keystone183 Wrote:Great info. In addition to this, what would you suggest as the most important steps to ensure a home build is set up to get the most accuracy possible out of the barrel? As far as build goes anyhow. Not talking quality trigger or glass, but construction tips. Thanks!
Having shot F Class/Target Rifle for a few years I can say that the general consensus among shooters is that all things being equal 80% of the guns accuracy is in the barrel. One local gunsmith who is also the National F Class champion buys barrels in for his customers (mainly Krieger) and spins them in his lathe looking for shadows, indicating a barrel that was not reamed true at the factory. No doubt he keeps the best and sells the rest to people like me in a massive conflict-of-interest. Similarly consistent with another story from a Bench Rest gunsmith who was telling me the world's best shooters will organise for ten barrels for the season, and discard eight as not being good enough for competition. A particularly good barrel is called a 'hummer' where I shoot, and is only screwed on for competition to save its finite life (assuming you have a vise and action wrench). Good gunsmithing is important and having an Olympic grade barrel manufacturer like Lilja is a must, but out of all the 50 barrels he is selling us, some will be better than others, and no-one will ever know why.
I have also noticed what we call 'The Golden Age' of barrels. After a few rounds of initial seasoning new barrels are at their best for about 300rds, then slowly deteriorate to a point where the group size exceeds your definition of accurate. Most committed shooters over here buy a barrel a year, which could be around 3,000rds before discarding. For 6mm barrels that can mean they are given or sold to a gunsmith who cuts them down to a hunting length, re-crowns, and sells them to roo shooters. My point is that as long as you have a good scope, trigger, loads etc the accuracy of the system is predicated on the barrel, and it is perishable.
I would say good barrel, scope, trigger and ammo...Followed by plenty of practise. If you are like me you never have enough time to practise, and while concentrating on building carefully with reputable parts is certainly important, it's not a proxy for practise.
OK, that said, I use high-speed/high-pressure moly grease for the barrel extension/upper join. Castrol make it for high-end performance cars. I also use a Davidson barrel vise when torquing, so the barrel is held rigid and takes the stress. Clamp the barrel as close as possible to where the torquing is going to happen. If you use those clam-shell type AR upper holders you risk stressing the upper when torquing. Seating the gas block. You need to line-up the holes exactly and that means measuring to see whether you need to sit the block the equivalent distance forward of the shoulder as the old clamshell forestocks would take. I think the newer clamping type blocks are superior to the older grub screw types. Pay particular attention to how the bolt carrier mates with the gas tube, so there is no run-out. I seal the carrier key against the carrier with Silastic (gasket seal) to prevent gas leakage. This assumes you are building the bolt carrier from scratch and not buying ready-made. Also assumes you are not installing a piston gas system like an Adams Arms. You can stengthen the extractor claw with a tiny o ring around the spring, or a commercial D-fender.
I have heard of people going to some lengths to eliminate the wobble between upper and lower with bedding the join. I reckon a rubber wedge does just as well.
Lastly, I'm going out on a limb here to suggest you might consider not using a muzzle device at all. Pay particular attention to the crown and protect it religiously from damage and crud. If you screw on a muzzle device it tends to build crud quicker than not and this will affect accuracy. Consider having the barrel re-crowned if at all in doubt down the track, it's not a big job. You can even buy a hand crown reamer from Pacific Tool and Gauge with it's own pilot guide and do it yourself.
That said, an AR frame will never be as accurate as the Stolle Panda, BAT action, heavy Palmer type 6mm bench-rest, bolt action specials. It's a semi-auto Assault Rifle and that keeps it in perspective for me.