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/articles/Cast%20In%20the%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.

[str8wal]

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

I would like to see some documentation on that. I have had to seat bullets a bit deeper in the case than suggested in data to get them to plunk in some barrels and if .003" would double pressure I should have had a lot of guns explode, which I haven't.

[Outpost75]

I would like to see some documentation on that. I have had to seat bullets a bit deeper in the case than suggested in data to get them to plunk in some barrels and if .003" would double pressure I should have had a lot of guns explode, which I haven't.

He's off a decimal, its 0.030" clearly states in Speer the Handbook narrative on 9mm Parabellum in the 10th and following all later editions.

[tazman]

I would like to see some documentation on that. I have had to seat bullets a bit deeper in the case than suggested in data to get them to plunk in some barrels and if .003" would double pressure I should have had a lot of guns explode, which I haven't.

One of the reasons to work up to the load you want to use by starting low is right there. Making a cartridge/boolit combination work in different chambers can be tricky as far as OAL goes. 9mm chambers being so inconsistent, is a major reason I seldom use full power loads for my 9mm cartridges.

[wv109323]

The bullet should pass the compression or push test with just the interference between the brass case and the bullet with no crimp. A taper crimp is to remove the case belling and slightly reduce the case mouth to aid in functioning the round in a semi-auto.
A revolver round that head spaces on the rim has a roll crimp usually in a canalure to prevent bullet movement during recoil.(inertia) I expect the inertia in a mag. revolver exceeds the compression forces of a semi-auto.
At least that is what I have always been told and understand.
I would want no set back caused by cycling the ammo through a semi-auto. In fact I would not shoot the rest of that ammo and contact the manufacturer.
Some manufacturers put a cannalure in the brass case to prevent bullet set back as further insurance.

[dansedgli]

I went through this on the weekend trying to load 9mm major out to 1.161.

On my 1050 dillon I had to remove my backup die which slightly flares the case and change out my Mr Bullet feeder die to the factory dillon one to solve the setback issues with the push test.

The rounds don't look crimped enough to me but any more crimp and they setback. They feed fine and don't move so that'll do.

[Burnt Fingers]

He's off a decimal, its 0.030" clearly states in Speer the Handbook narrative on 9mm Parabellum in the 10th and following all later editions.

Thanks for catching that. I was trying to type with a cockatoo standing on my hand.

[Outpost75]

Thanks for catching that. I was trying to type with a cockatoo standing on my hand.

Understood. I just had a cat on my lap. MUCH easier.

[gnostic]

The bullet size may be the problem. I size 9mm to .358 and taper crimp, the bullet would show some serious damage before it would be setback. Also, my 9mm handloads have a Coke Bottle shape, I don't think my bullets are going anywhere...

[charlie b]

The bullet should pass the compression or push test with just the interference between the brass case and the bullet with no csrimp. A taper crimp is to remove the case belling and slightly reduce the case mouth to aid in functioning the round in a semi-auto.
A revolver round that head spaces on the rim has a roll crimp usually in a canalure to prevent bullet movement during recoil.(inertia) I expect the inertia in a mag. revolver exceeds the compression forces of a semi-auto.
At least that is what I have always been told and understand.
I would want no set back caused by cycling the ammo through a semi-auto. In fact I would not shoot the rest of that ammo and contact the manufacturer.
Some manufacturers put a cannalure in the brass case to prevent bullet set back as further insurance.

I had setback with .45ACP and lead bullets. The combination that got me was pan lube (no bullet sizing) and just enough on the crimp die to remove the bell. IMHO the thing that allowed the movement was the slight amount of lube left on the driving bands. I went to a taper crimp and they were fine.

I had the opposite of setback with the .357 and heavy loads with no crimp. Tried it just because I had nothing better to do. I had the idea it might improve case life. Two bullets came out of the case a good 0.1" (also pan lubed and not sized). Interesting too cause only the two next to the firing chamber reacted enough to notice. The bottom three only moved a little bit (had to measure them to see it). The issue would have been that a bullet that went through 5 shots may come out enough to jam things up (especially something like a 150 SWC or heavier).

[tazman]

I had the opposite of setback with the .357 and heavy loads with no crimp. Tried it just because I had nothing better to do. I had the idea it might improve case life. Two bullets came out of the case a good 0.1" (also pan lubed and not sized). Interesting too cause only the two next to the firing chamber reacted enough to notice. The bottom three only moved a little bit (had to measure them to see it). The issue would have been that a bullet that went through 5 shots may come out enough to jam things up (especially something like a 150 SWC or heavier).

That is a typical problem for revolvers. The recoil tries to pull the bullets out of the case. Sometimes they will move far enough to bind the action.
The S&W models 27 and 28 used to do this because of their shorter cylinders.

[Black Jaque Janaviac]

"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!"

Ah. This may be part of the problem. I just tested the Federal Aluminum FMJ factory ammo and it failed this test miserably. Pushed down to exert 50 lbs and the bullet set back. Original OAL = 1.15", after test 1.06".

[tazman]

Ah. This may be part of the problem. I just tested the Federal Aluminum FMJ factory ammo and it failed this test miserably. Pushed down to exert 50 lbs and the bullet set back. Original OAL = 1.15", after test 1.06".

That is a problem the manufacturer needs to have brought to their attention.

[DougGuy]

Ah. This may be part of the problem. I just tested the Federal Aluminum FMJ factory ammo and it failed this test miserably. Pushed down to exert 50 lbs and the bullet set back. Original OAL = 1.15", after test 1.06".

I would contact their customer support, that is NOT supposed ot happen. You may have gotten a bad batch of ammo. I would not shoot any of those until you have resolved the issue with Federal.