With no mil-spec to standardize production, AR 10 rifles took time to develop. Finally, there seems to be an informal standard based on the DPMS spec. Now you can buy complete rifles or build a rifle from the ground up. Everyday there seems to be someone new offering receivers, bolts, barrels, etc. This has the added benefit of bring some lower cost options to market. I wish a major manufacture would offer one of the popular 6mm calibers – either 6XC or the 6mm Creedmoor. These two calibers are being used by many competitors, in bolt action rifles, to win tactical rifle competitions. Again, this is not mean to be an inclusive list, just some that I have experience with or explored:
- 243 Win – A standard case with great performance in a bolt gun. But hampered by the magazine length of the AR 10. Will be doing testing on this in the future to see if it is possible to shoot a heavier bullet (100gr +) from a magazine.
- 6mmx250 – A wildcat round that looks like an interesting solution to the AR 10 magazine issue. The 22-250 on which this is based is shorter than the 243. So, you should be able to load longer bullets for magazine feeding. Velocity should not suffer, there is still plenty of case capacity.
- 260 Rem – Started life as a wildcat – 6.5×308. Formalized for ammunition and rifle manufactures by Remington, thus the new name 260 Remington. Has had tremendous success in bolt action rifles. As you will hear with all the AR 10 calibers, hampered by the AR 10 magazine length. But with a custom barrel chambered around a magazine length round, it is a formidable choice. Initially, some gun were chambered with a twist of 1 – 8.5 in. I think this is border line for stability. I always prefer a slightly faster twist.
- 6.5 Creedmoor – Specifically designed around the AR 10 magazine. Also loosely base on the 22-250, it provides a round for shooter watching to by factory loaded ammunition. As with the 260, the twist rate varies between builders. I would stick with the 1-8in to be safe.
- 308 Win – The workhorse. So many options. Just a great choice for the casual shooter. Can be built for fun or extreme match accuracy.
- 338 Federal – Interesting round that just has not caught on in bolt action rifles or in this platform. Ballistics just are not great past 300 yards. I do not see what need it satisfies.
Hatcher's Notebook 