Gunsmithing Aeroprecision Barrels and adjustable gas blocks?

[Subwrx300]

Looking for advice/experience from anyone that's upgraded the gas block on an AP barrel to an adjustable. Ideally, .875 journal but curious if anyone has had success/trouble with swapping gas block. Alignment, fit, port location all matching etc.

Thanks in advance!

 

[GH41]

Looking for advice/experience from anyone that's upgraded the gas block on an AP barrel to an adjustable. Ideally, .875 journal but curious if anyone has had success/trouble with swapping gas block. Alignment, fit, port location all matching etc.

Thanks in advance!

Why would it be any trouble to swap a GB? The fact that you ask the question leads me to believe it would be best for you to have a professional instal it.

 

[ShooterwithNoName]

What kind of barrel and gas block? I recently purchased an Aero 300blk barrel and threw an old parts box gas block on it. Torqued it down and had no issues. Alignment and fit were good to go and that's on a cheap blackout barrel. I had to set it forward maybe 0.5mm to get it to cycle subs reliably. Depending on the manufacturer of the gas block you may have to set it forward a little bit to get reliable cycling.

I usually install a GB set all the way back against the shoulder tight as I can get it. Then gradually move it forward to get it to the sweet spot. I'm assuming your barrel is going to be a bull profile with a .875 journal. With an adjustable gas block, depending on the round, barrel, purpose, etc. I'll adjust the gas block about half way open/closed, with the block set tight against the shoulder. If it cycles properly there, I leave it then make my adjustments via the adjustable GB set screw or switch. If it's not cycling properly with the gas setting at approx half way, I move the GB forward until it does. This allows me to then use the GB adjustment to either: overgas if it's dirty, undergas if It's either hammering or for singles. Hope this helps.

 

[spife7980]

That makes no sense. Why not just have it back against the shoulder and then use the adjustment as it’s inteded instead of trying to reinvent it?

 

[ShooterwithNoName]

I've had barrels, usually cheaper ones, where the gas port on the barrel is a bit forward of where it should be. For instance:
I had a 20" barrel that had a gas port like this. I installed an adjustable gas block on it set tight against the shoulder. No matter what I did, even with the adjustable gas block fully open it would short cycle and not pick up the next round. I measured and the gas port was a little further forward toward the muzzle than normal. So I had to move the adjustable gas block forward to match the gas ports together to get it to cycle. It didn't take much, maybe 1mm or so. I never had another problem with it after that, cycled everything and the gas adjustment actually worked as designed.

Not sure what doesn't make sense? Not trying to reinvent anything. Not all barrels are equal. Differences in the distance in gas port to barrel shoulder, differences in gas port diameter, chamfer on top of the gas port can all make a rifle not cycle properly if the gas port in the barrel isn't aligned properly with the port in the gas block. Not to mention differences in the measurements in gas blocks.

So my point was: If the gas ports between the barrel and gas block don't match up properly, you may have to move the block to get them matched properly. The OP asked about Aero barrels, I have one right now on my desk in front of me that has a gas port drilled about 0.5mm forward where it normally is. You can butt an adjustable block up against the shoulder and open it all the way up but it's never going to cycle.

 

[Easy_E]

On the old barrels that had a front sight post they left a gap for the ring that held the hand guards . I bought the stripped barrel from them and waiting for the gas block to come in. A neat way to line them up is with a bore scope you know its 100% lined up .

 

[ShooterwithNoName]

That's a good idea Easy, reminds me i need to dig my borescope out of the safe.

 

[mahmoud]

I used an SLR dimpling jig which made it very easy. I only drilled the one dimple just in case i want to change the gas block again.

 

[Subwrx300]

Why would it be any trouble to swap a GB? The fact that you ask the question leads me to believe it would be best for you to have a professional instal it.

I've built a few AR15 variants and swapped several barrels and removed/installed gas blocks on a few different barrels, again AR15 barrels. My question is specifically about Aeroprecision Barrels and their gas port when using aftermarket gas blocks. The distance from port to shoulder is my primary concern.

I do not need to have a "professional" install it. I am simply asking the question here to save some time and money to avoid potentially purchasing a GB that is incompatible with an AP barrel (.875 AR10 variant). It is well documented both here and on other sites that the AR10 variants (DPMS, Armalite, Rock River etc) are not all spec'd universally. Of all the components on a gas rifle, the single biggest point of frustration during a build can be getting the gas system to operate cleanly. For this reason, I posted my question to avoid purchasing a GB that is know to have port set too far toward the muzzle and not have enough room to seat the GB to align the ports.

The other posters understood what and why I was asking. Please feel free to reply if you have constructive feedback on the topic. Thanks!

 

[Subwrx300]

I've had barrels, usually cheaper ones, where the gas port on the barrel is a bit forward of where it should be. For instance:
I had a 20" barrel that had a gas port like this. I installed an adjustable gas block on it set tight against the shoulder. No matter what I did, even with the adjustable gas block fully open it would short cycle and not pick up the next round. I measured and the gas port was a little further forward toward the muzzle than normal. So I had to move the adjustable gas block forward to match the gas ports together to get it to cycle. It didn't take much, maybe 1mm or so. I never had another problem with it after that, cycled everything and the gas adjustment actually worked as designed.

Not sure what doesn't make sense? Not trying to reinvent anything. Not all barrels are equal. Differences in the distance in gas port to barrel shoulder, differences in gas port diameter, chamfer on top of the gas port can all make a rifle not cycle properly if the gas port in the barrel isn't aligned properly with the port in the gas block. Not to mention differences in the measurements in gas blocks.

So my point was: If the gas ports between the barrel and gas block don't match up properly, you may have to move the block to get them matched properly. The OP asked about Aero barrels, I have one right now on my desk in front of me that has a gas port drilled about 0.5mm forward where it normally is. You can butt an adjustable block up against the shoulder and open it all the way up but it's never going to cycle.

Do you have the 20" 6.5 CM AP barrel? If so, do you happen to have the measurement from shoulder to gas port (either center or to front edge)? Had to return my AP barrel for exchange but should be back in the next week or two and want to purchase gas tube/block while in transit.

Thanks for the post @ShooterwithNoName !