LRP's vs. SRP's and Accuracy

While getting ready for this year's deer season, I did some pretty extensive testing with primers of different sizes. My most notable "discovery" was that my AR platform 7.62 X 39 would shoot MOA+ a little with LRP's of all kinds, but when I tried SRP's of different kinds, my groups shrank noticeably! I mean from MOA to ragged, one hole groups of 5 shots at 100 yards. I've noticed differences before when I changed primers (and brass, obviously) but never remember seeing such a dramatic difference. Have any of you reloaders seen really big differences in accuracy by going from large to small rifle primers?

Here's a good review of primers from Precision Rifle, but it doesn't really answer my question:
http://precisionrifleblog.com/2012/07/02/most-accurate-rifle-primers-for-precision-reloading/

I've seen sd's lower but that also could be from brass quality as well.

I found an interesting reference to small primers on the 6MMBenchrest site. They were doing an in-depth review of the 6PPC:

The small flash hole/primer accounts for much of the 6PPC's superior accuracy, though nobody really knows precisely how or why. The "short, fat" shape and nearly straight body contribute to efficient, consistent combustion and good "chamber behavior".


I wonder how/why they can say that "the small flash hole/primer accounts for much of the 6PPC's superior accuracy," and then, in the same sentence, say that nobody knows how or why!

Forgive me for getting a little off-topic. I know different brands of 7.62x39 brass use different size primers. Which are LRP and which are SRP? Thanks.

Not off topic, papa45! My Remington/Peters cases are small primer; my FC, Fiocchi and Winchesters are all large primer. I also have a handful of miscellaneous head stamped brass that I've picked up over the years, but they're all large primer as well.

My sd drop was noticed when switching from win 308 to lapua palma. The palma is a srp but with a ppc flash hole..... I remember some time back reading an article on it by either the AMU or 6mmbr guys (likely Mr Salazar) but it talked about the srp being more consistent in ignition.