A2 FH installation question

[nightchief]

I've had some crap crush washers that were too hard. I'd get another one or a shim kit.

I have some shims, so I may go this route and torque it to 30 lbs

[1168]

If you were within a few hrs, I’d crank it for you. Do you have a torque wrench or an experienced friend?

[elephantrider]

I have some shims, so I may go this route and torque it to 30 lbs

1. Why 30 ft-lbs? That is well above what is needed to hold a properly shimmed FH on.
2. How are you fixturing the upper/barrel to do this?
I'd recommend getting one of these: https://precisionarmament.com/produc...washer-system/
What I do is find the shim that is just a little too thick for the FH to time w/ moderate torque and then sand down a thousandth, as needed to get it timed with minimal torque force. Slowish process, but no chance of shearing anything, or squeezing the bore, etc. If a suppressor is going on the FH, then it'd be a different process.

[nightchief]

1. Why 30 ft-lbs? That is well above what is needed to hold a properly shimmed FH on.
2. How are you fixturing the upper/barrel to do this?
I'd recommend getting one of these: https://precisionarmament.com/produc...washer-system/
What I do is find the shim that is just a little too thick for the FH to time w/ moderate torque and then sand down a thousandth, as needed to get it timed with minimal torque force. Slowish process, but no chance of shearing anything, or squeezing the bore, etc. If a suppressor is going on the FH, then it'd be a different process.

Perhaps 30 is too much...20 lbs is probably sufficient. I have a Reaction Rod in a bench vise. I have the PA shims, I used them for SF suppressor adaptors. No suppressor is going on this, I removed the adaptor a few days ago, which is why it needs an A2. I'm planning to part with this upper and am wanting to return it to its original configuration.

[nightchief]

If you were within a few hrs, I’d crank it for you. Do you have a torque wrench or an experienced friend?

Thank you for the offer. I have a torque wrench and am pretty comfortable with the work, but I've not run into an A2 so far that was tightened to just beyond 1200, requiring and almost 360 turn to get it timed.

[elephantrider]

Perhaps 30 is too much...20 lbs is probably sufficient. I have a Reaction Rod in a bench vise. I have the PA shims, I used them for SF suppressor adaptors. No suppressor is going on this, I removed the adaptor a few days ago, which is why it needs an A2. I'm planning to part with this upper and am wanting to return it to its original configuration.

20 is more than enough. 10-15 is plenty. Sounds like you're good to go. One more word of advice is that I've found that sometimes the PA shims do not sit flush to the barrel shoulder behind the threads. Usually this is b/c of how the threads were cut (no run out groove), and there is an inside curve to the shoulder junction. In that case I relieve the inside edge of the PA shim so it fits flat against the barrel/thread shoulder and torques evenly.

[nightchief]

20 is more than enough. 10-15 is plenty. Sounds like you're good to go. One more word of advice is that I've found that sometimes the PA shims do not sit flush to the barrel shoulder behind the threads. Usually this is b/c of how the threads were cut (no run out groove), and there is an inside curve to the shoulder junction. In that case I relieve the inside edge of the PA shim so it fits flat against the barrel/thread shoulder and torques evenly.

Thanks for the tip...I'll check the BCM barrel for this, though the SF shims that were previously on it sat flush with the shoulder.

[Biggy]

I have used these with great results. Just another option.

https://www.tacticallink.com/Armaged...5-Barrels.html

[titsonritz]

There is no torque value for an A2 MD with a crush washer, timing is the goal. If it feels like you wrenching hard enough to snap your index pin you probably are.

[tehpwnag3]

Be sure to add a little lube or grease on the contact surfaces. This makes turning a lot easier. I just did one last night and it offered little resistance.