Today I received a TA31RCOM150CP ACOG in the mail for my SDM build and noticed below the reticle it is a M4 BDC instead of a A4 BDC as advertised on the site I bought it from. Am I going to notice any difference in point of aim and point of impact at known distance pop-up targets beyond 300m using the BDC and M855 ball? Also somewhat related, my optic came NIB with the JN8:12 filed off, I guess they decided the civy models didnt need Jesus markings either.
You won’t notice anything significantly different in relation to bullet strike/reticle relationship with the chevron out to 300m or so. Past that, you’ll likely notice the rounds printing higher than the indicated ranging stadia, because of the extra oomph from the extra 4.5" of barrel and the fact that the BDC of the M4 variant (AN/PVQ-31B, to the Corps) is taller.
You may or may not notice this in the following:
Are the markings on the one to the right what you are seeing @ 6 o’clock? Reason I ask is that I thought the Army went with the M150 variant for their kinda-sorta squad-organic DM capability with fixed-stock M16A4s before they decided to go with those metal-stocked M14 shoulder-beaters they’re trying to push out the door. EDIT: Strike that, I’m wrong, they went for both variants like the Corps did, only with a .5MOA/click adjustment on the screws instead of the .33MOA/click.
It’s still not a catastrophic difference, you just need to shoot and know your holds, just like you would if you conduct a proper BZO (100m) and shoot a yard-line range.
Thats what I was talking about with the “M4” marking under the reticle (right pic), I was disappointed that it wasnt the same as your left pic. The SN on the housing has TA31RCOM150 in it, but the reticle is M4 marked.
Dug a bit, and corrected my above.
The Army went for both M4 and A4 variants just like our happy little band of merry cutthroats, only they contracted for up to a total of 135,000 instead of shoving one out to every swinging Richard.
You noted the difference in reticle height? That’s the hash you face, so…
I guess you’re just going to have to reconcile yourself to getting a carbine. 
Funny you mention that, as soon as I saw the M4 etched in there I hit the net searching for another M4 barrel assy, to think I just sold a socom profile barrel assy in the EE during Christmas madness. Its looking like another Colt M4 barrel under a DD RIS II for this optic, in the meantime however Im gonna zero and shoot it on the SDM.