6 ARC Upper Build: 18” PVA Osprey (Rifle +2”) + San Tan Tactical Billet Upper + SOLGW M89 Rail

[WeR0206]

I previously had this barrel on a different upper during break in but wanted to switch to a San Tan upper for this build.

Barrel specs:

• Weight: 42.8 oz
• Gas port: 0.093”
• Gas system: rifle +2”

Build notes:

• Zev 7.62 Flash Hider/Compensator ($29)
• CMT .750 JAG Set Screw gas block ($25)
• Daniel Defense low profile .750 Clamp On Gas Block ($60)
• White Oak Rifle +2” Gas Tube ($17)
• Osprey 18” 6 ARC Rifle +2 barrel ($399) (+$125 with headspaced Rubber City bolt) (Total: $524)
• Rubber City M-16 Blacknitride+ Bolt Carrier ($80)
• San Tan Tactical Billet Upper ($175) (thermofit)
• SOLGW M89 15” Rail ($330)
• SOLGW Ambi Charging Handle ($80)
• Total: $1,295

I already have about 150 rounds through this barrel and shot a sub moa 10 shot group during break in (zero load development)

 

[WeR0206]

Barrel has been mounted in thermofit upper, I used a 1200 watt heat gun on high for 90 seconds to warm the upper threads up before sliding the barrel in. Still need to mount it on a URR & torque the barrel nut but I will be out of town until 8/5. The San Tan billet upper is too tight to fit my URR so instead I will use a magpul bev block

 

[sparky702]

I would be interested to see how this turn's out . I am considering building a 6 arc

 

[Redlion]

I do not yet have a 6mm Arc, but interested in building one at some point. I know nothing about Osprey barrels? They certainly appear to be quality. Where do they rank in the realm of quality? Accuracy?

 

[WeR0206]

I do not yet have a 6mm Arc, but interested in building one at some point. I know nothing about Osprey barrels? They certainly appear to be quality. Where do they rank in the realm of quality? Accuracy?

They are made by Josh (@bohem) at Patriot Valley Arms. I love mine so far and they seem to be near universally loved on this site with many others besides myself getting good results. They come in AR barrels, shouldered prefits, etc.. I don’t own any “premium” cut rifled barrels to compare to (proof, bartlein, etc.) but I do own Geissele, craddock RTR, and criterion AR barrels and the Osprey is probably the nicest of the 3 re: machine work, accuracy, etc..

Here’s some more info on them:

https://patriotvalleyarms.com/osprey-barrel-works/

 

[bohem]

I do not yet have a 6mm Arc, but interested in building one at some point. I know nothing about Osprey barrels? They certainly appear to be quality. Where do they rank in the realm of quality? Accuracy?

The Ospreys are gaining in popularity because the performance, price and availability has been very good. We're not perfect, but I think we're doing a lot more right than wrong.

Here's a thread on the announcement of the AR15 options from PVA last summer. @padom just picked up a 6mm ARC barrel to test out as well, he posted pictures of the 16" 223 Wylde barrel that he got last summer.

PVA now offering AR15 barrels!

Josh @bohem from Patriot Valley Arms posted up on Facebook that he is now offering Osprey match grade AR15 .223 Wylde barrels in 16", 18" and 20" length. Anyone who has used the other Osprey barrels knows that they shoot so I don't expect anything less from these barrels. Worth a look if you are...

www.snipershide.com

 

[Redlion]

I appreciate the information.

 

[Rob01]

Yeah I wouldn’t hesitate to get a PVA Osprey barrel. My 6ARC that I bought as a complete upper before PVA started offering them is past half its life and when the barrel is done it will wear a 20” PVA 6ARC barrel.

 

[black5.3]

Yeah I wouldn’t hesitate to get a PVA Osprey barrel. My 6ARC that I bought as a complete upper before PVA started offering them is past half its life and when the barrel is done it will wear a 20” PVA 6ARC barrel.

What round count are you estimating your current 6ARC barrel will go to?

 

[Rob01]

What round count are you estimating your current 6ARC barrel will go to?

Hoping to get around 3000 or so before swapping out. We will see. I’ve been contemplating doing a completely different upper build with an Osprey though. Started looking at parts and pricing out the other night.

 

[WeR0206]

Hoping to get around 3000 or so before swapping out. We will see. I’ve been contemplating doing a completely different upper build with an Osprey though. Started looking at parts and pricing out the other night.

When you so start your build please share your build list/notes. I love seeing what other people are doing/using for parts etc..

 

[Rob01]

When you so start your build please share your build list/notes. I love seeing what other people are doing/using for parts etc..

Will do.

 

[black5.3]

Hoping to get around 3000 or so before swapping out. We will see. I’ve been contemplating doing a completely different upper build with an Osprey though. Started looking at parts and pricing out the other night.

I was thinking the same neighborhood of round count. Im loading 108gr bergers with 29.0gr of leverevolution so not exactly a light load.

 

[WeR0206]

Barrel has been mounted in thermofit upper, I used a 1200 watt heat gun on high for 90 seconds to warm the upper threads up before sliding the barrel in. Still need to mount it on a URR & torque the barrel nut but I will be out of town until 8/5. The San Tan billet upper is too tight to fit my URR so instead I will use a magpul bev block

View attachment 8737570

Barrel nut has been torqued to 60 ft-lbs per solgw specs, muzzle device torqued to 15 ft-lbs, and upper build is complete. Now I need to load up some handloads, do function check, etc.. I verfied gasport alignment with a borescope so hoping for no issues.

The M89 rail fit perfectly with the San Tan billet upper by utilizing the anti-rotation pin. The black finish doesn’t match but I don’t care bc eventually this upper will likely get spray painted.

If they make one I might actually switch the muzzle device for a CMT one so it matches the CMT gas block (which had a nice tight fit on the barrel).

 

[WeR0206]

Barrel nut has been torqued to 60 ft-lbs per solgw specs, muzzle device torqued to 15 ft-lbs, and upper build is complete. Now I need to load up some handloads, do function check, etc.. I verfied gasport alignment with a borescope so hoping for no issues.

The M89 rail fit perfectly with the San Tan billet upper by utilizing the anti-rotation pin. The black finish doesn’t match but I don’t care bc eventually this upper will likely get spray painted.

If they make one I might actually switch the muzzle device for a CMT one so it matches the CMT gas block (which had a nice tight fit on the barrel).

View attachment 8741724

Handloads are done and heading to the range tomorrow:

Alpha brass, fed 205, N140 (25.6 to 26.4gr), and 109gr berger LRHT @2.260”

This range trip will be rounds 150-200 on the barrel so it should pretty much finish off the break in period.

 

[WeR0206]

Just got back from the range but it was a bit of a bust, only fired 10 shots. The barrel shoots great but I'm still dealing with short stroking (FTE, FTF, FTL) even when I switched to a buffer with 3 aluminum weights (using sprinco white spring) and I'd rather not use a reduced power spring.

I emailed @bohem to see what they recommend....I will likely drill out the gas port a bit from .093" to ~ 0.984" (using a 2.5mm bit), since this is 18" rifle +2 the dwell time is pretty short. I have tried pretty much everything else besides increasing the gas port size (set screw gas block, clamp on gas block, swapped BCG, swapped upper receivers, reduced buffer weights, etc.).

Im also going to clean the barrel and take another peak at the gas port alignment via bore scope.
*Edit: gas port alignment confirmed via scope

There is one more thing I can try, the clamp on gas block paired with the new BCG because I think the clamp on was tried with the other BCG but either way it seems to be on the bleeding edge and Id rather have a little wiggle room for colder temps, weak factory ammo, etc..

Re: my handloads, my velocities for the 10 shots were high 2300 low 2400 which is right around max pressure per Hornady load data for N140:

 

[black5.3]

Interested to see what @bohem says about the issue.

 

[bohem]

Just got back from the range but it was a bit of a bust, only fired 10 shots. The barrel shoots great but I'm still dealing with short stroking (FTE, FTF, FTL) even when I switched to a buffer with 3 aluminum weights (using sprinco white spring) and I'd rather not use a reduced power spring.

I emailed @bohem to see what they recommend....I will likely drill out the gas port a bit from .093" to ~ 0.984" (using a 2.5mm bit), since this is 18" rifle +2 the dwell time is pretty short. I have tried pretty much everything else besides increasing the gas port size (set screw gas block, clamp on gas block, swapped BCG, swapped upper receivers, reduced buffer weights, etc.).

Im also going to clean the barrel and take another peak at the gas port alignment via bore scope.
*Edit: gas port alignment confirmed via scope

There is one more thing I can try, the clamp on gas block paired with the new BCG because I think the clamp on was tried with the other BCG but either way it seems to be on the bleeding edge and Id rather have a little wiggle room for colder temps, weak factory ammo, etc..

Re: my handloads, my velocities for the 10 shots were high 2300 low 2400 which is right around max pressure per Hornady load data for N140:

We have a shop rifle at 0.093 and a couple customer rifles all with 0.093 running 18" no problem with factory ammo.
What I would suggest is:

1) Go buy a box of factory ammo, try the 108 ELDm if you can get it.
2) Check everything about the assembly and make sure everything that should be tight is tight, gas tube is aligned properly, etc.
3) Lube the gas rings, carrier, etc.

Go shoot the factory ammo and see what you get. Half the problems that we've gotten calls about went away with factory ammo. N140 is not really ideal powder for this case in a short(er) AR IMO, I would look at 2520 or Lever to start, I have used 2000MR very successfully in similar overbore cases with heavy bullets and had excellent speed results.

What I would strongly NOT suggest is to start drilling things.

Typically I reply to emails during the week but I'm programming things from home today and needed a brake from CAM software and stumbled on this. I'm leaving for a family vacation on Wednesday evening which will probably preclude me from getting back to you until the following Wed or Thursday. If I'm slow to reply, that's why. Ben and Danny will be in the shop but this is more my area than theirs. We'll help you get going, just a heads up I might be hard to get ahold of for a week.

 

[WeR0206]

We have a shop rifle at 0.093 and a couple customer rifles all with 0.093 running 18" no problem with factory ammo.
What I would suggest is:

1) Go buy a box of factory ammo, try the 108 ELDm if you can get it.
2) Check everything about the assembly and make sure everything that should be tight is tight, gas tube is aligned properly, etc.
3) Lube the gas rings, carrier, etc.

Go shoot the factory ammo and see what you get. Half the problems that we've gotten calls about went away with factory ammo. N140 is not really ideal powder for this case in a short(er) AR IMO, I would look at 2520 or Lever to start, I have used 2000MR very successfully in similar overbore cases with heavy bullets and had excellent speed results.

What I would strongly NOT suggest is to start drilling things.

Typically I reply to emails during the week but I'm programming things from home today and needed a brake from CAM software and stumbled on this. I'm leaving for a family vacation on Wednesday evening which will probably preclude me from getting back to you until the following Wed or Thursday. If I'm slow to reply, that's why. Ben and Danny will be in the shop but this is more my area than theirs. We'll help you get going, just a heads up I might be hard to get ahold of for a week.

Thanks Josh, appreciate the timely response on a Sunday (feel free to ignore my email since you responded here). I know there are a thousand different variables in gas guns that can cause problems and can be extremely hard to troubleshoot via email so I just wanted to make sure the .093 port on 18" +2 was the standard spec etc..

The first rounds I shot through this barrel (pic in OP) were with pretty spicy 2000-MR loads and still had short stroking. Figured I'd try some N140 at near max loads to see if there was any difference. I will definitely be running some factory hornady 108 ELD-M through as a benchmark and ensure a good gas system seal (by using clamp on gas block vs. set screw, etc.) before considering anything else.

Hope you have a wonderful vacation and by the time you get back in a few weeks I hope to have everything sorted out on my end and if not I'll reach back out.

 

[bohem]

Thanks Josh, appreciate the timely response on a Sunday (feel free to ignore my email since you responded here). I know there are a thousand different variables in gas guns that can cause problems and can be extremely hard to troubleshoot via email so I just wanted to make sure the .093 port on 18" +2 was the standard spec etc..

The first rounds I shot through this barrel (pic in OP) were with pretty spicy 2000-MR loads and still had short stroking. Figured I'd try some N140 at near max loads to see if there was any difference. I will definitely be running some factory hornady 103 eld-x and 108 through as a benchmark and ensure a good seal by using clamp on gas block vs. set screw, etc. before considering anything else.

Hope you have a wonderful vacation and by the time you get back in a few weeks I hope to have everything sorted out on my end and if not I'll reach back out.

Sounds like a plan, good luck. Thanks!

 

[WeR0206]

For the TLDR crowd my next steps are:

• Obtain some 108gr ELD-M factory ammo for benchmarking
• Switch to clamp on gas block (I just ordered a Daniel Defense low profile .750 Clamp On b/c hopefully based on its shape it will fit better under my 15" M89 rail, the YHM Clamp on I have on hand is a bit too beefy at the bottom to fit so I'd have to use a 13" M89 rail I have on a different upper and the gas block would be fully exposed).
• Confirm gas port alignment with scope
• Function check at range with factory ammo
• If factory ammo works ok potentially try some handloads with AA 2520

 

[flogxal]

Did you remove the handguard and look for soot/blow-by around the gas block journal/block interface? It sounds to me like some gas loss, or other mechanical resistance in the gas system.

I've experienced a gas block migrating before, didn't notice the tube end in the upper but removed the handguard and saw a tiny gap at the journal aft end, and soot all round the journal. The behavior just before I checked this was like you describe, failures of bolt speed mostly.

 

[WeR0206]

Did you remove the handguard and look for soot/blow-by around the gas block journal/block interface? It sounds to me like some gas loss, or other mechanical resistance in the gas system.

I've experienced a gas block migrating before, didn't notice the tube end in the upper but removed the handguard and saw a tiny gap at the journal aft end, and soot all round the journal. The behavior just before I checked this was like you describe, failures of bolt speed mostly.

Yeah I looked for soot when I removed the gas block and it looked normal. Before removing the block I also checked alignment with a borescope and it was also good.

I do suspect the set screw gas block was bleeding off some gas bc I didn’t bed it with 620 or anything. This is why Im switching to a clamp on block to rule that out and Ill likely bed the tube into the block to seal it off there as well. Everything else I will keep the same except for switching to factory ammo instead of my handloads.

 

[flogxal]

Hope you get it sorted. It's good to know the barrel is a shooter but the cycling is important too!

I would check the bore for the BCG rings/tail, and the rings, to ensure there isn't some mechanical friction in there. Especially since you had the gas block sorted on location. And especially since your buffer is lighter to help speed the bolt along.

It wasn't too much bolt speed from too much gas, was it? If the Superlative is in bleed-off, that should not happen. But too much bolt speed can cause FTF and bolt overrun that sometimes looks like too little gas in other ways.

 

[flogxal]

Also try running a piece of weedeater line or other similar flexi-rod through the gas tube on the BCG gas block to make sure something didn't get in there to obstruct gas flow.

 

[WeR0206]

Also try running a piece of weedeater line or other similar flexi-rod through the gas tube on the BCG gas block to make sure something didn't get in there to obstruct gas flow.

Thanks..I have some weedeater line for this very reason and I also have some pipe cleaners to check gas keys on the carriers for obstructions.

 

[thedude824]

So you didn’t have these problems with the other upper? I can tell you that my San Tan Tactical upper is the ONLY upper I’ve ever run across that was too tight for some bolt carrier groups. I had issues exactly like yours. I then switched to an older Colt BCG I had set aside and it solved all my issues.

 

[WeR0206]

So you didn’t have these problems with the other upper? I can tell you that my San Tan Tactical upper is the ONLY upper I’ve ever run across that was too tight for some bolt carrier groups. I had issues exactly like yours. I then switched to an older Colt BCG I had set aside and it solved all my issues.

I previously had this barrel in a vltor MUR non thermofit upper and had the same short stroking issues. If I remember correctly, using a clamp on gas block I was able to get ejection but it was still failing to feed and failing to lock back. It definitely makes sense for me to follow Josh’s suggestion to try out some well known factory ammo using a good clamp on gas block and go from there instead of messing around with my hand loads. I should’ve just did that to begin with, but I decided against it for whatever reason.

Not opposed to throwing it on a different upper or other ideas.