Gunsmithing 300 Norma Freebore Help?

I ran the standard Manson reamer, if I remember it's like .215 +/-. I don't think I'm lacking anything over a custom reamer.

Just to give you a data point - I could not get the 245s to shoot nearly as well as the 215s out of my 8.5 twist Norma improved. 215s at around 3200 were consistently one ragged hole, while 245s were closer to 0.75 MOA. I had way more flyers with the 245 that I could never eliminate. Both with N570 and Lapua brass. YMMV, just some food for thought before you throat specifically for the 245s. I know plenty of people love the 245s though.

Also keep in mind that 245s at max length with bearing surface above the neck-shoulder junction still won't fit in most CIP magazines. You will need something like the Long XL Lapua magazines from UM or a Wyatt's box. Which then begs the question - why not move up to the Lapua case and really get those 245s moving?

I run the 245 in 300 norma improved and have great luck with them shoot amazing. N565 and n568 is what I use. I mag feed them in cip 338 lapua mags 3.720ish is overall length. My speeds are not eye popping like others but working on new load now with new barrel I'm going to be 2900 to 2950 in 32 inch barrel but I look for consistency rather than an extra 100 feet.

Actually just had a conversation with Manson about this. With a standard 300 Norma reamer the 245’s seated out to the lands is about 3.72” COL. Have you measured the max length you can seat in your mag?

I've got custom reamers for the 300 Norma in the standard version and the 35* imp. version. We build these for mid range ELR shooters running the 245 Berger. My 35* reamer runs .2750" freebore to really get the 245's out here. The standard reamer runs .2150" freebore which will shoot everything from 215's to the 245's well. The 245's get stuck in the case is little bit but not bad at all.