I don't know who produced the first three-lug action; there must have been an early one but I can't think of who it may have come from. I'm thinking maybe the Texas Magnum (Wichita Engineering) or the Champlin. The Sportco (Omark) was three-lug design. GD
I have a Mossberg 800b in .243 Win. that shoots quite well. Looks like it came from the 1960's or 70's. Surprises me Mossberg would have a three lug design from that long ago.
I have a Voere Black Forest which is a Kleinguenther before they were Kleinguenthers. From 10’ it looks almost identical to a MKV. I was given it as a wedding present. It was a 7RM but the barrel was fried. I had a Shilen .270 blank so I matched the contour and chambered it for 270Wby. It shoots well, killed a bull elk with it this year.
Do the Kleinguenther rifles have the front two scope base holes side by side instead of one behind the other? I had to machine a custom one piece base for mine since I couldn’t find anything to fit the side by side screw holes.
The earlier three lug I know of is the Voere Shikar. Later the barreled actions were imported and made into the Kleinguenther K-14. This is the Voere made in Germany. Later the company was sold to Mauserworks and later sold again and moved to Austria where they still make Voere rifles. The three lug is their premium line made today and they also make some 98 Mauser types. I believe Mauser made this under their label as a Mauser 99, or at least it used some of the features. I do not know where the reference is but I believe Voere was going insolvent and thus sold to Mauser.
You can see the three lug bolt in this video. Haven't figured how to post photo's but in this video you can see the lugs. This was in either the late 60's or early 70's. If I remember correct the Olsen book on bolt action rifles has a section on this action.