Jump the Bump: Return of the 1911 FTB


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Candiru
April 9, 2006, 05:36 PM
I posted a thread a while back complaining about an issue with my SA Mil-Spec failing to go into battery on the last round when said last round was a Remington Golden Saber. Thanks to a useful post by 1911Tuner (http://forum.m1911.org/showthread.php?t=1959), I figured out that the symptom of the last round being chambered ahead of the extractor is usually caused by the lack of a dimple on the follower, or the inability of the case rim to engage the follower. Although my SA stainless steel mags had the dimple, my theory was that the new magazine's follower was hanging up on something and not letting the bump catch the rim of the last round. I dressed the follower of the offending magazine, returned to the range, and tried out a number of magazines loaded with only two rounds. They worked great.

However, a nagging doubt remained: I hand-chambered the first round when testing, a practice known to create a different chambering situation than the natural recoil action of the pistol. To assuage these doubts, I resolved to return to the range with more Golden Sabers and test an entire box by loading three rounds at a time in the magazine. That way, if I had inadvertently helped things by hand-chambering, it would become clear when the second-to-last and last rounds were both recoil-loaded.

Sometimes I really hate being right.

Turns out the failure to go into battery wasn't resolved by dressing the magazine follower, probably because it occurs no matter which magazine I use. This has me scratching my head and considering the following causes:

Horrific limp-wristing is forcing the round over the dimple. Possible, but not likely. I ran an entire box of ball ammo through the mags, three rounds at a time, limp-wristing as hard (or as limply, I suppose) as possible and wasn't able to get the same results as the hollowpoints. Ball ammo does have a longer overall length, but the difference in OAL between WWB ball and Remington GS is about .04", which shouldn't make much of a difference...or should it?

Something about the cartridge itself is causing it to jump the bump. Possible. Golden Sabers use nickel-plated cases, which might be too slippery for a stainless follower and feed lips. Or it could be that the GS's zippier loading is introducing just enough momentum to force it past the bump. This doesn't seem too plausible, though, unless it's also the case that...

The magazine springs aren't strong enough to hold the last round in place. The only problem with this theory is that I'd expect the last round to jump the lips entirely when the slide slaps the frame if the mag springs were too weak, resulting in premature slidelock and/or ejection of a live round. Or is there a margin of spring strength where the springs are weak enough to let the round jump the bump, but prevent it from coming clear of the follower entirely?

If you've read through this entire post but have no suggestions, then at least learn from my lesson: If you're testing how the last round or two feeds from the magazine, make sure to load three rounds at a time so that hand-chambering doesn't play a factor.

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wally
April 9, 2006, 05:49 PM
Since I rarely carry a spare mag, thats why I like the 8-round CMC mags (or 7-rounders for the Officers ACP sub compacts). I'll get 7+1 for sure and may get 8+1. At the range I seem to always get 8+1 which gives me confidence. Haven't noticed an issue with nickel plated 230 gr Golden Saber or 230 gr Federal Hydrashok in any of my guns or mags. These eight rounders lack the dimple, they work well for me YMMV.

Have you tried a different brand of ammo? Some guns just don't like some ammo and vice-versa, for whatever reason. I'd prefer my guns work with anything I can cram in the chamber, but sometimes tolerence stack-up just makes some combinations impossible to make reliable. If its only one ammo brand that causes the problem, I'd forget about it and buy a different brand of ammo and be done with it.

--wally.

1911Tuner
April 9, 2006, 05:50 PM
Thinkin'...Thinkin'...

The RTB failure...Round getting ahead of the extractor or a simple failure due to an overtensioned extractor or 3-point jam/stem bind condition?

wally
April 9, 2006, 05:59 PM
simple failure due to an overtensioned extractor or 3-point jam/stem bind condition?

If this were the situation, why would it be confined to only the last round?

--wally.

Candiru
April 9, 2006, 06:01 PM
I probably should have clarified exactly what's happening. The round is chambering fully, but the extractor claw is sitting behind the rim. I'm kinda scratching my head over why the extractor didn't ride over the rim, but if it did that I wouldn't even know about it.

wally
April 9, 2006, 07:03 PM
Bump on the follower in the wrong place, or weak mag springs. That'd be my bet based on the most recent info.

--wally.

1911Tuner
April 9, 2006, 08:29 PM
Wally:

>If this were the situation, why would it be confined to only the last round?<
********************
Happens sometimes...because the last round's feed angle is different from the others. I've seen guns gobble all but the last round and do FTRTB until the extractor tension is reduced a mite.

Okay Candiru...it's jumping the follower. You've got the dimple. How about mag springs? Wolff or OEM? Weak mag springs will do it too, and it doesn't always result in the round ejecting from the magazine. All it has to do is lose contact with the breechface while it's stripping...and yes...OAL can be a player, especially if the feed ramp angle is just a tiny bit out. It should be
31 degrees + one-half degree/minus zip. If it's 30.5 degrees, it can cause things to go haywire.

Candiru
April 9, 2006, 09:04 PM
My mags are Springfield Armory OEM and have the stock springs in them. Looks like I'll try putting in some Wolff springs. As for the feed ramp, I'll try to figure out a way to measure it. Thanks for your help.

1911Tuner
April 9, 2006, 10:19 PM
The Wolff springs will probably cure it. Springfield's OEM mag springs are pretty soft.

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