u/Visual_Ad8751

I've seen these out in the wild but now that I'm needing them I'm having difficulty googling them and coming up with what I need.

These are M4 x .7 set screws, at least 8mm long, that have machining or "out of round" ​on the threads that create a resistance against the threaded bore to prevent them from backing out. I'm not talking about knurled ends as this is a gas-flow valve that's not seated against the seat- the set screw controls the gas flow (non-flammable gas). Any idea what these are called and where to get them? Thank you.

After a few years of pistol ownership and building from parts ​and people told me I would eventually get into AR-15s I always asked why would I need to do that? Then I found a deal on a Sig MPX 16" rifle, which I love, and have built several 5.56 and 300blk pistols and rifles since then.

I just built an 11" 9mm PCC (with ​an Exomag setup ​that I haven't shot yet) ​and I have one stripped ​lower receiver left. I'm debating for another PCC build ​with a shorter barrel, like 5", or one around 8". Given the option which would you select? TIA

I've been buying the Anderson lowers at my local sportsmans warehouse the past 2 years since I started building my own. I know Anderson is no longer it's own business and stock would eventually run out, but what I don't understand is that other brands of lowers such as Spikes and Aero precision are also out of stock nationwide, at Cabela's/Bass Pro shops as well. Can anyone explain the shortage? I don't want to have to order lowers online, have ​shipped ​and pay FFL charge to receive them.