I don't lke a-bolts in the more powderful cartridges because they seem to produce more felt recoil than other rifles with the same cartridge.As for the boss system,I owned one and will never own another.If you don't reload they will allow you to tune the gun to improve accuracy with a given load.Then again I have found that my guns without the boss shoot just as accurately or moreso with proper loads.The standard boss is so loud that a single shot without hearing protection can cause your ears to ring for several hours.Either you hunt with hearing protection or after a few years your hearing will be so damaged that it won't matter.Additionally,the boss on my rifle kept coming loose which changed the point of impact.Lastly,the boss equipped rifles are equipped with shorter barrels to compensate for the length of the boss ,so they produce less velocity than non boss equipped rifles.
As for the BAR,I owned one in 7mmremmag and sold it after it jammed in cold wet weather.It also jammed twice for the friend that I sold it to under similar conditions.Yet it always functioned perfectly at the range or in warmer,drier conditions.