Rich My Friend!
Alas, I cannot be of much here as I feel that the Bushmaster and Colt are, in issue state, both pretty well made.
Bushmaster was made up in Wyndham Maine, (Quality Parts?) but I only owned one, and somebody bought that real quick.
I have an A-2 Colt in Pre Ban Config and I am NOT parting with it and have transferred it to "personal weapon" on my Log in/out book.
However, whtther it's a Colt of Bushmaster, if on e barrel doesn't shoot, try another.
It's an oddity that this particular std wt. BBL Colt shoot as well as any "matcht\" version I tried (tried 3).
But, when its this close, try the Colt. What Bushmaster has been up to is not known to me.
I still argue the M1A National Match Grade-rebarrell if it doesn't perform-I have at least loaded this combo extensively and shot it a t600 yds.)is for you.
If you liked your M-1, you'll love the M1A.