I think I may have this figured out . Looking at reamers I found a match reamer with a .252 neck and .075 freebore with a 1.5 degree leade. This should work and still be able to shoot .556 ammo also . I still need to check the neck length i'd like about .010 over the trim length. but it's the best I've found so far.
Scasa,
Lots of service rifle shooters use 0.0619 freebore from the Wylde original, launching mag length ammo as well as longer single loading 80 class bullets. Not sure which 75 grainers you intend to use, the 75 grain Hornady BTHP are meant for mag length, same class as the 77 SMKS, whereas the 75 VLDS from Berger, the JLKs, and the 75 AMAXs are best are best suited for single loading, required in 600 yard matches. I am sure there are some who have shot these in mag length ammo, but I am certain it is not a common practice. In your bolt gun situation they may work very well, especially the 75 VLDs. There are quite a bit of civilian shooters and team shooters who use these 75 Bergers for 600 yard matches, with these pills jumping about 0.035. Check this number against your 0.075 FB and see where the overall length gets you.
If you meant to shoot the other 75 class bullets, they should still work well in your 0.075 freebore, I have other reamers from 0.0884 to 0.100 freebores, optimized for the different 80 class bullets, that handle the mag length ammo real well.
If you are just doing just this one barrel for your bolt gun, I have a JGS carbide reamer with 0.252 neck (the other reamers I have were cut with generous neck diameter, 0.2558, for gas gun application) and 0.025 freebore, you may borrow it. Send me an email if interested.
81stfacp@gmail.com
I spent some time on the range last Thursday, was there for 8 hours testing different projectiles across different barrel twists and powders, one bullet you may want to consider is the BIB 72s from RG. I found them to be the best overall to shoot from 2.250 AR mag length to the optimized jump.
Another option if just shooting 2.250 mag length ammo is the 70 VLD, surprisingly tolerant to huge jump, they like to run at 2930 from 20 inch tubes. If you believe in published BCs, these do not give up much, if any, to the other mag-length-intended 75 class bullets.
Nez