Let's document getting my 6mm ARC to shoot right...

[KelsonAK]

...because why not make notes where someone else can benefit.

New build - the components:
Lower:
17 Designs billet
Geissele National Match Trigger
Magpul Precision stock
Carbine buffer tube (milspec Brownells)
Carbine buffer (standard weight)
Springco white spring

Ie: Normal stuff.

Upper:
Aero Enhanced
Rainier 22" barrel, +2 Gas
Thread protector
Sgt At Arms 17.5" Arco handguard
WOA Gas Tube
Wojtek .875 adjustable clamp on gas block
Rainier full mass carrier
JP Bolt
Radian Raptor
Vortex PST in a ADM Recon X mount

Used a bore scope to align the gas block after barrel installation - as well as the witness hole in the top of the gas block. Carrier slides into position without binding on gas tube. Bolt lugs do not strike barrel extension.

With gas closed - Shots 3-8 out of barrel were a nice 3/4" group at 100 using Hornady Black - manually cycling the action.
Open gas port on block - ejection is at 3:00 but NOT able to lock bolt back on empty magazine. Opening gas all the way does not rectify issue. Manually operating charging handle with empty magazine in place DOES lock back bolt.
Tried another Hornady loading. Same result.

Bleh.

Ok - so troubleshooting:
Wilson bolt uses one piece gas ring - replaced with traditional 3 piece for better fit in carrier.
Same result.
Replaced full mass carrier with Brownells light weight carrier.
Same result.
Took gas block off, inspected, and re-installed. Measured gas port - it is a .0860 (#44 dill bit) which seems pretty reasonable.
Same result.
Checked carriers for oversize 'anything' - and for loose gas keys - nope. Carrier is within 'normal' specs - not as tight as I would wish for overall, but still pass pin gauge inspection.
Still to do:
Measure tail of JP bolt.

[VASCAR2]

https://www.65grendel.com/forum/showthread.php?24529-Buffer-Wear&p=286355#post286355

https://www.65grendel.com/forum/showthread.php?17386-More-Ejection-Dejection

[KelsonAK]

JP Bolt tail measures pretty much .225 on the nose.
Carriers both permit a .252 pin to barely pass but a .253 fails to start in that part of the carrier. So.. not as tight as I would wish for, but still within reason and normally good function.
Carrier does not impact the lower receiver at full buffer spring compression (ie - when the buffer makes contact with the rear of the buffer tube) and ever so slightly depresses buffer upon shotgunning the receiver closed.
When swapping a .223/5.56 upper onto the lower - things work as planned and the .223 did the pew pew thing as expected. As I have several lowers making effective pew sounds I'll swap something in and see if there is any difference.
I haven't been able to find a 6mm arc gas port chart at this point - still a bit new I think. I'll email Rainier on the port size but won't hear anything till Tuesday I'm sure.

[StoneHendge]

I can't offer any advice that others haven't, but remember that you bought it from Rainier, so you can send it back if they can't help you and you can't get it to work.

[KelsonAK]

Brief update - spoke with Rainier today after a few emails back and forth. My opinion of the company remains unchanged - one of the best to work with. They confirmed my gas port size is what they were expecting it to be.

Confirmed my troubleshooting steps so far. Am going to do a few more things:
Run a pipe cleaner down the gas tube to check for obstructions.
Replace my lube (an oil/grease mix that is in fairly common use) with aeroshell only (Rainier recommendation)
Substitute a lower off another rifle to see if problem follows the lower - possible friction/binding in the buffer tube, from misalignment of the upper/buffer tube, possible trigger/hammer interference, or tensioning screw issue.
Replace gas block and gas tube. I've got another gas block on order.

If none of these works - they asked me to send the assembled upper to Rainier for them to try on one of their armory lowers and replicate the issue.

[danm]

Brief update - spoke with Rainier today after a few emails back and forth. My opinion of the company remains unchanged - one of the best to work with. They confirmed my gas port size is what they were expecting it to be.

Confirmed my troubleshooting steps so far. Am going to do a few more things:
Run a pipe cleaner down the gas tube to check for obstructions.
Replace my lube (an oil/grease mix that is in fairly common use) with aeroshell only (Rainier recommendation)
Substitute a lower off another rifle to see if problem follows the lower - possible friction/binding in the buffer tube, from misalignment of the upper/buffer tube, possible trigger/hammer interference, or tensioning screw issue.
Replace gas block and gas tube. I've got another gas block on order.

If none of these works - they asked me to send the assembled upper to Rainier for them to try on one of their armory lowers and replicate the issue.

Even though they say the gas port is in spec, I'm gonna bet it gets opened up to resolve the cycling
danm

[KelsonAK]

Got to range with 3 other lowers... and what do you know... it works with all 3. Triggers used were a big G national Match, a Larue, and a Centurion. Sooo.... the question is... is it the lower not quite right or is it the hammer that is dragging in such a way in that particular rig that is causing the issue. I'll swap triggers around and see if the issue follows the trigger or no.

[VASCAR2]

[D.Davis]

Do not know if this applies to you, but, I had to file the sides of my safety notch to fit my G NM trigger per G instructions.

[Dino11]

I know my situation is a little different from yours, but here goes.

I to have a plus 2" gas port on an Odin Works barrel, I was having the same issues you are experiencing.

Here is what is different with my 6 ARC.
My barrel is only 18" long, and I have a rifle buffer tube, spring, and buffer. So my fix may not work but it is worth a try.

Instead of using the white Springco spring get a reduced power spring. This will allow you to turn down the gas rather than drilling it out. It just may be your ticket.

On my setup I had to remove a bunch of weight out of the buffer along with the reduced power spring. But doing this it allowed me to turn the gas port almost closed to function the rifle. It is the Softest shooting rifle I own, almost zero recoil. Sounds like you would only need to purchase the buffer spring. And yes I know this goes against the norm, but it worked like a charm for me. And if you do the physics of this it make perfect sense.

[KelsonAK]

I've got springco whites in all of my lowers - so in this instance springing alone isn't the issue. Unless it's just a bad/heavy spring which is always a possibility but less likely with the Springco stuff. I have other springs (at least one of each of the springco colors ) in the parts drawers that I can look at using. I'll start by moving the G trigger from the lower that is NOT functioning correctly to a lower it IS functioning correctly in, to see if the issue follows the trigger. After that I'll try the buffer and spring. After that - I'll see if a buffer tube swap addresses the issue. Mostly curiosity at this point to find the one piece or stack of pieces that is causing things to not work just so...

[Dino11]

If you have a Springco yellow try that, It is 20% lighter.

[204 AR]

I had RRA NM hammers that had too much drag on the bc and needed very slightly shortened. Easy to measure with a caliper with the rifle apart.