Can you put a 16 gauge recoil spring in a 12 gauge, I have a shotgun that a buddy has inherited from his grandfather. He is rather small and when he is running bird loads it fails to eject. When I run it it runs like a an A5, I don’t know what else to do
No, the 12 gauge spring is for 12 gauge.
The 16-20 gauge springs are a different spring.
You can try changing the friction ring settings.
What you describe, works for larger you, versus not working for light weight him, is he doesnt have enough body mass to make the gun function. Like limp wristing a 1911.
You could try getting him to change his shooting stance, lean into the gun hard, to produce more resistance to the recoil.
You could check, clean, and lubricate the mag tube to eliminate that potential issue, then try the different friction ring settings to see if you can find a "set" that works for him.
Since it works for you, it obviously is working as designed...
When we were younger, and wanted to reduce the kick, we would use the heavier load setting to slow the recoil impulse.
Testing for function, we set the rings, then put the buttstock against a solid object (wall, post, tree, large truck bumper, something), and if the gun would fire 5 in a row, ejecting properly but slower, we were good to go.
Using the lightest load settings, with heavier loads, will lead to battering and can split the fore-end.
BUT, the lightest load setting with a heavier load "might" work for your featherweight friend.
Best to you, vr
jw