Just started gathering components to reload and have done fine except the primers. I have read that i can use magnum primers in non magnum cartridges but it obviously isn’t ideal. Since large rifle is non existent in the world right now I am going to try the magnums. Won’t have much to baseline off of but I will at least compare to some factory loads I have. Talking .243 and .308
Thoughts or experiences?
As always when you use a component different from those specified in the data you START at the starting load and work up! I rutinely use Mag primers in both pistol/rifle loads where not specified. Some powders don’t like the use of Mag primers what so ever! Try and stay away from the faster powders when using Mag primers! If you don’t have a chrony -GET ONE! Wild spikes in velocities is a very good indication that powder doesn’t like the mag primers! 
Most times you’ll never get close to max loads before you see pressure signs.
I’ve subbed Magnums in Small rifle, but never in Large rifle. 
markm
My main use for Mag primers in large rifle cases is for cast bullet use. This is where you reduced powder charges anyway or use slower burning powders. This is to ensure complete burn /more consistant burn of the powders used. In regular jacketed bullet use they can be substituted for regular primers but one must know and can Identify pressure signs - hence the old adage of going back to starting loads! Mag primers can and due increase burn rate/ pressures of certain powders!
I agree. I’d be reasonably careful before I tried a Magnum primer in Large rifle.
It might not be that big of a deal if you use reasonable caution in working up loads, (possibly depending on the specific magnum primer in question, though). I would stay away from the faster burning powders, however.
My old Speer #11 reloading manual (1987) shows quite a few .243 and .308 loads with the CCI 250 Magnum primer. It’s favored (looking at 150 gr .308 loads) with H414, W748, H335, and BLC2.
My LR primer of choice for the 7.62x51 semi-autos (FAL/SCAR-H) is the CCI #34 NATO Spec primer (less chance of a slam fire). IIRC, I recall reading somewhere that these are hotter than standard primers and I treat them as such.
As a side note and contrary to most manuals, I could never get close to the maximum powder charges shown in the Speer manual for some loads I developed “way back when”, regardless of the primer I used.