Learned something today!

[chromecrow]

Now I need somebody to explain to me just what it is that I learned. I have been shooting a light load of unique in a 375win. I got a new mold from Mountain Molds and it wouldnt group as well as a Lyman or Lee that I had been using. I adjusted the charge up .2g at a time. No luck. For some reason I decided to try WLP primers instead of WLR. Bingo nice tight groups. Tried the load again same results. Why? Do you think that the hotter rifle primers might be causing the boolit to start to leave the case a little bit before the pressure of the burning powder? It seems to me that if this were the case that inconsistent pressure would result and make the load inaccurate. What do you all think? Could I see further improvement through the use of an even milder primer? I would love to hear everyones thoughts on this, John.

[StarMetal]

What happens is the rifle primer blows the bullet into the bore and blast most, if not all, the powder forward and behind the bullet and it doesn't burn as consistantly as when it's lit off with a mild primer as maybe as mild as a pistol primer. I have this problem with my 22 hornet. I switched to a pistol primer and the groups shrank.

Joe

[Lloyd Smale]

John linebaugh said he uses fed std primmers even with 110 in big cases like the 500.

[lovedogs]

Well, you said you wanted to hear from everyone so guess I'll put my 2 cents worth in. There's lots of speculation and mystery about why primers act like they do. But it's pretty common for the match shooters to use "cooler" primers so there's got to be something to it.

In loading for my brand of accuracy, minute of prairie dog, I've noted that in one .22-.250 using 4064 I get just a hair more accuracy using the milder RWS instead of my usual CCI 250. It's not a lot but if you're trying to spoil a prairie rats day at over 300 paces it makes a difference.

That practice of using standard primers with hard to light, ball, or slow powders can sometimes get one in trouble. I can't tell how it would happen but know of one fellow who ran out of mag primers and substituted a standard in a .270 Ruger using 4831 and it blew up. It sounds impossible, but it did happen.

Where I live it gets cold in the winter and you'll get a rude lesson if you use a standard primer with ball powder. There are uses for all kinds of primers but I'm careful not to get too far from what's recommended and things seem to work out pretty good.

Best of luck to all

[HORNET]

chromecrow,
You might want to continue on with different primers. Every primer manufacturer has their own "special" mixture with different limits on performance when they test them. Apparently SAAMI standards are rather loose and the makers don't report the results of their brisance tests to us lowly users. Please note that some manuals still have the Fed 205M listed as a standard small rifle primer when it's probably the hottest SR MAG primer I've ever tried.
A while back somebody (CRS strikes) posted a link to some tests on LR and LP primers that shows this difference between brands and the different standard deviations within the brand. This was at Cabine Tree's web site:
http://www.castingstuff.com/primer_testing_reference.htm
I have been unable to find any similar testing results on SR/SP primers but have limited web search time.
I usually find best accuracy with the mildest primer that gives consistant ignition on the powder in use. Not sure , but I think that primer burn profile might make a big difference with different powders.