Have almost always seen a big difference in accuracy with the CCI 200 (and Federal 210), but it also depends on load density. The primer doesn't matter quite as much in a moderately compressed load.
John, can you expand on this statement, please?
Jorge,
The specific primer can play a definite role in accuracy, and to a certain extent temperature resistance in powders. But how much the powder fills the case can also be a factor in all of that.
In general, pressure labs have found most rifle powders to burn most consistently when the available powder space in a case/bullet combination is just about filled, and often even more so when the charge is slightly compressed.
All three factors--case fill, and the specific primer and powder--interrelate. Extruded powders in the medium burn-rate range tend ignite easily with just about any primer, so loads may not show much improvement with a magnum primer--though they still can when the powder charge gets to be big enough. The long-time rule of thumb is to use magnum primers in cases over about .30-06 powder capacity, and I have seen some very obvious examples. My .338 Winchester Magnum, for instance, gets great accuracy with 200-grain Ballistic Silvertips and a charge of 67 grains of Reloder 15, with 3-shot groups averaging around .6 to .7 inch. But that powder charge doesn't come close to filling the case, and is only accurate when ignited with a magnum primer. With standard primers it averages more like 1.3 inches.
Supposedly slower-burning spherical powders burn most consistently with magnum primers, due to being harder to ignite due to their deterrent coatings. I have found that to be generally true even in very small cases, such as the .17 and .22 Hornets, where CCI 450s tend to result in the smallest groups with "slow" powders (for the case size) such as Li'l Gun, Alliant MP-300 and CFEBLK. Haven't found it to be as true with faster-burning sphericals such as H110, where standard or even handgun primers sometimes work as well or better. But H110 burns enough faster than those other powders that with 40-grain bullets in the .22 Hornet it's not compressed, which may be why I've found it to work best with lighter bullets, in the 30-grain range.
Got an e-mail a month or two ago from a guy who had a new .22 Hornet and was getting 2-inch groups at 100 yards with H110 and 40-grain bullets, and was wondering if the barrel might be the problem. He knew I'd had one of those Hornets in the past and wondered how mine shot. I replied that it did very well with 40-grain bullets, Li'l Gun and CCI 450s--but not H110. He got some Li'l Gun and 450s and his groups shrank to well under an inch.
Another interesting example is my .375 H&H Whitworth with 300-grain bullets. I bought it almost 30 years ago and tried IMR4350, which needed some compression to reach the typical velocity of 2550 fps. Eventually H4350 appeared and wondered if I should switch due to it being more temperature resistant than IMR4350--but then I decided to see how my old load did in real cold. Tested it at zero F. and it only lost around 30 fps, right in the same range as H4350 does in other rounds. But in the .30-06 with 165s IMR4350 lost twice as much velocity, I am guessing because that powder charge isn't compressed. The load shot just as accurately at zero, but point of impact dropped two inches at 100 yards.
