Strange scope base

[TTB4570]

Sup folks,
I've recently come into possession of a swedish mauser that was sporterized at some point. at first glance it appeared that it had Weaver scope bases, however, the slots are cut rounded in profile instead of the squared off edges you'd expect. Anyone know what these bases might be? The front of the forward one is marked "Japan" and "45" and the rear one is just marked "55"

I don't suppose any of the grandmasters of optical knowledge might be able to me what these are?
https://imgur.com/a/ctL4a0N?fbclid=IwAR3BL_24ml0vaPK47AQRQ-0rAgrn2nPCkQL5Ts0BlI_vfqYDF3EvNQsj35I

Thanks!
TTB4570

 

[Potashminer]

I can't help with the "Japan" part, but otherwise they appear to be like the older Weaver bases with the half round cross slot. Earlier Weaver rings come with a round cross bolt - so only about 1/2 diameter protrudes down into the slot of the base - 1950's, 1960's maybe even later?. Typically, those cross bolts went through a hole in end of the ring, so were firmly attached to the ring. Newer ones, typically with much smaller tightening knobs, have square / rectangular cross "bolts" - often slip into a "U" on one side of the ring - tend to fall off / fall apart until the assembly is tightened up.

BTW - not a "grandmaster" of anything - just old, so am probably in error.

EDIT: I found an identical one to yours - The old and new Weaver bases that I have here, both half round and square slots, bear only on the right and left edges of the cross bolt, and not in the centre portion - and the centre grooved area of the base is quite low compared to the side rails. #46 and #55 are the correct Weaver numbers for small ring mauser bases. Your second picture shows a round bottom slot cut all the way across the base - The middle one in pictures below appears identical to yours - slot all the way across, centre portion of the base much thicker - "japan" stamped on one end / "46" stamped on other end - none of the three #46 shown have "Weaver" anywhere...

 

[TTB4570]

Hey thanks a ton!
Thanks to your info, I've managed to track down an older weaver scope with rings that should have the right type of rings!

If not, I'll just have to grab the newer bases off of trade ex, as it appears they use the same size threads with holes the same distance between the two

 

[Potashminer]

Yep - Weaver #46 and 55 will have same hole spacing and use same mounting screws, regardless of what era that they came from. I have had rifles with the round slot bases using round cross bolts in the rings - evidence that the ring clamps were not kept tight - can see the front edge of the slots on bases have "rolled" a bit - can only happen if the base of the ring was allowed to rise under recoil. Some find it confusing - a scope moves "forward" on rifle under recoil - sort of - actually scope and rings want to stay still and rifle moves rearward underneath - net effect is the force is applied to the front edge of a base slot, not to the rear edge... So when installing rings - give and hold a press forward while tightening up the cross bolt - want that cross bolt tight to front edge of slot - almost all have some back and forth slop if you check for it.