6.5-284 verse .284 Win

[ramrod45]

Due to the absence of .284 Winchester brass, I purchased Lapua 6.5-284 brass. Now I'm trying to develop a load for 180 gr 7mm Sierra Match King bullet. In between this forum and other similar, I've decided to start my load development using H4831sc. Studying the Hodgdon loading data information based on a 160 gr bullet (common bullet weight for both) 6.5-284 46-50 grains powder, .284 Winchester 50-55 grains powder. Both calibers have the same case capacity within 2 grains. 68.3 and 66.2 respectfully. It's obvious that I'm confusing myself.

So........

How do I develop a safe load for the 6.5-284 (nicked up to 7mm) 180gr SMK bullet using H4831sc ?

Thank you for your help

 

[ShootDots]

You are reading everything correctly>>>The terminology is what you are lacking.. When you have a cartridge such as the 6.5 x 284 there is an "expansion ratio" that is quite large. The reason is, is because it is an "overbore". When you go UP 20K you make it "less of an overbore" hence the expansion ratio goes down. There is almost a "1 to 1" expansion ration (if you will>>>the exact science I do not know<< if you had say a 458 Win Mag.. Neck it down to 7mm (which it now becomes the 7mmRem Mag) and your expansion ratio skyrockets. AND because of that, you need slower powders, even though you are pushing a 160 class bullet as opposed to a 500 grain bullet in the 458 Win. Mag! The exact same science goes for any "neck up or neck down" cartridge. You can use a heavier bullet, in the same case, that has been necked up and use MORE powder, however, generating "more or less" the same pressures.. So what you are reading is correct.

In a "straight" 284 Win. using 180 class bullets, I would start out at 53.0grs and work slowly towards 55.0 with the H4831. Another powder you might try is IMR 7828SSC.. It will perform about the same BUT with slightly less pressure.