George, still a bad day at the range is better than a good day at work!
The ejectors sometimes get stuck back with brass shavings in the AR15. Soft brass or whatever. I try to stick with US made ammo in mine. A good rule of thumb is, if you won't drink the water of a country, don't fire their ammunition either!
Another cause could be stiff lube since it was cold. Good luck on getting your tool back into fighting shape!
Sensop: The 243/308 rifles are called AR10, although they look like AR15s they are built to a different scale. The discussions on AR15.com
are very good to find out about these rifles.
My take is, the AR10 is not as good as an AR15. One of the reasons is magazines, very hard to find, unlike AR15 mags. The AR10 uses either a proprietary mag from Armalite, or they sell a conversion kit to convert a M14 GI mag to an AR10 mag, or you can send them your M14 mag and $55, and Armalite will convert your mag for you.
The spare parts are not as prevalent as the AR15 parts, either, though some may be interchangeable. I would stick to the AR15 for this pattern of rifle. HTH
Be mentally deliberate but muscularly fast. Aim for just above the belt buckle Wyatt Earp
"It is error alone that needs government support; truth can stand by itself." Tom Jefferson
If you have to shoot a man, shoot him in the guts, it may not kill him... sometimes they die slow, but it'll paralyze his brain and arm and the fight is all but over Wild Bill Hickok
Remember: When you attempt to rationalize two inconsistent positions, you risk drowning as your own sewage backs up.
45 ACP: Give 'em a new navel!