Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login

Site Notices
Posted: 2/13/2007 12:04:23 PM EST
I have a Colt 7.62x39 barrel that I removed the FSB on and want to install a a low profile gas block using set screws. I went to dimple the barrel where one of the set screws is and it is right where the hole was drilled for the pinned FSB. Can I weld up the hole, grind it down, re-contour it on my lathe and then dimple it? I am not sure if the barrel is 4140 or 4150 or if that even matters.

Thanks.

Link Posted: 2/13/2007 12:29:18 PM EST
Wouldn't it be easier to tap a new hole for the set screw?
Link Posted: 2/13/2007 12:50:05 PM EST

Originally Posted By webtaz99:
Wouldn't it be easier to tap a new hole for the set screw?


I think he is talking about the hole in the barrel itself, the setscrew is tapped in the gasblock itself.

As to welding up the hole in the barrel, yes but be carefull. I would put wet towels on both sides were you plan to weld, take your time so as to not heat the barrel up too much and you should be fine.
Link Posted: 2/13/2007 12:52:43 PM EST

Originally Posted By colklink:

Originally Posted By webtaz99:
Wouldn't it be easier to tap a new hole for the set screw?


I think he is talking about the hole in the barrel itself, the setscrew is tapped in the gasblock itself.

As to welding up the hole in the barrel, yes but be carefull. I would put wet towels on both sides were you plan to weld, take your time so as to not heat the barrel up too much and you should be fine.


Correct. The hole is tapped in the gas block, I just want to dimple the barrle so there is a mechanical lock between the barrel and gas block.

Is 4140 or 4150 hardened? If so, do I need to worry about re-hardening?



Link Posted: 2/13/2007 4:58:30 PM EST

Originally Posted By nugentgl:

Correct. The hole is tapped in the gas block, I just want to dimple the barrle so there is a mechanical lock between the barrel and gas block.

Is 4140 or 4150 hardened? If so, do I need to worry about re-hardening?





i think what WEBTAZ is trying to say is that it would be easier to re drill and tap a new hole in the gas block in a different location. either fore or aft of the existing one. that would move your set screw away from the taper pin holes and would keep you from putting heat to the barrell.

AR out
Link Posted: 2/13/2007 5:20:14 PM EST

Originally Posted By ARextremist:

Originally Posted By nugentgl:

Correct. The hole is tapped in the gas block, I just want to dimple the barrle so there is a mechanical lock between the barrel and gas block.

Is 4140 or 4150 hardened? If so, do I need to worry about re-hardening?





i think what WEBTAZ is trying to say is that it would be easier to re drill and tap a new hole in the gas block in a different location. either fore or aft of the existing one. that would move your set screw away from the taper pin holes and would keep you from putting heat to the barrell.

AR out


Ah, unfortunately I can't. There are two holes on the bottom of the new gas block but there isn't enough room for a third.

Link Posted: 2/13/2007 5:30:24 PM EST

Originally Posted By nugentgl:

Originally Posted By ARextremist:

Originally Posted By nugentgl:

Correct. The hole is tapped in the gas block, I just want to dimple the barrle so there is a mechanical lock between the barrel and gas block.

Is 4140 or 4150 hardened? If so, do I need to worry about re-hardening?





i think what WEBTAZ is trying to say is that it would be easier to re drill and tap a new hole in the gas block in a different location. either fore or aft of the existing one. that would move your set screw away from the taper pin holes and would keep you from putting heat to the barrell.

AR out


Ah, unfortunately I can't. There are two holes on the bottom of the new gas block but there isn't enough room for a third.



what type of block is this that you have?
everyone that i have seen has plenty of room.
but then again i learn something new everyday here.

AR out
Link Posted: 2/13/2007 5:43:20 PM EST
It was in my parts bin, but I *think* it is a CMMG micro block. If I drilled another hole between the two existing holes, I would be worried about there being too little material between each hole.
Link Posted: 2/15/2007 1:19:36 PM EST
Link Posted: 2/16/2007 2:17:49 PM EST
My preferred solution to your problem:

Link Posted: 2/16/2007 6:49:04 PM EST

Originally Posted By AR15barrels:
Drill the detent in the OTHER hole where there is no cross pin hole under the setscrew...


I prefer to put the dimple under where the gas goes into the gas tube. That way I get the most amount of down pressure, hopefully allowing less gas blow out.
Link Posted: 2/16/2007 6:50:34 PM EST
[Last Edit: 2/16/2007 6:52:27 PM EST by nugentgl]

Originally Posted By Ellery_Holt:
My preferred solution to your problem:

www.vltor.com/images/lpgb/GB-2C.jpg


I don't like side clamping blocks b/c you can't create a mechanical lock between the barrel and block where needed (the bottom). You can get one on the sides, but then the set screws will act as jack screws causing all kind of gas problems.
Link Posted: 2/17/2007 10:04:01 AM EST
A clamp type FSB will give you 0 clearance between the block id and the barrel. With a set screw type FSB, you will ALWAYS have the opportunity for gas leakage at the interface between the barrel and the block.

Welding of 4140 or 4150 requires someone who knows what they are doing. At a minimum, the barrel will need to be pre-heated to 300 - 350 degrees F and a post heat will not hurt to prevent cracking.
Link Posted: 2/18/2007 8:49:15 AM EST

Originally Posted By Herzo:
A clamp type FSB will give you 0 clearance between the block id and the barrel. With a set screw type FSB, you will ALWAYS have the opportunity for gas leakage at the interface between the barrel and the block.

Welding of 4140 or 4150 requires someone who knows what they are doing. At a minimum, the barrel will need to be pre-heated to 300 - 350 degrees F and a post heat will not hurt to prevent cracking.


My humble experiences have shown me that the clamp on gas blocks don't work nearly as good as the set screw gas blocks (once you dimple the barrel).
Link Posted: 2/18/2007 6:24:20 PM EST
Why not thread the hole for 1/8" or so and bottom out a suitable screw?

Saw it off and file it flat to the barrel. If it ever does leak, it won't for long. A 1//16" screw is going to be practically invisible.
Link Posted: 2/21/2007 5:33:45 PM EST
I had a guy at work (who is an excellent welder) weld up the rear taper pin hole with Inconel. I turned it on the lathe and then dimpled it. Tomorrow I will test the weld by doing some full auto mag dumps.
Link Posted: 2/23/2007 12:35:03 PM EST
Weld has held up to about 500 rounds on F/A and haven't noticed any gas blow by. So I guess it did the trick.

Just thought I would let everyone know.
Top Top