We cannot provide specific information due to liability considerations. Safe loads vary, depending on a number of factors. Check here: http://www.handloads.org/
Yes, you need to use large rifle magnum primers.
Never change components when reloading.
Never change out a component when reloading unless it is published.
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Buy a reloading manual.
Compare exactly wit your reloading-datas. Small Pistol Mag primers have about 12 Joules and normal ones about 5 Joules. 357 mag 158 gr bullet on s&w 686-6": Vectan SP2: normal primer : 0.85gramms max mag primer : 0,77 gramms worked fine Accurate 2 : comparable, about 10% less powder. start smootly with about 15% less at least.
The .243 IS a large rifle primer cartridge. However, you should stay with standard primers unless a trusted source of information lists a magnum primer for a given load. When you change ANY one component- powder, bullet, primer- go to the starting load and work up. Magnum primers can give unexpected pressure levels with some powders.
Small Pistol Primers are used for small caliber pistols, any of the various 9mm calibers such as the .380, the 9mm luger, the 9x18 makarov, the .38 special, the .32 acp, the .25acp etc. and even some larger calibers such as the .40 S&W. Large caliber pistol primers are used in .45 caliber and larger. Still other calibers, such as the .357 Magnum for instance, require primers known as magnum primers.
small pistol large pistol magnum pistol small rifle large rifle magnum rifle .50 BMG These are the primers used in all pistol and rifle ammo that is commercially available. Larger, artillery type, ammunition uses much different primers, obviously.
Never deviate from published reloading data. You risk injury or death if you do.
If you are asking about the Remington 6.5 rem.mag round,then this cartridge takes large rifle/or large rifle magnum primers.The .223 Remington cartridge takes the small rifle primer.Both of these center fire primers differ in size and cannot be interchanged.The .223 Rem cartridge requires small rifle primers.
Sorry- but you have not yet asked us a question. There are basic Youtube videos on reloading. However, I would recommend that you start by READING. The ABC's of Reloading is a great tutorial for reloaders. It is available through Amazon at very low cost.