Its all new to me
"Jack of all trades master of none" LOL
The differences In the M1 and M1A1 are talked about a lot on the net, but as always its tough to get a solid answer.
But with straight cut and paste from the net
Some of the differences that the CMC does replicate are:
====="The main difference between the M1 and M1A1 was the bolt. The M1 bolt had a floating firing pin and hammer, the bolt of the M1A1 had the firing pin machined to the face of the bolt, eliminating unnecessary parts"
The term "hammer" above is not how I would describe the system, but I guess you could lol The CMC is a classic example of how I can now fully understand the system by having seen and touched, much better than a book/web. worth a google
From web below sums it up and I think CMC have done a cracking job on these... Maybe the best CMC model and the best Thompson M1 replica I ever saw ????? Yep I reckon
"The flip-up adjustable Lyman rear sight was replaced with a fixed L sight. Late M1s had triangular guard wings added to the rear L sight, which were standardized on the M1A1. The slots adjoining the magazine well allowing the use of a drum magazine were removed. A new magazine catch with the provision for retaining drum magazines removed, was produced, but most M1s and later M1A1s retained the original. The less expensive and more-easily manufactured "stick" magazines were used exclusively in the M1, with a new 30-round version joining the familiar 20-round type. The Cutts compensator, barrel cooling fins, and Blish lock were omitted while the buttstock was permanently affixed. Late production M1 stocks were fitted with reinforcing bolts and washers to prevent splitting of the stock where it attached to the receiver. The British had used improvised bolts or wood screws to reinforce M1928 stocks. The M1 reinforcing bolt and washer were carried over to the M1A1 and retrofitted to many of the M1928A1s in U.S. and British service. Late M1s also had simplified fire control switches, also carried over to the M1A1. "
Of course as always I could have it all wrong!!
Ohh markings are very good on them as well .