Erratic pressure signs on previously safe load

[Doodle]

Hi Guys,

I've got a load for my 300 wsm consisting of Norma brass, fed 215, 64.5 grains imr 4064, and a 124 hammer. Load clocks about 3700fps, produces sub moa groups, and has not exhibited pressure signs before.

I gave the rifle a light cleaning before taking it to idaho this Friday, and after doing so I'm getting erratic pressure signs. The first shot fired had a nice swipe and a flattened primer, which I chalked up to not getting all the clp out. Then the weirdness started: shots would randomly show pressure on 2 out of 3 rounds. Some were fine, others had a swipe.

Brass is from the same lot, all 1x fired (this was the second firing), primers from the same lot, powder from the same can, bullets from the same package. Temperature difference between no pressure and erratic pressure was about 15 degrees (65 and 80, in the shade both times). Charges were double weighed. I also checked the chamber to see if I got a little oil in there but it seems to be dry.

I don't really have time to work up a new load before leaving, so I have a two-fold question: 1) what do you think may be causing the pressure? And 2) with hammers, can I just back off a grain and more or less expect decent groups? I have time for one more trip to the range before I leave, so I'm in a bit of a tight spot.

Thanks in advance for the help.

 

[Tidus56]

This brass that was safe the first time was virgin brass? Now it is 1x fired going into its second firing? If that's the case and you developed a load on virgin brass. You need to develop loads on 1x fired brass or even 2x fired brass because the first shot or shots are fire forming the brass to the chamber this takes some of the pressure to expand the case to the chamber. If you full length size maybe this isn't as big of a deal I don't know as I bump size.
So a load that was safe on virgin brass can show pressure on 1x fired brass because it isn't using as much energy to push the case out to chamber You should be seeing velocity that's higher as well.
Ex I had a cartridge shooting 60.6 grains on virgin brass and was safe. Loaded it for second time at 60.6 without thinking about it and had pressure signs and higher velocity. I dropped my velocity back to what it was before by decreasing powder charge and it no longer shows pressure and have same accuracy as first load.
I would guess that's the issue but I could be wrong, that's just a possible culprit.

 

[sedancowboy]

Tidus has nailed it. This is your problem and it is a wide spread issue. Crops up all the time.

 

[dok7mm]

Yep !!!

 

[Doodle]

Thanks for chiming in everybody.

To bring more clarity to the brass issue: this was originally factory Norma ammunition (the first firing). I cleaned and resized about 60 cases or so, and loaded 30 for load development and trajectory validation. The other 30 were just sitting there waiting for a free afternoon. So none of them were loaded on virgin brass, and they were also not partially loaded on 1x and partially on 2x……all were on the same firing rotation - only difference was the day they were loaded

If it makes a difference I full length size.

 

[vancewalker007]

If you were tight on pressure at 64.5gr maybe the temp increase bit you. Did the loaded rounds close smoothly before being shot? Did the fired cases extract smoothly? Tight going in may indicate an incorrect case size issue, like length, head space, web area etc. Again tight on extraction could point to marginal sizing issue. I've found even 5/10,000 too much at the web on some cases can cause pressure.

 

[Doodle]

If you were tight on pressure at 64.5gr maybe the temp increase bit you. Did the loaded rounds close smoothly before being shot? Did the fired cases extract smoothly? Tight going in may indicate an incorrect case size issue, like length, head space, web area etc. Again tight on extraction could point to marginal sizing issue. I've found even 5/10,000 too much at the web on some cases can cause pressure.

I had a stiff bolt lift on the first round, but actual extraction seemed fine. The bolt closes easily on the loaded cases.

 

[vancewalker007]

I had a stiff bolt lift on the first round, but actual extraction seemed fine. The bolt closes easily on the loaded cases.

It could be you are close to pressure and the temp change boosted you just enough. That powder is based on older tech do it might be a little sensitive. Try putting them in a cooler at the range and see if that changes things. We used to do this in Phoenix with 7mm STW when shooting RL22 in the summer.

 

[nwmnbowhunter]

You are using a really fast powder in a large amount. Pressure is going to come fast and be wicked.

I would back off my speed closer to 3600 fps.... even 3550.

Everything is showing you are over pressure.

With 63gr of h4350 I was over 3500 with 300 saum and the 124 hammer. 22 inch barrel, zero pressure signs.

You could also use regular large rifle primers and that would cool your load off a bit. Many report using standard large rifle primers in saum cases.

 

[ARlife4me]

I've used the same win264 mag brass going on 10x reload at full length sizing every time. Loaded with imr4831 @ 61.3gr and Sierra 140spbt @ 3.340" and not 1 single issue. Maybe my time is running out? According to Sierra #5 it's 1/2 grain over their load data. I know I know some guns can be loaded over posted data and some will be less than max.

 

[Doodle]

You are using a really fast powder in a large amount. Pressure is going to come fast and be wicked.

I would back off my speed closer to 3600 fps.... even 3550.

Everything is showing you are over pressure.

With 63gr of h4350 I was over 3500 with 300 saum and the 124 hammer. 22 inch barrel, zero pressure signs.

You could also use regular large rifle primers and that would cool your load off a bit. Many report using standard large rifle primers in saum cases.

The crazy thing is that the previous 30 rounds had no swipes, nice round primers, no bolt lift issues….not a shred of pressure evidence. That's why I keep wondering if it has something to do with the cleaning, or maybe I left a little sizing wax on a few of the rounds, or maybe I'm crazy, who knows!

I do have a 26" barrel which seems to be on the fast side - the factory Norma 165's were flat out sizzling out of my barrel…like 100fps faster than advertised.

 

[slikmrc]

I would check the velocity of the load first. Could be the throat is wearing in and your load was at max to start. Or maybe there was enough temperature change to cause it. May want to give the barrel a good cleaning again to rule out a carbon build up. Back the load down a grain and shoot them to foul the barrel and see how they look. Hope you get it figured out

 

[MagnumManiac]

Have you annealed the brass?
Every sizing causes the brass to harden, hardened brass has no give.
Are you sure there was no lube or cleaning fluid left in the chamber/bore after cleaning? I have seen this a few times myself.

Cheers.

 

[JTH]

I'm guessing it's the temperature. Not familiar with the characteristics of IMR 4064, but I've got a load with N570, which I've read is supposed to be very stable, but it gets funny close to and above 80 degrees. Groups open up a little and stiff bolt lift.