn't have much to do with the lockup anyway. The hammer spring does provide additional resistance to the movement of the slide, but once again, this is more relevant to slide movement than lockup.
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Old 02-12-2013, 18:28   #97
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Originally Posted by TDC20 View Post
AnyCal, if you have a link to a slow mo video of this phenomenon, please send it to me or post it. I'm very interested in seeing this.

Also, has anyone ever tried to keep the action closed on a Glock during firing by applying pressure to the back of the slide? I seem to remember someone mentioning this on GT, that you could keep the slide locked simply by pressing your thumb against the back of the slide. I'm calling BS on this, unless someone can say that they actually did it. I think your thumb would be broken or very sore if you tried it.
I watched the slo mo. I agree that the low force spring gives more time, and the high force spring gives less time in the slide action.

But I disagree with the notion that the high force spring DOES NOT give ENOUGH time for the slide to load the next round. The slo mo does not give us evidence to say that the high force spring does not give ADEQUATE time. Less time ? Yes. But perhaps it was adequate to load the next round.

We need different evidence to conclude a high force spring gives inadequate time to load the next round.

EDIT: the high force spring being the 18lbs on the video for this 1911. Of course, a 50lbs spring would not load a round, but that is not what the spring mfgr is selling. Translate to G29, the max spring is 23lbs. In other words, I trust that Wolf spring knows the 23lbs for G29 would still adequately load the next 10mm round. It's been in the market for years. (but stranger things have happened).

Regarding pressure to keep slide close, I remember a redneck Gentlemen in my CCW class came to class with a nearly healed wounded hand. When asked how it happened, he told the class that he didn't know enough to wrap his hand below the slide. I never forget how humbled and honest he was and how sorry I felt for him.

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Old 02-12-2013, 20:19   #98
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Then it is far less than 17lbs or 23lbs at full battery. And it would be a bit more involved to understand the actual force at full battery on a stock spring vs. a replacement spring (perhaps even a variable or torsional spring). Such data never got quoted to compare and we replace them at will.
In doing my spring measurements, I found that in the G20/21 pistols, when the slide is all the way to the rear, the recoil spring is very close to full compression. Not all the way, but enough to make the approximation that full compression force is pretty much equal to the force when the slide contacts the spring.

Here's an image of my spring testing. Hopefully some of you will be as disturbed about this as I was. Note the chart of the ISMI 17# spring (slightly heavier than a new Glock stock spring), and then notice how the 20# and 24# springs are only marginally heavier than the 17#? (Again, the high load numbers are at almost full compression; the only way those 24# springs would yield 24# is if they were compressed all the way, and pushed some more.)

I have not tested any Wolff springs; I've heard they are closer to the rated weight but they don't work in a long slide.

The 10 Ring

Edit: the "dual spring" that gave the 28.5# result is one of those Sprinco-type "recoil reducing" guide rods, with a small inner spring supplementing the main recoil spring.

Last edited by Yondering; 02-12-2013 at 20:22..
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Old 02-12-2013, 20:27   #99
Yondering
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Originally Posted by TDC20 View Post
Also, has anyone ever tried to keep the action closed on a Glock during firing by applying pressure to the back of the slide?
Yes. Not with my thumb, but with the heel of my left hand. It's not difficult, and isn't likely to hurt you. It doesn't take much to keep it from cycling. You can do the same by wrapping your hand around the front half of the slide and frame (like in a self defense situation).

Any Cal is correct that these are recoil operated locked breech actions, not blow back, but you can do the same with a blow back action as well. (I've tried it in a 45 blowback, but not a 10mm.)

With my suppressed .22 pistol also, I sometimes hold the slide closed with my left thumb to make the shot quieter.
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Old 02-12-2013, 21:57   #100
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Originally Posted by Any Cal. View Post
There is very little difference between 1911s and Glocks in their operation. Neither are blow back designs, they are both a short recoil operated design. The locking block on the Glock works exactly like the barrel link in the 1911,(disengages the barrel from slide), and the barrel hood on the Glock works exactly like the barrel lugs on the 1911,(locks slide to barrel).

The Glock doesn't have a hammer, but it doesn't have much to do with the lockup anyway. The hammer spring does provide additional resistance to the movement of the slide, but once again, this is more relevant to slide movement than lockup.
Different wording for basicly the same operation...some use either to describe the action of the forces acting on the slide's breech face to drive the slide and barrel back from the locked condition. SORRY! Not trying to be argumentive.

Here is where I do see a difference in my setup with a Glock-29...
I use the Wolff Gun Springs non-captive two piece recoil rod and matching 21 lbs springs. I would venture to say that the non-captive spring generates slightly more spring pressure than a captive stock unit in the locked position...Why do I say this? Because I have to compress the recoil springs to get them inside the notched pearch on the barrel lug.

Now the question for those who rattle off numbers and stuff...Does this increase the dwell time holding the barrel and slide locked? Keep in mind this does increase the amount of force needed to rack the slide, therefore it is more force than the stock captive system. No I haven't measured the differences but someday I just might.

If it takes more energy for me to pull the slide rearward, then it must be working to hold it closed a little tighter than the stock arrangement. Does this hold the slide and barrel in lock for more time? I say yes! Why? Every action has and equal and opposite reaction!

I agree that the maximium spring poundage is seen at the full compression. These dual springs tend to stack their poundage faster being shorter than that of the longer G-20 units. I think the newer Gen 4 G-20's are now using a dual spring arrangement.

BTW, the S&W1006 uses a non-captive spring system and it takes quite a bit of compression to get that spring inside the notch on the barrel lug. This is a great deal of pressure being applied to hold it into battery, and it too needs to be over come to break the locking arangement of the slide and barrels as it is cammed downward out of lock. (If you loose control of the recoil rod and spring during instalation, it will fly for quite some distance or force.)

I not a 1911 guy, but it is my understanding that the the recocking of the hammer against its mainspring, works to add drag to the slide to help control the slide velocity more so than the recoil spring in its action, with the recoil spring providing the slide return. ???
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