i was testing some rounds today and i noticed something about my primers which i think indicates pressure.

i was developing a load for a 30-378 Mark V. i'm using 250 grain bullets and WC872 powder. i started my loads at 105 grains and am up to 115 grains. i am getting absolutely no sticking of the bolt or unusual flattening of the primers. these are the two things i look at for pressure indications. however, i have noticed that starting way down at 107 grains, i am getting a very slight ring around the firing pin strike on the primer. this ring started at 107 grains and is getting no worse all the way up to 115 grains. the cases show no discoloring or rupture indications.

since the 115 grain load is 4 grains above the maximum suggested load of H870, i am going to stop here long enough to chronograph the load.

my question is whether that primer ring is an indication that i ought to stop? since the bolt is operating so freely, it seems like i am not yet getting too much pressure. am i reading this wrong.....

i appreciate your help.

Yes that is usually a sign of pressure. Or you might have a sloppy firing pin or a weak firing pin spring. That is a called a mooned or a cratered primer. If you get very much more pressure you're firing pin will punch through the primer. I exceeded the pressure to much when the Scirocco came out. In my 7mag and 7stw was working up some loads cause there was not any data out. I started loading 3rd load from the top load for a 150gr bullet in both guns. Was in to much of a hurry and did not notice that the Scirocco had more bearing surface than any other 150gr bullet. Knew I had a 1/4 mooned primer, plus the primer was not flat. The bolt opened freely but I pushed the limit a little more. Smoke blew back in under both bolts on each gun, and I had to hit the bolts handles hard to open the bolt let alone to hit them to pull the bolts all the way open.. Then both cases were stuck in the chamber. Lucky I had my dads old steel cleaning rod with me to beat the cases back out. Lucky I had on saftey glasses. Both guns were in a Wby model.

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If there is a bit of extra clearance around the firing pin (hole in bolt is sloppy) the primer material will extrude into this at a moderate pressure and means nothing. I've never been a believer in looking at primers as a pressure indicator unless they fall out or get loose to quickly (5-6 reloads). In my experience primer appearance is just not reliable as a pressure indicator. The best example i know of is a .416 Rigby with Fed 215 primers probably the same ones you're using in .30-378 I can't tell the difference between a 2400 fps load and 2700 fps and I know the pressure went up when I added 8 grains of powder.

STEVEN'S==Better start thinking about what you are telling people before you really know what is going on with there gun. How the Hell do you get loose primer pockets if not from eccessive pressure. Pressure will alway's show up on the primer flat or cratered, and ecessive pressure will tend to leave a bright ejector mark on the head of the brass on the head stamp. For got to mention that the 7stw case also forced some brass in to the ejector slot and I had to push down on it several times before the tiny piece of brass came un-wedged when that brass had got stuck in the chamber.

4bambam, jstevens is correct that primer cratering doesn't necessarily mean excessive pressure. Cratering around the firing pin indentation is common with rifles exhibiting a small clearance around the tip of the firing pin and may be seen with rather mild loads. When combined with notable flattening of the primer and filling out of the rounded edge of the primer cup in the edges of the primer pocket, it's likely a sign of excessive pressure. And primer pocket loosening is certainly a sign of excessive pressure as the brass case head is deforming to cause this. It may also occur with "normal" pressures if the brass is soft, but in that case the pressure's too high for the brass, anyway. (I didn't notice the original questioner mentioning loosened primer pockets.) Primers will NOT always show excessive pressure either, and there are a number of good examples posted online of photographs of cases deliberately overloaded to successively higher pressures that don't show ANY visible signs of excessive pressure until it's gone way past the proof load level. We need to be aware of the signs that can mean excessive pressure, but also be aware that they can be misleading.

As an example, check this link: http://www.accuratereloading.com/ubbthreads/showflat.php?Cat=&Board=UBB6&Number=302200&Forum=f6&Words=45%2F70&Searchpage=0&Limit=25&Main=302192&Search=true&where=bodysub&Name=4&daterange=0&newerval=&newertype=&olderval=&oldertype=&bodyprev=#Post302200

The cartridge is the .45-70, usually loaded to far lower pressures than generally used in the .30-378 and similar cartridges. But he went well above safe .30-378 pressures before the primers showed any worrisome appearance. (And cratering was present in every one of them, starting at pressures way below .30-378 territory.)

As far as the Questioner mentioning loosned primer pockets,I was refering to Steven's statement. He said fall out or get loose as a reliable pressure indicator. And like you said youre self said, beware of the pressure signs. So who knows for sure if there is a sloppy firing pin hole in the bolt's face or pressure causing the cratered primer. All I am saying, there is one or the other causing the problem. I have been there from my own experience and know pressure signs. I had a crater 1/4 the primer's circle to a blown hole in the primer and 2 stuck cases in the chamber in 2 different guns from my experiment's. I will not tell Bill its all right, wait until the primer falls out or the primer pocket is loose. Like you said youre self, beware of the signs they can be misleading. Put youre foot in YOURE MOUTH

I hardly think I put my foot in my mouth. Everything I said above is accurate, and I stand by it.

I agree that the circumstances you describe sound more like an ill-fitting firing pin/hole than extruding primer due to excessive pressure.

Also, in my experience with WC 872, it is substantially slower than H870, so the loads you are using based on H870 data are not likely to be excessive. Remember, however, that the buring rates of different lots of surplus powder can vary substantially, so my experience my differ from yours.

But why don't you go ahead and chronograph those loads and see if your velocities are consistent with excessive pressure, rather than just having us all speculate (and expectorate).

My father and I both have Mark V's that were originally 30/378's that we had rebarreled in 338/378. Both of them always gave primers that cratered look, even at moderate pressures. Where we both started seeing excess pressure was on the headstamp of the brass. The ejector button leaves a shiny spot in the headstamp. The spot gets progressively worse as pressure increases. That's the only place either of our Mark V's have exihibited pressure signs.

Hope this helps.
Tom

well, i finally made it to the range and chronographed my loads. i am a little confused, but i got my answeres.



previously, i had shot one round each using loads from 105 grains up to 115 grains. this primer issue occurred at 107 grains and continued up to 115. however, the bolt lifted easily, no case indications of pressure.



today, i took 10 rounds using 110 grains, 10 using 113 grains, and 10 using 115 grains. i shot the 10 using 110 grains and got MV = 2846, sd = 12, es = 31....no problems. everything cycled well. cleaned the rifle and proceeded.



next, i started on the 10 using 113 rounds. shot 4 rounds. on the third and fourth rounds the bolt stuck. i don't mean it was hard to open.....it stuck. i waited about 5 minutes to let the case and chamber cool and then was able to open the bolt. on both of these case heads i could see an ejector impression. and both cases had a bright ring just ahead of the belt. quit shooting and came home.



i am confised why the 113 grain rounds locked the rifle up today, when 115 grains did not lock it up previously. do you suppose that the additional heat generated from the other rounds was enough to cause the pressure rise?



in any case, my load will be 110 grains. today was about 50 degrees. if i shoot these in hotter summer weather, i may even need to reduce the load further. but hey, a 250 grain bullet moving 2846 fps is not bad....



the only other question i have is this......i loaded these rounds to an overall length of 3.79 inches. if i shorten them to 3.7 or 3.6, for example, this will increase my freebore and should lower the pressure.....shouldn't it? i'm just asking. the load i have is sufficient. i'm just curious.