How much Setback is too much?

General Firearms Reloading & Ammunition
1

From my research, it seems that setback isn’t really an issue for bottleneck rifle cases except for in extreme cases…the pressure doesn’t change much with different seating depths (or setbacks) in rifle cases…However, for straight walled pistol, even a little change in length will cause much different pressure levels.

Is this true or false?

Also, I did a little experiment testing my neck tension, crimp, ect to see the effect it all had on preventing setback for both rifle and pistol. I loaded dummy rounds (no powder or primer), measured COAL, then loaded into a mag and dropped the bolt/racked the slide to chamber. The round was chambered 3 times each, and COAL was measured after every chambering.

For Rifle

I found that my COAL actually grew (slightly) when “hard chambering” a round. Usually averaged .0010"-.0015" per chambering.

The only brass that I tested was Lake City.

For Pistol

I found that my COAL after chambering varied depending on the brass used. I tested Aguila, FC, and Blazer.

The best was Aguila with an average of .001" of setback after all three chamberings.

What prompted my testing, and my question (below) was the setback I was experiencing with FC and Blazer brass. Aparently, from my research, this is common with these headstamps, and is commonly alleviated by using a “U-Die”.

With FC cases, I experimented with crimp/no crimp (really the crimp is just taking out the belling), belling the case mouth/no bell, ect. Here are the results:

WITH case mouth bell AND “MORE” Crimp:
My COAL ranged from .006-.009" of setback PER chambering

WITH case mouth bell AND “LESS” Crimp:
My COAL ranged from .004-.0055" of setback PER chambering

WITHOUT case mouth bell OR Crimp:
My COAL ranged from .0025-.005" of setback PER chambering

*Do the math, and if you chamber the same round 3 times, you could get a setback of up to .027"…although granted, I rarely chamber the same round even twice…

My Question:

How much setback is too much? What is enough for a KB? Does the above setback that I found even matter at the max loading?

(I will probably only load to mid data range for plinking, and mid-high for the “social” stuff.)

Also, should I get a U-Die for mixed range brass to take out the variability for case thickness, OD, ID, ect.? If so, which one?

2

IMO, it’s not something you need to worry about with pistols. Just don’t re-chamber more than once. (A lot of this and the primer may not go bang - I think the Doc discussed this somewhere.)

I once re-chambered a WWB .45 ACP multiple times. It was scary bad. When I clear a SD handgun, the chambered round rarely goes back in. It’s marked with a sharpie and put back in the box for range use. For the 3-Gun pistol it just goes back in the range bag with all the rest.

3

You need to worry about set back when the case neck no longer has any grip on the bearing surface. The bullet Will be completely loose. Powder Will be able to spill out around the bullet. This is when you should worry.

You found a problem most overlook. In the Ar the bigger problem is the overall length growing. When the bolt slams a round home, and the bullet stops abruptly at the shoulder loading the round is actually acting like a kinetic bullet puller. Sierra used to put this in there manual. Im not sure if they still do. I dot have a new Sierra manual, and gave the old one to my buddy.

In the Ar setback does not happen often. It is possible, but generally if a bullet is being set back it Will not load. It Will usually jam below the feed ramps, and not load.

As for pistol Im not as well versed on the ins and outs. I load pistol , but absolutely despise it. That might change now i got my 550.

4

I can not speak to the issue in regards to a rifle but I have seen set back in pistol cartridges, 9mm and .45ACP. 9mm, in both my Glock and 92 are not really bad or apparent, though after repeatedly chambering the same round the glock will cause set back sooner then the 92, I suppose the Beretta feeds smoother. In .45ACP my TRP will eat figuring rounds up after repeated chambering them, PMC Starfire(I was young and dumb and they cheap, don’t judge me) looked like someone had hammered on them after being chambered half a dozen times or so, the face of the hollow point itself even looked deformed, and what should also be noted is that the felt recoil from the round after being chambered repeatedly felt greater and in out poor man ballistic testing using a phone book the repeated chambered round failed to expand properly over a new round. On a side note Winchester Ranger T .45ACP seems to hold up to repeated chamberings better in my personal testing them other loadings I had carried in my TRP, PMC Starfire or Hornady TAP, of course my TRP has perhaps the most violent chambering of any pistol I would use for defensive use. In 9mm, I haven’t had as drastic of an experience, however, I don’t chamber rounds more then a few times(And that habit will actually be limited soon with new job starting I will likely limit defensive ammo to a single chambering before it becomes range fodder) before they get dropped in the box O’ randomness to be loaded in cocktail mags for range use or just for shits and giggles ammo testing.

In short, with pistol, repeated chambering a round does appear that it can cause increased pressure, but more importantly with some JHPs it can cause round failure.

5

I’ve often wondered how much is too much, really just with .40. I have a Glock 23. While I don’t reload pistol right now, I hope to in the future.
I think if it were really a huge issue, we would know much more about it. Think about police chambering and re-chambering often.

6

I’ll re-chamber then mark each round with a slash, re-chamber second time it’s an “X” then rotate it to the bottom of my spare carry mag. Once all rounds are marked I shoot it down range for practice.
I’ve been doing this same routine for over 10 years with Glocks in all calibers and never had an issue with that “Practice” mag.
The only time I have seen set-back issues with pistol is when playing with ubber fast powders to major power factors and pushing it hard.
I watched a buddy blow up a Limited G35 with a 165g FMJ Titegroup load once… we check the remaining round in the blown out mag and found he had really weak neck tension in the brass.

7

If you have proper neck tension set back is very rare. On thing that can lead to set back is excessive crimp. If you crimp to much the brass will actually cause the bullet to have a ring that is a few thousandths less then the bullet diameter. When the brass springs back it Will make the crimp ineffective. Some people i getting set back in pistol rounds will start to add more crimp which Will make the problem worse. Neck tension in pistol rounds is a little harder to control than with rifle rounds, but as long as you have your dies properly set up neck tension should be sufficient.

8

Your thinking is completely wrong set back in pistol rounds can quickly lead to large spikes in pressure. You can choose to think there is no problem with set back in pistol rounds, but i would recommend you listen to the experts.

9

And where do I say it doesn’t? I said I had rounds that after repeated chamberings had the round pushed back and upon firing them their appeared to be a increased amount of recoil.

10

My bad my dislexic brain imposed doesn’t where you put does.

11

This is absolutely true.

The setback that you’re seeing isn’t a real problem, IMHO (but don’t take my word on it).

I’ve been reading up on .40S&W and OAL and pressure over at Brian Enos forum. You should look in the caliber-specific forum for your cartridge there.

For .40 S&W, the differences are typically 0.01 or so. For example, some manuals say to load to a 1.125 OAL, others say 1.135.

The reloading sages to load as long as possible, because longer means less pressure and felt recoil for a given velocity.

Having tinkered with OALs, going from 1.135 to 1.150 makes a visible difference, if you’re looking for it. That’s 0.015 difference, which is a lot more than the setback you’re seeing after chambering.

My loaded rounds vary ±0.002, depending on the exact shape of the bullet or how I’m holding the cartridge in the calipers, so that I get measurements between 1.148 and 1.152.

Looking at the loaded cartridges, the 0.004 difference is imperceptible.

I wouldn’t bother. I don’t know what a U-die is, but pistol cases headspace on the front edge of the brass, so changing that measurement seems like a bad idea.

I don’t think the bell or the crimp is your problem — notice that you had LESS setback the LESS you crimped.

I think the problem is your sizing die. Bullets are held by neck tension, not by the crimp. It seems to me that you need to size your brass down a couple 0.001s more, so that you have more neck tension.

12

Just to be clear, the problem that Doc brought up was chambering rounds in the AR or other service rifles with floating firing pins.
The pin dings the primer a bit every time a round is chambered. If you chamber the same “first” round several times, you may damage the primer to the point that it won’t fire.

Pistols tend to have firing pin springs, and they don’t ding the primers of the cartridges chambered.

+1

No, spilling a bit of powder wouldn’t be a big worry. The big worry is that the bullet is pushed back into the case so far that the powder is compressed, pressures go up several times normal, and the gun explodes.

Again, I wouldn’t worry about deforming JHPs so that they don’t perform if/when I need them. I would worry about the gun blowing up.

Again, this is key. I sounds to me like you’re not sizing enough.

FWIW, for .40 the manuals all say to size to 0.423, but everybody seems to be sizing to 0.421 or so. I size to 0.420 or 0.421, and NOTHING except putting them in the gun and firing them moves my bullets once they’re seated.

13

Could you be over belling your pistol brass?

I could see over bell and over crimp leading to setback.

I’ve also see WWB 9mm all over the place regarding OAL and never noticed it to shoot differently.

14

Bimmer if there is set back that is compressing the powder that is not a problem compressed loads are perfectly safe to shoot. If compressed loads led to kb’s you would not see load data that has compressed charges. If your load density is high enough that will help eliminate setback.

As ironmam8 showed in his post with an Ar the bigger problem in the loading sequence is that the overall length will grow. The Ar when loading acts just like a kinetic puller. With rifle rounds longer the oal the higher the pressure.

The powder spilling with excessive set back is not the problem it is just a good warning. If the bullet has been set back so far the neck no longer holds the bullet. The bullet will no longer be in proper alignment with the bore. Once the bullet is fired all kinds of stuff can happen.

The reason setback with the pistol was worse as crimp is increased is due to brass springing back. When you over crimp it swages the soft copper, and lead which does not spring back while the brass does. So you when your brass springs back it makes the crimp ineffective. There is actually a little space between the case mouth that is crimped and the bullet.

That is why if you are having set back the last thing you do is increase the crimp, and that is the dirt step virtually everyone will take till they learn what is actually going on.

Tb-av is exactly right about the bell and crimp.

15

Just to be clear: you’re right that “compressed” charges are OK, when they’re loaded that way on purpose to appropriate pressures.

I meant that a bit of setback can have catastrophic consequences if it means compressing a load that is NOT meant to be compressed.

See the first table here to see how imperceptible changes in OAL can lead to catastrophic pressure increases in pistol cartridges:

http://greent.com/40Page/ammo/40/180gr.htm

Just 0.04 setback (from 1.115 to 1.075) is enough to increase the pressure dangerously. Another 0.04 or so and pressures are double what they should be (ka-boom!).

16

That is a pistol round. The part you quoted me on in your first post was dealing with rifle. I do agree that set back in pistol rounds is dangerous. With rifle rounds set back can be a problem but it has to be a lot. The dangers are not high pressure.

When a rifle round has a shorter overall length it has a lower pressure. Rifle rounds that are longer have a higher pressure.

If set back causes a forty round to be compressed the bullet would be set back past the give with most pistol powders. There are a few powder that fill the case enough to compress with less set back.