PSA 2nd Gen AR10 project ...

[wquiles]

Ian has been helping me and providing guidance on my AR10 build. The PSA prices are SUPER low, and I am starting to see some small areas as to why

So I got the upper:

I then remove the muzzle device since I want to index and install my Griffin suppressor mount. Crown looks like it is OK, but look at the threads: 1) no thread relief, and 2) no sharp/square shoulder for the suppressor to index to

So I removed the barrel, mounted on the lathe, and gave it a little bit of relief and cut a "little" shoulder for proper indexing - nothing "beautiful", but a solid, squared shoulder (this stainless was tricky and gummy!):

 

[wquiles]

Then took the barrel off the lathe, and started working on indexing the suppressor mount:

I then cut the handguard to my preference:

Then bolted back the barrel:

I installed the adjustable gas block while I had everything apart:

And now I am ready for the lower to arrive

(man, this upper almost screams for an SBR configuration, right!!!)

 

[Ian]

18" is short enough for a .308, believe me. Hard to get decent velocity out of it and muzzle pressure is through the roof with full-power loads using conventional powders, which is real tough on silencers.

Yeah, sorry, I forgot to tell you about the barrel shoulder (or lack thereof). The whole shebang would fit through my mini-lathe headstock so I just popped off the handguard and gas block/tube and indexed it with my outboard spider and 4-jaw so the muzzle just barely came through the chuck. Very sharp/finely honed HSS cut the material like butter even using my toy lathe.

Did you get a Superlative Arms gas block?

 

[Ian]

Also....to avoid having to face the muzzle back and to aid in indexing I used a washer from the Brownell's accu-washer kit, same as I do for most of my other rifles. I need to order another kit, it seems there are three sizes I keep needing over and over again.

 

[wquiles]

Yeah, I was "really" tempted it when I had the barrel in the lathe to cut to 16.1" and re-thread, but I decided to leave as is based on your feedback. That was a close one

The Griffin comes with quality shims in 3x thickness to do the indexing, which I have checked and verified already, BUT, I still like the "old school" indexing of the adapter in the lathe, simply because I can and I know how to do it. I "know" squaring the barrel shoulder and the Griffin suppressor mount in my lathe setup will give me the best alignment to my suppressor (which of course was also done in the same lathe/setup).

And yes, superlative arms gas block. Already installed and ready to go

I think tomorrow or Wed is when the lower gets here to Texas. Making progress.

 

[Ian]

so I guess I missed that last photo somehow, DOH!

 

[freebullet]

Nice job, looking forward to your progress with it. Might take a look see at the throat & test fit some dummies while you wait for the lower. Psa track record on useable throat entrances isn't great for me.

 

[Ian]

Hopefully it's like mine, just a scuff fit on .3098" bullets and a SAAMI-spec freebore length and taper. .3435x.3450" chamber neck.

 

[wquiles]

I think I still have some soft lead that I can use to make an impression.

 

[wquiles]

Got the lower

Just barely under 8 pounds even - not bad at all!

I hope to check the chamber this weekend and start some loads to try it out.

Thanks Ian

 

[freebullet]

Nice, oughta be a fun one.

 

[wquiles]

Ian, I know I got the adjustable gas block to control over-gassing the system, but on the lower side of things, given the heavier bolt in the AR10, when working loads in Quickload, what is the lower limit PSI on the pressure at the port I should be looking at?

 

[Sig556r]

Then took the barrel off the lathe, and started working on indexing the suppressor mount:

Is that the minimalist Griffin tapered mount?

 

[wquiles]

Yes. The one I use on all of my rifles now - great, solid suppressor mount.

This one on the AR10 I bought, but the one on my 300BLK I made myself.

Will

 

[Gary]

Dang; I really like that 6 jaw chuck; gonna have to save my clinko's.

 

[Ian]

Ian, I know I got the adjustable gas block to control over-gassing the system, but on the lower side of things, given the heavier bolt in the AR10, when working loads in Quickload, what is the lower limit PSI on the pressure at the port I should be looking at?

On the LR-308, I have no idea. I do know that wide-open is still overgassed severely with 35.5 grains of RX-7 under a 174-grain cast bullet with the suppressor. I had to go past "off" and into the "restriction" side of the adjustment to get it dialed in. I have a feeling that the system would run some very mild loads if you opened it up all the way.

 

[wquiles]

Dang; I really like that 6 jaw chuck; gonna have to save my clinko's.

Outside of flood coolant which allowed me to work and extend life of cutting tools on steels, but specially Titanium, that Bison 6-jaw Tru Chuck has been the single, best investment ever for my PM12x36 lathe. I re-index the chuck every time after cleaning/lubricating it to less than 0.001" TIR, and it stays at less than that time after time. Simply amazing.

I use a Sharpie to mark the stock/piece relative to the "0" on the chuck and do my best to stay at the same depth within the jaws - I can cut/remove from lathe/test fit/put back in the chuck and the part stays true/centered pass after pass.

The one time where I still try to minimize removing/remounting a part is when doing several operations on a part that need to stay concentric/aligned. Otherwise, not having to re-center every time is literally priceless, and I honestly I am so spoiled, that would be lost without this chuck/feature.

 

[wquiles]

On the LR-308, I have no idea. I do know that wide-open is still overgassed severely with 35.5 grains of RX-7 under a 174-grain cast bullet with the suppressor. I had to go past "off" and into the "restriction" side of the adjustment to get it dialed in. I have a feeling that the system would run some very mild loads if you opened it up all the way.

Gotcha. I will start on the restriction side as well and see how it goes. Thank you

 

[Ian]

Try it both ways, that load is bumping 50K psi and a lower-pressure load might work fine on the full-vent setting, which would be preferable because it supposedly won't carbon-up over time. I got over 350 rounds of full-power PC through mine and haven't touched the adjustment since the very beginning so no problems yet, but you know "internet wisdom and marketing wank" says a restriction block will choke up over time.

 

[popper]

I'd start about half way open with bunch of jacketed & wet bolt to get the barrel and BCG broken in, then add the can and adjust. Be sure to wiggle the adjuster after each session to keep it loose. I did clog a gas key shooting hot PB/PC in the BO but no problem in the 308W as I use GCs. I did clog the adj one on the BO pistol, but it's in the right place anyway. Got a couple boxes of hornady GC for Christmas and a gc mould for the BO so I'm good.