Re: 0 moa or 20 moa pic rail for 10/22?
What you may find when you mount the 20MOA rail is that with your particular scope, there's still quite a bit of 'unusable' elevation adjustment below your close-distance zero. You can actually get that back by custom shim/bedding the scope base.
I center my windage, bottom my elevation, then raise it 3-5MOA above the bottom. I mount the scope, and from that point, do not fiddle with the adjustments. I do my re-zeroing using shims.
I establish the zero near, but not at, the bottom of the elevation range to ensure an unbound windage adjustment range. Because it is near the end of the elevation range, the windage range will be limited, but also, since it's at the closest practical shootng distance, windage adjustment needs are smaller.
This practice allows longer zeros to be establishe deeper into the elevation adjustment range, allowing more windage adjustment limit out there further, where it's more significantly needed.
I use cut pieces of aluminum beverage cans as shims.
To raise my POI, I add a shim at a time under the extreme rear edge, and tighten the base fairly tight until I'm impacting within an inch or less, on average, of my POA's height at 50yd. Close as I can get. Better a smidge more shim than less.
If there's some windage error, I loosen the base screws and apply some 'twist-bias', moving the front of the base toward the POI, and the rear opposite, tightening the base screws while doing this.
You may not be able to get rid of all the windage error, but this is the best you can do without modifying the base. Additional adjustment can be effected using Burris Signature rings and replaceable/tuneable bushings. 'Zee'-type is intended for Weaver-style bases.
Now remove the base and shims, and apply a reliable coating of release agent to the receiver where and around where the base covers it.
Mix up some epoxy, nothing faster than a 60 minute cure. Apply this epoxy to the bottom of the base, thicker in the rear, and see if you can leave some area dry around the mounting screw holes.
Hold the base above the receiver, insert the front screw, and push down on the screw with the screwdriver.
Bring the base down, holding the base out of contact, and engage the front screw about a turn, while continuing to hold the base clear.
Still holding the base clear, insert and engage the rear screw for about a turn as well.
Replace the shim(s) under the extreme rear edge of the base, and tighten the screws flush and gently firm, front first.
While doing the final tightening, reapply the same 'twist bias' you had applied earlier, tightening the screws just tight enough to keep it from creeping free.
Be absolutely certain not to tighten the screws enough to establish any flex or stress in the mounting; let the epoxy establish the new contact relationship.
Any ooze should be immediately wiped, and finish up with a pad soaked in acetone nail polish remover.
Several hours later, when the epoxy is definitely cured, undo the screws, remove the shims, and if you wish (it's optional), separate the base and remove the release agent. I use Vinyl Acetate release agent, and cleanup can be performed with plain old rubbing alcohol.
Sometimes the underside of the base will be so smooth, the epoxy will pop off when you separate it from the receiver. This is why I say that separating is optional. If this occurs, just remove and reapply the epoxy the same way, and omit the separation step. If absolutely necessary, the shims can be left in place, but this may be unsightly; so if you redo the expoxy, this time install them flush with the base's rear edge.
When reassembling, reapply the same 'twist bias', and ensure that the metal contact area has a light application of preservative oil, etc., to to resist corrosion.
This process customizes the base's slope to take maximum advantage of the scope's inherent adjustment range. There is really no reason why all your bases can't be custom sloped in this manner.
Greg