[Gab101]

I would like to now if bore size on a one piece is the same for the entire length of the barrel or the bore size will change like if I was used an two piece barrel?
thanks

[SNAKESNIPER (Banned)]

Depends on the barrel.

Most stepped-bore one pieces will have a certain control bore length, and then a wider bore for the end of the barrel.

[Gab101]

And what's th difference between both...? Best accuracy on a stepped bore size or not... And what's the difference for the effciency?

[SNAKESNIPER (Banned)]

Any underbore will give you better efficiency than an overbore. IMO stepped bore is quieter because it allows more air to escape after the initial force of the underbore has been spent. Accuracy has more to do with paint quality and weather conditions than anything else, so no barrel is more accurate than any other.

TL;DR Stepped bore is better, Accuracy is a paint issue, not a barrel one.