You should be fine so long as you let the bolt run forward on its own and all rounds are fed from the magazine. This applies to any semiautomatic rifle. The bolt carrier on my SKS can hang up slightly on the receiver if you ease it forward, but it cannot fire if the carrier is far back enough to move the bolt out of battery.
P.S.: Lee Enfields are generally .303, not .30-06. As for your shotgun, it should be fine with lead shot assuming good condition. It is the older guns with Damascus barrels that you have to worry about with smokeless powder.
RIGHT! Oops.. my bad... Yeah.. 303 British...
Thx for the info on the SKS.
The Belgain shotgun barrel does not have a spec of rust or pitting on it. It is described as Pre-WWII, 70% original bluing, tight action, case hardened receiver, well made plain gun with years of service left. Didn't think it dated all the way back to the great depression until I verified the markings.