All of my reloading to this point has been with brand new Factory brass in several different cartridges. Currently working with a 7 PRC load with 168 lrx and h1000. I think I finally gotten the load I want to with that. Took a while. Because of the price of 7 PRC brass being significantly higher than everything else I’ve been using and decided it was time to actually try to reload and not just hand load.
Brass is Peterson, 50 pieces . Federal primers, h1000, Barnes lrx 168. Follow the standard protocol on the backfire channel. Remove primer, wet tumble, dry, resize with 2 thou shoulder bump, measured the length on five cases and they were above the trim two length but below the maximum allowable length so I did not trim. Chamfer and deburr, mandrel for neck sizing, then Prime with the Federal primers. Loaded up 15 with the h1000 at the previously noted charge weight that I used with new brass and seated the bullets to the same depth.
Took them to the range today.
Things are looking good initially. Velocity right where it needs to be. Actual improved standard deviation and extreme spread from where it normally is with new brass and good accuracy and point of impact being same of new brass. But shots 6-9 gave me a noticeably stiff bolt lift. Two of those four had noticeable ejector swipes.
Never seen over pressure with this gun before. Even when going up to Max load at the very beginning of load development months ago. I’m currently running about two grains below Max.
Shot six rounds of new brass loaded ammo through it and they went through swimmingly well with absolutely no problems. Then shot four more of the once fired brass and while I didn’t have the massive bolt lift stiffness, I did experience clicks with all of them when manipulating the bolt.
What would cause overpressure when using fired brass but not new brass??
Oh, and jim, while I was letting the 7prc cool in between strings of fire I took out the 300 WSM with the newly installed backstop. That thing makes a major difference in this rifle! Very impressed.
Have you checked the carbon ring on your barrel? Jim has a video about 7prc (I think) quickly developing carbon rings and showing signs of pressure. I believe he said it could even been as soon as 50 firings.
Yes, today’s session actually started out with a completely clean barrel and I did a borescope of it and did not see anything that was concerning to me for a carbon ring.
Hey Carter. Great questions and very glad to hear the Backstop made a big difference on that 300WSM.
This is a bit perplexing. Let’s think through this.
You didn’t mention any issue with the brass fitment in the chamber. Seems the bolt closed easily so that’s a good sign.
I would worry about perhaps the case being over the trim length which could be long enough to extend into the chamber and crimp on the bullet. But this was just the second firing and I doubt you’d need to trim until round 3-5 with that brass.
If the shoulder got pushed back too far, that could certainly cause an issue. But you said it’s just 2 thou. So that sounds correct.
If it’s a known good load, we shouldn’t have issue, but what was the charge weight?
Best I can guess is somehow the neck tension was very high. Did you use the expander ball in the die? Chamfer the edge of the mouth?
Charge is 67.1 grains. That’s a little above what Hodgdon recommends but below the maximum that Barnes has on their website.
I took off the expander ball since I was using the mandrel. Yes, chamferred and deburred using the fa case prep Center that you recommended.
Shoulder bump is an interesting thought. It’s not like every piece that I measured with the comparator gave me the exact same length to the 0.001 level. Therefore I just took a mean of about five, adjusted the die so that the mean of the next five was 0.002 shorter. But there is definite variation at least to what I can measure and I am using the expensive calipers.
one thing i am noticing different in your two loads is annealing. new brass is softer than fired brass. If you are close to your chambers ideal pressure that may be edging you just over. Personally i anneal every time. Just an idea as it the only difference between them
My best guess is that it’s just a bit too hot of a load. Maybe it had to do with slightly different brass shape on a second firing or just the gun being a bit hotter.
I can’t explain why Barnes has the load listed that high, but 67.1 gr of h1000 would be too hot for what I’d consider acceptable. I look at the max load in a few books, take the lowest listed max, and still come down from there by around half a grain. The Hosgdon data seems more reasonable maxing out at 66.
I’d have to think if you back off the load a bit, you wouldn’t see any pressure issues. If you did, you’d know for sure something is up with the brass.
You may have sized the brass too much and are now experiencing bolt thrust due to excessive headspace; that’s my best/only guess. New brass may not grow to fill the chamber on the first firing, leading to undersizing if you do a shoulder bump immediately.
My loads for 7prc with H1000, Hornady 175gr ELDX, and large rifle magnum primer, calls for 67.1 gr H1000 according to Hornady. I averaged 2818 fps over 20 rounds through my Fierce Mountain Reaper. That was with fired brass 2nd reload.
I was a little surprised when Barnes published their load data with the 7PRC and saw the differences with Hodgdon.
But i do have to say that at least with my particular rifle, it behaves exactly how the Barnes data predicts. With Hodgdon data, it’s shooting 150+fps slower than predicted and I’m already applying a 60-80 fps cut because of barrel length.
But I’ve got another 30 or so pieces of once fired primed and ready to be loaded so i can experiment with a lighter load. Which gives me another opportunity to work with the Supertrickler and figure out what needs to be done to make it work more consistently.
you said that it was shots 6-9 that showed pressure signs. How many shot are you firing each string, how quickly do you shoot that string, and how long are you allowing your gun to cool in between strings?
5-10 min between strings. Gun was cool to touch before starting again.
First five shots with the once fired brass were fine. The next four shots were definitely overpressure. I stopped right after number four and let the gun cool down again. Then shot six shots, two strings, with brand new brass that went perfectly well. Then finished up whatever is left of 15 of the once fired brass with Clickers.
So, quick update. Went to the range today with 12 new loads of once fired brass with 64 grains of h1000. This is two grains below Hodgdon Max load, and as it turns out where I started many months ago with this particular round.
Absolutely zero stiff Bolt. Also no ejector swipes. I feel like there may have been a clicky or two but that’s a bit subjective.
Accuracy was pretty good. I shot all 12 at one particular Target and got a one MOA group with 12 bullets. Unfortunately my velocity is now back down to 2730-2750.
What Was the ambient temperature on the day you were shooting? If you’re running a load, that’s a little bit Towards the hot side. you may be having Ambient temperature issues. I have had issues with over pressure shooting the same load on a hot day Versus a cooler day. I have gone out with Max loads on a cooler day and they shoot fine with no over pressure signs and then go out when It’s a hotter day outside and I start getting flattened primers. Just food for thought.
The day of the overpressure signs it was roughly 75 to 80°. That’s significantly cooler than when I initially started working on this load with the new brass back it was the mid 80s if not mid to high 90s.
Carter, I have never used that brand of brass, so dont know how consistent the brass weights are for each piece; but, even in Lapua brass, Federal Match, I have seen variances from 1 - 2 grains of case weight in sampling just 20 by weighing each one individually.
Might be interesting to compare the pressure case weights to the non pressure cases; if the pressure cases are 1 - 2 grains heavier, and the load is at the upper end, that might be your culprit.
Good luck
John