I’ve had a few customers inquiring recently as to whether they can shoot 5.56 NATO ammunition in their Varmint Exterminator rifles since the barrel is marked “223”.
The Varmint Exterminator is safe with decent factory loaded 5.56 NATO ammo. We put .223 on the barrel as that is what is recommended for best results – match grade .223 ammunition.
The VEX has what is called a “5.56 Compass Lake” chamber. This means the leade (amount of freebore before rifling) is shorter than on a 5.56 but not as short as a .223. Also the angle into the rifling is a little different. The overall chamber dimensions are slightly tighter as well and the bolt is matched to the chamber for better accuracy. Frank White, of Compass Lake Engineering, developed this chambering many years ago for competition shooters and this chamber is widely used in many service rifles used for target competitions at Camp Perry.
I have fired Federal M855 5.56 NATO ammo in VEX rifles with no ill effects. If you should fire any foreign 5.56 ammo through it, just keep checking the primers to make sure they aren’t backing out, popping out or severely flattened. Some of the foreign military ammo can run a little hot and may not run efficiently in the tighter chamber of the VEX rifles.
Erik Winter, Gunsmith