Just had this done, unbeknownst to me, until it was pointed out and I started to pay attention.
Haven't seen or heard it discussed much before. What's the point? A little more breakover clearance? A few thousandths straighter shot into the chamber? Something to do with timing of the firing cycle? - it's more favorable to functioning somehow, I surmise.
Or not even close?
There are a couple reasons for that... depending on the gun and what it's doing.
One is obtain clearance between the barrel and the bed so that the barrel doesn't hit the bed before or at the same time it hits the vertical impact surface. This is done by actually removing material from the frame. Removing metal from the frame also increases the ramp to barrel gap a little. Be aware that there's a limit. When you lower the bed itself, you also raise the contact point between the barrel lug and the VIS. There's also a limit on that gap. Too much is as bad as not enough.
Removing a few thousandths from the bottom of the barrel provides a slightly straighter shot at the chamber, but the minimal amount allowable doesn't make a whit of difference. It also provides a slightly reduced breakover angle... but still not a lot of difference. Every little bit helps, though.
The main enhancement is that... in the pistols that get the barrel ramp bumped by the incoming round... the strike is a little higher. This reduces the tendency to push the barrel forward, creating the infamous 3-Point Jam. Remember that the barrel ramp is a clearance, and not a feedway or bullet guide... and it'll start to make more sense when you visualize the function.
The combined effects of removing a little from the lower radius of the barrel are like tolerance stacking in the right direction. Alone, neither one makes a lot of difference.
Together, they often make a major difference in the way the gun feeds. Sort of a question of the sum of the parts being greater than the whole. When the gun is properly set up, it almost feels like it's going to battery on an empty chamber, and bullet setback is a thing of the past.
Of course, it greatly depends on correct feed ramp geometry, and the way that the magazine releases the round plays a major role in it. While you can very often compensate for incorrect ramp geometry by playing with the other aspects... there's a limit beyond which nothing really helps, and the only alternative is to have the ramp remachined and/or a correct ramp insert installed. Unless it's really bad, a little careful fine-tuning usually works wonders.
Hmm. Sounds like I should have had the barrel and frame looked at together, rather than thinking the barrel ramp alone needed clearancing. Maybe something to look over after I see what effect barrel ramp correction adds to function.
"One is obtain clearance between the barrel and the bed so that the barrel doesn't hit the bed before or at the same time it hits the vertical impact surface. This is done by actually removing material from the frame. Removing metal from the frame also increases the ramp to barrel gap a little."
So the order of impact needs to be vertical impact surface first, frame bed second? How do you tell which is occurring first? Are there visible marks I should look for or some kinda functioning anomaly? Does this result in a tendency toward or contribution to a particular problem when part of a larger whole?
Okay, I'll bite on this one:
"Removing metal from the frame (bed?) also increases the ramp to barrel gap a little."
I'm trying to picture this and the elevator ain't rising to the top. Somehow it seems like if the barrel is lower in the frame bed it ought to get closer to the frame ramp. At least, if the vertical impact surface isn't the limitation.
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So the order of impact needs to be vertical impact surface first, frame bed
second? How do you tell which is occurring first?
To find out, perform the timing tests from Schuemann Barrels - they're in our Technical Issues section.
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Somehow it seems like if the barrel is lower in the frame bed it ought to
get closer to the frame ramp. At least, if the vertical impact surface isn't
the limitation.
The VIS is indeed the limitation. The contact between the aft vertical surfaces of the barrel feet and the VIS firmly fix the aftmost position of the barrel in the frame when the barrel's linked down.
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So the order of impact needs to be vertical impact surface first, frame bed
second?
VIS first, with a little clearance between barrel and bed. It doesn't have to be much clearance. The thickness of cigarette paper is enough.
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How do you tell which is occurring first?
Color the bottom of the barrel with layout fluid or a Sharpie marker and assemble the gun without the recoil system. Put the slide into battery and whack the muzzle sharply with a heavy rubber mallet a few times. Disassemble it and look at the barrel to see if any ink has been removed. If it has... it needs a little clearance. Take about .003 inch off the barrel and re-test. If it needs more... take another .003 out of the bed.
If you also happen to need to increase the ramp to barrel gap... do the frame bed first, and kill two birds with one stone. Look carefully at the angle in the feed ramp to understand why the gap grows. It may help to draw a picture of a right triangle, with the hypoteneuse (C) facing right, and visualize a pistol with the muzzle pointing left. If you erase a portion of the apex and draw a straight line from the hypoteneuse to A... you can see that the distance from C to A increases as the line gets closer to B.
Right triangle: The side from the floor to the apex is A... or altitude. (Height) The side at the bottom is B... or the base. The angled side is C... the hypoteneuse.
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And, cuz I was in a hurry for my 40 winks and overlooked it,
The VIS is indeed the limitation. The contact between the aft vertical surfaces of the barrel feet and the VIS firmly fix the aftmost position of the barrel in the frame when the barrel's linked down.Cheers
It's been discussed constantly, but I've never have found a definition.
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Put the slide into battery and whack the muzzle sharply with a heavy rubber
mallet a few times.
Sorry if I got confused here, but didn't you mean to say "lock the slide back and whack the muzzle sharply"???? That's when the bottom of the barrel bottom is likely to contact the frame bed.
Vertical Impact Surface. It's the area of the frame where the feet of the barrel hit, as the barrel comes down and back. Or at least that's the surface that should stop the barrel, in a properly tuned 1911. If the barrel hits the barrel bed first, before its legs hit the VIS, then you have a problem. If you look inside the frame, there is a slot cut, where the barrel's legs go. The rear area of that slot is the VIS.
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but didn't you mean to say "lock the slide back and whack the muzzle
sharply"?
Nope. I said what I meant.
So Tuner, let me get that straight. You have the slide all the way forward and slap the muzzle with the mallet, allowing it to move all the way back? Is that the way to do it?
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You have the slide all the way forward and slap the muzzle with the mallet,
allowing it to move all the way back? Is that the way to do it?
Yes. Starting with the slide full rearward, the barrel is on the bed. If you hit the muzzle with the barrel on the bed, you'll remove ink regardless of whether there's adequate clearance. By starting with the slide in battery, the barrel moves rearward... stops on the VIS... and drops the final couple thousandths of an inch to the bed. If it has adequate clearance, no ink is removed.