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6/27/2018 6:11:08 AM
 
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Section 16: Gun Work Subject: 1911 Barrel Throats Msg# 1018216
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Your test makes good sense. Reloaders who have used their pistol's barrel as a cartridge OAL length gauge recall that the base of the case should sit flush with the back of the hood. Perfect way to check a round and see where it sits, as you suggest.
As to using GI mags with JHPs, yes I've tried them. Sometimes they work fine. When they don't the problem can be the shortness of some loads not being able to properly bounce off the hood and into the chamber. This usually happens with target SWCs, though. Today's JHPs tend to be round-nosed and mimic ball ammo in shape, however, unlike earlier JHPs which tended to be SWC in shape. Remember the old 1911 saying, the closer your load resembles ball ammo the more reliable it will be? I believe JHP ammo makers took that to heart. That being the case, a late release isn't a problem like it can be with short and stubby SWC target loads. It isn't so much the width of throating, in my opinion, it's the irregularity of the bullet shape bouncing off the underside of the barrel hood and then the into the throat. If they get a late release (via GI mag) they are less likely to smoothly transition from bounce to chamber. Russ Carniak was smart to bevel that edge of the hood, this is custom touch too often ignored. Then, throating about halfway between I and what was shown in the photo at the start of this thread is probably enough to insure reliability with most loads. |
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For reference, the above message is a reply to a message where: A lot of this magazine and feed ramp tuning is just black magic to me. I confess I don't know enough about it so take some of the comments below as open questions rather than any attempt at answers. 
But the way a .45ACP feeds out of a 1911 is that it comes up at about 30 or even 40 degree angle and bumps into the underside of the barrel hood, then down into the chamber. The idea that it releases smoothly from the magazine, slides up the feed ramp and into the chamber is inaccurate. Very true. In fact, Russ Carniak, who turned my Colt jam-o-matic into a very reliable 1911 actually eased over the top chamber edge, where it meets the hood, so a round will slide past with less chance of hanging up or bouncing away. Target SWCs and JHPs are generally used with magazines that release the round so early you might still be parking your car at the range. Now that you mention it... At any rate, it seems to me that most pistols don't really need that uber wide barrel throating as shown in the photo. Does it hurt anything? Good question! There are two dimensions to concern us with a throating job. The obvious one is width. I think "more is better than less" has been the motto of most smiths, just to account for the variability in nose shape and release angle of ammo and magazines likely to be encountered. I doubt that hurts anything. The second dimension is depth of cut. The re-throat shouldn't intrude any deeper into the chamber than the original throat did. Ideally this is less deep than the thickness of the base web of any cartridge casing encountered. There should be no real concern if this is the case. The issue of oversized chambers, like the Glock, while illustrative of possible complications, isn't quite the same, I think. So here's what I would do. First take an empty casing from your favorite 1911 cartridge, measure down the interior to find the point at which the side walls begin to constrict at the base and scribe a line around the outside of the case corresponding to this depth. Then do your "drop it into the chamber" test and see if that scribe mark is visible anywhere around the circumference. If you can't see it, I would say there's no concern. What do you think? Stu |
I've often wondered why this early release.
This is something that I should have been more aware of but wasn't. Have you ever just used GI magazines with more modern SWC or JHP ammo and seen any problems? i confess I've been oblivious to the difference.