AR-15 6mm ARC my build and getting it working

[jabbrwoke]

Today's results: The first two shots are for zeroing the scope and the next three:

(Indian Hill Shooting Club: 100 yards using Caldwell Lead Sled on Bench)

My build:
1) Proof Research PR15 6mm ARC 7.5 twist 18"+1
2) JP Rifles 6.5 Grendel Bolt & BCG
3) JP Rifles SCS
4) JP Rifles low profile adjustable gas block
5) Aero Precision M4E1 upper, lower, trigger and lightweight handguard

When first fired, the casing jammed badly in the chamber and had to be pounded out with the Strike charging handle. Here are the casings:

Through the Teslong bore scope there are some burrs in the chamber:

I cut a slit in the end of a dowel, inserted and wrapped 600 grit sandpaper, and polished **the heck** out of this. It took me several tries i.e. polish then shoot and really I had to polish more than I expected. I was worried that I polished too much but today it worked and the accuracy is terrific!

I also used a Dremel to polish the interface between the feed ramps on the barrel and the upper. The AR-Stoner/ARC magazine is working great.

 

[bigjake83]

Why not send the barrel back to PR for warranty work??

 

[LRRPF52]

I’m kind of surprised Proof let that out.

They normally make superb rifle barrels with excellent finish, fit, feel, and presentation.

 

[jabbrwoke]

Why not send the barrel back to PR for warranty work??

I should have!
- except that a friend at the range says he polishes his new barrels as a matter of course and
- I’m impatient and didn’t want to wait xxx months to get the barrel back.
- learning exercise

Now that I have borescope I’ll do a better inspection before I put together.

 

[10ring'r]

Besides the chamber, NICE looking rifle! Thinking of a build/purchased upper in 6mm ARC myself. Glad it shoots! Mac

 

[jabbrwoke]

I’m kind of surprised Proof let that out.

They normally make superb rifle barrels with excellent finish, fit, feel, and presentation.

I was lulled into complacency based on the parts I bought. Certainly the exterior finish was perfect. I couldn’t be happier with the MOA. My take home lesson was to get and use the cheap borescope ($45).

 

[GONE BAD]

Wow! This should take some pressure off the Faxon bad reviews. Lol

 

[jabbrwoke]

Wow! This should take some pressure off the Faxon bad reviews. Lol

I don't know. I'm posting for educational purposes. The flip side is that I have an AR-15 with < 0.5 MOA on stock factory ammo (Hornady Black) so I'm thrilled. I will have no hesitation to run some 600 grit sandpaper in my new chambers in the future.

 

[jabbrwoke]

I don't this issue is unique to Proof Research. Here is a brand new Aero Precision barrel (16" M4E1):
There were a few more jaggies but the photos turned out out of focus...

and then after polishing with 600 grit sandpaper:

 

[Dolomite_Supafly]

I have built about a 1/2 dozen now using a WOA extension. It definitely is an impressive round. A buddy is getting 2,900+ fps with a 75G bullet out of the 13.5" barrel I built him. I have a 20.5" I built that I haven't even shot yet, too busy building a 10" 458 SOCOM bolt gun.

 

[tasty_chicken]

nice shots! I have the same barrel that i'm itching to get out. What ammo were you shooting?

 

[jabbrwoke]

nice shots! I have the same barrel that i'm itching to get out. What ammo were you shooting?

Thanks! I have Hornady Black and Match and those happened to be Black. The build shoots super smooth.

 

[JS8588]

Wow! This should take some pressure off the Faxon bad reviews. Lol

Nope. This is one PR barrel that had some finish issues in the middle of one of the biggest runs on 2nd Amendment related products in history AND the barrel still shoots. Faxon's been a dumpster fire pretty much since Nate left the company. I'd tell someone to roll the dice with Bear Creek (or Rosco) before recommending Faxon (or Ballistic Advantage/Aero Precision...when it comes to barrels, anyway).

That said, I just ordered a lightweight 556 barrel from 2A Armament which I'm aware is OEM from Faxon but I trust 2A's QC.

 

[lennyo3034]

I should have!
- except that a friend at the range says he polishes his new barrels as a matter of course and
- I’m impatient and didn’t want to wait xxx months to get the barrel back.
- learning exercise

Now that I have borescope I’ll do a better inspection before I put together.

Are you sure that’s a good idea?

Not all of the pressure from a round is exerted directly into the bolt face. Some of it is held by friction between the case and chamber walls. Polish a chamber too much and you might see an increase in force pushing on the bolt. Considering 6ARC is already tip toeing on the edge of bolt strength and you may be affecting fatigue life of your bolt.

I don’t know what the surface finish call out on a chamber is so 600 grit may be just fine, but something to double check.

ETA: I think you’re ok with 600 grit. You’d have to polish to very fine for significant impact.

 

[jabbrwoke]

Are you sure that’s a good idea?

Not all of the pressure from a round is exerted directly into the bolt face. Some of it is held by friction between the case and chamber walls. Polish a chamber too much and you might see an increase in force pushing on the bolt. Considering 6ARC is already tip toeing on the edge of bolt strength and you may be affecting fatigue life of your bolt.

I don’t know what the surface finish call out on a chamber is so 600 grit may be just fine, but something to double check.

ETA: I think you’re ok with 600 grit. You’d have to polish to very fine for significant impact.

Good considerations. If you look at the casings you see that the markings were along the lower or proximal 1/2 of the casing. I concentrated my polishing there. The round mostly grips toward the neck. The 600 grit isn’t mirror smooth (see the photo) and I’m guessing that’s why it’s considered a good compromise. I did use the JP EnhancedBolt 6.5 grendel but if pressure is seen as an issue perhaps they will make a HP version for 6mm ARC.