I'm an old guy with lower back pain, and I think I already know the answer to this question, but I'll ask it anyway....... is there any circumstance or condition that will allow a back brace or belt on the line?

Maybe in a local or fun match it would be OK, but in a registered match it would not be allowed as it's an artificial support device. See NRA Rules Section 3.12

Yeah, that's what I thought...... I had read the rulebook, but..... can always ask, right?

Shooting vests provide some support, but there are rules on how tight those can be worn.

I'd say go for it if it makes shooting more enjoyable....you won't have any protests till you start winning all the big prize money

DennisC wrote:I'd say go for it if it makes shooting more enjoyable....you won't have any protests till you start winning all the big prize money

Yes you can. But to make it right you must get a letter from doctor and forward to NRA Silhouette to get approval letter. I have know people that shoot in wheel chairs. Also one that supported forend of the rifle with a lanyard hanging from a tripod because his left arm didn't work. Contact NRA Silhouette Dept. for info on what you need to do.
But as others have said just do it and have fun.
The shooting vest should not provide any lower back support. They should hang from the shoulders and be loose down below. Not cinched up tight on the sides. I believe a 4 inch pvc pipe should be able to easily slide up the front.