TheRifleman

Exhausting propellent gases from around tdc line of sight will lessen the pressures from the side and downward ports.

Never replace the weights with anything lighter than the carbide/spacer stack. If you're running a standard buffer setup, then consider replacing that with a CAR buffer, using the standard-length buffer spring (assuming you're running a rifle tube). Of course, you can also use a reduced-weight carrier but, assuming your barrel is accurized and the rig runs well, optimal cycling/accuracy/rapid acquisition is best achieved through the loads you craft through trial and error. Replace with a CAR buffer? I don't think I want to replace my key nor my beautiful JP lightened bolt carrier that often. Ah, what do I know, only been shooting them for 25 years or so.. We are not going for more reliable cycling per se here, I am assuming we are going for the least amount of muzzle movement. Why else would you run a lightened carrier/buffer? ....because the mechanics of cycling will affect muzzle movement, to some extent. Lightened parts have always been used with mixed results. In one case, I replaced the standard buffer with a heavier CAR (4.3oz), using the rifle-length spring and tube. Result was complete controllability and rapid acquisition, for this particular rifle (he was using skeletonized stock w/standard rifle tube). Using a heavy CAR, perceptible muzzle movement already occured at the time in which the buffer bounced back to contact the carrier surface and move it forward. His custom compensator did the brunt of the work. Carrier and key are fine after two years and 6,700 rds. As with anything, you have to go with whatever works.

Never replace the weights with anything lighter than the carbide/spacer stack. If you're running a standard buffer setup, then consider replacing that with a CAR buffer, using the standard-length buffer spring (assuming you're running a rifle tube). Of course, you can also use a reduced-weight carrier but, assuming your barrel is accurized and the rig runs well, optimal cycling/accuracy/rapid acquisition is best achieved through the loads you craft through trial and error.

LEGAL issues aside (as per your post). I don't think the Rock river receiver extension tube is threaded on the end for a stock.. however, I could be wrong. Also, I don't think it is the same lenght as a A2 rifle stock receiver extension tube. Best case, you take care of the legal issues, You slide on an A2 stock and add spacer and screw. done deal. Wost case, you change the extension tube with one that with fit either an A2, A1 or 4/6 position stock, then add the stock. The lower design will not effect the ability to add a stock. Start from scratch. Buy a stripped lower and Form 1 it. That way you'll have a reciever that can accept any stock, commercial or mil-spec, and particularly if you change your mind or develop another stock preference at a later date. Also, the lower won't be marked as pistol (since legally it won't be, once your F1 has been approved). Of course, the lower is marked once made into an SBR. Even so, I've done a few SBR conversions for customer's on "pistol" lowers that have stocks attached, and an LEO still conducts a check. Just make sure to specify on your F1 what length of barrel you intend, and then estimate the OAL of the gun, depending on what stock you prefer, as both these must be listed as terms pending approval. I'd recommend waiting to order parts until after your receive approval, as you don't want to possess a short barrel without having a registered SBR (i.e., you must first obtain approval to possess an SBR, and only then can you make a purchase for a barrel shorter than 16"). You can PM me if you have any questions.

Definitely go for the longer 18 or 20 inch barrel, preferably ported rifle-length (middy's cycle reliably and well, but rifle tends to cycle smoother). Stick with gov't. or heavy profile. If you choose to go chrome-moly, stick with 4140; otherwise 416R SS is the preferred material for superb accuracy with an 8 or 9 twist. Most of the top-end bullets are self-stabilizing