It isn't usual for plainbase to out shoot gc, but you have a good internal finishes and dimensions, in which case they will definitely shoot as well as gc, when velocity is held to a point where leading isn't a problem. Which is to say, if you'd have laoded to maximum pressure the gas checked bullets would have been most accurate. Apparently the gas checks weren't seated perfectly square.
To insure perfect squareness of gc's I like to bump them at the bottom of the sizing stroke if using a Lyman or RCBS sizer, and with these sizers, I cup the stop plug slightly and face off a flat ring around the outer edge of the plug end, about 1/32 wide, which imprints into the check quite easily, even if the sprue is raised a little. With a Star sizer, I use either a flat or similarly cupped pusher punch and push bullets nose first.
If max power is wanted, consider that fact that gas checked bullets will leave the muzzle with a bit over 100 fps higher velocity when loaded to the same pressure as plain base. I'm speaking here of heavy loads. The higher velocity isn't apparent at moderate pressures, nor is the above of concern if real heavy loads aren't on the agenda. The savings in cost and sizing time with plain base makes them most attractive in this case.
