AR Pistol Help

[GibsonL5]

Fixing to build my first ar pistol in 5.56. I plan on using a criterion 12.5" barrel (carbine length gas) and the sba3 pistol brace. As I understand, the brace doesn't come with buffer, buffer spring, castle nut, or end plate. So, is just a standard carbine buffer and spring recommended?

Thanks for any help.

 

[RyanScott]

Ask Craddock which buffer to use, but normally with a 12.5 you'd use an H2 buffer.

 

[skipjack]

Yes sir.

 

[GibsonL5]

Thanks for h2 recommendation. What about buffer spring, just standard buffer spring?

Thanks

 

[skipjack]

Are you using a adjustable gas block?

 

[GibsonL5]

Yes, I plan to use the adjustable odin if I can find it in stock.

 

[AMGtuned]

10.5" cmmg 1:7, carbine gas, Aero low profile GB. Have run std., H1, and H2. Currently using a home brew 3.5oz with no issues.

SBA3 requires carbine buffer tube, with standard attachment hardware (I use QD end plate), buffer, buffer spring.

 

[GibsonL5]

Would a sprinco colored spring be beneficial with the h2 buffer. If so, which color?

 

[GibsonL5]

Ok, so I need help. Got the pistol built with San tan receiver set, CMC BCG, 12.5 criterion barrel (pre dimpled)/carbine gas, Odin adjustable gas block, spikes standard carbine buffer spring, spikes T2 buffer (3.99 ounces)

The pistol won't feed next round or lock bolt back after last round. GAS block was set closed to start and I gradually adjusted until wide open. At first it wouldn't eject, so I started to open gas block until wide open. It started ejecting at about 60% open, but barely. At wide open it ejects at 3 o'clock, but only throws brass maybe a foot. So, what to I need to check or try? I've already disassembled to check gas block alignment. Barrel is pre dimpled. Tested with compressed air to verify alignment and air is flowing.
Thanks for any suggestions.

 

[hlee]

Ok, so I need help. Got the pistol built with San tan receiver set, CMC BCG, 12.5 criterion barrel (pre dimpled)/carbine gas, Odin adjustable gas block, spikes standard carbine buffer spring, spikes T2 buffer (3.99 ounces)

The pistol won't feed next round or lock bolt back after last round. GAS block was set closed to start and I gradually adjusted until wide open. At first it wouldn't eject, so I started to open gas block until wide open. It started ejecting at about 60% open, but barely. At wide open it ejects at 3 o'clock, but only throws brass maybe a foot. So, what to I need to check or try? I've already disassembled to check gas block alignment. Barrel is pre dimpled. Tested with compressed air to verify alignment and air is flowing.
Thanks for any suggestions.

I had a very similar issue on a 224 predator build with a JP heavy SCS. Sounds like your buffer is too heavy. Get a standard weight buffer and I bet it runs like a top...

 

[GibsonL5]

I had a very similar issue on a 224 predator build with a JP heavy SCS. Sounds like your buffer is too heavy. Get a standard weight buffer and I bet it runs like a top...

Appreciate it. Ill round one up and give it a try.

Thanks

 

[loveha]

Same barrel in an SBR, here is what I have going on. Functions flawlessly.
12.5" Criterion (Carbine Length)
Lantac Gas Block (Not Adjustable)
Sprinco Hot White Buffer Spring (Red/White)
H2 Buffer
Full Sized Cryptic Coatings BCG

Have not shot it suppressed yet. Might get out this next weekend finally. May be a little over gassed, but plan to run a couple mags through it to see how it does.

 

[Lawless]

Something strange, with the gas wide open a carbine gas 12.5 should run even an H3. Could be the gas port is sized small to run a standard carbine buffer or could be misaligned.

Buffers heavier than carbine don’t cause short stroking unless the rifle is on the cusp of not running reliably anyway. Heavier buffers slow the action a little in the first stage of movement to aid extraction. If going up to an H2 causes the rifle to malfunction then it was on the edge anyway.

 

[GibsonL5]

Something strange, with the gas wide open a carbine gas 12.5 should run even an H3. Could be the gas port is sized small to run a standard carbine buffer or could be misaligned.

Buffers heavier than carbine don’t cause short stroking unless the rifle is on the cusp of not running reliably anyway. Heavier buffers slow the action a little in the first stage of movement to aid extraction. If going up to an H2 causes the rifle to malfunction then it was on the edge anyway.

Thanks for the response. I ordered a standard carbine buffer to try via earlier suggestion, but I'm also concerned on what your saying about gas port size. If that's the case, what are my options..? Reach out to criterion possibly?

Something else that was suggested by a local friend, is coating the bcg in lube...any merit to that philosophy?

Thanks again

 

[hlee]

Wait, are you running the gun dry? Yes, lube the bolt carrier. It needs some- doesn't need to be drippy, but should at least be lubricated.

 

[GibsonL5]

Wait, are you running the gun dry? Yes, lube the bolt carrier. It needs some- doesn't need to be drippy, but should at least be lubricated.

Ok. Ill lube it with some clp. Everything is brand new. I fired exactly 26 rounds yesterday and did notice light wear in the finish in 3 or 4 spots on the bcg.

 

[loveha]

How to Lube an AR for Maximum Reliability

There's no voodoo here - when lubricating an AR or any gun, this is your universal rule: Learn to examine your guns in terms of "friction surfaces" - when this becomes habit, guns reveal nearly all of their operational and reliability secrets, and it tells you exactly where to lube, even on...

www.cherrybalmz.com

This is obviously targeted towards the use of using their product. (Which I use primarily now.) But in general it applies to other lubricants as well.

CLP is okay, but thin and cooks off to easy. This could easily turn into a what lube is best thread. So I will just leave it at, use what you like, just keep it lubed.

If you want to run it dry.

Militec-1 Synthetic Rust Preventative Metal Conditioner 8oz Liquid

Militec-1 Synthetic Rust Preventative and Metal Conditioner is a synthetic metal conditioner used by our troops in harsh environments. This rust...

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[flyer]

Use a standard spring and a standard buffer. If that doesn't work with your gas block wide open, enlarge your gas port until it runs at least a few clicks less than wide open.

Lube it and look at the buffer tube to see if carrier tilt is causing a problem. If your buffer tube is getting hit by the bottom edge of the carrier, you can get a buffer tube that is extended around the retainer pin notch to eliminate carrier tilt problems.

Be careful who you take advice from, starting with an H2 and running dry might be your only issues.

 

[Lawless]

Something else that was suggested by a local friend, is coating the bcg in lube...any merit to that philosophy?

Yeah man, run ARs wet.

Be sure the bolt itself is wet and especially the cam pin.

Don’t change parts until you run it properly lubed.

 

[GibsonL5]

Use a standard spring and a standard buffer. If that doesn't work with your gas block wide open, enlarge your gas port until it runs at least a few clicks less than wide open.

Lube it and look at the buffer tube to see if carrier tilt is causing a problem. If your buffer tube is getting hit by the bottom edge of the carrier, you can get a buffer tube that is extended around the retainer pin notch to eliminate carrier tilt problems.

Be careful who you take advice from, starting with an H2 and running dry might be your only issues.

I appreciate the advice. I'm running the pws enhanced buffer tube with the notch cut for buffer pin. Is that what your referencing?

Also, to enlarge gas block hole is there any tutorial you would suggest watching? I just don't want to mess up a $250 Barrel.

Thanks

 

[GibsonL5]

Yeah man, run ARs wet. I use either 5w-30 or 0w-30 synthetic motor oil.

Be sure the bolt itself is wet and especially the cam pin.

The carrier should be well lubed too.

Don’t change parts until you run it properly lubed.

I just found that the CMC BCG came with frog lube. Ill lube it and give a shot.

Thanks

 

[loveha]

I would be surprised that the gas port is too small. There is a tiny chance that it may not have been drilled completely through. You would need a pin gauge to check gas size and if it's drilled through. Double check gas block alignment.

 

[Landon4]

I had a 9mm ar I know it’s blowback and not gas but it wouldn’t cycle correctly when brand new so I lubed the bolt up pretty heavily and ran several mags thru it, now it cycles perfectly with all ammo that I’ve tried, just needed some breaking in.

 

[GibsonL5]

I would be surprised that the gas port is too small. There is a tiny chance that it may not have been drilled completely through. You would need a pin gauge to check gas size and if it's drilled through. Double check gas block alignment.

With it pre dimpled, should I worry about it being dimpled incorrectly by criterion. This is my first factory dimpled barrel, so no experience with this matter.

Thanks

 

[GibsonL5]

I had a 9mm ar I know it’s blowback and not gas but it wouldn’t cycle correctly when brand new so I lubed the bolt up pretty heavily and ran several mags thru it, now it cycles perfectly with all ammo that I’ve tried, just needed some breaking in.

I will say this is my 6th AR build and I've used aero receivers until this build. I used the San tan tactical billet set and these things are tight. When I took possession, I had to hold the lower and another person hold the upper while we both pulled in order to unpair them. I'm hoping your right and everything is just really tight being new.

Thanks

 

[flyer]

A PWS buffer tube should be good. Some less expensive tubes are equally good.

If you drill out your gas port, I would insert a cheapo aluminum cleaning rod when you drill so you don't accidentally put a divot opposite the gas port. A Criterion barrel should be drilled and dimpled properly so use a standard buffer and spring with lube on the bolt before you look at the gas system.

One more thing, if your gas block is a clamp on type, there is a chance that it's made to line up when a handguard retainer is between the gas block journal shoulder and the gas block.

You could be off by the thickness of handguard retainer sheet metal.

If it is just marginal with your adjustable gas block, you might try a non-adjustable gas block. That should be a cheap experiment.

While you are looking at that, make sure your gas tube hole lines up with your gas block. A shitty tube might restrict the gas.

 

[GibsonL5]

UPDATE..

I put in a standard buffer and spring plus lubed the BCG and it ran flawless. Set the gas block wide open and left it there. Ejecting brass at 3:30. Feeds perfect and locks back on empty mag. I guess I didnt need the adjustable gas block. Thanks for all the help and the 12.5" criterion is really accurate!