So, I was thinking of getting one of these:

http://www.dtechuppers.com/ar-15-wssm-upper-receivers.html

I absolutely love the .243 WSSM, but in a heavy varmint bolt rifle. The thing nails the little sage rats out to 350 yards and so far has done so while shooting groups in the low .2's to .3's, depending on me. In the Dtech upper the case can be necked up to 6.5, .308 or .358. Downside is that the brass is seasonally produced, but I have several thousand cases on hand. Just for fun I stuffed a few dummy .243 WSSM cartridges loaded with Barnes 62 grain Varmint Grenade bullets @ 2.240" AOL into a Colt magazine and they fit and functioned flawlessly, although in a single center stack.

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The nominal OAL of the .243 WSSM is 2.360", drop that to 2,240" max and they should feed through the standard AR-15 magazine.

The velocity of the Barnes bullet is 3,587 fps out of my Brux 24" barrel. A 95/100 grain Nosler Partition can be driven up to 3,010 fps with Rl-15, or 3,222 fps with VV N165 in a 24" barrel. Now we have a .535" case head diameter and more powder capacity. In either case head diameter that capacity is going to be diminished by the need to seat heavier bullets deeper.

Sometimes we have great notions, but still the AR-15 was a compromise and not really the perfect platform for flexibility, yet for the tinkerer it offers hours of fun and frolic.

Last edited by WranglerJohn; 07/15/13.