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

[cmshoot]

There is a possible issue with nitrided bolt carriers. Well, more than one, but I'm going to discuss one of them here.

Usually, when the carrier and gas keys are machined, they leave the bores oversized so that they can be hard chromed, which is a relatively thick finish as finishes go. The thickness of the hard chrome makes up for the difference in the oversized bores, and brings them down to the proper dimensions.

Nitriding does not add thickness. It penetrates the surface down to a certain depth, and does not sit on top of the surface.

In many nitrided bolt carriers, you end up with oversized bores in the gas key and the carrier. These oversized bores result in gas leakage around the gas tube and the bolt.

 

[greg vess]

If you're installing a gas block that uses set screws, the barrel needs to be dimpled. It may run for a while, but eventually the gas block is going to start walking forward. It moves far enough forward, or rotates to one side, and the gas port in the gas block will no longer be aligned with the gas port in the barrel.

Customer brought in an AR that he had bought from another metro area shop. It had stopped cycling when fired, so he took it back to the shop where he bought it. An employee there found that the gas block had moved forward. He "fixed" it by putting it back in place, reusing the old gas block screws, and tightening it back down. The barrel was not dimpled.

Next range session, the gas block walked forward again. Customer brought it in to me at TruPrep.

I pulled the gas block, threw away the old set screws, and cleaned the red Loctite out of the holes in the gas block. I dimpled the barrel twice, and installed new set screws with Rocksett.

I also found that the gas key was not securely installed. Overall, except for the gas key, the BCG looked decent. It was marked "1B1B6" on the left side of the carrier (in the area where Colt commonly stamps their "C"), and I hadn't seen that before. It was phosphate coated, and the carrier bore was hard chromed. The bore in the gas key, however, was not hard chromed.

Removed the old gas key and cleaned up the mounting surface on the carrier. Decked the new gas key, and installed to the carrier. I used Permatex on the mounting surfaces, and in the two threaded holes. Screws were Optimized Carrier Key Screws (OCKS) from Michiguns, who also made the staking jig I used to stake the screws after torquing to 58 inch/pounds.

Lubed everything and reassembled.

Agreed!

 

[greg vess]

It's better to check your specs as you're building, rather than waiting until your build is done and won't function properly.

Customer's new build. Ballistic Advantage 18" 5.56 barrel with rifle length gas system. It would eject the expended casing, but the bolt wasn't coming back quite far enough to pick up a new round from the magazine.

Gas block was reasonably aligned, but the barrel wasn't dimpled for the gas block screws.........so I dimpled it.

The spec for the gas port for this barrel should be .0995". I gauged the port and found it to be .087". There's the issue.

I reamed the gas port out to the proper size while the customer wait, and reassembled all. That should have taken care of the issue.

Same goes for engine building. Everything gets checked. Tolerance stack analysis is done on bearings I.D. of bearing installed in their places and torqued to spec.. O.D. is checked and subtracted from it perspective place on the rod journals and main journals. Sometimes on older engines more so, a second set of bearings is obtained to even out the clearances as close as possible if swapping bearing halves around doesn't produce the desired effect. Putting a 1000 to 1500 hundred dollar gun is one thing. Building a 10,000 engine is a completely differnent animal. You can leave no chance for error for parts that are machined and aren't even close to the same in tolerances. Everything from checking rod length to degree the cam. Front and aft. Motion of the crankshat ( thrust ). There is a lot to check and it's exhausting but absolutely necessary. I am a little less particular with an AR15 but I do check things like gas port size and dimple the barrel. If everything else goes smoothly it's double check and test fire. We don't have that luxury with a older engine. With a flat tapped cam engine you wipe a cam in seconds. Today's engines are far easier due to better machining. It is still a pain in the rump and nerve racking!

Guns rock and are just easier on the back. You ever try install a set of headers. Oh lord help us it's aggravating on some cars.

 

[Outlier]

Customer's new build. Ballistic Advantage 18" 5.56 barrel with rifle length gas system.

The spec for the gas port for this barrel should be .0995". I gauged the port and found it to be .087". There's the issue.

How often have you seen barrels with undersized gas ports? I have a Criterion barrel with a rifle length gas system that was also undersized. It wasn't quite as small at .092" but it makes me wonder if certain configurations are more prone to that issue?

 

[cmshoot]

How often have you seen barrels with undersized gas ports? I have a Criterion barrel with a rifle length gas system that was also undersized. It wasn't quite as small at .092" but it makes me wonder if certain configurations are more prone to that issue?

I've seen quite a few over the years. Better under than over!

 

[greg vess]

How often have you seen barrels with undersized gas ports? I have a Criterion barrel with a rifle length gas system that was also undersized. It wasn't quite as small at .092" but it makes me wonder if certain configurations are more prone to that issue?

If you order a 6/8 SPC barrel from AR Performance they run a little bit undersized and won't cycle Remington ammunition. He used to specify that you specifically say you're going to run the Remington ammunition so he can open the port up. I haven't found much use for Remington ammunition for 6/8 but he runs a little small on those barrels.

 

[BEREZKA]

I got one for you.

My best friend bought a PSA entry level gun. 16", carbine gas, pinned FSB. I take the upper off the gun, pull handguards and put it on the reaction rod. I notice it made a weird clink. Well, as i put the wrench onto lock nut it was so loose barrel can move in forward. IDK how this gun did not expolode. Anyway It now has nice BCM handguard, lowpro gasblock with dimpled screw holes. We shot like 100rnds, cycle fine, everything zero's good

 

[greg vess]

I got one for you.

My best friend bought a PSA entry level gun. 16", carbine gas, pinned FSB. I take the upper off the gun, pull handguards and put it on the reaction rod. I notice it made a weird clink. Well, as i put the wrench onto lock nut it was so loose barrel can move in forward. IDK how this gun did not expolode. Anyway It now has nice BCM handguard, lowpro gasblock with dimpled screw holes. We shot like 100rnds, cycle fine, everything zero's good

Well once the BCG is engaged it will keep the barrel in place or it will push it forward and won't allow the firing pin to engage. It still dangerous to say the least.

I bought a Toolcraft BCG from them because it was a good price. Should have known. The bearing surface on the bolt was about an 1/8 of an inch and allowed rotation in the bolt. I am talking up/ down/ side to side and round and round. I replaced the bolt with a new spare I had that had a bearing surface of about a 1/4 of an inch twice the width of whatever it actually was. Fit much tighter and took the slop out of the bolt. So I ended up spending 140 bucks anyway on a 69 dollar BCG. Something about their parts just doesn't inspire a lot of confidence for me. Aero Precision is a much better option parts wise but rifles are higher.

There will always be that one that got through Quality Control. It's going to happen especially when humans are the final check. They may be day dreaming and let one by or whatever the case may be it's just going to happen. I am sure they make a half way decent product but I yet to get one or work on one. Pitty!

 

[BEREZKA]

Well once the BCG is engaged it will keep the barrel in place or it will push it forward and won't allow the firing pin to engage. It still dangerous to say the least.

I bought a Toolcraft BCG from them because it was a good price. Should have known. The bearing surface on the bolt was about an 1/8 of an inch and allowed rotation in the bolt. I am talking up/ down/ side to side and round and round. I replaced the bolt with a new spare I had that had a bearing surface of about a 1/4 of an inch twice the width of whatever it actually was. Fit much tighter and took the slop out of the bolt. So I ended up spending 140 bucks anyway on a 69 dollar BCG. Something about their parts just doesn't inspire a lot of confidence for me. Aero Precision is a much better option parts wise but rifles are higher.

There will always be that one that got through Quality Control. It's going to happen especially when humans are the final check. They may be day dreaming and let one by or whatever the case may be it's just going to happen. I am sure they make a half way decent product but I yet to get one or work on one. Pitty!

This is not good. It means they have a very bad process of parts making and probably spot check a few parts per batch

 

[greg vess]

This is not good. It means they have a very bad process of parts making and probably spot check a few parts per batch

Well according to a recent article I read they have 70 brand new CNC machines making their lowers and the same company makes barrels. The company is DC machine otherwise known as Death Choppers machine shop and it's co-owned by Jesse James or was started by him anyway. I'm not so sure it's the machine Shop is where the problem is. I think it's the final step of assembly and of course obtaining some subpar parts from wanker parts makers. Somewhere between those two is the problem. I just keep on hearing the hits rolling in about their parts. The first PSA I worked on the guy wanted me to swap out a flat top upper from one of those cheap carry handle uppers so it can mount Optics. It was actually lighter than a drinking straw and it felt like just pot metal. I swear I'd never buy anything from them until I broke down and bought a boat Carrier Group it wasn't completely happy with that. They definitely have issues no arguing that point at all.