I picked up two external hammer forged semi-machined receivers. One for usual slid-in sidelock and one for a back action lock. I thought they might come as 12's but for my purposes this didn't matter. Both are double bit and the usual sidestock style has a workable but semi-finished Greener crossbolt and a working top lever with sliding bite lock.

The first has a flat water table. The other back action style has a decidedly rounded body. I mean as in a piece of lengthwise milled bar stock. The water table is slightly radiussed also and the mating monoblock or chopper lump would be as well. Both are made for a top bite consisting of the doll's head form.

As near as I can tell the center distance between the pin holes is 7/8". My Baikal 20 seems to be 1".

Are these receivers most likely to be 28 gauge? Who might have been destined to use the round body back action receiver? And who made a 28 with Greener cross bolt?