Yeah, they will cause drag. Here's an interesting pic:
Here you can see a secondary shock wave, which is adding drag, cause by the bullet's cannelure. That bullet's cannelure is much more shallow and "less square" than the grooves on the TSX's.
When the TSX's first came out, I didn't think it would be very significant but when actual tested BC's were surprisingly low (even to me [img]/ubbthreads/images/graemlins/laugh.gif[/img] ) I started to think the grooves are at least partially to blame.
Anyway, the MRX's should still have nice BC's--a big improvement over the TSX's. The tip alone will improve them a bunch having a much smaller meplat and making the ogive longer (a length that does
matter) even with the same profile.
And no, you don't need to worry about the shorter shank due to the tungsten core hurting their BC's at all. Here
is a good discussion about that from the past. Those who have been here a while probably remember discussion of the 253 PRL which was shorter than a 210 Berger but had a BC of .880 or so....