Perhaps more info than you wanted, but I'd like to be complete:
I've shot grip mounts for both sides and slide and frame mounts on my 1911 .45s and by far prefer the slide mount.
1) left side grip mount - the version I had required two extra holes to be drilled into the frame in addition to using the grip screws to hold it in place. The grip was comfortable, but the scope rode very high above the open sights and I could never get the screws to stay locked down through a string of fire.
2) right side grip mount - I believe it's the B-Square you mentioned, but I'll describe it for all readers. The bottom mounting screw takes the place of the mainspring pin and because of this the mount needs more meat (metal) to grab into at the corner of the grip. I find this too uncomfortable for my size hand. Again, the scope rides high to clear the sights. The second mounting screw replaces the hammer pin and this will not match the correct dimension if your gun has had oversized pins installed. You can also ovetighten this pin which can restrict the hammer fall. The grip itself, at least on mine, is very smooth, so there is no "grip" to the grip.(smile)
3) frame mount on dust cover - usually need to remove the rear sight so you can get the slide off for cleaning. Also commonly needs a "charging" handle to operate the slide due to the mount concealing most of it. Coincidentally, the removal of the rear sight allows for the charging handle to take its place. But, ironically, the handle will need to be removed for breakdown. The scope rides closer to the gun than the above two grip mount versions.
For all three of the above, the gun can use the same load as it did for open sights. The slide will cycle quite quickly and some find it returns from recoil faster, since there is less mass to move.
4) slide mount - depending on the version, one or both open sights may have to be removed. Again, depending on the version, the scope will ride the lowest possible on the gun. The scope essencially becomes part of the slide, so it can be used as the "charging" handle. Holes must be drilled into the slide and I always recommend an adhesive be applied to the contact points between the mount and slide to help prevent screw shearing. The loads and/or recoil spring will most likely need to be adjusted for proper cycling.
I have used all of the above styles and find the slide mount most to my liking, with the frame mount next. I don't really like either grip mount, but do use them for testing.
Another option which I have not personally shot, but have seen, is a dovetailed miniature sight that replaces the rear open sight. The versions I have seen have had poor optical quality and/or adjustments that prohibit (or make cumbersome) the change from 50 to 25 yards.
If the Aimpoint Microdot (which I have not studied closely) falls into the category of dovetail mounting, that might be a good version that would take care of the above deficiencies.
Take Care,
Ed Hall
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