A Tale of Two Crush Washers, or Two Crush Washers One Barrel, and other AR oddities

[cmshoot]

This is pretty much how this LMT MARS-LS came in the shop. Screw slot buggered all to hell, and pistol grip cut off short to allow access to said screw.

I cut the second slot, because the original one was so tore up I couldn’t get a driver to bite in and stay.

Definitely waaaaay too much of some sort of Loctite, and possibly cross-threaded as well. Put a 14” box end wrench on a screwdriver, had a guy leaning on the driver while I turned the wrench. Nothing. This was after soaking in Kroil overnight, and an application of heat.

Finally just cut the head of the grip screw off.

Cleaned up the shaft of the screw nearly flush with the surface. Drilled into it, inserted an EZ-Out bit into it and attempted to turn. Snapped off the EZ-Out.

Ended up drilling through the screw from one end to the other, then opening the hole with progressively bigger bits. When doing that, usually one of the drill bits will end up turning the screw shaft out. Not in this case.

Drilled it out enough to re-tap the hole to 1/4x28 (factory spec for the grip screw).

I don’t like how the finished threads look, and I don’t like the now raw aluminum that comprises what threads there are. I think that in the future, this could be an issue.

Ordered an 18-8 stainless helicoil. I’ll drill out the hole, permanently install the helicoil, and she’ll be (arguably) better than new, and still use the 1/4x28 factory thread pattern.

 

[cmshoot]

Proof research AR10s has barrels that the same way. I think white oak armory has just about every length imaginable on gas tubes. I don't know about the big frame guns, but the small frame noveske has a wierd one, also.

Several companies, like Noveske, Black River Tactical, and a few more that escape me right now, have an “intermediate” length gas system that is slightly longer than midlength. That exact length varies slightly from company to company, so stock up on gas tubes if you’re running one.

I have a few of the BRT barrels with their intermediate length gas system, so I have several gas tubes for it marked and stored in the shop.

 

[Asbestos]

This is pretty much how this LMT MARS-LS came in the shop. Screw slot buggered all to hell, and pistol grip cut off short to allow access to said screw.

View attachment 9289671

I cut the second slot, because the original one was so tore up I couldn’t get a driver to bite in and stay.

Definitely waaaaay too much of some sort of Loctite, and possibly cross-threaded as well. Put a 14” box end wrench on a screwdriver, had a guy leaning on the driver while I turned the wrench. Nothing. This was after soaking in Kroil overnight, and an application of heat.

Finally just cut the head of the grip screw off.

View attachment 9289928View attachment 9289929

Cleaned up the shaft of the screw nearly flush with the surface. Drilled into it, inserted an EZ-Out bit into it and attempted to turn. Snapped off the EZ-Out.

Ended up drilling through the screw from one end to the other, then opening the hole with progressively bigger bits. When doing that, usually one of the drill bits will end up turning the screw shaft out. Not in this case.

Drilled it out enough to re-tap the hole to 1/4x28 (factory spec for the grip screw).

I don’t like how the finished threads look, and I don’t like the now raw aluminum that comprises what threads there are. I think that in the future, this could be an issue.

Ordered an 18-8 stainless helicoil. I’ll drill out the hole, permanently install the helicoil, and she’ll be (arguably) better than new, and still use the 1/4x28 factory thread pattern.

this thread makes me feel good about my guns

 

[ReservoirDawg10]

L M T. Learn Machining Together

 

[cmshoot]

So, what was the initial problem shemp? locktite? wrong pitch thread? can you overtighten screw without cracking plastic grip?

I'm not 100% sure what all the parts of the problem were. There is definitely a lot of Loctite on the threads, and I do not know what kind it is. I even boiled the receiver in water in case it was Rocksett.

Could be cross-threaded, or the wrong thread pitch.

 

[ReservoirDawg10]

I'm not 100% sure what all the parts of the problem were. There is definitely a lot of Loctite on the threads, and I do not know what kind it is. I even boiled the receiver in water in case it was Rocksett.

Could be cross-threaded, or the wrong thread pitch.

To be fair, that is not the standard grip that comes on a MARS. Wonder who put it on there.

 

[renagadeinjun]

I'm not 100% sure what all the parts of the problem were. There is definitely a lot of Loctite on the threads, and I do not know what kind it is. I even boiled the receiver in water in case it was Rocksett.

Could be cross-threaded, or the wrong thread pitch.

Pencil tip butane torch works for locktite (from what I have been told) would that have worked for rockset?
Just thinking out loud you have seen more than I ever will ......... carry on

 

[Spas-12 Owner]

I'm not 100% sure what all the parts of the problem were. There is definitely a lot of Loctite on the threads, and I do not know what kind it is. I even boiled the receiver in water in case it was Rocksett.

Could be cross-threaded, or the wrong thread pitch.

Are we suppose to loctite grip screws?

Cause, I gotta say, I've never once thought to do that.

 

[renagadeinjun]

Are we suppose to loctite grip screws?

Cause, I gotta say, I've never once thought to do that.

LOL, and you can see the lock washer still on screw for crying out loud

 

[cmshoot]

To be fair, that is not the standard grip that comes on a MARS. Wonder who put it on there.

I'm not an LMT fan, but I'm fairly sure that someone outside of LMT installed that grip.