mp43
03-26-12, 20:46
Sent a KAC URX rail, a used KAC bare upper, a new 12.5 in CHF DD barrel, and an AAC Brakeout to a known great gunsmith. On testing I was disappointed to get 8 inch ten round groups at 50yds. I then noticed the barrel was loose, and it was canted to the right as it exited the rail.
The smith said the barrel extension was too narrow and the old receiver was a bit worn, resulting in a nasty tolerance stack mismatch, which he admitted to missing before shipping it to me.
I returned it to the same smith , and he reassembled it with a new BCM receiver. After unpacking it the second time I noticed that it was still tilted to the right, less than before, but now the barrel was tight. However, though improved it was still inaccurate, printing 4 inch ten round groups at 50 yds. Function was otherwise perfect.
I put it away until recently, and decided to separate the components for other builds. I was surprised by how tight the AAC Brakeout was torqued. I purchased a Brownells receiver torque tool to avoid damaging the receiver, and after soaking overnight in water it still required a two foot cheater pipe on my wrench to break it free. I estimate this thing was tighter than a barrel nut, easily 60 foot pounds. Two other suppressor adapters I removed the same day came off with normal effort. These were installed by another gunsmith. To my surprise I did not see much Rocksett residue on the threads of the tight Brakeout.
My question thus is whether or not this over torqued adapter could have been the cause of the poor accuracy. I've heard that over torquing the barrel nut can degrade accuracy, but does that apply to the flash hider also?
Now that I have removed the adapter will this barrel shoot better, or should I chuck it? Should I cut it down to 11.5in?
Or perhaps it was an out of spec barrel extension.? (Accuracy seemed to improve after the same barrel was re-installed on the new BCM receiver).
Your thoughts?
The smith said the barrel extension was too narrow and the old receiver was a bit worn, resulting in a nasty tolerance stack mismatch, which he admitted to missing before shipping it to me.
I returned it to the same smith , and he reassembled it with a new BCM receiver. After unpacking it the second time I noticed that it was still tilted to the right, less than before, but now the barrel was tight. However, though improved it was still inaccurate, printing 4 inch ten round groups at 50 yds. Function was otherwise perfect.
I put it away until recently, and decided to separate the components for other builds. I was surprised by how tight the AAC Brakeout was torqued. I purchased a Brownells receiver torque tool to avoid damaging the receiver, and after soaking overnight in water it still required a two foot cheater pipe on my wrench to break it free. I estimate this thing was tighter than a barrel nut, easily 60 foot pounds. Two other suppressor adapters I removed the same day came off with normal effort. These were installed by another gunsmith. To my surprise I did not see much Rocksett residue on the threads of the tight Brakeout.
My question thus is whether or not this over torqued adapter could have been the cause of the poor accuracy. I've heard that over torquing the barrel nut can degrade accuracy, but does that apply to the flash hider also?
Now that I have removed the adapter will this barrel shoot better, or should I chuck it? Should I cut it down to 11.5in?
Or perhaps it was an out of spec barrel extension.? (Accuracy seemed to improve after the same barrel was re-installed on the new BCM receiver).
Your thoughts?