I had an old ruger tang 300 win mag. I ran hornady flat base 180 interlocks in it w/82 gr of RL25 for 3050 fps. It had a super long throat and didn't like any other bullet I tried...or powder for that matter. It was a compressed load and the OAL was limited by the magazine to about 3.340
Now that would be a hot load (82 gr)by todays standards but this was RL25 from the mid to later mid 1990's. But it showed no pressure signs and the velocity was not out of line with what should be expected of a 180 in a 300 Win Mag. I say it should be a good fit for the 200 gr if you can get enough room in the case to get enough powder to get her up to speed (assuming you are limited to 3.340 OAL). I would look for a powder to get me somewhere from 2900 to 3k with a 200 gr bullet. RL 25 might do that for you. Definitely want a chrono for this type of work... you need to have a close eye on things.