Bullet setback...?


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mpthole
August 13, 2004, 12:08 AM
I'd heard of it before... you know, every time you chamber a round the bullet can get pressed back into the case a little bit each time - therefore, one should always rotate/shoot their carry ammo every now and then and not chamber the same round every time. Right?

** Disclaimer: I realize that loading live rounds while not at a shooting range is potentialy dangerous... and that manually cycling live rounds may not be the best idea either. Safety precautions where taken at all times. ***


So, tonight after I cleaned my gun (1911) and installed a new 18.5# recoil spring, I loaded it up and manually ejected a couple rounds to see how it was going to work. Upon inspecting the ejected rounds I discovered that some had been set back something terrible! Compared to a new round, there was as much of a difference as .050 inches - and this was all on new factory ammo! I thought that seemed like a lot, so I tried it with some of my hand loads. The set back on my own was usually less than .010.

I switched back to the old recoil spring to see if that made any difference. Sure enough, the setback wasn't nearly as bad, but still around .020.

Then I tried hand cycling both the factory ammo and my own in my full-size USP. Setback in the USP was more like .002 for each type of ammo.

What the heck is going on...?
a) bad factory ammo
- or -
b) too heavy recoil spring

Ideas?

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JohnKSa
August 13, 2004, 12:27 AM
Want a real eye-opener? Try your test with some Blazer ammo.

Hint: You can put your calipers away before the test.

Setback from chambering rounds is going to vary with the gun and the ammo.

The tighter the case holds the bullet, the less setback.
The straighter the feed into the chamber the less setback.
The more violent the impact against the feedramp the more setback.

I don't have a 1911, but I'm guessing that the bullet is pretty much aimed at the feedramp out of the magazine.

In the USP, the bullet is aimed right into the chamber. It's going to glance off the feedramp on the trip, but the nose of the bullet won't touch the ramp. It's there to guide the round, not redirect it. That means less impact and less setback. It also means some other things, but I don't feel like stirring up a nest of hornets...

only1asterisk
August 13, 2004, 12:43 AM
Yup, bullet setback is real!
(and a little scary)

David

mpthole
August 13, 2004, 10:09 AM
Want a real eye-opener? Try your test with some Blazer ammo. Actually, the factory ammo I used was the new CCI (Blazer) Brass. Kind of makes me not want to shoot it in the 1911.

JohnKSa
August 13, 2004, 09:45 PM
The aluminum Blazer is worse.

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