Take it from my experience... ALWAYS shoot a few boxes (might get away with 2) of .223 after using a CMMG/Spikes style conversion without capping the tube first.
I shot 400 rounds of .22 (150 cci, 250 dirty wildcat) without shooting .223 after (rifle range was closed...used the pistol range), and my gas tube was plugged pretty bad at the muzzle end... thankfully for a small nominal fee the boys at Alberta Tactical Rifle removed my front sight and installed a new gas tube and quad rail gas block.. much easier to remove....
Ill never make that mistake again! Serious pain in the a$$!
A dedicated 22 upper and a well broken in 50rd BD drum mag would be awesome!