Repairing Scope Mount Threads in Stainless Barrel

[Sidewinder]

The 21" stainless .22 Hornet barrel I recently bought for my Contender seems to have some boogered scope mount base threads. The person I bought it from, said it had a scope mounted on it when we were negotiating the sale. I told him that I didn't want the scope, instead wanted the original iron sights. He removed the scope and base, and reinstalled the rear sight. I got a scope mount in a deal yesterday, and decided I'd install one of my scopes. That's when I found that the screws would just barely catch and then seemed to lock up. I have not forced them, and decided to repair them before further mounting attempts.

 

1. First thought is to try to clean and chase the threads with a tap.

 

2. If this does not work, I'm considering having the four holes professionally drilled and re-tapped.

 

3. Should option #2 become necessary, who do you guys recommend, that would do a professional job?

 

4. How much can I expect to pay for this service...a reasonable fee?

 

5. I noticed something down in the thread holes that was grey in color. I used a tiny twist drill in my fingers to see if it would come out. The drill is about 1/3 the size of the hole, so I did not molest the threads. Non metallic chips started coming out...looked kinda like hardened JB Weld to me!

 

6. I'm also considering buying a "bottoming" tap, to see if chasing these threads will give me enough strength to mount the scope...the thread holes do not go all the way into the chamber.

 

7. If there are "do it yourself" types on here, that have been through this before, I'm open to suggestions.

 

8. This is the same barrel that is missing one of the forearm mounting nuts. So, she needs a little TLC!

 

Thanks.

[Omega]

Contact the seller and ask what the material is. It may some unconventional or off brand thread lock that should clean out with a tap. Or it just may be a bit of jb weld after the threads got damaged. Sorry can't help with the smithing part of the question as I did my own when my .270 had that issue and all I did was use the next size tap, drilled it out by hand and slowly tapped it. It held ok, probably still going strong. Edited August 23, 2014 by Omega

[LawEnforcementSalesTN]

Nothing wrong with trying to chase the threads just be sure you have the right thread pitch.  I usually will recommend folks to just step up the next thread pitch to be safe but not familiar enough with the scope mounts available to the contenders.  Would have to see your mount to make further recommendations.

 

Highly expect you should be able to find a smith local to ya but if you don't and the DIY doesn't pan out... PM me and we'll discuss options, happy to help ya out.

[Sidewinder]

Thanks for the information guys. I read on a Contender forum that the scope threads are 6-48, which is pretty much standard, I think. Is the next larger thread size, used on some scopes 8-48, or 8-40?

[gary_boom]

We use Helicoils where I work. That way you could keep the original screw size.

[Sidewinder]

We use Helicoils where I work. That way you could keep the original screw size.

Gary, I've used Helicoils in aviation work, but didn't know they made them this small. I took a stick pin and bent the point 90 degrees, and have been able to clean out some of the threads. Would be great if I could just put a drop of some chemical to dissolve the thread locker / JB Weld material. Whatever it is, it won't let the screw go in, until it's all cleaned out. I sure don't want to snap off a screw, down in the hole!

 

Any idea where these tiny Helicoils can be bought...and the cost of them? In aviation, there is a special tool to install them, then a tang is snapped off to clear the bolt hole. Is there one required for the small ones? Thanks for the information.

[gary_boom]

I have never used a Helicoil that small but they make a # 1 coarse and a #2 fine and on up. Looks like there are several makers and more types than I ever thought.

[DWARREN123]

If you decide to chase the threads use plenty of tap oil as SS is very hard to tap otherwise.

[Sidewinder]

If you decide to chase the threads use plenty of tap oil as SS is very hard to tap otherwise.

Dwarren,

Thanks for the heads up. I've been working a stick pin point in the threads, and screwing the screw in and out, after soaking in some Bore cleaner. They're going in a lot farther than they were. I'm thinking if they were gently chased with a bottoming tap, I could probably screw the mounting screws in until they bottomed out on top of the chamber. I don't have such a tap, so I guess I'll keep doing what I'm doing. It's slow, but I do see some progress.

[Sidewinder]

I have never used a Helicoil that small but they make a # 1 coarse and a #2 fine and on up. Looks like there are several makers and more types than I ever thought.

Thanks Gary, Tennessee Gun Owner is the site to get educated on! I had no idea they made them that small. But, it's good to know that they do. Tedious work, I'm sure.