Home Forums Hunting & Shooting AR and Tactical Rifles Couple of technical build questions

I'm in the process of gathering all of the parts for a build. I've never changed out parts on either of my ARs, let alone built from scratch, but it's something I want to do. Going with an 18 inch barrel with rifle length gas. Carbine stock.

1. When installing the barrel, do you lightly oil the barrel extension where it fits into the receiver?

2. I am going to use 15 inch floated handguards. The barrel nut doesn't have the u shape slots for the gas tube, so tube alignment during tightening of the nut isn't an issue. From what I understand, most(?) guys tighten to about 30 foot pounds, then tighten enough more for proper gas tube alignment. Since I'm not going to be dealing with tube alignment through the barrel nut, how tight should I go? 40 foot pounds?

3. I don't have either buffer tube assembly or the gas block yet. I've never had the opportunity to mess around with a rifle length gas system with a carbine stock. Assuming the standard carbine spring/buffer, any issues, typically, over or under gassing? Will be using a standard weight bolt carrier group. I can go with adjustable gas block, or should the standard block be good to go? Thanks

1. No I usually loctite the extension into the receiver.

2. Yes 40' lbs is where I try to stay.

3. It all depends on the gas port size. There is no standard rifle gas on an 18" barrel. The 2" of barrel you'll lack will shorten the dwell time and usually requires a larger port. Ask whoever made the barrel what they recommend. I've seen carbine buffers work and I've seen H2 buffers needed just going from a rifle stock to a carbine stock. This is where an adjustable gas block may not help. If you need more gas, you'll have to go lighter buffer. And just because it works in 90 degree weather doesn't mean it'll work when the snow flies.

You can put some lube on the extension when installing the barrel.

I would make sure it was tight but not farmer tight.
It does not to be baby huey tight.

The carbine stock/buffer should work if that is the stock you want to use.

I have a adjustable gas block because the hole was drilled to .110 diameter.

It did not do much.All of my other rifles have a standard gas block,you will have to shoot it to see if it is gassed right.

Hope this helps.

Thanks guys, for the advice. I appreciate it.

Mostly what's already been said, depending on what you want to do.

Depending on the upper / extension fit: if it slides in easily, you can loctite it in or not. There is enough evidence to say that loctiting it improves absolute accuracy. Best of both worlds is a thermo fit & I prefer that. BCM uppers require thermo fit, other may require it to various degrees.

Some free floated rails come with a specified torque for the barrel nut; SLR specs 35, WOA specs 50,don't remember what BCM specs but I think it was 45 or 50. If nothing is spec'd with your rail, I'd use 40 if it's aluminum & 50 if it's steel..............be sure to use a good lube like AeroShell 33.............I use a high temp product from Loctite. And be sure to lube the face inside the nut that tightens against the barrel extension face.

I like adjustable gas blocks, but likely you really won't need it on a rifle gas barrel...............I have them with gas ports from around .088" to .103". The .088 runs perfectly with a fixed GB & an H buffer with a Spring White (standard) spring woth .223 ammo & 5.56 ammo.

On another barrel with.103" gas port, with a carbine buffer & a slightly heavier spring, the AGB is pretty wide open to reliably lock the bolt open............so you really never know until you shoot it.

If your gas port is less than .095", it's almost a certainty that you can get by just fine w/o the AGB; on the other hand, it will work just fine if you put it on & end up running it wide open.

Good Luck.............buy as many dedicated tools as you can afford as life is much easier that way. Some kind of upper clamping block & a decent vise are a must for installing barrels.

MM

Thanks Montana Man. Which loctite is used on the extension?

I use 680 on the barrel extension; but I prefer a thermo-fit upper like BCM if available.

MM