semi-auto setback - how much is too much?

[Black Jaque Janaviac]

I understand that bullet setback is a normal thing with semi-auto pistols when one repeatedly cycles ammo from magazine to chamber.

But what about just once through? As in, you load the gun with brand new ammo, fire a round, and the next round in the chamber is now 0.03" shorter than original? Am I being picky?

[RED BEAR]

I will admit i haven't checked mine but i would think any movement is not a good thing. .03 is a good amount that can change pressure a lot. You may want to look at how you crimp these rounds.

[Black Jaque Janaviac]

You may want to look at how you crimp these rounds.

We're talking factory loads too.

[rintinglen]

I seem to recall a Ramshot study where in a 1/10 inch decrease in length raised pressures in a 9 mm nearly 7,000 psig. A similar decrease in a 40 was even more impactful in raising pressures, to the order of a 25 % increase. Minor reductions, .03 or less, have only a minor impact and can be ignored, but I just trashed a 380 round that had made a few too many trips from mag to chamber. If it looks too short, it probably is. Don't take a chance.

[Texas by God]

I've been loading .45 ACP since 1977 and haven't noticed it at all so either it hasn't happened or it was a non-event (to me).

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[Black Jaque Janaviac]

If it looks too short, it probably is. Don't take a chance.

The problem is, this amount of setback is just from shooting the gun once. You'll never see it unless you shoot, then manually eject the next round. Who does that as a matter of regular practice?

However, if 0.03" isn't enough to spike the pressures I guess I won't worry.

[Black Jaque Janaviac]

I've been loading .45 ACP since 1977 and haven't noticed it at all so either it hasn't happened or it was a non-event (to me).

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I suspect that it would only happen to semi-autos with a feed ramp fixed to the barrel. Many .45s don't have that ramp hanging down from the barrel.

If you have a gun with a feed ramp that integral with the barrel, try starting with a loaded magazine, firing a round, then manually ejecting the next one. You have to do this on the range because hand-cycling will not have enough force to duplicate what is going on with my gun.

[tazman]

Ed Harris has some information on bullet setback in his article on loading for the 9mm. http://www.hensleygibbs.com/edharris...0the%209mm.htm

"Paying strict attention to seating depth, proper crimp and testing for "bullet push," no more than 0.005" shortening of cartridge OAL after 5 secs. at 50 pounds compression pushing against your bathroom scale, is very important. This should be a routine test precaution when setting up the loading machine and is essential to be repeated whenever you change lots of brass or bullets!"

I don't think any setback should be acceptable and the testing I have done with my reloads tells me it should not happen if the case is properly sized and crimped. Mine don't get setback when fed through my semiauto handguns. I may get a slight spot of damage to the nose(depending on the hardness of the boolit used) from hitting the ramp but no setback.
I tested with both ramped and unramped barrels in 1911 and other handguns. My 9mm 1911 is ramped and all my XD series barrels are ramped.

[DougGuy]

Nope setback is not normal. ZERO setback is or should be normal. If you are loading small cases like 9 and 40 to their max, as little as .010" can send pressures into unsafe territory.

Couple of years ago, a female shooter here on this board had a KB in her 45 ACP 1911, blew the magazine apart, blew wood splinters into her hands, we pretty much determined it was from setback.

Factory loads making the trip a time or two shouldn't be an issue, check your handloads by pressing them against a solid bench, if they move at all, they are not ready for prime time you need to go over some things like primarily crimp type and how much.

[onelight]

Did you measure the same round before and after or compare two different rounds?

[Black Jaque Janaviac]

Did you measure the same round before and after or compare two different rounds?

I compared two different rounds. But several brand-new and several once-through.

[Outpost75]

Factory law enforcement and military ammunition has the jacketed bullets "glued" into the case mouth with an asphaltic varnish known in the trade as Black Lucas. In addition to waterproofing the ammunition, it serves to prevent set-back when rounds are fed vigorously in SMGs.

In reloading the taper crimp should be enough to pass the bullet-push test as described in the Ed Harris link at Hensley & Gibbs as quoted above.

[Black Jaque Janaviac]

I think there is some confusion. I don't think the ammo is failing the push test. I am wondering if the gun is exerting more-than-typical force.

[Outpost75]

I think there is some confusion. I don't think the ammo is failing the push test. I am wondering if the gun is exerting more-than-typical force.

50-pound push test was based on the M1928 Thompson SMG.

I highly doubt any autopistol that you can easily cycle by hand is going to exceed that.

[onelight]

Is the bullet tip deforming any ?

[Ramson222]

I experienced set back like you described while trying to load subsonic 9mm. first test round was subsonic next one went super, third one was supersonic with a blown primer, didn't try the 4th round. Any set back is a bad thing and should never happen.

[tazman]

Is the bullet tip deforming any ?

I would occasionally have a rub mark(not really deformed but noticeable) on the edge of the meplat when using RNFP in my 45ACP. Never got any setback though. I wondered about that when I saw the mark and tested several cartridges.

Ramson222---- What you describe is scary. I wonder why it only happened with subsonic loads though. I would think the powder charge should have nothing to do with setback.

[Ramson222]

I would occasionally have a rub mark(not really deformed but noticeable) on the edge of the meplat when using RNFP in my 45ACP. Never got any setback though. I wondered about that when I saw the mark and tested several cartridges.

Ramson222---- What you describe is scary. I wonder why it only happened with subsonic loads though. I would think the powder charge should have nothing to do with setback.

It only happened that one time. All I know was that the primer blew on the 3rd, I never did measure the oal to see if set back had actually occurred. I was told that was most likely the cause by a experienced reloaded. It could have also been pressure spikes due to very small powder charges.

[charlie b]

I have had setback before. Bad loading on my part.

I put a heavy taper crimp on my auto bullets and a pretty heavy roll crimp on my .357 rounds. I have not seen them move.

FWIW, the Harris thing says .005". I would not be able to see that, even if it did occur. I have never measured bullets before and after with a caliper to see if they moved. I have ejected quite a few to look, but, the movement would have to be closer to .030" (~1/32") for me to see it.

[Burnt Fingers]

RCBS has seen 9mm ammo more than double in pressure over a .003 set back.