What causes bullet setback?

[Big Calhoun]

I was cleaning my Beretta 96FS last night. While clearing it and removing the magazine, I noticed the chambered round looked funny. So I set it up on a table along with a round from the magazine and could see the bullet in the chambered round had gone into the casing some. Aware of the dangers of high-pressure, I set the round aside to discard next time I go to the range.

Does bullet setback happen over time? Or is it from a round sitting chambered for too long?

I had read that constantly chambering and clearing the same round can cause setback, so that round had been there for a good 3 months or so. I'm glad I took notice.

But if anyone could offer advice to prevent this from happening, I'd very much appreciate it.

 

[EddieCoyle]

Repeatedly chambering and rechambering the same round can do it.
Recoil can do it to bad ammo (Amerc is famous for this).
Chambering a round that exceeds the cartridge's maximum O.A.L. will do it.

 

[mete]

Repeated chambering is usually the cause .This can be dangerous and is one of the reasons for 'kabooms'. For example in a 40S&W ,if the bullet is set back .10" the pressure will be DOUBLE !

 

[Big Calhoun]

Yeah, I've read about the dangers of high pressure so I discarded that round and replaced it with a fresh one. In hindsight, I do think it was chambering/rechambering that caused the issue.

That Beretta is the only firearm my wife is familiar and comfortable with and we regularly practice using snap caps. Well, I obviously have to clear the pistol to put in the snap caps. So I think that's where the problem came in at.

 

[mbartel]

Bullet setback in semi-autos usually occurs for two reasons. The major cause is when the bullet impacts the feed ramp before entering the chamber. The other minor cause, is when the bullets in the magazine impact the front of the magazine under recoil. This is more common with very hard recoiling handguns. The round at the bottom of the magazine would be affected the most (more battering cycles). Too long an overall cartridge length should not be a cause, as the "LONG" round will not feed through the magazine.

 

[Sunray]

Factory or handload? Aside from the bullet getting bashed upon chambering, there could be insufficient crimp with a handload.

 

[JohnKSa]

Or is it from a round sitting chambered for too long?

It can not happen from simply sitting chambered. Possible causes.

1. Improper seating depth when the round was manufactured/handloaded.
2. Heavy recoil while the round is sitting in the magazine can cause setback.
3. Repeated chambering, especially with ammo that has a weak crimp.
4. Dropping the ammunition or otherwise improperly handling the ammunition--again, generally/especially if the crimp is weak to begin with.

 

[HSMITH]

Crimp in an autoloading pistol cartridge has nothing to do with setback. A round with more crimp than one prepared otherwise identically will exhibit a tendency to setback more, try it for yourself.

Setback prevention is 110% done in the sizing of the case prior to bullet insertion. If the case is sized to grip the bullet tightly it won't set back. My handloaded 9mm and 40 can be chambered 25 times and not set back more than a couple thousandths of an inch. The setback prevention done in the sizing of the case can be reduced or eliminated by an oversized expander plug or excessive crimp.

Don't chamber your factory ammo more than a couple times, take the top round off the mag and toss it in a container to be shot at the next range session and use a fresh round for the top round.

 

[Big Calhoun]

Sunray, factory load....Hornady TAP I believe.

I'm fairly certain is was the recmabering of the round that did it. I checked my other firearms last night and all cartridges are normal. Thanks for everyones insight! Lesson learned!

 

[bakert]

HS Smith has it right. Some reloaders believe you can rely on crimp alone but a case sized correctly to give the right tension or bullet pull needs very little crimp except to help maybe help feeding. Like he said too much crimp can actually loosen the bullet which can cause setback. Also like he said continuous chambering can cause factory loads to set back too..

 

[JohnKSa]

So I should say this instead?

1. Improper seating depth when the round was manufactured/handloaded.
2. Heavy recoil while the round is sitting in the magazine can cause setback.
3. Repeated chambering, especially with ammo that has been improperly crimped/sized.
4. Dropping the ammunition or otherwise improperly handling the ammunition--again, generally/especially if it has been crimped/sized improperly.

 

[HSMITH]

I would agree with that 110% John.

 

[chicane]

One of my friends did a test on several brands of .45acp ammo, and all brands show a measureable amount of setback after being chambered.

Not one round that he tried was still "In spec" after 10 chamberings. Some were out of spec after as few as 5 chamberings. All displayed below allowable minimum O.A.L.

Some of the rounds tested were
Corbon
hydrashocks
gold dot

American Eagle
Blazer

He might have done more, But those are the only ones I saw the results of.

After seeing the results, I started chambering a round twice and then putting it in the range pile. There are all kinds of issues when a round is below acceptable O.A.L. Including interenal pressure and feeding issues. (This even more of an issue with .40S&W)

 

[AK103K]

I used to load and unload my pistols each time I wanted to practice, I always saved the top round in a tub for practice.

Now I just leave them loaded and rotate the guns each week.

I have duplicates of what I carry. I practice during the week with the one not riding in the holster. When I go to the range, I shoot with the one in the holster. When I get home, the practice gun gets loaded up and goes in the holster while the other gets cleaned and rotated to practice for the next week.

Took awhile for this whole explanation to sink in with my wife as to why I needed two of each gun I have. I dont think she really bought it though, and just gave up bothering me.