I've had the chambers checked and they are 2-3/4". If need be, I can load 2-1/2" with roll crimps. The friend I bought the gun from used to shoot the Wally World "low brass" shells and AA skeet shells; I knew they were way too hot. The gun weighs under 6 lbs and I think it may have the thin frame walls. In anycase I didn't want to take an unnecessary chance on cracking the frame. That's why I used 2 dram of black and 3/4 oz of shot and have turned here to see if anyone can help with a smokeless equivalent. Those loads using Unique sound good. I do not need any load faster than 1200 fps. Most have read the "Finding Out for Myself" series from Sherman Bell where he discusses 10 and 12 ga pressures although he doesn't talk about smaller gauges and what is considered low pressure for them. The pressures talked about here, 5500 thru 7500, psi at least give me an idea of what would be "low pressure".
I do not know how thick the barrels are around the fore end but at the muzzle they aren't very thick.
Jack K
