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Bullet setback? Who frequently rotates their mags?
#1
Figured it would be a good subject.

“setback,” which is when the bullet gets pushed deeper into the case than it was designed to be. This can happen when the same round gets chambered over and over, as in unloading and reloading a carry gun regularly without rotating the ammunition. The deeper the bullet is pushed into the case, the harder it is to push it back out again, and that can lead to dangerous overpressure and possibly an explosion. In effect, it becomes easier for the powder to blow the back of the case apart than to drive the bullet out the front.

There are three easy ways to prevent bullet setback. First, don’t unload your gun every time you set it down. Second, use ammunition that has the top of the case crimped into a cannelure. Third, if and when you do unload your carry weapon, rotate the ammunition so that you’re not always rechambering that same first round.

It tends to happen more frequently in lever action rifles, where the bullets are loaded into a tube with the base of one cartridge resting on the nose of the preceding bullet. The cartridges are under spring tension so they will feed when the lever is operated. (This is why tube-fed firearms recommend using flat or round tipped bullets, to avoid the sharp point of a bullet setting off the primer in the next round). The spring tension can force a bullet deeper into the case, so the bullets are normally “roll-crimped” into the case. That is, the top circumference edge of the brass case is squeezed or rolled into the “crimping groove” or cannelure of the bullet, thus locking the bullet into the case.

Bullets can also be pushed back into the case by higher levels of recoil in the more powerful cartridges.

Bullet roll-crimping can only be done on rimmed cases, where the cartridge “head-spaces” on the rim. So-called “rimless” straight-walled cases (.380, .40, 9mm, .45 ACP, and most other rounds for semi-autos) head-space on the front circumference rim of the case, so they cannot be roll crimped into the bullet. (Because that would change the effective length of the casing as far as the head-spacing is concerned, leading to another dangerous situation.) Most tapered rifle cartridges head-space on the shoulder of the case – see below.

Therefore, rimless straight-walled cases are usually “taper-crimped”, where the bullet is held in the case by the inward pressure of the case – sort of like a hose-clamp on a rubber hose – to keep the bullet from being forced back into the case by recoil.

You do not want the bullet forced back into the case because (depending on the bullet and powder load involved) this can actually result in the bullet compressing the powder, or lessening the space above the powder, thus increasing the pressures generated by firing that load.

Pretty lengthy answer, but I can’t think of a simple way yo explain why the bullets are crimped.

“Head-spacing” is the critical length of that portion of the cartridge that determines how deeply into the firearm’s chamber the cartridge will go at the moment of ignition. Cartridges are head-spaced on the rim (like a .22LR or a .38 Special), the mouth of the case (like a .45ACP), or the shoulder of the case (like a .308 rifle). Head-spacing is important in a cartridge because improper (too long or too short) head-spacing will result in (1 – too long) the cartridge not being fully chambered when the firing pin hits the primer, and the firearm may then fire when the slide/bolt is not fully locked up (BOOM), OR (2-too long) the cartridge will go too deep into the chamber and the firing pin may not be long enough to ignite the primer, or if the primer ignites, the bullet/case may enter into the rifling and be squeezed too tightly together by the smaller dimensions – therefore increasing pressures to dangerous levels (also BOOM).

This lengthy and complicated explanation illustrates why reloading is a VERY exacting process, requiring a high level of attention to detail. (As in “trim-to” lengths on fired brass cases.)
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#2
I run into it when i re-chamber the same round a lot of times. When i do, i grab a pair of pliers, pull the bullet out to the right depth, and put the round in the range ammo "loosies" box.
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#3
The first couple of mags I shoot at the range are what I'm currently carrying. They get fresh rounds when I get home.

Justin
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#4
I try to stick to carry ammo that is crimped to prevent it. The Winchester Ranger T and Bonded are what I currently have in my guns and both seem to resist setback. The guns that I have designated for carry or home defense do not get unloaded except when they get shot at the range. When they are unloaded the rounds get dumped back into the appropriate ziplock bag of ammo so the same round is unlikely to wind up on top two times in a row.
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#5
I feel like I just read this in a magazine and I cant think of which one.

Anyways, I digress. I rarely ever unload my carry gun or my night stand gun but when I do (magazine rotation) I make sure that I put the ejected round in the magazine first. I like to have three magazines, for each of my handguns that I keep loaded and I number them. Every 4 months I unload the magazine I keep loaded and use a different magazine for the next 4 months. Just the system I have stuck with.

GB
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#6
GreenBlood10;44250 Wrote:I feel like I just read this in a magazine and I cant think of which one.

Anyways, I digress. I rarely ever unload my carry gun or my night stand gun but when I do (magazine rotation) I make sure that I put the ejected round in the magazine first. I like to have three magazines, for each of my handguns that I keep loaded and I number them. Every 4 months I unload the magazine I keep loaded and use a different magazine for the next 4 months. Just the system I have stuck with.

GB
http://www.thetruthaboutguns.com/2012/08...led-carry/
Read the comments.

seriously...
Some people need to read this book: http://www.amazon.com/dp/1936976021/ref=...jwbZH1GAZF

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#7
39Flathead;44330 Wrote:
GreenBlood10;44250 Wrote:I feel like I just read this in a magazine and I cant think of which one.

Anyways, I digress. I rarely ever unload my carry gun or my night stand gun but when I do (magazine rotation) I make sure that I put the ejected round in the magazine first. I like to have three magazines, for each of my handguns that I keep loaded and I number them. Every 4 months I unload the magazine I keep loaded and use a different magazine for the next 4 months. Just the system I have stuck with.

GB
http://www.thetruthaboutguns.com/2012/08...led-carry/
Read the comments.

seriously...

Anything in particular I should be reading? I don't have time to sift through all those on my phone.

GB
[Image: IMG_6916_zpsfa73efcb.jpg]


Certified Range Safety Officer. Proud member of the NRA, GOA and GSSF. PA2A since Sep 2012.
Give me a follow @MikeCo88
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#8
GreenBlood10;44331 Wrote:
39Flathead;44330 Wrote:http://www.thetruthaboutguns.com/2012/08...led-carry/
Read the comments.

seriously...

Anything in particular I should be reading? I don't have time to sift through all those on my phone.

GB

From Matt in FLA:
Quote:There are three easy ways to prevent bullet setback. First, don’t unload your gun every time you set it down. Second, use ammunition that has the top of the case crimped into a cannelure (I’ll let you Google “crimped cannelure” yourself, because if I put a third link in this comment, it’ll go to the spam filter and it’ll be hours before you see it). Third, if and when you do unload your carry weapon, rotate the ammuntion so that you’re not always rechambering that same first round.

From Idaho Pete:
Quote:Bullet seat back is when the bullet is pushed back further into the brass cartridge case, so it is “seated” deeper in the case than the loading specifications for that round. It tends to happen more frequently in lever action rifles, where the bullets are loaded into a tube with the base of one cartridge resting on the nose of the preceding bullet. The cartridges are under spring tension so they will feed when the lever is operated. (This is why tube-fed firearms recommend using flat or round tipped bullets, to avoid the sharp point of a bullet setting off the primer in the next round). The spring tension can force a bullet deeper into the case, so the bullets are normally “roll-crimped” into the case. That is, the top circumference edge of the brass case is squeezed or rolled into the “crimping groove” or cannelure of the bullet, thus locking the bullet into the case.

Bullets can also be pushed back into the case by higher levels of recoil in the more powerful cartridges.

Bullet roll-crimping can only be done on rimmed cases, where the cartridge “headspaces” on the rim. So-called “rimless” straight-walled cases (.380, .40, 9mm, .45 ACP, and most other rounds for semi-autos) headspace on the front circumference rim of the case, so they cannot be roll crimped into the bullet. (Because that would change the effective length of the casing as far as the headspacing is concerned, leading to another dangerous situation.) Most tapered rifle cartridges headspace on the shoulder of the case – see below.


Someone is plagiarizing someone somewhere.

I think Andrew should have put a disclaimer on his post that it was some information he found on the net and is just passing along.




As for setback, I've only ever noticed it when I had a 229 in .357Sig.

As long as I loaded one directly into the chamber and didn't drop the slide I never had a problem.
Some people need to read this book: http://www.amazon.com/dp/1936976021/ref=...jwbZH1GAZF

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#9
39Flathead;44334 Wrote:
GreenBlood10;44331 Wrote:Anything in particular I should be reading? I don't have time to sift through all those on my phone.

GB

From Matt in FLA:
Quote:There are three easy ways to prevent bullet setback. First, don’t unload your gun every time you set it down. Second, use ammunition that has the top of the case crimped into a cannelure (I’ll let you Google “crimped cannelure” yourself, because if I put a third link in this comment, it’ll go to the spam filter and it’ll be hours before you see it). Third, if and when you do unload your carry weapon, rotate the ammuntion so that you’re not always rechambering that same first round.

From Idaho Pete:
Quote:Bullet seat back is when the bullet is pushed back further into the brass cartridge case, so it is “seated” deeper in the case than the loading specifications for that round. It tends to happen more frequently in lever action rifles, where the bullets are loaded into a tube with the base of one cartridge resting on the nose of the preceding bullet. The cartridges are under spring tension so they will feed when the lever is operated. (This is why tube-fed firearms recommend using flat or round tipped bullets, to avoid the sharp point of a bullet setting off the primer in the next round). The spring tension can force a bullet deeper into the case, so the bullets are normally “roll-crimped” into the case. That is, the top circumference edge of the brass case is squeezed or rolled into the “crimping groove” or cannelure of the bullet, thus locking the bullet into the case.

Bullets can also be pushed back into the case by higher levels of recoil in the more powerful cartridges.

Bullet roll-crimping can only be done on rimmed cases, where the cartridge “headspaces” on the rim. So-called “rimless” straight-walled cases (.380, .40, 9mm, .45 ACP, and most other rounds for semi-autos) headspace on the front circumference rim of the case, so they cannot be roll crimped into the bullet. (Because that would change the effective length of the casing as far as the headspacing is concerned, leading to another dangerous situation.) Most tapered rifle cartridges headspace on the shoulder of the case – see below.


Someone is plagiarizing someone somewhere.

I think Andrew should have put a disclaimer on his post that it was some information he found on the net and is just passing along.




As for setback, I've only ever noticed it when I had a 229 in .357Sig.

As long as I loaded one directly into the chamber and didn't drop the slide I never had a problem.

Ahhh, yes sir. I went through 10 magazines last night because I know for a fact I read this in a magazine. It had pictures and everything of a round that had been chambered repeatedly. I couldn't locate it.

Good topic nonetheless.

GB
[Image: IMG_6916_zpsfa73efcb.jpg]


Certified Range Safety Officer. Proud member of the NRA, GOA and GSSF. PA2A since Sep 2012.
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#10
Yes, it is a good topic.

I'd just have liked to see that disclaimer. It comes off strangely when it appears someone has posted word for word posts/articles found elsewhere and the reader gets the assumption that the words are of the author of the post.
Some people need to read this book: http://www.amazon.com/dp/1936976021/ref=...jwbZH1GAZF

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