Re: Chassis or stock
I have both the stocks you mentioned. The AICS is about 3.25lbs heavier, if that is a consideration. Folding is nice when you want it, but you have to be realistic about whether it really is important. You'll be able to adjust the cheekpiece to your proper height with the AICS. The B&C M40 will require a stock pack or some other means of raising the comb. The AICS will work better in the prone because the heel of the stock is higher and doesn't dip as low in your shoulder pocket. Of the B&C stocks, I have a preference for the 2956. The front is the same as the M40, however there is no drop at the heel, has a "hook" on the underside of the buttstock, and has a slightly longer pistol grip.
Any one of the stocks is going to bolt right onto your receiver and get the job done. And obviously the B&C is about $800 less than an AICS. I may have an AICS 2.0 in FDE available soon. Good luck in your decision.