Judda,
I have a Remington 243 PSS which is essentially the same barrel and action. 49 grains of N165 under a Hornaday 100grain BTSP interlock gets a good group, although you should start a little lower and work up to this.
I understand that the barrel is not free floating on the sps and you will not get really good groups untill this has been done.
You can you guess what the brass is though!!!!!
Lapua 243
The photos show test firings of several different rifles none which are free floated.
First shots after a 2/3 day cleaning to remove years of fouling build up. I thought the barrel would need replacing and brought it with this in mind then test shot it. Notice copper fouling to started to clean it out. After a weekend and bit of P-H 009 then Forest Bore Foam the rifel was tried again. Not bad at all for on that is 60 years old. Oh it's a .270 Win.
Testing different loads/bullets through a Brno ZKK 601 in .308 Win. Scope is the Zeiss Jena ZF4/N with Tri Post reticle. It did not like the Win factory 180 grn Silver Tips.
Testing Hornady's 55 grn SP through a 56 vintage BSA Regent with IMR 4198 powder
test shooting a newly acquired Midland 2100 in .243. With mod fitted shots move left
.
P-H 1100 Lwt. It did not like some old hand-loads with the Speer 200 grain bullet but loved the Hornady 130 grn SP and BLC-2
30-30 using the 130 Grn Hornady SP
None of the above rifle have floated barrels yet shoot just fine. I have no doubt that a better shot than I could tighten up the groupings more. A rifle does not need to be free floated to shoot well but it does need perfect or almost perfect bedding. be that synthetic ( glass fibre etc) or carefully hand bedding into the stock as it used to be done. Interestingly, to me at least, the rifle which has given the most hassle in reliable grouping has a factory floated barrel:-
Chambered for the Remington 6mm cartridge the bedding is suspect as the stringing out shows.