High Density & Model 25

[Boxerrider]

I'm wanting to take my Winchester Model 25 turkey hunting. 12 ga, full choke & chambered for 2 3/4 only. I tried some Winchester, buffered, copper-plated lead in #4 and even at 25 yds it was kind of loose. I would like to try some high density loads of various shot size to see if it tightens up. I won't shoot many rounds through it once I find a load it likes but it may take a while to get there. Do I need to worry about putting a bunch of 1 1/2 to 1 5/8 oz loads through this old gun? I don't want to do something stupid to a gun that is such fun to shoot small flying birds with.
Other suggestions welcome as well.

Thanks!
Jeff