Just a small update while I wait for some free machine time to attempt machining the bolt heads once more. I managed to track down what I believe to be the ideal optic for this build: An IOR Valdada Pitbull!
IOR discontinued these around 2015 or thereabouts. Younger me I really wanted one for my AK way back at the start of the LPVO craze. Back then I was too poor for a $1400 optic, and by the time I stopped being so poor, it was discontinued and so I couldn't find one. I ended up getting an ACOG for my AK, but my search for an optic to go on the 8.6 BLK Mosin reminded me of the Pitbull.
I was originally going to go with a Nightforce NX8, because I wanted something with a fairly short OAL so it wouldn't throw off the aesthetics of the build by being disproportionately large. Having an optic longer than the barrel would certainly be goofy, no? The Pitbull is a full 1.5" shorter than the NX8, and has a larger eyebox at 4x than the NX8 has at 1x. Eyebox matters a lot for this build, because of the offset optic making eye alignment slightly more tricky.
I managed to score one on Gunbroker for $960 all-in. Knowing what I know now having played with it a bit, I would absolutely not have been happy with it had I paid anywhere near the $1400 MSRP back when they were in production, but I'm glad I got it at the price I paid. It's a tank. The 35mm tube is steel, it's a chonker at 23oz. Luckily, the short OAL and its position on my rifle doesn't make it overly noticeable from a balance standpoint.
The steel parts of the optic are paint-over-park, which is a cool combloc touch that adds to the vibe of the build in my opinion.
I ran into some issues mounting it though: The LaRue LTR rings I got were too wide to fit between the elevation turret and the power ring, so I shaved off .050" from each side of the rear ring to make it fit. Additionally, I had to mount it further back than expected in order to get proper eye relief and also to ensure the windage turret cleared the stripper clip guide. As such, I will probably switch to a rear-biased RSRegulate lower to get some more overlap between the lower and upper halves of the mount.
Since I had some free time over the Christmas break, I designed a KAC T-2 style battery cap that has room for an extra battery, and also a killflash, since neither of those two tings were ever made for this optic. I have no delusions that I will ever sell one, but It'll be cool to me to have unique accessories just for the hell of it.
I also wanted to be able to shoot this at night, so I am currently prototyping a picatinny adapter to go on the unused portion of the RSRegulate lower rail to allow me to mount an IR laser on the side mount as well. We'll see if that pans out or not, I have no idea if it will work or not.
Another thing of great importance to the build was getting a bent bolt handle. I sent four handles to Jim the Boltman for conversion to the PU style. His lead times are lengthy, but the quality of work is 100% worth waiting for. If you're patient, I can't recommend his services highly enough.