overpressure with cow?

bingo1010

bingo1010

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is it possible to overpressure a case when fireforming it with pistol powder and cream of wheat?. the reason i ask is that i fireformed 200 pcs of lapua 30-06 brass with 12-14 grains of bullseye topped with cow. after the first round of full power loads the primers barely stay in the case. i am shooting hot loads no doubt about it, just as a check i loaded some previously fireformed remington brass with the identical loads and the primer pockets are still tight (and this brass has been loaded a couple times prior). any thoughts out there??
 
I find Lapua brass thicker than most and loads that were fine in remington brass were too hot in the lapua. Any other signs of pressure? Primers flattened or ejector swipes?
 
the weird thing is that i am getting ejector marks on the lapua but not on the rem cases. as i was waiting for responses on here i took a brand new rem 280 case, loaded it as hot as the lapua cases were loaded and fired it. punched the primer out and reprimed it, it was still firm seating. fired it again and the primer still had more resistance as i punched it out than did the lapua after one full power reload. the rem cases actually have less capacity than the lapua...that i did check. so if anything the rem cases are loaded hotter than the lapua.


i should also clarify that the gun is a 280ai
 
I just did some 338 RUM with COW and I think I used 9 grains of shotgun powder, I think 14 would have been a hell of alot. I definitely think you can over pressure using this method. The method I used to determine the amount of powder was to fill the case till overflowing and use 10% of that weight. You still have to "work up" a load to the point you are getting good case formation.
 
i did originally start around 9-10 grains but was not getting real good shoulder forming so i stepped it up. this was my first go at fire forming with cow... apparently a little expensive as i now have 200 pcs of good for nothing brass. i guess i will order 200 more and just fireform with with lead rather than cow. lesson learned...the hard way as usual!! oh well
 
Sure can screw it up if not careful... did you perhaps leave the COW in the case for more than 24h? Was it particularly humid when you loaded it?

I've heard of the COW forming a solid 'plug' that would certainly up your pressure... humidity is the culprit.

-M
 
The COW method will not fully form your cases with a sharp shoulder. You get a case with the shoulder relocated and a slight curve in the corner of the shoulder/case body junction.

The first smokeless powder load will sharpen the shoulder.

The 8 to 10gr sounds about right.

Yep, me thinks the brass is toast.

Jerry
 
Ouch Steve, I'm afraid they're done. Jerry is right in that you are just trying to approximate the new shoulder, and that the sharp shoulder forms with the first true load.

The 280 is a long case and it has a whole lot of COW to move in front of it. One of our shooters is FFing 243AI's with 15 grains of Tite Group and I was surprised he didn't have problems.

I see your email here this morning... I'll call ya later.
 
FWIW Hornady advertises a hydraulic system for forming brass.A fellow I know uses it and says it ends up semi formed (6.5 Gibbs) as was fireforming with COW.Have to hit a piston with a hammer but using a weight on a track above piston is more accurate.

Personally I fireform in a "sacrificial" chambered tube attached to an old cheap action.
By using a 22 caliber bore with a 6.5 chamber ,the pressure required is easier to reach using bullseye and old dirty tumbling media with paper wads.Be sure forming chamber is cut short to give backpressure on case against bolt. This will keep case expansion uniform.
Like tuning loads to shoot,you need to tune the load to form.If your cases are having
the primer pockets expand fireforming,I would imagine the shoulders would be blown sharp and maybe experience "sticky" bolt extracting.
Chris Long published a good article on fireforming brass on 6BR.Worth a search.
Gord
 
hmmm remington brass and tight primer pocket in the same line ....kinda a oxymoron.
i like to set up a false shoulder to hold it back against the bolt face...
 
i am by no means implying remington brass is quality stuff... don't put me in that group!! it is just that the lapua pockets are loosening up when the rem is not. weird i know but it is happening. the rem were fired in the previous barrel using full power loads, the lapua in the same barrel using cow and pistol powder. as i am going from 30cal to 280 i am adjusting my bushing to give a snug bolt close. the problem isn't in the shoulder or the neck but rather at the other end.
 
15gr of titegroup in a 243 case? WOW, that is crazy hot. You just want to move the shoulder, not age the brass the same as 15 firings :)

Not sure why the big hate on for Rem (or other US manf for that matter). It is relatively soft but no worse (actually tougher) then Norma.

I have shot my smallest 1000m group on paper using Rem brass so there is nothing wrong with it.

If loads are kept in the normal magnum pressure range (which is not a bad idea for safety AND accuracy), it lasts quite well.

Jerry
 
i agree jerry as i have shot some awesome groups with rem brass as well, it is just the consistency that sucks. i recently turned some necks on rem brass, some the cutter never even touched, others were cut full length of the neck. but in my situation here the rem brass is standing up to some pretty stout loads with out failure/primer issues
 
I neck turn all brands of brass and I get varying degrees of hit and skip.

But once, done - all the cases are prepped as good as I can make them. And the results on paper, show they work just fine.

Also remember to touch up your necks after several high pressure firings. Brass flow is a wonderful thing and can cause some real fun if not addressed.

Jerry
 
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