04-21-2023, 03:40 AM
Darryle Wrote:I have several Aero XL uppers and several BCM uppers in the safe. I am building around the Liberty 16" medium weight fluted barrel and I want to squeeze every bit of accuracy I can out of this build. Do I use the BCM because of their thermal fit or do I truck on and build the Grendel like I did the 6mm ARC on the Aero XL upper and bed the extension with Loctite 620?
Thanks
It is easier to lap the front of a standard receiver than a thermal fit upper..Lapping can improve accuracy if done correctly. I have witnessed this first hand..
When torquing the barrel nut to a standard receiver, the receiver will compress around the barrel extension..How much more a thermal fit upper improves accuracy is debatable and can be a pain to lap, requiring a lapping tool that will fit the smaller I.D. of the thermal fit upper...The I.D. of the upper receiver's carrier bore can effect accuracy if the I.D. is too sloppy with the bolt carrier O.D. I have pin gauges to match the best inside upper to my selection of bolt carriers O.D. Keeping the bolt as straight as possible with the bore can improve accuracy..That said, most commercial upper receiver's bolt carrier bores being manufactured today are smaller than the mil spec of 1", which means it is not a real problem in most cases..
Bedding the barrel is also not universally accepted as improving accuracy either, but I'm on the side it can be beneficial. Even with a thermal fit upper, the loctite will fill small imperfections in the barrel extension channel..
If my choice was between a thermal fit or a standard upper that I could lap, I would choose the standard upper..Be careful when lapping any upper as this can move the barrel feed ramps further into the upper receiver creating the over hang of the barrel feed ramps with the upper's feed ramps..
The quality of the barrel is my main concern, matched with a good BCG, trigger, optics, etc if accuracy is priority..