Ive got a smooth bore vepr 12. I am looking for the most powerful 3" shells i can find just for the novelty. Ive shot them before and its pretty bad. So im planning on changing the trunion and adding a kynshot recoil reducing tube and a fab defence gl shock to see how much difference it makes. Anyway...so my question is...there are some shells...one type of winchester slug is advertised at 2000fps but it says its for rifled barrels. Im guessing it will fire either way but will there be a significant velocity loss or will it be way off? Is there any reason not to use it? I see others that say they are for rifled barrels only. Brenneke makes a rifled slug thats around 600 grains and does 1500fps. Dixie slugs has a 730gr slug. Any recommendations or advice?