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Pressure question

Discussion in '10mm Reloading Forum' started by AMSting, Jan 1, 2013.

  1. AMSting


    Oct 1, 2011
    I have been reading a lot about pressure and what signs to watch for. That got me to thinking about aftermarket barrels. Everyone here says to watch out when using full power loads in a stock barrel, and to be careful of "glock smilies". Some say they went to an aftermarket barrel and the pressure signs disappeared. That may be the case, but the pressure itself did not disappear. If you have high enough pressure to cause a smilie, going to an aftermarket barrel with better support may make the signs disappear, but the pressure is still there.

    So this leads to my main question. What do the SAAMI specs really mean? If they use a test barrel, how does that relate to the factory barrels and what pressures are safe to use? If I go to an aftermarket barrel and keep working up a load, the first time I may see pressure signs is when the back of the case explodes, so how is that any better then using the stock barrel to see the signs earlier?
  2. Any Cal.

    Any Cal.

    Oct 27, 2008
    That is pretty much the gist of it. An AM barrel masks pressure signs, but doesn't change anything. The small advantage is that slightly overpressure loads can be fired without damage to the gun, but yes, it is also getting rid if one safety feature. Saami is what the guns and barrels are built to, along with a margin. I ran the numbers on 10mm barrels and burst pressure, and see how far into'the margin you run when you blow past saami specs... it is really not pretty. The only saving grace is that it is somewhat difficult to build extremely high pressues when it is not a fully closed system. If anything goes wrong though, hotter loads in the am barrel will be MUCH higher pressure than loads in the stock barrel. Running at the top edge of a powders pressure curve may not hurt anything, until you get a bore obstruction, or an oversized bullet, over length brass, etc... then you get a90kpsi explosion rather than a 40kpsi case blowout.

  3. HunterLee


    Dec 18, 2012
    Some of the earlier Glock barrels for .40 S&W and 10mm had poor case head support so that would lead to case bulges.
    As I understand it this was corrected in Gen 3 Glocks but also may include Gen 2 barrels as well but I am not well versed on the Gen 2 vs Gen 3 barrels in 40 and 10.
  4. AMSting


    Oct 1, 2011
    So is there a way to correlate brass deformation with pressure? From what I have read here, having a smilie typically means you are at or above the max loading for a particular powder. That means you are at or above SAAMI pressure. Is brass for a particular caliber made such that it won't deform under the max pressure, so if you see deformation your pressure is too high?
  5. blastfact


    Aug 15, 2011

    Honestly,,, we all read our brass and primers. Glocked brass. Really does not tell us anything about pressure. Tells me it's a crap chamber if it's bulged. I've seen new retail ammo bought and shot in 9mm, .40 Smith and .45 ACP Glock's and it's came out bulged in this persons pistol and fine in his buddy's pistol. Same retail ammo. Go figure.

    I find reading primers gives me more insight than brass. Esp. primers struck with a Glock firing pin.
  6. AMSting


    Oct 1, 2011

    So now I am rethinking whether an aftermarket barrel is a bad idea in working up a load. I would assume the test barrel provides a fully supported chamber, so brass deformation would never really be anything they would see. I think it would just make it more difficult, and could hide a lot of the early pressure signs.

    I do watch my primers as well. They seem more difficult to read though. There are degrees of flattening, and I cannot find any true measure of how much flattening is the upper limit. Maybe my stock G20 Gen 3 barrel is a good choice after all. I can certainly read bulged brass better than flattened primers.
  7. Any Cal.

    Any Cal.

    Oct 27, 2008
    Bulged brass really isn't a problem, except that it shortens brass life. The cost of an aftermarket barrel buys a LOT of brass. I found a Gen 3 barrel to smile, which ruins the brass with a sharp line, right around or above max book loads, which would have been right around max pressure. Doesn't seem to be a problem if you don't mind sticking to safe reloading practices, and you get the benefit of the excellent reliability Glocks are known for. This makes sense, the manufacturer needs enough case support for spec loads, but beyond that the larger chamber helps reliability, so why tighten it up?

    I did end up buying an aftermarket barrel for added length and to run a compensator, and was squeamish when I realized that I could run the pressure higher without the same signs. If you get a kB in a stock barrel, it smacks your hand, dumps the mag, and cracks the frame. What happens when the case support allows pressure to build much higher before releasing? Then what is the failure point? Does the chamber peel apart and blow bits of slide into your eye?

    As it sits, my reloads will smile a bit in the factory barrel, but not in the AM barrel. If I get them mixed up, it won't mess the gun up if they go through the stock barrel, but it will ruin the brass. I am pretty sure they are over spec, but not by a huge amount. For the risk and the added 1/2" of barrel, I get about 90fps. Whether or not that would be worth it is up to each person. -Edit- You could probably equal the performance with a safer system overall by going to a 6" barrel, whether it was Glock or AM.
    Last edited: Jan 3, 2013
  8. Taterhead

    Taterhead Counting Beans

    Dec 13, 2008
    Boise, Idaho
    AMSting~ Great questions.

    Primers are a poor indicator of pressures. Flattened primers can be a symptom of excessive pressure - and care should be given to determine the cause of the flattened primers. They can just as easily be primers that weren't fully seated, or a headspace issue; thus giving a "false positive." Also, excessive pressures can be present without primers showing any symptoms whatsoever. This has been shown to be true in laboratory testing as well as the numerous photos of blown cases. Some primers have highly varying cup shapes and hardness so they do not consistently "track" from round to round. Winchester comes to mind.

    One point to consider is that pressures will be higher in a "match" chamber than in a stock chamber. The reason is that the volume of aftermarket chambers are smaller. Same combustion event in a smaller volume = higher pressures. Granted the barrel itself will influence pressures too, but a chamber size that is smaller will have higher pressures. I personally would not shoot a round in a KKM/Barsto/Storm Lake/Lone Wolf barrel that I deemed to be unsafe in my Glock barrel.

    My experience with the Gen 3 G20 barrel is fairly extensive. It is a solid barrel. I had originally intended to get an aftermarket barrel, but I found it to be totally unnecessary. I have personally done dozens of unique workups with at least 6 different 10mm powders and many different bullets. Bullet weights from 135 to 200 grains. These have been worked up to maxes (and beyond, in some cases). I have also shot the higher pressure "boutique" high performance ammo too with good results. I have less experience with .40 S&W , but my G23 barrel has been great too. No problems. At all.

    What I have consistently found is that brass shot in Glock barrels do have a characteristic bit of a hog belly. That is normal. It is not unsafe. If brass has a smile, then that is a problem. It may be a symptom of excessive pressure for that system, or it might be an indication of premature unlocking of the slide. Either way, the cause must be explored.

    When measuring the maximum expanded diameter, in my barrel and with Starline brass, the following measurements are consistently observed:

    Starting charges: 0.431"-0.432"
    Medium range loads are 0.432 - 0.433"
    Max loads and a bit beyond will approach 0.434"
    Beyond that and smiles will be observed.

    Note that I have only encountered smiles with one workup out of dozens. It was a load published by Hornady, but exceeded the powder mfg data by a ways.

    When all is said and done though, we cannot devine pressures from brass or primers. We can only follow pressure-tested load data and look for problems in our setups.

    My suggestion is to keep your stock barrel, follow good load data, and look for indications of excessive pressures. I doubt you will have problems. What you will likely find is a highly reliable platform that is not particular about COL or bullet profile. If that doesn't work out for you, then an AM barrel might be the solution.
    Last edited: Jan 11, 2013
  9. _The_Shadow

    _The_Shadow Ret. Fireman

    Jul 23, 2007
    Southeast, LoUiSiAna
    We stated Taterhead! However the pressure spike, be it in factory and aftermarket still needs to be within the SAAMI specifications for the "boutique" high performance ammo!

    I think (from my observations) that StarLine brass is soft (not a bad thing for reloading) and will start to "smile" before other makes like Winchester or Remington using the same powder charges.

    The best part about Handloading is being able to adjust for the componnets being used for the best performance!
  10. nickE10mm

    nickE10mm F.S.F.O.S.

    Apr 13, 2004
    Wichita, KS
    EXCELLENT post, Taterhead... well stated
  11. blastfact


    Aug 15, 2011
    Good info here. I have stopped using Starline 10mm brass myself. It is just to soft. I have to pay twice as much at a LGS for the Winchester brass. But it seems to hold up better to max book loads. The primer pockets seem to stay much tighter than Starline.

    And yes I'm one of the crazy folks. I shoot 10mm and I want them at max book or above. And yes I'm one of the crazy sot's that tore up there over priced and under preforming Delta. The DE was what got me into 10mm ooo so many years ago.

    You can live on the edge like I do. Or play it safe. Either way one has to keep up with the condition of there brass, primers and function of the weapon being used. And never ignore a sick feeling in your gut. Be it at the bench or at a range shooting. Never second guess your gut feelings.
  12. TDC20


    Apr 11, 2011

    Excellent advice from Taterhead and Any Cal. These guys have a lot of experience and know what they are talking about. Reading primers can be useful, but it can also be confusing.

    There is a lot that can be said about reading pressure signs and load work-ups. I will add two more things to what has already been said. First, don't try to make a powder that is too fast work with top end 10mm loads. If you shoot a lot of 9mm and 45, and you only have two powders on hand, that's fine. You can probably find some safe load to use in 10mm for Power Pistol, Unique, etc. But those are NOT top end loads! I see this quite often where someone wants to drive a 180gr bullet at 1300fps out of the stock G20 barrel with Power Pistol. Can it be done? Probably. Can it be done safely without exceeding SAAMI pressure limits? NO! So don't even go there. If you want top end performance, use the powders that are going to get you theren safely, like Longshot, 800-X, A#9, and maybe Blue Dot. These are the powders you want to be using if you're going to make serious 10mm ammo. Leave the Unique, Power Pistol, HS6, etc. for the low velocity plinker loads.

    Secondly, I STRONGLY advise doing load development with a chronograph. Yes, they are going to cost you $100, but you can use them with every caliber you load, and the data you collect from various chronographed loads is an invaluable tool. A chrony provides feedback for what you are trying to achieve. If you are getting 1300fps with a 180gr. bullet using Longshot or 800-X with standard primers, you are probably not going to see any smiles. I have worked up 180gr bullets to 1300fps with both Longshot and 800-X using both a LWD and the G20 barrel, using "soft" Starline brass, and still have not had a single smile (note that the 6" LWD barrel fires the exact same 1300fps 180 gr load from the G20 barrel at 1400fps from the 6" barrel). Without a chrono, how do you know where one powder does better than another? How do you know you have achieved "full power 10mm loads?" You don't. You are flying blind, trying to read primers and guessing. There is plenty of data that has been compiled by the handloaders here that back up a 1300fps 180gr. loading with Longshot and 800-X, but you probably won't find those loads in any reloading data book. So my advice is to stick with book loads and book loads ONLY if you don't chrony your test loads. Trying to achieve an unknown velocity with an unknown amount of powder is a recipe for disaster.

    So, if you don't have a chrony, stick with book loads. Even then, you aren't 100% safe, so work up from a safe point backed off of the maximum listed loads. A conservative loader will consult 4 different references, and take the "max load" from the most conservative reference as his guide. An unwise loader will look at the 4 different references and try for the highest value that he sees. The unwise loader is the guy that gets the smiled brass. The loader with chrony sees the trouble coming from a long way off, and rarely ever gets to the point of smiled brass, unless he chooses to push it to that point.

    BTW, all of the 10mm ammo that I load runs fine out of both the stock G20 barrel (22lb spring) and 6" LWD barrel without any smiles or other problems. Not only is it possible, but I believe if you are loading within SAAMI pressure specs (maybe with a small but responsible amount of margin) it should be expected.

    Good luck and be safe!
    Last edited: Jan 10, 2013