280 ackley pressure question.

[bpotter]

I am in the final steps (I hope) of working up a hunting load for a 280 Ackley.
25 inch barrel. 160 AccuBond

I am trying to find out what pressure 55.4 - 56.4 grains IMR 4831 generates.
Hogdon lists 61,900 PSI for 55.5 grains and this is about where this rifle begins shooting well.

Can anyone tell me what pressure the high loads (e.g. 57.0 gr IMR481) in the Nosler run or has software to calculate this?

Missed a loose primer or pocket and split a primer. No other pressure signs. Just making sure it is just old brass or WLR primers that is the problem.

Thanks

 

[DrMike]

No one can tell you what the pressure will be. QuickLoad projects a pressure, assuming STP and the use of the coolest primer possible. Under those conditions, QL projects:

Cartridge : .280 Ack Imp
Bullet : .284, 160, Nosler AccuBond 54932
Useable Case Capaci: 64.303 grain H2O = 4.175 cm³
Cartridge O.A.L. L6: 3.330 inch = 84.58 mm
Barrel Length : 24.0 inch = 609.6 mm
Powder : IMR 4831

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-20.0 80 45.60 2380 2013 33543 9223 97.3 1.577
-18.0 82 46.74 2435 2107 35749 9443 98.0 1.539
-16.0 84 47.88 2490 2203 38089 9649 98.6 1.496
-14.0 86 49.02 2544 2300 40571 9838 99.1 1.452
-12.0 88 50.16 2598 2398 43204 10012 99.5 1.409
-10.0 90 51.30 2652 2498 45995 10167 99.8 1.368
-08.0 92 52.44 2704 2599 48957 10305 99.9 1.328
-06.0 94 53.58 2757 2700 52099 10423 100.0 1.291
-04.0 96 54.72 2809 2802 55433 10531 100.0 1.254 ! Near Maximum !
-02.0 98 55.86 2860 2905 58974 10636 100.0 1.219 ! Near Maximum !
+00.0 100 57.00 2910 3009 62735 10738 100.0 1.186 ! Near Maximum !
+02.0 102 58.14 2960 3114 66733 10837 100.0 1.153 !DANGEROUS LOAD-DO NOT USE!
+04.0 104 59.28 3010 3219 70985 10933 100.0 1.122 !DANGEROUS LOAD-DO NOT USE!
+06.0 106 60.42 3060 3326 75512 11026 100.0 1.092 !DANGEROUS LOAD-DO NOT USE!
+08.0 108 61.56 3109 3433 80334 11116 100.0 1.063 !DANGEROUS LOAD-DO NOT USE!
+10.0 110 62.70 3158 3542 85478 11202 100.0 1.035 !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 100 57.00 3002 3203 74436 10367 100.0 1.104 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 100 57.00 2770 2725 51070 11126 99.1 1.296

Note, that to obtain this projection, I set the Pmax to 65000 psi.

I would be inclined to increase the charge in small increments if there are no overt pressure signs.

 

[JD338]

bpotter

Due to many variables, there is no real way to calculate pressures, chamber dimensions and powder lot differences will also affect pressures.
If you have loose primer pockets, that is a sure sign of high pressure.

You might want to take a look at RL 22. I have had excellent results with the 160 gr AB, gettong 3000 fps and sub .2" accuracy from a 24" barrel.

JD338

 

[bpotter]

Dr. Mike:
Thank you. Yes, I should have said pressure estimate. I was assuming 65,000 PSI for manual but wanted to make sure. Previously, I had worked up in .3 grain implements and had been checking for pressure signs. None until issues with WLR primers.

Also, thank you for your earlier recommendation on the IMR powder. Very accurate and fast enough. I hope I can make it work. I don't think this is a pressure issue from this powder but may be.

JD338: Not so sure this is not a primer issue. Not fall out loose. F210s seem to fit tighter 5th load off new brass. Have some 20 unprimed cases to check. The two little pits on my bolt face from the split primer are not attractive.

I have tried RL22. Best accuracy around 58 grains. Another node starting around 60 grains.
215 M primers same or worse than 210 M. Was looking for something my gun liked better.

Will start a new batch of brass.

 

[JD338]

I started using the GM215M primer at my gunsmiths request and my accuracy improved. My rifle is throated long so I have additional powder capacity. In MY rifle, I loaded R-P cases to 62.0 grs, accuracy was excellent but case life was short with loose primer pockets. I dropped down to 60.0 grs, accuracy is great and long case life.

JD338

 

[nvbroncrider]

I am in the final steps (I hope) of working up a hunting load for a 280 Ackley.
25 inch barrel. 160 AccuBond

I am trying to find out what pressure 55.4 - 56.4 grains IMR 4831 generates.
Hogdon lists 61,900 PSI for 55.5 grains and this is about where this rifle begins shooting well.

Can anyone tell me what pressure the high loads (e.g. 57.0 gr IMR481) in the Nosler run or has software to calculate this?

Missed a loose primer or pocket and split a primer. No other pressure signs. Just making sure it is just old brass or WLR primers that is the problem.

Thanks

Might try 7828. I'm shooting 62.5 half grain above book max 1/2 MOA and I don't think I've done my part yet.

 

[bpotter]

Thanks all.
This rifle needs to be shooting at an elk in September so I am getting short of time to do to much reinventing the wheel.

I was hoping this combo could work. Nice big sweet spot at .7 to 0.2 inch 3 shot groups. 2840-2860 FPS with an additional 40 FPS with WLR primers. Very clean shooting and minimal fouling.

Had been thinking of 7828 SSC and can always go back to RL22 or shoot 140s

Any other suggestions would be welcome.

 

[DrMike]

It sounds as if you have it in hand. I wish you every success for elk this fall; you have a fine cartridge to tackle those bulls.

 

[onesonek]

I started using the GM215M primer at my gunsmiths request and my accuracy improved. My rifle is throated long so I have additional powder capacity. In MY rifle, I loaded R-P cases to 62.0 grs, accuracy was excellent but case life was short with loose primer pockets. I dropped down to 60.0 grs, accuracy is great and long case life.

JD338

Looks like a load that is near perfect in that rifle Jim! Sure like the looks of that rifle and then, the groups it shoots. And I will agree, too many variables, but blown primer pockets is not a good thing. I go there carefully, just to find out where the limits are, and like Jim then back off. If one has room for more powder at that point, then switching to slower powder may gain some performance.

 

[Oldtrader3]

My analysis experience on this type of primer failure indicates a defect issue either with the primer metal extruded cup or the case being damaged, allowing gas to escape. This may or may no be a chamber pressure issue and could be simply a primer cup or case primer pocket failure. Hard to know because you did not include any pictures of the primer failure or a description of what occurred exactly to make you believe that you had a pressure problem.

It could be a chamber pressure issue but the load does not appear to be one which should blow a primer. Just curious?

Attached is a picture of another primer cup that failed because of soft materials and/or a case dimensional issue? Note blowout and tensile failure (crack) of primer wall in what is a normally safe load in this particular 7mm rifle

 

[onesonek]

Defective primer certainly could be the issue Charlie,,,I agree.

 

[bpotter]

Thanks guys
I have the primer and will try to take a picture and figure out how to post it. IIRC it was just a crack in the side of the primer. It was not backed out. The reason I noticed it was the soot ring around primer area on bolt when I cleaned the gun. Noticed the offending case right away. Crud and corrosion around primer. I saw the split when I popped the primer out. It came out with little effort. No unexpected change in velocity etc.

I do not think it is pressure but am trying to be through.

This batch of brass is on its fifth firing. Has basically been used to work up loads. I loose track of what has been fired through a case once they go through the tumbler.

Come to think of it, I should clean the pocket out on this case and two the others that show the slightest hint of soot. Re-seat new 210 and WLR primers to check tension. Should answer pocket size question. Other cases fired before and after that day, including higher charges, are fine.

 

[Oldtrader3]

You might try to take a picture of the soot ring in the case pocket if you can and look for a path of gas cutting (usually in the radius at the cup pocket opening) or a scratch from the primer failure. Just would be interesting to see.

 

[bpotter]

I can't get a clear picture of primer or pocket.
Small crack from top edge of primer then down side. Hole is not as distinct as Oldtrader3s photo.
Pocket rim rough and pocked.
There is a very/very small grove cut in the primer pocket presumably matching crack in side of primer.
Can try to use a better camera tomorrow if anyone interested.

 

[Oldtrader3]

That is okay, sounds as though it was a cup tensile stress failure. Every now and then, the manufacturers make a cup which is not hardened or annealed properly at whatever manufacturing stage. The picture that I posted the pic of was one of these and it sounds as though yours was also. I would not use that case again, now that it has been gas cut.

Some cups are higher tensile strength and hardness than others. If you have any more issues, I would switch primer manufacturers.