I've looked all over the web and my Kuhnhausen books for a discussion of the 6 degree angle in the barrel link/underlug area, as shown in the top view of the frame drawing, but I can't find a thing. It appears that each side of the .365 + .005" wide barrel link/lug "channel" should be tapered 6 +/-1 degrees from the front (widest point) to 1/8" back. Six degrees is about .001" per .010" so the channel should be .365" + (2 x .0125) = .390" wide at the front tapering to .365 (give or take stated tolerances)? (.001" per .010" inches is actually 5.7 degrees but it's still within spec and it's easier to program into my mill than 6 degrees.)
This angle doesn't seem to be present on the frames I've inspected. Am I missing something here?
If this 6 deg chamfer is on an Army Ordnance blueprint but you haven't seen it on a frame, you're not missing anything. Whoever made the frame(s) is missing something.
I would think tighter at the front would repeatedly locate the barrel in battery better. (accuracy wise)
Notice the "pad" welded on this Giles barrel to eliminate play.
PICTURE 404
PICTURE 404
It measures .3645, the channel you discuss tapers from .365 to .368 at the front/muzzle end of the frame.
This is on a '65/'66 Colt .38 Super, rechambered for .38 Spec.
Quote:
I would think tighter at the front would repeatedly locate the barrel in
battery better.(accuracy wise)
Notice the "pad" welded on this Giles barrel to eliminate play.
Interesting! That "pad" would tighten the lug at the back to only a quarter thou' per side but it only leaves only .00175 per side where it enters the channel. I guess that's enough, but I'll chamfer my frame to 6 degrees this time and leave the high performance tweaks for later, once I prove my success with ordnance specs. Thanks for the pics, shovelwrench. Your knowledge gives me some idea of what can be done.
Post #2 was done while I was on the road without access to either my blueprints or a 1911. Am home now with both and a Remington Rand frame has the chamfer shown on the Ordnance blueprint.
Looks like all the chamfer does is make it a little easier to slip the frame on the upturned slide/barrel/bushing during assembly. Once together, I don't think the chamfer does a thing for the gun.
Quote:
I would think tighter at the front would repeatedly locate the barrel in
battery better.
YES. Giles was 100% correct. The first thing I do to the frame is machine the lug slot on the frame rail centerline; true and square the sides... When done, it is what it is, then fit/adjust the barrel lug accordingly.
Thanks you very much! Your comments both make sense to me. It sounds like a tight fit with the barrel lug performs better but a little chamfer makes it easier to replace the slide--which is probably more significant when the side clearances are tight.
Quote:
Notice the "pad" welded on this Giles barrel to eliminate play.
While we are on the subject, I guess welding this pad would require re-heat treating the barrel?