Home Forums Reloading Big Game Rifles Small vs Large primers for Creedmoor

For those that use small primers, does using them make a difference in how much powder it takes to get a given velocity?

To put it another way, if you find a good load using standard primers would you need to adjust the powder charge if you go to small primers?

Sorry, can't help. Have never used small-primer cases when loading either the 6mm or 6.5 Creedmoor. As noted in Ask the Gunwriters, I live in Montana where it can get very cold, and have even had problems with some powders in some cartridges with large rifle magnum primers.

A shooting partner and I did a SMALL test of this in 6.5 Creedmoor with the Pressure Trace and a chrono somewhat more than a year ago. There was not a noticeable (I don’t recall whether I did any statistical analysis, but if I did I didn’t save it) difference in pressure or speed between Lapua and Norma (SR and LR primers, respectively) cases with the same charge of 4451 under 140s, using Wolf SR magnum and Wolf LR primers. We did the test in quite moderate weather, neither hot nor cold.

THIS WAS NOT AN ALL-ENCOMPASSING TEST, NOR WAS IT EVEN A MODERATE-SIZE TEST. DON’T COUNT ON THIS RESULT WITH EVERY COMBO YOU MIGHT TRY. The Lapua and Norma cases we used were both non-ballon-head cases, meaning the bottoms of the cases are flat on the inside. Hornady cases, at least the ones I’ve always received, _are_ ballon-head, so there would be a capacity difference between them and the Lapuas that one would expect to make a difference in pressure.

I should note that a similarly small test using Win 748 and light varmint bullets showed me something that made me decide I would not use the SR-primed cases to hunt in cool to cold weather with a heavily-deterred propellant like that. In fact, I’m happy to stick with LR primers for all Creedmoor hunting cartridges. For match shooting, I wouldn’t care what primer size I used for most matches (unless it was going to be cold).

MZ5, thanks for the information. I'm assuming that any differences in case volume due to the ballon-head/non ballon-head would show up in weight differences, as would case thickness differences?

Not enough of a difference to go screwing around with small rifle primers and smaller decap pins in my dies.

Hmmm, smaller de-capping pins for all brands of dies? The one I'm using is a Redding Bushing die.

Yep, and its not just that they use small primers, the flash hole is smaller and can cause ignition problems.

You got to deprime eventually. For that, youll need a smaller decapping pin. Good luck finding them at your lgs. Btdt..

I haven't tried the Lapua 6.5 Creedmoor brass. However, I ran into the small flash holes with Lapua 6.5 Grendel brass; the flash holes were smaller than the decapping pin in my Hornady dies. The first pass through the die fixed that though, now they're all exactly the size of the decapping pin. I don't recall if I had to tighten the decapper down more than usual, but didn't have any other issues with it.
IIRC I did the same thing on that brass with a Lee 6mm PPC sizer die too; that one has the newer one piece decapping pin and didn't give me any issues at all to open the flash holes.

Has that worked for you in the Creedmoor brass, or have you tried?

Sure, but the trick is to know how much of any weight difference is due to which of those differences. An SR-pocket case of necessity has more brass in it, at least if it's non-balloon-head. So it's heavier because of that, but no more capacious.

The reason we chose to compare those Lapua SR vs. Norma LR was, in part, because they were both flat-bottom cases. I don't find it terribly tedious to measure the volume of fired brass, but I realize that we're all different in what we find tedious.

You're talking very cold weather I assume?? Hard to wrap my head around why a reputable company based in Finnland would go with a design that doesn't work well in cold weather.

Small-primer 6.5 cases weren't designed for hunting in cold weather. Instead they were designed for target shooting, for those shooters who firmly believe less primer flame can result in better accuracy, and especially for those who like to load to higher pressures, where the extra brass around the primer pocket results in less expansion. Thus making higher velocity possible.

But aside from biathhlon (which combines X-country skiing with rimfire shooting) most target shooting with centerfires takes places in more moderate temperatures.

Here is a great read on SRP vs. LRP with some velocity data you can compare smokepole.

http://alphamunitions.com/kaubers-corner-large-vs-small-rifle-primers/

Thanks MD and hig, great info.

I found this tidbit quite interesting. It’s not consistent with my experience.


Chronograph: MagnetoSpeed V3
In addition to the 10 test rounds of each caliber and primer size, I loaded an additional 10 to shoot without the MagnetoSpeed attached. What I found was the MagnetoSpeed shifted the point of impact generally high left .5 – 1.25 MOA but did not affect group size.

Wasn't it Tubb (he knows a thing or two) who says he found no difference in performance by using regular primers over the small ones?

Magneto adds almost a mil of elevation rather consistently in my experience.

I remember Tubb being pretty adamant that the 6xc needed large primers.

Higbean,

Exactly, In fact Tubb says on his website that tests proved LR rifle primers worked better, but doesn't specifically name the test.

There are several holes in the Kauber test, including the fact that10 shots isn't a sufficient sample for valid standard deviation in velocity.

Have also seen Magnetospeeds drastically affect group size, not just POI.