I've "built" several ARs, several stripped lowers, but only used barreled uppers up to this point. I came upon a new condition billet stripped upper for a bargain and bought it. I've been sitting on a lower for a while, so I have a stripped receiver set to start out from. Add in my first suppressor just started its wait in jail, I figured this would be a good time to make a fun host gun, and possibly be my new go-to to replace the 14.5" midlength rifle that currently stands ready.

Between the parts bin and little component swapping between current rifles I'm pretty much just in need of a BCG, barrel, and rail to finish off a pretty nice pistol build.

This is my first .300 gun, so I'm still a bit confused by the options available for the barrel - twist rate it seems is pretty dang important, as is matching the rifling and barrel to the bullets you'd be firing. Scratching the surface a bit I have the impression there are possible combinations that result in such poor stability I could end up putting new holes in my suppressor (or at least making the main one bigger).

Another factor, especially with the large difference in cartridge shooting sub- and super-sonic ammo, is gas management. I have a Sprinco enhanced spring with a standard weight carbine buffer in the parts bin that, according to what I'm reading, should work for suppressed subsonics and unsuppressed supersonics. But unsuppressed subsonic may be under-gassed, while suppressed supers will be over-gassed. Since I haven't gotten so far as a gas system, do I want to build in adjustment somewhere? Where is the best place? There are adjustable gas blocks, bolt carriers, and playing with buffer weights as means of adjustment, I'm not sure which one provides the best route to success. There are also different schools of thought on port size in the barrel.

Should I just get a Ballistic Advantage Premium 8.3" Hanson barrel and call it a day?
https://ballisticadvantage.com...-premium-barrel.html

And recommendations for a rail would be great. Currently thinking the BCM MSMR, they make a 7, 8, and 9" version depending on what barrel length I go with.

The challenge with 300blk is balancing the component options to meet your needs.

A twist rate of 1:12 is likely the best for a supersonic 110 grain load. But a subsonic 220 grain bullet probably works best with a 1:7 twist in a a shorter barrel. IMO no one barrel will optimal for the variety of blackout loads on the market.

Similar with gas systems -- any one setting won't be optimal for all. Some adjustable gas systems work pretty well, others not so much.

I have a 1:8 twist 11.3" barrel, used with a suppressor. I mainly shoot supersonic ammo, so my gun is over-gassed and accuracy may be negatively affected by too much twist.