I did not want to hijack the changing defensive ammo every three months thread but it raised this question for me. I don't get to shoot all that often, when I do I usually fire off the defensive rounds in the mag and then go to range ammo, clean and reload with fresh defensive ammo. But in between range trips, I will periodically field strip, clean and lube/oil my guns from time to time. I eject the chambered round and after cleaning rechamber a round off the top of the mag, then place the previously chambered round back on top of the mag and reinsert. So essentially the top two rounds tend to get rechambered a few times. I have never had any problems with this, but I have seen comments from time to time about potential issues with rechambering rounds but don't understand the concern. So what's the deal?

Repeatedly chambering the same round can cause bullet setback, where the bullet is gradually pushed further rearward into the case. This can cause excessive pressure when that round is fired.

Due to differences in bullet design and feed angles, certain handguns in certain chamberings are more prone to this than others, but any caliber in any handgun could develop it over time.

If you're rechambering rounds, keep an eye on them. Comparing them to unchambered rounds is a quick way to gauge if the bullet's suffering from setback, like the one on the right below:




And some rounds are crimped around the middle of the case, or the mouth of the case is crimped into a cannelure groove cut around the bullet, either of which can help prevent setback:

one reason I have always been a fan of the Fed 9mm +p+ (9bple)

it is 'crimped' mid-body as pictured above. never had an issue with set back with them

i have found 9mm Gold Dots highly resistant to setback also

but always good to inspect them after repeated chamberings and discard (shoot) them with regularity

-----------------------------------

Thank you. understand the concept now and will start checking for setback when I reload. Easy. new question. If I see that the bullet is compressed into the case do i dispose of that round? And how would I safely dispose of it?

Since you're a reloader you probably have a bullet puller. Pull the bullet, dump the powder, reload the case. If it's ammo you loaded, you can re-use the bullet too.

Each time I rechamber a round, I mark the base with a permanent marker - a line a 12 o’clock, then 3, 6, and 9.
After 4 times, I will shuffle that round to the last round of the magazine.
It’s an arbitrary number, but better safe than sorry. Plus HST and Gold Dots aren’t as prone to setback as other rounds so I’m not really all that worried.

I usually shot and replenish my carry ammo once a year, so there aren’t that many rechambered rounds in there.

All that’s good information, and although I believe the “overpressure from setback” worry is overblown, it can’t hurt to be careful. One of the things I do to avoid the problem is to chamber a defensive carry round slowly so the bullet isn’t slammed into the feed ramp at full speed. Some people will object to that practice and tell me I’m developing a bad habit, but I don’t do that in training, and I chamber rounds in training far more frequently than the times I chamber a defensive cartridge. So I avoid the setback and don’t develop bad habits.

I don't reload, truth be told I am probably in the lower percentile of the people on this forum in terms of firearms knowledge and experience. But my takeaway is that my practices are unlikely to cause me any problems. I tend to carry HST or Gold dots, and the rechanbering duty is shared by the top two round which probably don't get rechanbered more than 3 or 4 time each at most. And now I know what to look for when I do reload after cleaning. I think I am good. Thanks to all.

If you don't pull the bullet, you could drop it off at a range or maybe Police dept or small mom&pop gun store ?

Personally I wouldn't be that worried about just throwing it in the regular garbage. I'd guess the chance of it going off is pretty slim and even if it does, the damage it could do is minor anyway (since it's not inside a barrel to contain the pressure).

quote:

Originally posted by kho:
If I see that the bullet is compressed into the case do i dispose of that round? And how would I safely dispose of it?

If you reload you can pull the bullet.
If o you don’t, you could chuck it in the trash, as it will wind up in a landfill.

You could ask around at the local range you attend-someone may dispose of it for you.

When I was a cop, people would bring us guns and ammo because they inherited a gun and didn’t like them. We cut up the guns after a judge ordered them destroyed and we threw the ammo in the landfill.

When I was in the CG and people brought ammo to the base we accepted it, but burn it it the next range day, in a 55gal drum. Having EOD destroy ammo/pyro cost us a lot of money. They billed us.

If you have a burn barrel at your home you can burn it safely, as the projectile is heavier than the case. When the powder gets hot enough to burn the case will fly away from the projectile. The case will be contained by the drum. Don’t drop a whole box of ammo in the fire. We always did one round at a time.

The way you chamber the round has an effect on the setback. Slingshotting the slide forward with more force will have a pronounced effect on setback, while easing it forward slowly, not so much. Some ammunition and some cartridges in general are much more prone to setback.

.357 Sig seems more prone to it than nearly any other handgun cartridge.

When re-chambering a round, I check it first, but I rotate the rounds in the magazine, rather than re-chambering, and before I put a magazine in the pistol for carry, I check the cartridge agaisnt a new one, for overall length.

If you're shooting 9mm, there's wide range of cartridge overall lengths that are acceptable, without getting into dangerous chamber pressures, but that margin erodes when using extra-pressure ammunition (+P or +P+).

Crimping can reduce setback, but also has a negative impact on cartridge accuracy, and crimping also increases chamber pressure by some small margin, depending on the crimp.

Repeated rechamberings can scratch or nick up the case from contact with the extractor and ejector. I don't like to rechamber the same round more than once, maybe twice.

If you have a spare "range mag" put your previously chambered rds in and load fresh
new rds into your carry mag.

I mark the case of the round that goes into the chamber when I first load the pistol up with SD ammo. (I use whatever permanent marker that happens to be available.) Then, each time I take the pistol to the range, whatever round was in the chamber goes to the bottom of the magazine.

When I see the marked round rise to the top, I shoot that mag-full of SD rounds.

That way no round is re-chambered more than once, and my pistols are regularly "re-qualified" with my SD rounds.

quote:

Originally posted by gjgalligan:
If you have a spare "range mag" put your previously chambered rds in and load fresh
new rds into your carry mag.

Hmmm... That may be better than my idea. Less labor-intensive, anyway