Backyard Proof House

[Rod N. Gunn]

I have a new/old 10ga, 0 grade, twist-barrel, hammer gun (pictures posted on other threads) that I want to turkey hunt with. I grew up in a house where shooting a "damascus" gun was tantamount to Russian roulette. I don't harbor that view but I would like to "proof" my gun so to speak. I thought I'd use a long string and a safe seat behind the engine block of my Chevy. The gun is a 3 frame with meaty walls and 2-7/8" chambers. Very light pitting. Smith says should be fine with low pressure loads. Here are my questions:

1) Can I cram a 3-1/2" load in there and light it off a' la Sherman Bell (just for proofing not hunting).
2) Have others done this? Should I just bungie it to a tire?
3) What should I look for in the way of damage post-test? I have a bore mic and a wall-thickness gauge.
4) What do folks think of 2-7/8" RST #4 Hevi Shot as a turkey load?

Thank you in advance for your thoughts on these questions.