Gold Cup Barrel Hood and lugs

[nitetrane98]

Have you ever had some nagging little thought running around in your head and you can't seem to figure it out? Well I ordered a 40S&W barrel for my 10mm Gold Cup and though I haven't received it yet it looks like I'm in for a sure 'nuff barrel fitting project. I was reading up on slide fitting and it seems as though the barrel hood on a Gold Cup is narrower than a regular govt model. I had read that somewhere before but it didn't click.
Anyway, I was looking at some fitting tools at Brownells and I could use one for the barrel hood fitting. The lower lugs would have to be trial and error. Does anyone have a govt model barrel handy that they could measure the width of the hood and give me an idea how much I'm going to have to take off each side? The 10mm measures .355. The slide and frame mating areas are measuring about .365. .005 on each side doesn't seem to be fanatically snug. The slide stop pin appears to all that holds it parallel to the frame amd slide anyway. If it's going to be a lot of filing it may be time to visit my buddy at the machine shop. It doesn't look like jigging a barrel up is an easy thing to do. Not crazy about spending 150 bucks for a jig either. I'm mostly worried about getting an equal amount off each side. Strangely enough the hood and lug on the original are not perfectly parallel.
Maybe there is somewhere that has Gold Cup specific tools???
All help appreciated.

 

[krs]

I'd guess that if your 10mm GC hood is .355" calling it not fanatically tight is an understatement.

Without measuring the barrel hoods a late model .45 Gold Cup has a notch that's .400" wide, and an old government model essex slide is .040" more at .440". These are the width of the notches to which you'd want to achieve a reasonably snug fit at say .395" or .435" respectively. (I like a .005" fit, but that's just me).

In looking at a 1972 70 Series Government model I find that the notch is exactly .435" wide.

So hopefully this will mean that you have less work to do than you anticipated.

I've found barrel hoods in many 'states of fit' over the years so to me it makes more sense when fitting a barrel to determine the size of the notch and cut only enough off of the hoods to bring them to the desired fit. After all, even in a pistol meant to achieve the best possible reliability accuracy never hurts.

The job can be done without jigs but it is important to place the barrel vertical in the frame. or in the slide depending on how you're looking at it. It's pretty rare that equal amounts need be taken from each side of a hood.

Kart sells a little kit for fitting their barrels. The enclosed tools can be very useful in fitting any barrel to any slide/frame. There's a little block that's used to put the barrel correctly vertical in the slide so that the amounts to be taken from each side of the hood can be observed and finally measured. The worst thing would be to go happily filing the hood to size only to find that even though it's the right width it's offset to one side or the other when the pistol is assembled. The simple little tools do a decent ballpark job of keeping mistakes at bay. Costs some $40. at retail, Brownell's probably still has them.


edit: BTW, Colt decided to narrow their slide notches/barrel hoods on all models. The narrow ones are not necessarily "Gold Cup" - it's true of all models since sometime in the 1980's, I think, someone can say better exactly when that change was done. I'm saying that a late government model barrel will fit a late gold cup, but a late either one will be a loose fit in either kind of earlier gun. I'm getting all screwed up trying to get this across - but it means that your barrel is not narrow because it's a gold cup barrel - it's narrow because it's a later model gold cup, OK?

 

[nitetrane98]

You've brought up several things that I realize I just don't know about. First is that I'm just presuming that the 10mm/40S&W hood on a non Gold Cup is the same as a .45. May very well not be. I think that .0025 (less than the thickness of a piece of paper) on each side will be challenging with a file. But I agree, tighter is better up to a certain point. Since I've got to do it, might as well shoot for the best. Looks like there are several areas for tolerance stacking to show up. I'm showing about .004 on each side for link to lug, throw in a few more thousandths for pin to link. I wish I had a finely fitted 1911 just to feel what these parts feel llike wiggle-wise. I don't think they're supposed to be a sliding fit in the machinist sense of the term. As far as the tools go, if the 10mm/.40 hood and lug are narrower than the .45 they wouldn't do any good unless I possibly shimmed the sides to make up the difference.
I certainly don't know what to think about the whole idea that I can fit this barrel better than Mr Colt. Stranger things have happened I suppose. I think I'll go looking for some hard data.
Thanks for the reply.

 

[nitetrane98]

"Without measuring the barrel hoods a late model .45 Gold Cup has a notch that's .400" wide, and an old government model essex slide is .040" more at .440". These are the width of the notches to which you'd want to achieve a reasonably snug fit at say .395" or .435" respectively. (I like a .005" fit, but that's just me)."

There's no doubt that the GCs have a narrower barrel hood. The MILSPEC drawings call for .436+.004 (so your Essex is max but in spec, probably well within measuring error.)The MILSPEC for the barrel hood is .415 -.005. Talk about wiggle room.
Glad to find that there is evidently no change to the bottom lug. Mine measures .365 which is precisely the lower limit of MILSPEC. This would mean that my worries about the slide tool were unfounded. I'll likely go ahead and get one now.
From the drawings I can now see what you mean by not worrying about top and bottom being parallel. The edges of the hood were only parallel on one side of the MILSPEC barrel. I think I've got a good enough handle on this to manage the task when the barrel comes in. My last remaining question will be how tight is too tight? Maybe I'm putting too much faith in it being a GC but I'm seeing things one could think would be easily fitted at the factory to tighter tolerances. Maybe they don't matter as much as I would think they do. The gun has had it's fair share of ammo through it but there is no sign of foul play involved on any of the surfaces and it's still extremely accurate. I'm getting pretty stoked for the whole thing.

 

[krs]

I bought a 2007 Gold Cup Trophy and was at first somewhat nonplussed to find that the hood had .010" clearance in it's notch. Nonplussed until I fired the pistol seriously and found it to be able to group 1" at 25 yards.

Sometimes they'll shoot beautifully when all reason says that they should not do that.

Even so, I like a snug fit and will be sure to fit a hood to a .005" fit on the sides of the hood. Some of this is subjective, some is anality. Too tight guns tend to stovepipe more than looser ones.

 

[nitetrane98]

The more I read the more confused I get. When I bought mine I wasn't into tinkering with it. I just shot the bejesus out of it and it still shoots better than I can. So I know that taking measurements now is somewhat futile but even still I can't help but imagining some Colt gunsmith reading all the stuff available about accurizing a 1911. "Hmm, that's BS, that's sorta true, not if you do this, totally unnecessary, ahaa, somebody gets it."
At any rate, I can't think of any dimension that will improve accuracy by being sloppy so I intend to make mine as tight as reliability will allow. I can always take off more.

 

[krs]

Yep, you can always take off more, but you can't put it back so go slowly.

If problems develop don't be too quick to blame the new issue on something you just did. I mean that when you tighten tolerances the change could reveal a new condition for something that's seemingly unrelated.

I guess this could be called "inverse tolerance stacking". The pistol is a compilation of parts each with an operating range with tolerances. Change one, possibly change another. Try to keep focused on the bigger picture of the assmbly as a whole, and good shooting!