All it could really do is the same as if you used tape. The ball simply doesn't touch the sides of the barrel, which provides even drag around the circumference, but no actual seal. Using an underbored barrel will do the same thing, but increase efficiency at the same time. The only difference in trajectory (out of the barrel) would be if your bore-matched barrel is somehow manufactured poorly or dirty. Anything else you perceive is fictional.
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my vote as others have is the eigenbarrel. however, this depends on your local paint. i get rollouts at times with a .672 so i really want an eigenbarrel. i love everyone telling you to get what you already have or more expensive. there are also people who can bore out barrels for freak inserts, i know ive got locals who charge $20 a barrel and now a stock barrel is a freak! if you have that option id do it. if not the CPs are also an amazing choice for the price. the ifit could also work, prevents roll outs and some places you can order with one insert and adapter
super cheap pump option: grab a random barrel and put a bit of tape on the inside, hockey tape works well though any kind with some cushion to it works