Yeah comb is too high on the BC M40 stock. The laminate comb is lower and will work. You can get higher sights but that may end up costing as much as finding a stock with a lower comb.
Going to do a free bag of modules with the UML kit for the rest of February. Just put ROKUML in comment box at checkout.
https://www.arrowheadrifles.com/product/uml_replacement_plug/
Sabots suck. As you push pressures, they become more and more sensitive to barrel fit and temperature. It's even worse with solid copper bullets as they don't have as much give as a lead core. Is it possible to get accuracy out of them, yes. But I don't guarantee it, and I don't have time...
Brux is cut rifled and hand lapped, preferred is button rifled and not lapped. Brux are definitely smoother loading and maybe don't foul quite as fast, but you're still getting 50+ shots on either one without cleaning if you're using smokeless. Currently, biggest advantage with the Brux...
How is the front site attached?
DOVETAIL
Which height on the front site did you end up using?
As you probably know, it's critical to calculate rear height to get front height right right. Travis' was about 1.5", but would have to check my notes to be sure. Barrel diameter also factors...
I wouldn't go below 24" and would recommend 26" for a bh209 gun. You're not gaining much weight reduction with going shorter and you loose sight radius as well as approx 50 fps/in velocity loss with BH209. Not to mention, recoil just gets nasty once you get in sub 7# range.
Sorry to burst...
tight fit is name of the game with the 10ML2's.
Harvester black crush rib sabot and a 458cal bullet is best option that I've seen
https://arrowheadrifles.com/
Sabots ASG064
Bullets Barnes origianl ASG060
Hornady HP ASG062
I sell 10 packs if you want to experiment.
Also, make sure...