Just got a 60@28 Bear Montana longbow. I'm pulling 27in and want to shoot carbons with 225 grains up front. What is the best size to start with as far as tuning goes?

225 plus a brass insert, or 225 total? a 400 might work if its 225 total, but I don't know about 325

225 total that's a 100 grn insert and 125 point

TTT

I shoot a 29 inch GT 3555 (.500 spine) Trad arrow with 200 grains plus std alum insert out of my 50# Montana at my 28 inch draw and it bareshafts perfectly for me. I would think that with your setup, the same arrow cut to 29 inches or shorter would put you about where you want, but you'll need to bareshaft tune to know for sure.  I believe a CE Heritage 150 (.487 spine) would be another good arrow to try with your setup. Just don't cut them too short at first when you start tuning.

I'll try that Reaper. Thanks

Before trying the GT 3555 Black,you should be aware that your arrow wt will be down to ~7.9 gpp.

I'll try that Reaper. Thanks