I have two Swedish RBs that started life as 12.7x44Rs. One is an original M1867 military long rifle, and the other is late production Husqvarna commercial action with an 1873 manufactured barrel shortened to 30 inches. Both barrels have a .512 groove diameter with a .500 bore (one is actually .497!). They have the deepest grooves/most prominent lands of anything I've ever seen. I've found the Lyman 515141 450 gr sized to .512 with soft alloy does well. I use Starline 50-70 Gov't brass loaded with 65 grains of Goex FFg for 1168 fps or 60 gr Goex FFg over a 5.2 gr SR4759 duplex priming charge for 1254 fps, so your 4198 load is in the same ballpark. Both my loads shoot about 2-3" at 100. One thing I noticed about the barrel steel when barreling and rechambering the sporter is that it's extremely soft, so be careful with it.