Bullet setback

[fbcmrjrtykr]

i'm curious as to how many times one can safely chamber a round without inducing bullet setback? If I have to eject an unfired round (pistol cleaning or inspection) i always rotate a new round into the chamber, rather than re-feed the ejected round. I compare the ejected round to others to ensure it looks okay but have often wonder, as what point does the round become unsafe to use. If setback occurs, is there a point where the setback creates an over-pressure situation?

I check my rounds by placing them upright on a flat surface and placing a level across the top of the round. Is there a better to check for bullet setback? In that same vein, what do y'all check for when inspecting rounds?

Thanks,
JR

 

[ginzo]

How many times? Good question, no good answer. I don't know where the "point of no return" is on setback and pressure, but I do what you do. I chamber it a few times, do a quick straight edge check, then send it to the bottom of the mag.

I'm anal about rotating SD ammo out about once a year. That may be extreme, but we all have our quirks. Then my new batch gets enough rounds through the auto's to make me feel comfortable that it will cycle properly, and I'm good to go.

Not so much worry on my revos. Just burn a few rounds each year and keep them ready as I rotate SD guns pretty regularly.

I had an instance with a certain brand SD ammo, that looked like this after just a few weeks sitting in the mag. These rounds were like 4 or 5 deep in the mag. I went to another brand, was satisfied, sent the other stuff down range. It all fired, go figure?

Hope this eases your mind.

Chuck

 

[scooter123]

Setback depends on multiple factors.

1) is the gun and the "smoothness" of the feed path. A steep barrel ramp with a slam bang feed cycle will cause more setback that a barrel ramp with a shallower angle that allow the round to feed in with ease. Typically the shorter the barrel the shorter the Action Stroke of the feed cycle will be and this will increase the potential for Setback. This means that Compact pistols are more likely to have Setback issues than a Full Size pistol.

2) The second major factor is how the cartridge was assembled. Bullets with a cannelure that are crimped well are less likely to set back than bullets without a cannelure and a light crimp. I've also noticed that the force required to pull a jacketed bullet from a Nickel case is much higher than the force required to pull a jacketed bullet from a Brass case. Finally, lead bullets produce less friction in a gun barrel than a plated or jacketed bullet so it's likely that lead bullets also have less friction to hold them in place in the cartridge.

3) then their is the weight of the bullet. Relatively light for the caliber bullets tend to be shorter in overall length and have less length engaged in the case. IMO a shorter length of engagement will increase the potential for setback.

4) Finally there is the specific caliber. One reason I am not overly fond of the 357 Sig is that the surface engaged with the bullet in the case is IMO a bit on the too short side.

Now, for measuring the setback. IMO nothing beats a digital caliper for a quick and easy check. Since calipers can now be purchased for less than the cost of a box of ammunition there really isn't any reason to not have a caliper.

As for how much is too much, it is dependent on the caliber but IMO a safe limit for calibers of 9mm parabellum and larger 1/32 inch (0.031) of setback calls for shooting that round so it won't get any shorter. For the 380 that limit should be about 0.024 inch and 32 caliber should be 0.02 inch.

 

[robkarrob]

Why risk setback by reloading the round from a magazine on your carry gun. If you often unload and reload the same round, you risk setback. I have been dropping the unloaded round into the chamber and letting the slide slam closed on all my pistols (not 1911s) for many years without one problem. The extractor is spring loaded and snaps around the rim and locks back into the extractor groove. You do not get any setback loading this way. This may not be how the gun was designed, but it has worked perfectly for me for many years, on many different pistols, Springfields, Rugers, and my current Shield 40 for over 2 years.

Bob

 

[Rpg]

OP: your system for judging setback sounds great.

Nothing more precise is necessary.

If one of your rounds looks too short, set it aside and use it for practice.

I think setback is more an issue for reliable function in a pistol than a safety issue.

As long as the bullet isn't 'set back' so much it compresses the powder charge pretty significantly any pressure increase would be well within safety limits.

Just my opinion, of course.

 

[fbcmrjrtykr]

Thanks all for the responses. I agree that a digital caliper is worth a look.


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[Jiman]

FYI: loading a pistol by putting a round in the chamber and dropping the slide is very hard on your extractor. I've seen it as the cause of extractor failures many times over the years.

How a round is affected by repeated chambering depends on the cartridge also. A .357 sig for example, due to the necked down brass, loads with minimal issues. 40 cal on the otherhand is much more sensitive to any setback issues, as well as, possible feeding issues of due to the truncated rounds.

Aside from using calipers and other cartridge measuring devices, a relatively easy visual cue is to make sure the 'crimping line' has not sunken into the brass.

Set back is definitely a safety and reliability issue. Set back raises the pressure of the cartridge because there is less room for pressure to go. If you ever take a bullet apart, you'll see that there is a lot of void volume (I.e. Air) as part of the design.

As the bullet gets pushed back from 'setback', the airspace is lessened. This decreased area increases the possibility of case rumpture, primer blow outs, or worse.

Replace your SD ammo regularly (at least once a year). It's not just for set back but cleaning solvent, oil, and other environmental concerns as well.

I know some guys who spent, in their mind,a lot of money on some super special safety slug, black talon, manstopper that they've had for 20 yrs. It might still work, but I wouldn't trust my life on it after all that time. I guess some do.

 

[walkin' trails]

The one documented case that circulated a few years ago was with a Glock in 40 that was owned by a nuclear power plant security team , was repeatedly 're-issued two or three times during a day, and reloaded pretty frequently. I've only seen set-back occur once in 25 years on carrying a gun, and that was with an AR15 and a bad magazine. Seriously, just pay attention to your gear and rotate ammo every 3-6 months.

 

[Doug M.]

There have been some pretty long discussions of this before. With the exception of the problems relating from ammo and air travel, I do not chamber a round twice in any self-loading (non-revolver, in other words) platform. As noted above, the .40 is really prone to problems with setback according to the data I have seen from hard use shooters who train a lot. Ammo is cheap compared to the platform and my body parts.

 

[fbcmrjrtykr]

FYI: loading a pistol by putting a round in the chamber and dropping the slide is very hard on your extractor. I've seen it as the cause of extractor failures many times over the years.

.

Agreed. Never even considered manually loading that way though many do.

Thanks all.


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[ggibson511960]

In all my years of shooting firearms, factory ammunition and reloads, I have never managed to get a magazine fed repeater to set a bullet back in the case neck. I have mangled them many other ways, including backing bullets out, but that's another story. The incidence angles of feed ramps minimize the axial force vector from friction and impact on the bullets axis. The most extreme example would be the old S&W Model 52 that fed .38 Spl wadcutters generally without problem. My belief is that bullets get battered out of alignment or scuffed by repeated chamberings. If gun and ammunition are in reasonable working order, I believe you could chamber a jacketed round a ridiculous number of times before wearing down its intended profile. But Murphy lurks, especially around reloads and bent magazine lips. Reasonably modern ammunition just goes bang every time. My last mis-fires happened in the 1960's to old paper shotgun shells (water), a .22 rimfire without priming compound, and a .45 ACP with a dud primer (oil soaked from my careless reloading).

I'm really curious about the pictures of the dented cases in the second post. I don't think my fingers could push a round in a magazine that had springs powerful enough to dent cases that badly, and cartridge brass doesn't have metallurgical creep fast enough to ever notice. It's hard to bend small brass cylinders that much without with a reloading press. I have done it. A seriously messed up autoloader could do it if the rounds were cycled through and stovepiped. A magazine speed loader and stout fingers might do the trick, and reloads could result in all sorts of case wounds. I've done most of those, too.

 

[ginzo]

The ammo in question is Federal Guard Dog PD40GRD 135gr. I "believe" the cases are nickel. They were loaded by hand and or with an Uplula. It looks to me as the dents were just beyond where the bullet was seated in the casing. I loaded/reloaded them several times when I 1st got them just for practice. The denting was not apparent at that time.

Several weeks later, approx. 2-3 weeks, I unloaded them for whatever reason (I don't remember why). At that time, being new to handguns, I was NOT running one in the chamber. This is when I noticed the dents. They were untouched in a fully loaded mag (15 rounds).

Called Federal, they picked them up/sent replacements and the replacements did the same exact thing. Called Federal, they never would give me any answer to what might have caused it. At that point, I did not have any confidence in them for SD, hence my comment "sent them down range" all went bang. No other brand of ammo I have used has ever done this either.

I then changed to Hornady Critical defense and never had any issues.

That's the story in a nutshell.... It is a big nut!

I'm really curious about the pictures of the dented cases in the second post. I don't think my fingers could push a round in a magazine that had springs powerful enough to dent cases that badly, and cartridge brass doesn't have metallurgical creep fast enough to ever notice. It's hard to bend small brass cylinders that much without with a reloading press. I have done it. A seriously messed up autoloader could do it if the rounds were cycled through and stovepiped. A magazine speed loader and stout fingers might do the trick, and reloads could result in all sorts of case wounds. I've done most of those, too.

 

[DarylCoda]

Rotate Carry Ammo for Safety

Repeated chambering of the same round can not only cause setback, which could arguably lead to kaboom, it DEFINITELY can also cause primer compound separation, which was the documented cause of a Georgia police officer's failure to fire in a situation requiring deadly force. It's in the video:
http://youtu.be/5VSfSPuEC6M

 

[fbcmrjrtykr]

Repeated chambering of the same round can not only cause setback, which could arguably lead to kaboom, it DEFINITELY can also cause primer compound separation, which was the documented cause of a Georgia police officer's failure to fire in a situation requiring deadly force. It's in the video:

http://youtu.be/5VSfSPuEC6M

Great vid. Thanks


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[WR Moore]

I can't recall where I read the comment, but someone from one of the ammo companies noted that expecting no setback after rechambering more than 3-5 times isn't reasonable. Some calibers/ammo/weapons systems are much less prone to the problem than others. The current practice by many companies to depend upon neck tension alone to hold the bullet in place doesn't help. [Saves a few pennies per 100 rounds in production cost.]

A cannelured bullet has already been mentioned. Some ammo companies still place a cannelure in the case to help prevent bullet setback.

 

[Jiman]

Some LEO agencies require, for the lack of a better word glue, to aid in neck tension. Ammo companies will do a lot regarding technical specifications for an agency if the order is big enough...so will gun manufacturers.