A friend of mine recently purchased a RIA 12 gauge semi-auto shotgun (yeah yeah, I know RIA is cheap, but it was the best he could get his hands on). The manufacturer stated that you need to run “2-3/4”, 1250fps, #7.5 1-1/8oz” rounds for a break-in period. Makes sense. Where we are confused is their definition of “light load” vs “heavy load”. The shotgun comes with interchangeable pistons, one for light load and one for heavy load. My friend emailed the manufacturer, who said that the light load configuration was for 2-3/4” rounds and heavy load configuration was for 3” rounds (and yes, the shotgun can handle both sizes). That didn’t make sense to us. The reading I had done said you can have both light and heavy loads for both size rounds, that the load size is determined by shot size.
Can anyone provide some clarification? My friend and I are new to shotguns, apologies for the ignorance.
Dunno anything about RIA but yes, shotgun pellets are rated at different sizes. The sizes are determined by numbers, higher numbers = smaller pellets. Bird shot ranges in size from a 9 to a 1, depending on the game you are going after. The next bracket is then Buck where it starts at 9 down to a 1, where 1 is the largest buckshot pellet size.
Edit: Buck is a special case because the pellet size gets even larger after 1 with 00 and 000 shot. https://www.wideners.com/blog/shotgun-load-types/