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

[cmshoot]

Unbelievable! On a factory piece no less. Wonder what people are thinking when they do something like that. Probably nothing at that moment. Daydreaming on the job.

No, a LGS installed the Keymo adapter with all the threadlocker. Aero didn't do it.

 

[cmshoot]

If you can’t diagnose and FIX problems on an AR, you probably shouldn’t be BUILDING AR’s.

 

[Moondog1]

If you can’t diagnose and FIX problems on an AR, you probably shouldn’t be BUILDING AR’s.

Hey cmshoot , on one of your post you put out some good info on nitride carriers and gas leaks. How do you inspect and tell if your nitride carrier is in spec and not leaking gas? I've seen a few other things in the internet stating exactly what you were saying and it seems like really good and relevant info with all the nitride and coated carriers being pushed out.

If you've already answered this and I missed it sorry!

 

[greg vess]

Hey cmshoot , on one of your post you put out some good info on nitride carriers and gas leaks. How do you inspect and tell if your nitride carrier is in spec and not leaking gas? I've seen a few other things in the internet stating exactly what you were saying and it seems like really good and relevant info with all the nitride and coated carriers being pushed out.

If you've already answered this and I missed it sorry!

Nitrided parts only increase by .0002-.0003 since it is a surface treatment it can be applied to finished parts. Size change is very minimal. Phosphate is also a outside coating and can also change outside size. Both can change outside sizes but both are minimal.

 

[cmshoot]

Hey cmshoot , on one of your post you put out some good info on nitride carriers and gas leaks. How do you inspect and tell if your nitride carrier is in spec and not leaking gas? I've seen a few other things in the internet stating exactly what you were saying and it seems like really good and relevant info with all the nitride and coated carriers being pushed out.

If you've already answered this and I missed it sorry!

There is a specific measurement of the diameter of the bore of the gas key and the carrier. That’s the best way to check if you have the possibility of leaking gas at through either bore.

The bore of the gas key steps down twice. The gas tubes only interacts with the first .82” of the gas key bore, which has an ID of .1806” + .0008”. It then steps down to .172” + .005” for the next .1”, and finally down to .116” + .005”.

The end of the gas tube is .1800” - .006” at the end inside of the receiver. The only seal where the gas tube goes into the gas key is the small size of the gap between the two.

If the ID of the gas key is oversized, or the carrier bore is oversized, you can leak gas around the gas tube or bolt. This is almost impossible to see, as those parts get pretty dirty anyways. If you have new gas rings on the bolt, and it fails or comes close to failing the gas ring test, it’s a good sign your carrier bore is oversized.

I’ve seen several nitrided and NiB BCG’s leaking gas around the sides of the gas key lately. In the case of the nitrided carriers, I wouldn’t say that the culprit was the fact that they were nitrided; the fault is because they were cheaply made. Where the base of the gas key mates against the carrier, both surfaces need to be smooth and flat. Not smooth and flat, you can get an incomplete seal, and blow gas around the base of the gas key. Easiest was to see this is to start with a clean BCG and fire a few rounds. You’ll see the fan shape of the gas blow-by up the side(s) of the base of the gas key.

If a NiB carrier and gas key are NiB’ed before assembly, there’s a good chance you’re not getting a good seal in between the two parts.

 

[cmshoot]

cowboytuff66 posted this recently in another forum here on ODT. Barrel from a factory Radical AR. Notice the index pin is at approximately 12 o’clock, and the feed ramps are severely cocked to the left. I’ve seen misaligned barrel extensions before, but nothing anywhere near this bad.

 

[Asbestos]

cowboytuff66 posted this recently in another forum here on ODT. Barrel from a factory Radical AR. Notice the index pin is at approximately 12 o’clock, and the feed ramps are severely cocked to the left. I’ve seen misaligned barrel extensions before, but nothing anywhere near this bad.

View attachment 5351274

Why so critical? They got one of em pretty close. You’re obviously just trying to push your own barrels. You truprep guys are so nit picky.

 

[greg vess]

Why so critical? They got one of em pretty close. You’re obviously just trying to push your own barrels. You truprep guys are so nit picky.

That's one of those polish left handed barrels. LOL

 

[greg vess]

cowboytuff66 posted this recently in another forum here on ODT. Barrel from a factory Radical AR. Notice the index pin is at approximately 12 o’clock, and the feed ramps are severely cocked to the left. I’ve seen misaligned barrel extensions before, but nothing anywhere near this bad.

View attachment 5351274

That's a new one for me. I know what it is. In fact I am sure of it. Who ever installed the CNC machine installed the machine up side down. Jez! You just can't get good quality minimum wage help these days.

 

[cmshoot]

Yesterday, had a customer that brought his AR in because his gas tube fell out. Turns out the holes in the gas block were bored too large, so it wasn't retaining the pin. New gas block and he was back in business.

Today was a first. Another customer had a gas tube fall out of his AR. I looked at the gas block, and it appeared that the gas tube pin was still in it. I could see it from both sides. Looked at the gas tube, and found that the center section of the gas tube was still in place, which means the pin had broken into 3 pieces. Never seen that one before.