Barrel Fitting using Feeler Gages

[garandsrus]

Hi,

I have a barrel I bought that is loose on my frame.  I have read the FAQ and mostly understand how to fit it. 

My question is in trying to determine the correct amount to add to the lug.  Can I use a gage across the barrel, between the barrel and receiver, to determine the amount to add to the lug?  I can close the action with a .010 gage but it will not lock up with a .011 gage.

If the above works, I assume that I would add .010 to the lug and then a little filing would be necessary due to the thickness of the epoxy.

Thanks,
John

[quickdtoo]

I just cut test shims of different thicknesses and mark them so I know what thickness they are, then try them for the best lock up, you want to over shim so you can file the pivot down so it's as close to the .375" hinge pin size as you can get it. If you use a shim without cutting it to a .375" diameter, the pivot will only be contacting two points with a gap in the middle since the diameter of the pivot is already .375", put a .010" shim in and the diameter is now .355". The actual shim you end up with after filing the pivot covers only about one third of the pivot surface. I use a .375" stud I got at the hardware store to put in the pivot, hold it up to a light to see how it fits, if there's a gap between it and the pivot surface, then file the pivot to make sure I have as close to 100% contact as I can get, the more the better.

Tim

[krod47nw]

Tim?
Are you removing the shim and filing the base metal, or filing the shim?

[quickdtoo]

No, I epoxy the shim in with JB Weld, then file it to fit. I usually use shim stock from smallparts.com if comes in sheets, but I've also used some .026" stainless steel that I had to shim a barrel that someone really messed the pivot on in an attempt to fit it, I filed the pivot oversize to make it round again so it would require less epoxy to fill between the shim and pivot. Smallparts sells both.

Tim

http://www.smallparts.com/s?searchNodeID=16310161%7C468240&searchKeywords=steel+shim+stock&Action=submit&x=11&y=11

[krod47nw]

Do you have a scientific method of determining how much to over shim?  In your example, if a .010 test shim makes it lock tight, it will be contacting on the top and bottom, and not fully seated in the radius of the pivot.  When filed it would be loose due to the pin seating fully in the pivot, correct?   

[quickdtoo]

Don't use a full size test shim, it's just big enough to take up the slack, .002"-.003" or so thicker will be big enough to allow some taper to the actual finished size after filing to fit.  Some members just wrap a shim around the hinge pin and call it good, that works, but isn't the best since the bearing surfaces are a lot less than ideal, specially for some of the higher pressure chamberings.

Tim

[garandsrus]

Tim,

So you are just putting one or more narrow rectangular pieces of shim material in the middle (bottom) of the hinge pin to see where it locks up tight?  Does the final thickness of the shim correlate at all with the measurement you get when putting a gage between the barrel and receiver, which is what I did?

In one post you said that "The actual shim you end up with after filing the pivot covers only about one third of the pivot surface", which makes sense since the shim is reducing the size of the hole as you mentioned.  I assume that the 1/3 that remains is in the bottom arc of the pin, moving the pivot point out.  The edges of the shim get filed away to retain the .375 diameter.

Thanks again,
John

[quickdtoo]

Yes, that sums it up pretty good, I'll check some barrels to try to find one that's a good representative of what it actually looks like when finished and try to get a good pic of it to post. The epoxy will show a little where the shim ends and the underlug material starts. The feathered edge of the shim will also flake away a little right at the edge as it gets too thin to resist the file pressure. I've added this discussion to the barrel fitting info as I've done in the past to help anyone else that has asked similar questions to clarify the process, barrel fitting is kind of a continual learning process as everyone contributes a little different perspective and asks questions as John and others have done. 

Tim

[dw06]

I've had very good results using accuglass with the stainless steel powder in it for fitting barrels. I got it from Brownells. I've done two so far, and the 223 barrel in now a year later and 3-400 rounds later and still locks up tight as when I did it. Also did a 308 barrel, but have since sold it. If you try it, just be sure and put a couple coats of release agent on the hinge pin, and fill any voids in under lug with molding putty.

[krod47nw]

Some members just wrap a shim around the hinge pin and call it good, that works, but isn't the best since the bearing surfaces are a lot less than ideal, specially for some of the higher pressure chamberings.

Tim

I have one that looks like someone did this to it.  It looks like they either filed the pivot area larger to allow for the shim, or it spread under load.  I guess in this case, I would have to put a full shim in it and refile to fit.

Kevin

[quickdtoo]

Here's a pic of the 500S&W barrel, it's been shimmed twice, after the first time I put it on a different frame and made a new shim for it, you can see the 2nd layer and where the shim flaked away on the left side(right side of underlug) on the pic.

Tim

[coyotejoe]

How's that holding up Tim? That 500 S&W round seems to really beat the gun as well as the shooter and would be a real test of the durablity of the barrel fit.

[quickdtoo]

Great, well over 100 180 rounds so far, including the 700gr RR at 1400+fps, having a solid pivot point with more bearing surface makes a big difference.

Tim