I bought the Magpul 10 round mag for my Oryx chassis for my 6.5mm CM but it wouldn't let me seat out far enough to get to the jump I wanted.
The Brownell's 5 round AICS mag (for the .308 short action - part number 100-014-686WB ) @ $39.99 gives me just short of 2.900 O.A.L.
I shot a load of 140 ELD-Ms seated at 2.898 on Wednesday with no problems.