Troubleshooting erratic pressure

[Seth1913]

In preparation for a third season hunt I’ve been working up a load for my 280ai and the last two trips to the range have me fully confused. So I need some help understanding what went wrong. A little side note I’m still fairly new to rolling my own. I have had good success with .243, .30-30 and 6.5-300wby but never push it to the max as I’m not trying damage anything or myself.

So here’s the story. I went to find a node and find pressure working up this load from 55 grains to Barnes max at 58 grains. Temp was around 86. Working up I was noticing some much higher than book velocities (56.5 averaged 2844) but no pressure signs until 58 grains and boom blown primer. Didn’t see any ejector marks leading up to it so wasn’t being weary. This was with virgin brass.

Second outing I decided to play around at the 56.5 range as it grouped the best and had the best sd/es. So I loaded up 5 at 56.5 and 5 at 56.5 with a crimp from a lee factory crimp die to see how it would affect the load. This go around d was with 1x fired brass and FL sized. I forgot my adapter for my chronograph so no velocity data unfortunately.

First shot with the crimp and blown primer. Normally I would have stopped there and not moved on but I thought it must have been an error on my part during the charging process. So I moved to the non crimped rounds two where shiny ejector marks and one with nothing. Went back to the crimped rounds, 2 ejector, one nothing and they grouped really well. Weather was 60-70 degrees with a strong cool wind.

I can’t imagine I over charged all 10 cases. Anyone have any ideas to what could have gone wrong and what steps I should take next?



Below are the components used.

Bullet 168gn Barnes LRX
Powder 7828ssc
Brass Nosler virgin and once fire brass
Primers CCI BR2
Redding FL die
Forester micrometer seating die
RCBS balance scale with a cheap digital scale for cross reference.

Rifle
Custom built on a Ruger M77 action
Bartlein barrel 1-8 twist at 22”

Any advice is appreciated!

 

[sdupontjr]

I was gonna say your scale is wondering but I see you checked it with another. I haven't had this problem but have read it before, possibly a bad batch of powder?

 

[tom338]

Pull a bullet and re-check the powder weight in the loads

 

[Wapiti1]

It means that in your system, it is burning faster than it did in their system. It's not unusual to find a powder/bullet/primer combo that doesn't behave exactly like it should. I get similar results in one of my .300 Win Mags with 7828. Hits pressure way early. In my .340 Bee, 7828 is perfect.

I would pull the bullets, drop back to 55 grains, and consider that the max with that powder/bullet/primer. Those velocities being higher than book for that charge said that you have more pressure than they did at the same charge since velocity is a proxy for pressure that we can measure. You have both velocity and physical signs on your cases. I doubt you threw charges wrong.

If you get good groups at 55 gr or less, go with that. Could try a different bullet. Usually, the primer doesn't matter much, but I have gone to LR from LRM and seen improvement. Going from LR to LRM, you should drop half a grain to start.

Could be that this just isn't the right powder for that rifle.

Jeremy

 

[Seth1913]

Thanks everyone. I will pull bullets, double check powder and try again at a lower charge.

Also have some 145 lrx’s coming that I may try with h4831sc.

 

[Harvey_NW]

First off, Nosler brass is trash. The only erratic pressure signs and issues I ever got were from Nosler brass, and I had 4 cases split on me first firing. Outside of that, if you properly resized your brass and bumped shoulders back .002", pressure will increase a little bit because less energy is absorbed by the case expanding to the chamber wall. Crimping can also change the pressure curve. I would drop charge weight at least a grain or a grain and a half and see what happens.

 

[Seth1913]

Didn’t get the chance to pull bullets this evening but was thinking I do have some fireformed Hornady cases that might be worth trying. I’ve read conflicting reviews on it. Anyone have a better experience with Hornady than Nosler?

I do think I will get some Peterson brass coming, as it seems to have the best reviews.

 

[Harvey_NW]

Didn’t get the chance to pull bullets this evening but was thinking I do have some fireformed Hornady cases that might be worth trying. I’ve read conflicting reviews on it. Anyone have a better experience with Hornady than Nosler?

Hornady won't handle the same pressures the better brass will, but if you don't hot rod it I do think it's better than Nosler. I got good results with Hornady brass in my 280ai, because it was all I could get at the time.

I do think I will get some Peterson brass coming, as it seems to have the best reviews.

I'm a big fan of Peterson, that would be my suggestion is to skip the waste of components and just buy a lot of quality brass and start over. Euro optic and Graf's usually have Peterson in stock.

 

[Packmansion]

What do you mean by primer blown out? Is the primer falling out or is it just pushed out a little? light loads can actually cause primers to push out a little. Primers falling out is different.

Do you have a heavy bolt lift?

The relationship between velocity and powder charge weight is linear. There are no nodes, just small sample sizes and noise. Find a safe load at a velocity you like. If it isn't accurate you can fiddle with seating depth (0.003 increments) or start over with new components. Changes in components will have big impact on accuracy, changes in powder charge weight have a small impact.

There is no need to crimp for a hunting load. If you read up on neck tension best thing is a mandrel and GOOD brass. I'm sure your Nosler brass isn't that bad. I use Remington brass which is total trash and it works fine for me.

I am not familiar with 7828 SSC and how well it handles temperature. if you develop a load in 40 degree weather and then go to Africa with it on a hot African day you might get pressure signs with what was a perfectly safe load at 40 degrees. You might want to try H4831 SC if you can get some.

 

[Seth1913]

Bolt was definitely stiff with blown primer and No it didn’t just back out it fell out of the pocket completely. Bolt wasn’t really stiff with other firings.

I understand crimping isn’t necessary but wanted to see what it would do for me for. For now I just full length size. Maybe one day I’ll get into mandrels and different sizing dies but for now I’ll stick to fl size.

Have some 4831sc I’ll tinker with after hunting season. 7828ssc is temperature sensitive from what I understand but not that I can see in the temperatures I’ve shot at.

 

[Seth1913]

A little update from suggestions earlier on.

-pulled bullets and definitely didn’t over charge

-picked up Peterson brass and it’s much better quality.

So I went out again and loaded some 145lrx’s up with 7828 and found an okay enough load for hunting, 3/4” group at 100 will have to do but definitely not happy with it just not a whole more time to mess with things.

I have come to the conclusion that this batch of 7828 must be hotter. It pressured up pretty quickly with the 145s too and I believe 54 grains was the best group (don’t have my notes on me)

I know this rifles is capable of nice groups as I’ve shot one ragged hole with 150 nosler AB over 4831sc. I wanted to try the 7828 as it seems to give a 100fps edge over most other powders listed in barnes’ data and with a 22” barrel that would be nice but I’m going to chalk it up that this combo of powder and bullets just aren’t meant for this rifle and will mess around with it after season.

Thanks everyone for the help.

 

[VA2MT]

this is pretty common in a lot of different caliber like the 300Wm and the 6.5 PRC. In my experience those two cartridges have a lot of expansion in virgin brass for the particular rifles I load them in. One of my 300’s I load 75.6 grains of H1000 in virgin brass and get 2915 fps. Second fired brass I need to drop down to 74.8 grains to not have pressure and achieve the same 2915fps. Several 6.5PRC’s I have go to 58.1 grains before pressure on virgin brass, but once fired I hit pressure at 56.3 grains.

 

[wind gypsy]

Working up I was noticing some much higher than book velocities (56.5 averaged 2844) but no pressure signs until 58 grains and boom blown primer. Didn’t see any ejector marks leading up to it so wasn’t being weary. This was with virgin brass.

This IMO illustrates how chronographs can be most valuable during load dev. It tells you a story in relation to pressure. Some brass/chamber combos hide pressure better than others but if a chrono is showing way higher velocities than what is typically published chances are it's caused by pressure.

This isn't specifically directed at the OP but the idea that we need to test until we're piercing primers, have a bolt that's hard to open, or stamping the case head with ejectors is silly if we have a chronograph telling the story.