Bullet Profile Biggest Determinant of COAL?

Discussion in 'Reloading' started by xTerpx, Jun 11, 2020.

  1. xTerpx

    xTerpx Preferred Pronouns: (It, Ya'll, Bruh)

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    I have some specific OAL questions, but still digesting lots of info and doing my due diligence to figure this out before I ask for confirmation that I understand it. :)

    However, after sitting here for a couple of days with dimension diagrams of 9mm rounds, calipers, and a smorgasbord of different weights and profile bullets, it seems I was wrong thinking seating is standardized.

    I assumed that no mater the bullet profile, so long as the weight is the same (e.g., 124gr), every bullet, regardless of profile, would have the same amount of material seated in the case and the 'usable cavity' would be the same to standardize pressure across profiles...if that makes sense.

    I assumed that the differences would be in the shape OUTSIDE the case. This isn't true, is it?

    In my tests, were I to load to an OAL of 1.142 as called for in the recipe I am analyzing, roughly ~.150 of a 124gr TCFP would be seated in the case, whereas ~.190 of a similar weighted RN would be seated...holding the OAL constant.

    There isn't some unwritten rule about >25% or whatever % of the bullet must be seated in the case for stability/pressure/whatever reasons?

    I am still working on my question but it has to do with 2 different loads published for two different 124gr bullets, yet there are a dozen or more combinations of plated and coated and truncated and flat point and round point, etc, etc, etc...and both recipes call for the SAME OAL....which got me thinking—no way, can't be. Seating some considerably deeper than others changes pressures, so if creeping up toward maximum load, I could get into trouble trying to seat all these different profiles the same OAL (and toss in the fact my Glock likes shorties and I am getting nervous)...but that's another thread as I research more and gain a better understanding. :)
     
    Last edited: Jun 12, 2020
  2. Taterhead

    Taterhead

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    Well, there's a lot here. Wheels must be turnin'.

    True that the depth of the heel is important for pressures. But not the complete picture. Bearing surface, guilding materials, alloy, lube...

    That being said, you can pretty much skip over all that.

    Cartridges must fit in the mag. Then the other thing to think about is the location of the bullet shoulder and the extent of freebore/throat. COL must be short enough that the shoulder doesn't contact the lands.

    Once that length is determined, do the load workups as usual. A chrony is useful to validate the pressure differences that you alluded to in your post.
     
    Last edited: Jun 12, 2020
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  3. exfed2001

    exfed2001

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    Unlike, say, the 45, the 9 is a tapered case and has case walls that begin to thicken as you go towards the case head. If you load your bullet too deep, it will case the case to expand and may affect chambering.

    In my case, my 147's would work fine in my SIG, but would not chamber properly in my 43. You could see a slight ring in the case about 1/4" back from the mouth. Increasing the OAL just a few thousandths prevented this and caused 100% reliable chambering.
     
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  4. Collo Rosso

    Collo Rosso

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    Taterhead is calling it freebore, I refer to it as the chamber throat. In the chamber you have the rim or step where the case mouth (rim) headspaces. From there to the start of the rifling is the throat or freebore. It determines how deep you seat the bullet so it doesn't engage the rifling before stopping the gun going into battery. That distance determines your O.A.L. along with to long so it doesn't fit in the magazine.
     
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  5. Rick James45

    Rick James45

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    @Taterhead nailed it. For semi auto you have a given of COL that will fit in the magazine. Next, will it function? F2F ect are issues? Then there is the freebore. All 9mm barrels are not created equally. My Gen3 Glocks are very genrouse on freebore. I load to 1.145 for a particular 125 Blue Bullet. It will run in both my stock G3s 9mm and SS 1911s. It absolutely will not run in my Storm Lake G35/G22 9mm barrels. Contacts the lands in a serious way. I have to drop down to 1.120".

    However, that same 1.145" length in a Hornady XTP has no issue in the above due to the shape of the bullet.

    In the .40, for my hicap 1911 (Para's), I have to load at least to 1.165 for reliability. I usually hover around 1.175. This is for 180 FP BlueBullet. These loads will not even come close to fitting a Glock 40 magazine. For I while I searched for a happy medium between the Para 40 and Glock. Never found it. So I essentially have in my mind 2 different calibers when I sit at the bench. 40 for Glock and 40 long for Para. PITA.
     
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  6. Samuel_Hoggson

    Samuel_Hoggson

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    What Taterhead said.

    You've discovered why data differs as a function of bullet ogive, distance from tip to full diameter.

    What really matters is distance from tip to the "major diameter", where bullet first engages rifling (or throat, if bullet diam is > bore diam). That distance will be slightly less than the ogive. http://www.mssblog.com/2018/03/23/reloaders-corner-bullets-101/

    A long ogive necessitates deeper seating/greater powder encroachment by the cylinder below.

    Max COAL is usually set by the magazine, but not necessarily.

    As mentioned there are other variables that will affect pressures (and data) such as material, lubrication, etc.

    Experience teaches us to seek data involving the particular bullet we're loading, and to note the listed COAL. Not to mention stuff like primer, brass mfg, etc.
     
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  7. 9x45

    9x45 Millennium Member

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    It's simpler than that. OAL is bullet specific, whatever it takes to case gage (ammo check) and plunk test (gun check). Assuming you are not over-belling then over-crimping. If it checks at maximum 1.170" for a particular bullet, good, if not, start shortening. I have loaded between 1.175" and down to 1.060" Just depends on the bullet. Now if you shorten it by more than .030", you will need to drop your charge weight to adjust for the smaller case volume. That's usually where a chrono comes in to make sure you can still hit the Minor floor power factor.

    Left 125 gr Montana Gold JHP at 1.175", right 125 gr RN Bear Creek at 1.060"

    [​IMG]
     
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  8. 9x45

    9x45 Millennium Member

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    My standard Minor floor loads, 125 round nose truncated HiTek coated Black and Blue bullet left, 125 truncated hiTek Bayou right. Both at 1.100" over 3.3 grains of TightGroup. Goes about 1,050 fps out of a G17 with OEM barrel.


    [​IMG]
     
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  9. fredj338

    fredj338

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    This is such I diff concept for even experienced reloaders. Bullet & bbl specific. As tater notes, it has to fit the gun, mag & chamber. Fretting over how much bullet is in the case, blah, blah, doesn't really solve the problem if they dont fit the gun.
    Make a dummy round, seat the bullet long then try it in the gun. Keep seating deeper until it firs chamber & mag. That is your oal for that bullet & that bbl only. Check it in other bbbls & seat for the shortest throat. That is the max oal for that bullet in all your guns. Really that simple. As long as you are working the load up with that oal/bullet, gtg. If you switch bulles, process starts over.
    I've run chrono tests starting long & seating 0.010" deeper & retesting. What I found is with midrange & lowervloars, even seating 0.060" deeper doesnt move the vel/pressure needle much. I only tested to powders & two bullet wts in 9mm, but its just something I dont worr about. Nowcif you are working to max loads, yes, then everything matters, oal, case brand, primers, everything.
     
    Last edited: Jun 12, 2020
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  10. sciolist

    sciolist On the Border

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    OAL is measured from bullet tip to rear face of case. Seating depth is determined by the way the seating die interacts with the bullet, which is not necessarily at the tip, and varies with profile.

    Your ammo needs to run in the mag, in the gun, and accomplish the desired ballistic results. For practical pistol, it's really not rocket science.

    My experience has been that 9mm bullets tend to group better if they are loaded toward the long end of what will chamber. Most of my stuff is 147, though - with some 124/5 for steel.

    So for my purposes, there wouldn't ever be any reason to load below 1.130 or above 1.150. If you have a very restrictive barrel, like maybe a CZ, that would be a consideration. But seems like the solution there would be to have the barrel reamed.

    There's definitely variation between different guns in terms of what ammo they will accept. But I'm not interested in having a big science project with ammo. And it's not difficult to come up with something that will work well across a range of guns.
     
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  11. 9x45

    9x45 Millennium Member

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    It's even easier for me because I have six G17's......
     
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  12. ironhead7544

    ironhead7544

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    Every handload you make is an experiment.

    The 1.142 COL is shown for a number of loads in the VV load data for the 9mm. This works fine for the 147 gr XTP bullet. But for the shorter XTP bullets there is not enough bullet in the case, IMHO. Check what Hornady shows.

    fredj338 is right about COL. Set it up to fit all of your firearms in that caliber.
     
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  13. Taterhead

    Taterhead

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    Setting up a single COL to fit all firearms is ideal. That being said, there are examples where that doesn't work. E.g. one gun needs a VERY short COL to plunk. Another won't feed smoothly that short. Likes longer for shallower tipping angle, or it gets misfeeds.

    So there are exceptions to the rule.
     
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  14. xTerpx

    xTerpx Preferred Pronouns: (It, Ya'll, Bruh)

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    Yes, sir. That's exactly what got me thinking. I have 3-4 different 124gr bullets from a few different manufacturers and was looking at the VV load data and researching to figure out how best to select the right recipe without getting into trouble. :)

    VV shows 3 loads for 124gr sitting on top of N320 and all had the same OAL (and I assume this is a minimum value at the upper end of the load?), I said no problemo...but after I got some adult beverages in me and the calipers out, I noticed different 'lengths' of the bullet and that some will be seated further in the case than others and thought that can't be right.

    I had to take a science in college and took geology for the easy A (got a B-) and not physics, but assumed there must be a certain amount of the bullet engaged with the side of the case for stability/friction to keep it stable (not wobbly...say .15 has to be inside the case) and have a consistent release and consistent speed of pressure buildup or something or other. lol



    Thanks for all the info, guys...truly appreciate it. I'll take all this in and regroup. To me, this is the most important part of the process, so need to have a total command of these concepts before I pull the handle. It just didn't seem right some would be materially deeper in the case than other bullets of a similar weight purely as a function of their shape.
     
  15. xTerpx

    xTerpx Preferred Pronouns: (It, Ya'll, Bruh)

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    Yes, sir. That all makes sense to me now, since I ran into this issue with an early G19..."short throat" and freebore and plunking were foreign to me up until I ran into problems...believe the line on the bullet below is precisely what you are referring to, right? Contacting the lands there and scoring it trying to spin while in the chamber? (And assuming the gouge out of the mouth is a bad 'crimp'/didn't fully remove the bell? It feels really pronounced there, but wasn't sure if it's because the walls are thicker in the nickel-plated.)

    plunk.jpg


    [edit: put that old round on the calipers and measured 1.102...and still hit the lands?!?]
     
    Last edited: Jun 12, 2020
  16. Taterhead

    Taterhead

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    If it isn't plunking, keep shortening it. Then do your workups.

    The missing chunk on the nickel rim is probably not crimp induced. Probably smacked something in a prior firing.

    It does look like you could further close the case mouth with a touch more crimp.
     
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  17. sig357fan

    sig357fan

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    I always try to load to the longest COL that functions through a particular firearm.

    a pretty simple way to determine max COL for any case/bullet combination is to make up a dummy round loading the bullet too long and record the COL, do the plunk test and measure how much of the case sticks out past the barrel hood, subtract that measurement from the too long COL and that should be the max COL with that case/bullet combination for that chamber.

    then make up a couple dummies to that COL and check for function from the mag by hand cycling, if they cycle from the mag you'll still need to shorten them up so as to not be hitting the rifling/chamber throat/free bore.

    if they FTF, shorten the COL until you get function and that is the max COL for that case/bullet/chamber/magazine combination, than compare that COL to the manufacturers specified COL, if your over that. look at how much of the bullet is in the case and decide if you need to set it deeper, if it too short you may not want to use that bullet.
     
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  18. unclebob

    unclebob DFC, MSM, 12 Air Medals.

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    Take the barrel out of the gun. Drop a bullet in the barrel and then using your calipers measure from the hood to the base of the bullet. Is the measurement more or less than .754? If it is more than you can use any COL you want. If it is less than you need to shorten your COL for that combination of barrel and that make, style, weight, bullet
    I don't think you have stated what power and amount of powder you are using. Unless you are loading max or close to max you can be more flexible in what your measurements can be.
    Since it looks like you need to crimp more, I would suggest you get a case gauge and set your crimp using the gauge.You are only removing the bell you put on the case, you are not crimping the case into the bullet. The size of the bullet, case being used, the die being used, even when in the production of the die being built, dictates the amount of grip is being used on the bullet.
    Just in 9mm I have to get the same bullet and amount of powder, COL to work in a G43X, 2 G26, G19, 3 G17 one with a Wolf barrel, G34, and a G 24 with a KKM 40/9mm barrel. I also had a G43 and a 92F that I sold.
     
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  19. xTerpx

    xTerpx Preferred Pronouns: (It, Ya'll, Bruh)

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    Yes, sir...saw a post of yours from a decade ago about this and was on the list of things to do today...got sidetracked with some case gauge/short case theory. :)

    I'll do this today for sure, especially on a couple other Glocks that gave me problems.


    It's a factory HST (never shot) that I put aside when I first ran into problems with an early G19.5....measures 1.102 and still hit the lands/difficult to spin.

    Yea, I definitely feel more of the case mouth around the bullet on the HSTs vs plain ol' AE 124gr range ammo...had boxes of them out with those adult beverages and calipers at 3am last night. :)

    IMG_0570.PNG
     
  20. xTerpx

    xTerpx Preferred Pronouns: (It, Ya'll, Bruh)

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    Will do...creating dummies seems to be a common theme, so will definitely do this. Thanks.

    ...to follow-up with one of my over-analyzed questions. :)

    I took some time to watch videos explaining ogive and measuring and basic ogive theory, but I am wondering:

    • No matter what shape of the bullet, the material between the ogive and the mouth of the case, more or less, would have the same circumference (.355 or .356, for example for my 9mm rounds) and it is ONLY between the ogive and mouth that a bullet will touch the lands?

    Does that make sense? So a round nose, having more 'girth' (or less taper?), per se, toward the tip than a TC, would still only touch the lands between the ogive and the case mouth, correct?