Freak Inserts and A/C Barrel?
So I've been collecting details for my dream sheridan build. One thing I am imagining in terms of barrel setup. Have an upper tube (I will be hand loading twist lock bolt action fsr, so this "upper tube" would house the barrel/bolt tube) installed with a 1" OD. Directly at the front end of the bolt (at rest/closed position) I am thinking about having the 1" OD upper tube bored for freak inserts. At the end of the insert there will be threads to take an A/C barrel. Obviously this tube will not be all that long, and the lower tube housing the 12g will be cut to match length wise.
First off, I'm wondering if there are necessary to center the barrel or something, I don't care if they're just there to make it so the insert doesn't slide freely out when the barrel is removed. Are the o-rings in factory freaked barrels necessary? I've seen some freak bored homemade barrels without them, and haven't heard of any problems. Should I have the upper bore of this sheridan setup with o-rings like a factory stock freak back? Is it even possible?
Second, what do you think about the feasibility of having a chamber setup to take freak inserts and then on top of that an autococker barrel? I'd use a smooth bore 8-12" ported 0.685 ID PPS barrel on top of a .684 insert. Will there be problems making it so that the insert's transition to the autococker barrel is seamlessly smooth and even?
Thanks for your help! I think that is it, but for some reason I feel like I've forgotten to ask another question or two...