State Arms or AR-50 in 50BMG
I have both.
My State Arms rifle is the Shorty model with the optional 30" SS barrel.
My AR-50 is an older model with a very long throat. 3/4" of freebore.
Both have mil-spec chambers, i.e. 0.562"diameter neck in chamber.
Both shoot very well once your ammo has been fine-tuned for the rifle.
In my AR-50, I have shot a 5-shot group under 5" center-to-center at 1000 yards in FCSA competition. It may have been a fluke as I have not been able to repeat it. The Spring 2011 shoot at Alliance Nebraska was plaqued by 45+ mph winds while we shot. I was shooting a 800 grain brass boreRider from Lehigh, over 235 grains of VV 20N29. Ammo was heated to 135 degrees prior to shooting.
My State Arms Shorty has not received as much reloading attention, so groups so far ar in the 10-12" range shooting Prone at 1000 yards. This is with Hornady Amax 750 grain over 225 grains of H50BMG.
Each rifle can be purchased NEW for less than $3000, dependent on options ordered. A good scope such as a Luepold Mark IV Tactical 8.5 X 25 X50 or a Night Force 5.5 X 22 X 56 is recommended. I have Luepolds. Scopes are 1300 - 1800 $ plus good mount for $80.
Either are good !!!! My State Arms is a better Prone gun, my AR-50 is a better Bench gun. As configured.
Now reloading equipment can get very expensive, but is the only way to develope top loads.