The Firing Line Forums - View Single Post - Best caliber for AR-15 lower

globemaster3 · January 31, 2013, 10:52 AM

First, you need to realize the limitations of your AR-15 lower. You are not going to be able to switch to an upper made for the .308-based cartridges or others of equivalent length. The dimensions of the magwell prevent this. Since you mentioned 6.5 Creedmore, I thought it important to mention.

Now, for your situation, there are a lot if cartridges to consider, and a quick search on the forum will reveal a lot of threads where they are listed. 6.8 SPC and 6.5 Grendel are 2 good choices, but you can go to WSSM chambering if you so desire.

In the end, you need to come to terms with exactly what you want this new upper to do and then look at the cartridges that can realistically perform, taking into consideration ammo support and reloading possibilities.

January 31, 2013, 10:52 AM	#4
globemaster3 Senior Member Join Date: January 28, 2006 Posts: 1,482	First, you need to realize the limitations of your AR-15 lower. You are not going to be able to switch to an upper made for the .308-based cartridges or others of equivalent length. The dimensions of the magwell prevent this. Since you mentioned 6.5 Creedmore, I thought it important to mention. Now, for your situation, there are a lot if cartridges to consider, and a quick search on the forum will reveal a lot of threads where they are listed. 6.8 SPC and 6.5 Grendel are 2 good choices, but you can go to WSSM chambering if you so desire. In the end, you need to come to terms with exactly what you want this new upper to do and then look at the cartridges that can realistically perform, taking into consideration ammo support and reloading possibilities.