6mm ARC

[SDguy]

7.62x39 or 6.5G Cz's are easy enough to rebarrel. Below is my 18" 6 ARC.

As for why 6 ARC over the 6.5 Grendel, a 103-108gr class 6mm bullet at 2600fps (18") vs. a 120-125gr bullet at 2450fps. The ARC has slightly higher energy at the muzzle, and the higher BC bullets (.530's on the low end, up to over .6 on the high end) will retain it better down range. You also get a wider envelope of really useful bullets for the case capacity, IMO. 55gr thru 110 and all perform really well. With the 6.5 it's hard to find much below 90gr, and anything over 125 is really starting to ask a lot of the limited case capacity.

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Mind if I ask how or why you settled on 18 " & which barrel mfg you went with?
Both of my 24" 6.5 Grendel do surprisingly well w a full or compressed case of LVR pushing a 129 gr. Hornady FB Spire point. Would not mind giving a good 6mm ARC barrel a try i suppose. have to imagine I would appreciate the lesser recoil if nothing else.