Looking to build a load for varmints in a heavy barrel Ruger that has been sitting in the safe. I believe it is a 1:9 twist.

Anyone here have info on this particular load?

I dont load a 55 but have loaded a 58 Vmax. My starting loads were IMR4350 at 45.5 from the Lyman 49th edition, max load was compressed at 50(3776 fps), so be careful. I didnt Chrono but velocity should be around 3300. I will check if I can find some data for the 55 for you. I wonder if the 1 in 9 will stabilize the 55 grn bullets. Typically as in a 223 the 1-9 twist needs a 60 grn or better if Im not mistaken. The 65 grn vmax is awesome for coyotes btw.

I too run 58gr Vmax in .243, but getting excellent accuracy using H4895 powder (~41gr - see load data at hodgdon site).
My gun is 1/10 twist.
Don't have chrono, but velo is way up there around 3700 (see hodgdon load data) without high pressures.
These rounds shoot like a laser.
Liquifies a 'yotes insides without any pelt damage.

https://www.sierrabullets.com/store/product.cfm/sn/1515/243-dia-6mm--80-gr-SBT-Blitz

This has been my varmint bullet in The Tikka with IMR 4064. Unzips a yote from stem to stern.

It also shoots real close to same POI as my 100gr Sierra BTSP load with IMR 4350

H4895 will push a 55 a little over 4000fps

I can't wait to reload for my .243!