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260 pressure help

 
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  #1  
Old 07-04-2012, 02:40 AM
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Join Date: Dec 2011
Posts: 17
260 pressure help

Ive been working on a .260 load. With 140 gr amaxs, h4350, nosler brass and wlr primers, trouble is that 43 grains of h4350 @2.8 oal shows no signs of pressure with virgin brass.
When I neck size once fired brass and shoot the same load I am cratering primers, occasionally blowing out around primer, and bolt lift is sticky, What causes this differentiation between the same loads but virgin vs once fire neck sized brass?

Gun is savage model 10 predator max 24"
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  #2  
Old 07-04-2012, 06:31 AM
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Join Date: Jan 2008
Location: Northeast
Posts: 2,284
Re: 260 pressure help

I have been down that road. I would try the following:
First off, if you have a head space gauge, check your new brass vs fired. The rifle may have a headspace issue.
Back off 1 grain
Full length resize
Try different primer
Try Lapua brass, stay away from Remington and Winchester. Recent poor quality.

I have run a grain or two more without pressure problems in my Savage LRP but I seat further out, and do need to full length resize. I also use Lapua brass which may make a difference in charge weight/pressure. I have found with my 260 and 308 that the recent lots of Win LR primers fit too loose, I use Fed or CCI match. If none of these things work, have a smith check out your chamber.
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  #3  
Old 07-04-2012, 04:54 PM
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Join Date: Jul 2009
Location: Northern MN
Posts: 205
Re: 260 pressure help

I agree with Greyfox....Back off your charge a grain or even more....

The powder burn in a new unfired case, for me, has always shown less velocity with the same load/components....If you can correlate velocity to chamber pressure that would mean once fired cases will have more but this may not always be the case and it is only my opinion....In theory volume increases with fired cases and more volume should decrease pressure....My chambers are tight and volume differences from new FL sized brass are usually negligible (depending on the manufacturer)....The biggest factor I believe is a burn rate influenced by the reflectivity and/or conductivity of the new brass and any factory coatings or oils imparted upon the new "shiny" brass by the manufacturer....

Make sure to check your primer pockets the "hot" loads may have stretched & ruined them...Also you should check your cases for signs of head separation.....After sizing and before cleaning I make these two very important inspections to my cases....One is a quick and easy visual inspection of the cases lined up in a plastic cartridge strip with a flashlight (mini-mag)....The "gray" soot riding upwards out of the pocket will be obvious when compared to the others good ones in the strip...A quick measurement of the suspect pockets usually if not always shows over size....Also before case cleaning I check every case for premature signs of head separation with the "paper clip" method....Actually my paper clip is a special ground and bent screwdriver...I do this every time and have found especially with new brass and suspect "high" pressure loads that you will detect this before it actually happens.....Not that it matters but the "paper clip test" will also give you a little "feel" for the difference in powder residue inside a fired new case and a seasoned case (at least it does for my with various calibers & powders)......The residue to me feels "sticky" in the first fired new case....After the second firing my head separation tool slides more easily over the remaining carbon.....At least for me that shows that the burns are different and I can only speculate why...

I have 3 .260s and one of my pet loads also uses 43.0 grains of H4350 but only with 123 AMAXs at .020 off the lands...I am pretty certain I would have pressure problems with 140s with 43.0 grains.....Even a new lot of powder (1 lb bottle) had me dropping all the way down to 42.1 to achieve the same velocity.....The next lot out of an 8 lb jug had me back at the original 43.0 grains...So there is always a possibility your powder is a little hot so you can't and another reason you shouldn't always go by the book.....I use both Nosler and Rem brass and find that with the reduced case capacity in the Noslers I also cannot load them up as much....

Also I normally use CCI or Rem primers but have used Win primers during the "shortage"....That lot flattened and cratered a lot more than I see with the CCIs and Rems....I believe but have never proved it that the cups were softer (or thinner) than they should have been.....

One last thing I have noticed that on some of my rifles with the tighter chambers that if I don't bump the neck sized cases every time I will get stiff bolt closings and sometimes stiffer openings....These stiffer openings did not indicate higher pressure but definitely got me thinking....I always check neck sized cases in the rifle chamber before loading them....My opinion is that the should chamber easily and not "tight upon closing"...If they are they should be bumped....

In your case the leaky primers definitely are the telltale of a pressure problem....The craters are probably related but could be a result of firing pin settings shape & hole size....These are common problems with Savages and can be remedied in several ways....

There are lots of things that may be causing your problem, I hope that you find it because the .260 is one sweet shooting caliber....

Good luck and make sure to let us know,
Randy
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  #4  
Old 07-04-2012, 07:09 PM
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Join Date: Aug 2003
Location: NC, oceanfront
Posts: 3,268
Re: 260 pressure help

This isn't normal, so you should pause & concede that you're doing something wrong.

I'd focus on what you changed that's spiking pressure.
What specifically are you doing with the necks & seating depths?
Have you changed ANY component?
Have you done anything with the barrel?
Same temps?
Pulled a bullet & re-verified charge weight?
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  #5  
Old 07-04-2012, 10:47 PM
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Join Date: Dec 2011
Posts: 17
Re: 260 pressure help

Thanks for the helpful advice , I inspected my brass from the earlier load development and trashed the brass I found with indeed loose primer pockets, I switched to the slower h4831 sc at 45 grains and am not having one issue and getting .4" 5shot groups and pushing the 140's at 2660. Im happy with that. I'll keep the h4350 for the 123 gr loads (had no issues with) just wanted that .585 bc from the 140amax.

Again thx
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  #6  
Old 07-05-2012, 12:56 PM
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Join Date: Jul 2009
Location: Northern MN
Posts: 205
Re: 260 pressure help

It is good that you found the problem....Load development sometimes brings you to the "edge" as far as pressure ...Most times when a primer pocket is enlarged in new brass (with warm to hot loads) you do not notice any gas leakage at that time because the pocket starts out fitting tight...As the pressure spikes the energy is extended into stretching the pocket....You usually notice however that at the next loading primers start to seat too easily...New brass is most suseptible to primer pocket enlargement because it is at its softest and most pliable state...

Even after inspections & measuring you will notice from time to time a primer seating easier than the rest.....Was it the primer or the case?.....I mark the base of these with a felt tip pen....At the next loading I double check these for gas leakage with my "flashlight inspection" and measure them again....Even indications of the gray soot creeping part way up the pocket will trigger a discard....

Sometimes a person can "stretch" the life of your cases by switching primer brands....I have had Rem cases develope mildly loose pockets after 10 or so firings using Rem or Win primers....A switch to CCI primers gave my 15 or more loads from the same cases....The CCIs measured only a 1/2 a thou more in diameter but combined with their metallic properties they tightened up the seal....

Randy
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  #7  
Old 07-05-2012, 02:47 PM
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Join Date: Dec 2011
Posts: 17
Re: 260 pressure help

thanks guys do any of you have experience with sizing 7/08 to 260, do I just run through 260 die?
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