This has come up before so I thought I would do a little study:
I took my .260ai out for a spin Sun. I loaded 5 loads, all the same except for the primers. The load is 47.5gr IMR7828ssc, Lapua O.F. brass, 142grSMK, OAL 2.810". Here are the results:
1)Fed210M = 2862fps SD 15fps
2)Fed210 = 2861fps SD 11fps
3)RP9 1/2 = 2853fps SD 13fps
4)RP9 1/2M = 2869fps SD 7fps
5)CCI BR2 = 2882fps SD 10fps
Loads were shot over an Oehler 35, @ 4000ft/45deg F, 3 shot groups @ 100yds (very high winds). The rifle is a M700 w/ 27"PacNor bbl. It was really windy, 20-25mp @ 9oc. My best group was 0.312" w/ the Fed210. The worst group was well over 1" w/ the Fed210M but I had 2 called flyers due to the wind. At least w/ this caliber & this powder, changing primers seems to have little effect. Interesting that the match primers showed the largest SD, but 1/10gr of powder up or down could cause that. Just thought I would share.

Thank you for your input, Fred.
Problem is one shot per primer does not say much.
To get a picture, you need to use at least 10 shots per primer brand.
One should use the same cases in the order (i.e. cases numbered from 1 to ten).

Powder charges should be weighed and not thrown, and temperature of barrel and cartridge should not vary.

You see that thes tests are really time consuming - and this setup does not even take care of case hardening.

I guess I should have given more input. These were 3 round avg. time between shots was 1min. Charges were weighed, but even the best scales can vary 1/10gr. By using quality cases, weighed, you don't have to worry about case hardening.
This was intended to be an exercise in the validity of switching from one primer to another to see if it effects groups ize, uniformity or pressure (as measured only by the chrono).

Thanks Fred. Your info supports my rather limited trials.
While the larger the data base the more accurate the info, you gotta start somewhere. And, regardless of how large your data base, there would be someone that just has to "pick at it".

quote:

Originally posted by fredj338:
a-) By using quality cases, weighed, you don't have to worry about case hardening.
b-)...to see if it effects groups size, uniformity or pressure (as measured only by the chrono).

a- Don't underestimate case hardening. Many shooters start annealing after 5 firings, and I don't think they are simply anal.
I once fired 10 pcs .30-06 cases of different brand with the same load over and over again. I could distinguish groups brandwise when I started the test, but after 5 to 8 firings, it became one pattern - case hardening was overruling influences of different case shape and material.
b- Fred, can you please say something about group size and uniformity (performance) ?

Thank you

And, iwzbeeman, thanks for your important input.

waita, you can reread the original. I show avg. vel. & standard deviation. It was really windy, gusts up to 25mph, so groups are a bit suspect. I don't think I could derive any usefull info there, jsut too many flyers on my part, but groups were from a bit over 1" to 0.312".
I'm not discounting brass hardening at all. In fact, the reason I used o.f. cases is to limit another variable.
iwz, sure, more shots would be helpfull. Also better weather conditions would allow me to shoot out @ 200yds for a better idea of group size vs SD. I have shot several of these loads out @ 300yds & been able to keep .5moa w/o a lot of wind.

Thanks for the data.

Although small variations in SD may reflect uniformity in loading, they do not necessarily translate into accuracy. (You must be good because I'd be very happy with any of the SD's you report!) I don't know why loads with large variation may be accurate.

I will say that your data does substantiate my thought that priming is the last variable to look at when searching for max accuracy. Thanks again for the info. Kudude

You cannot calculate standard deviation with only 3 shots. Your chrono may spit out an SD for only 3 shots but it will be absolutely meaningless. Use at least 10 shots.

FWIW--I've seen posts where people have said that when using pressure testing equipment there were swings of as much as 8-9000psi by switching primers. I have a book by Stan Watson where he really spent alot of time testing the 30-06 in various modes. I don't have the book in front of me but I don't think he saw much more than 3-4000 psi difference in primer switching.
I do personally know of a friend that loaded up a ton of his favorite load for prairie dog hunting...only difference was primers and when he got there he had pressure problems with his batch of 500-1000 loads....yikes.
I guess my take on all this is that in some cases it might not make a difference but with the next combination of cartridge and powder in might really pick up and be a problem.
I would have to say....'RELOADER BE WARY" cause I guess it can go either way pretty easily.

You are absolutely right kraky about being caliber specific. This was just a test for my own info. I'm sure smaller volumn, smaller bore carts. would show a greater swing in pressures/vel. Since I have know way to measure pressure, the vel. readings can give me some idea (ie, if I got 100fps increase w/ one load over another) but the only way to be sure is pressure test.
popenmann, you are sort of correct. Yes a larger sample would obviously give a better final output, but hey, it's not rocket science & you can calculate SD using 3, 5, 6, 8, 10, or whatever, the data isn't imperical it's just to get an idea. "Absolutley meaningless", hardly (who comes up w/ rules like " you must use 10shots"). Sure if I shoot 100 the data will be tighter, hell if I shoot 1000 even better, see what I mean. Some of you guys need to get out more.

A couple weeks ago at the range, my cousin was shocked at the result he got from just changing primers in a load he always get sub 1/2 moa.

Without going into specifics, the only change was from WLRM to CCI Mag. The 10 shot group opened up to 1 1/2" at 50 YARDS.

Just in passing; The results from changing primers seems more pronounced when using ball powder in fair size cases than extruded powder. This statement is based on casual obsevation rather than specific test data. I never intentionally tested for this. roger

I use CCI primers and find that if I switch to Federals my groups open up. However, since I developed the load with CCI I kinda expect to see that.
The only way to compare primers is to develope loads in tandem with both primers.
Even then, it only means that primer X works better than primer Y with this powder/brass/bullet/barrel combination.
With the next set of components primer Y may be the best.

It all works on the FM principle.....