Are Magnum Rifle Primers needed when loading Blackpowder in Cartridges? I've read where a couple reputable writers recommend them. I don't have any, should I buy some? What are you fellows using?

When Spencer Wolf wrote his book on loading for the Trapdoor Springfield, he noted that the primers in the old days were oversized and had more priming compound in them than modern primers do.  He postulated that this excessive priming helped break up the compressed powder charge and improved ignition and burning in a way that maximized efficiency and minimized fouling for accurate repeat shots.

He said the only way to reproduce this effect with modern primers was to use the most powerful ones possible, ie, magnum rifle primers.

Of course, an alternative explanation could have been that the large amount of priming compound (and the large diameter firing pins in the rifles firing them) might have been because of the lack of reliability of the primers manufactured then.  Putting in excess compound and smacking it with the largest impact area possible might make an underloaded primer or one that was going bad from poor shelf life go off regardless.

Modern BPCR shooters noted the accuracy levels of some of the old-time loadings, and the fouling controls the old time shooters used, and also noted that when smokeless powder came along, the old black-powder primers were very unreliable igniters of the new propellant.  So modern smokeless powder primers, regardless of size, could be said to be overly powerful for black powder ignition, and might even push the thumb-seated bullets varying distances into the leade before the charge fully ignites, causing vertical stringing, flyers and other inaccuracies at distances.

So now the idea is to use mild primers, even attenuating the flash with a paper “primer wad” at the bottom of the case for the mildest ignition possible, and no push on the bullet until the entire charge is burning.  As far as fouling is concerned, proper lubricant and blow tubes, or wiping between shots is how that is handled now.

Of course, your own rifle is the final arbiter of these arguments.

I’d say that you’d need a chronograph to tell you what works best. 
In my opinion, primers are a load tweak. Pick one type and stick with it to find a good shooting load. Then start playing with different primers.
Depending on what you’re doing with the rifle, I doubt you’ll see much difference out to mid range. Long range is a whole nuther game.
JKR

Magnum rifle primers will give you a slightly lower velocity than standard rifle primers.   Don't ask me why, but that is what my chronograph has shown me many times.

George

Magnum primers are not required and may actually be the worst choice.
Large pistol primers are very popular these days and for good reason.
Personally I’ve been using rp 2 1/5 or 9 1/2 or if the rifle prefers br2.
Fouling control and lube , and using a bullet length to match the barrel twist and velocity may just be more important than primer choice when searching out the best accuracy

Remington 2 1/2 large pistol work well for me in my 40-50SS and 45-90.

many of the books and articles written in the early years of the B P sport are no longer valid in most areas  art

Gentlemen, Thank you for your thoughts, opinions and experiences. I have a few large pistol primers, so I'll try them first. If any issues are given, then I'll try the large rifle and/or the magnum large rifle primers. I do have a chronograph, sounds like it may come in handy for load development.