Repeated rechambering of live rounds: setback and pressure problems?

[Richard.Howe]

Morning all. I keep a Sig P220ST at my bedside -- this pistol and the .45 ACP is the topic of this query.

About twice per month, I drop the mag and clear the chamber. The ejected round goes back on the top position in my single-stack magazine. I cycle the action a few times, dry fire, check the rail/barrel lubrication, and reassemble. Upon reassembly, the initially ejected round is re-chambered.

My question is: what are the chances that this top round is being slightly compressed (i.e. the bullet is being pushed back into the case)? What would be the consequence were this to occur?

Not knowing the answer to this problem, I keep a box of loose ammo which consists mainly of this "top round" after it has been cycled into the gun about 4-6 times.

 

[steveno]

I shoot the magazine up after unloading and reloading the magazine 6 or 7 times. the bullet tension after that many cycles will be less than one that hasn't been cycled at all

 

[jlh26oo]

Instead of rechambering the same round over and over again, why not just purge it at the range, then do your little check (since you do it only a couple of times a month anyways)?

Not sure how significant of a risk it is, but I'm of the mind to just play it safe and avoid repetitive rechambering.

 

[mete]

The risk is very high. Many Kabooms are caused by this. One of the ammo companies did tests and found , for example, that if a bullet in a .40S&W cartridge is set back .10" the pressures DOUBLE. That's going from 35,000 psi to 70,000 psi !!!!

 

[Walt Rauch]

The risk is very high. Many Kabooms are caused by this. One of the ammo companies did tests and found , for example, that if a bullet in a .40S&W cartridge is set back .10" the pressures DOUBLE. That's going from 35,000 psi to 70,000 psi !!!!

Correct! The company was Hirtinberger of Austria with a .40S&W. One tenth of an inch set back took pressure to 80,000 CUP!

 

[RyanM]

I'd throw rounds that have been chambered more than 3 times in the practice pile. More than 6 times, and I'd pitch it.

 

[blackpanther]

Rechambering a round WILL get you in trouble at some time.When I check any of my five house pistols I throw the chambered round in the garbage can every time.Some brands of ammunition do not have a strong crimp.

Ed

 

[Dr.Rob]

It's very common with .357 Sig.

In 380 and 9mm there are so many mfg's of ammo, each case is a little different... slight setback in one might mean nothing, while in another can be catostrophic or a compressed powder load.

It's one of the reasons that reloading manuals suggest you use only ONE brand of brass when loading 9mm.

I've seen set back in .45 ACP more often that in 9mm.. I'm guessing in part its due to how a Colt 1911 chambers a round vs. a BHP, though I've also seen setback in .380 cases. If you see evidence of set back, best thing to do is set the cartridge aside in a box marked "BAD" or use a kinetic bullet puller to dispose of it.

 

[oh blanky]

Zowie.

Very good question I never considered.

Thanks!

 

[pete f]

the forty smith is a very high pressure round compared to most pistol rounds, and it is often the most susceptable to set back of all.

I usually just check them with a caliper once in a while. i get a couple of hundredths under and i toss them

 

[orionengnr]

good post, and food for thought...

Perhaps, after chambering round #1, and subsequently (a week or a month later) ejecting it, you could put it at the bottom of the mag? That way each month you'd be chambering a fresh round, and by the time you get through the mag (chambering each round once), shoot 'em all off and start fresh.

Another option--once the round has been chambered once (by the slide), if you eject it and want to re-chamer, how about locking the slide back, dropping that round into the chamber through the ejection port, and after it is seated, drop the slide, then insert the mag? That way no round is slammed up the ramp, and no setback should occur, am I right? (and I know you won't hestiate to tell me if I am wrong )

Seems as if you could re-chamber round #1 an infinite number of times this way, and not have to "keep track" of the bottom round, etc.

 

[tbeb]

I'm not answering your question, but, why do you do this? I guess just for handling pistol is a good enough reason. Anyhow, I have a .45 ACP with a single stack magazine. The only time chambered round comes out is when I fire pistol.

 

[RyanM]

Another option--once the round has been chambered once (by the slide), if you eject it and want to re-chamer, how about locking the slide back, dropping that round into the chamber through the ejection port, and after it is seated, drop the slide, then insert the mag? That way no round is slammed up the ramp, and no setback should occur, am I right? (and I know you won't hestiate to tell me if I am wrong )

Won't work with most pistols. If you try that with a 1911, you'll probably damage the extractor. With a Glock, in my experience, the extractor will just ram against the back of the case instead of hooking over it. Seemed to work okay with a .380 NAA Guardian, though.

An alternative may be to slowly "ease" the slide shut when chambering the first round, but that will still probably set the bullet back some. Not as much as chambering normally, though.

 

[Sam]

Just go to the range and shoot off the loaded mags each week. Keep in practice and keep that setback at bay.

Sam

 

[torpid]

Guns are scary.

 

[english kanigit]

Hmmmmm, this is definately food for thought. Whenever I'm not wearing my new XD around the house, it's in the safe unloaded. When I get home, the holster goes on and the gun gets loaded.

I guess I ought to go rotate my rounds... in fact, I think I'll do that right now.


*11:03 Top rounds rotated...

 

[MNgoldenbear]

Probably not a problem

Just checked the ammo in my Glock 19. (This is in 9mmP and not 45ACP, but still a nominally straight-walled pistol cartridge.) I carried it daily this summer at work, loading each morning and unloading each evening. The first round was the same all summer, so it was chambered at least 60 times. The round measured the same OAL as the rest of the rounds that had not been chambered. (There is some variation in OAL due to differences in nearly all bullet noses, but within the range of a few thousandths.) This is commercial ammo -- Federal Hydrashok (current "PD"-type light bullet, high velocity loading). Should take a pretty good wallop to push a bullet in 100 thousndths! (Unless there was insufficient neck tension, big time.)

 

[Ken Rainey]

I only noticed bullet set back when using Winchester SilverTip ammo in both 45ACP and 9mm but more so in the .45s that were rechambered in a 1911. I haven't noticed it in any other type ammo in these calibers. The bullet coating of the "SilverTip" must provide less grip for the case to hang on to compared to other jacket materials ??

Your practice of only chambering the top round a few times is a safe one....you can measure this cycled ammo against fresh ammo and if it's within a few thousandths (heck, if it just eyeballs real, real close to the same length) then I'd use it for range practice...good way to practice with the ammo you use for defense.

 

[KAR120C]

Was going to post on this topic, then thought to search first, and found the answers I wanted.

Since this thread is a year old I don't feel bad about resurecting it, and hopefully enlightening some new members. Since this is an obscure topic, not often covered in training, I think it worth mentioning from time to time.

I have a Sig 226 in 9mm. I've frequently had to unload it and reload it for various reasons, such as when traveling to property in a near by non-carry state, or when switching to cheaper ammo for IDPA, etc... . I had been just rechambering the top round every time. I noticed recently that the bullet is now significantly deeper in the casing than non-chambered rounds. I'd hate to think what kind of pressures would be obtained by firing this round.

I'm going to pitch it, and from now on I'll rotate ammo, look for set back rounds, and try to minimize on the unload/load cylces for my carry ammo.

 

[ABBOBERG]

I have found the worst 9mm ammo for setback is the Blazer ammo since it has no crimp nor any adhesive. I have a batch where I can push the bullet in with my thumb! I have found that most hollow points have an excellent crimp and some brands additionally have adhesive. I think they do this because the flat tip of hollow points make more of a direct hit into the feed ramp, so increased crimp is necessary.

So if you re-chamber a round dozens of time and see no setback, don't be surprised since the many manufacturers take this into account.

 

[High Planes Drifter]

You know, its something that never really comes to mind, but can be a safety hazard. Good thread. I think I'll check my carry ammo tonight !

 

[ZeSpectre]

Was going to post on this topic, then thought to search first, and found the answers I wanted.

Since this thread is a year old I don't feel bad about resurecting it, and hopefully enlightening some new members. Since this is an obscure topic, not often covered in training, I think it worth mentioning from time to time.

I agree that this -should- come up again from time to time.

Rotating the rounds was one of the things mentioned by my NRA instructor. He showed me evidence of a kaboom from a repeatedly re-chambered round that had pushed back.

I'll re-chamber a round twice and that's it. After it's cycled a second time it's gone 'cause my safety is worth way more than one round here and there.

If I'm really trying to check the action I try to stick to high quality snap-caps.

 

[Falconeer]

+1 on rotating rounds.

I've seen visible set back on 180grn 45acp Gold Dot rounds after dropping a slide on them a time or two in my GSR. Keep an eye on those carry rounds, folks!

PS: I used to reload 357 Sig so I was good and wary of set back. In actuality I never round commercial 357 Sig to be any more liable to set back than other calibers. Reloads, different story.

 

[Phil DeGraves]

"Won't work with most pistols. If you try that with a 1911, you'll probably damage the extractor."

A clarification. It WILL work, but Ryan is correct that you risk damaging the extractor. It is not a process that is recommended.

 

[Helstrm]

I have seen this with my .45 ammo. I always rotate my rounds.