Help flat primers

[DennisPA]

Ok so I think I screwed up but I’m not sure where so I need some help. I finished last year shooing my 7WSM bench gun with fully prepped Winchester Brass, Fed Match Primers, 61.0g H4831SC, and sorted Berger 168g. That combo shot well and I was hitting ok at 1000 yards.
Over the winter I wanted to get some better brass and I rebarreled to shoot the Berger 180 Hybrids. So I found 200 Norma 270WSM brass and I expanded them to 7mm with my K&M expander and did a full prep. I needed to fire form them and I didn’t want to use my good components, so I used the 270 Norma Brass, CCI large rifle primers, 61.0 grains of H4831SC and Nosler CC in 168g. I did loosen up on the power measurement too but it was still +/-.05g.
So with the barrel being new I gave it a good cleaning and starting shooting. I wish I was more careful about putting my fired brass back but about 1/3 of my primers are extremely flat. So I know it was not the first 6 or so shots because I looked them over pretty good checking for pressure because of all the changes I had made from last year. But out of the 25 shots I took before I had extractor problems, about 6 of them have extremely flat primers. Any ideas what I did wrong? Why only 6 out of 25?
My thinking was since my load from last year was middle of the road, even though I had the smaller “boiler room” of the 270 brass I would be ok. Also my concern was I didn’t want to go to light a charge I’ve heard bad things can happen there too.

 

[jonbearman]

Why not a lower book charge instead of the obvious hotter load. The Norma may be a thicker brass or whatever but starting out without working up is dangerous as you changed the whole load. It is a different barrel also in a completely different caliber as well. The chamber could be tighter. So start over and load one of each load from the book and load up each one with 3 tenths more till you see pressure and then back off a half a grain.

 

[noload]

I haven't shot a 7WSM but I do know Fire forming brass in a 284 Shehane is a little tricky when you have to jam the bullet a bit to keep the brass rim tight to the bolt face. That bit of jam can really spike the pressure up, so you got to watch the powder charge and the amount of jam. I've trashed my share of Norma brass, also I find in my caliber the Norma brass does not have the boiler room that Lapua does.

 

[Patch700]

A couple things would come to mind... The first being the difference in actual bullet surface area between the bergers and the noslers.. Perhaps the noslers by design have a larger surface area?

I was going to say possibly a wet chamber after cleaning but you mention the first group seemed fine so that probably rules that out.. Were you jamming bullets to fireform?

One thing you didnt mention was how much your cases grew with respect to base to shoulder once they were fired , perhaps there was an excessive amount of headspace prior to fireforming and the cases got to take a run at the bolt face without having the bullets jammed?

 

[KMart]

The 7 WSM chamber is about .040 longer from base to shoulder than the 270 WSM. Add to that the fact that new brass is usually shorter from base to shoulder than fired brass, you may be having a lot of case growth happening.

 

[DennisPA]

Thank you all for pointers. A question came up about seating depth. they are 0.010 off the lands same as I ran last year on the old barrel. Would seating them deeper say 0.030 - 0.040 off the lands help lower the pressure enough to get these fire formed?

If not what should I do with the other 75 rounds I have loaded? Some thoughts I had was to pull the bullets take a grain of powder out and re seat the bullets and see if that works. Or since I am moving the shoulder so much do I need to do this in stages. Maybe a pistol powder and a wad firing then reload and finish fire forming them bullet.

I'm willing to bet that the brass did get a "run" at the bolt face. That's probably why my extractor broke. It makes sense the a brass would be shoved forward from the striking of the firing pin then slammed back when the main charge goes off. If that's the case why wouldn't everyone that fire forms with bullets have the same problem?

Again thanks for the help.

 

[searcher]

While there are other factors at play - being .010 off the lands, using unformed brass could surely cause the problem you describe about "getting a run at the bolt" especially when it is erratic as you describe. It can also take several firings to have uniform brass unless jambed.

 

[searcher]

I'd probably partially pull your existing bullets with a collet bullet puller if you have one - then reseat to depth you want. I'd pull completely and recharge cases if you think the load will be too stiff to jamb.

 

['Freak]

Don’t even add to the already .010” jump. The body of a 270 WSM case is shown .038” shorter than the body of a 7 WSM case from case base to the body/shoulder junction, per the case cartoons in a Nosler #6 manual. To make up the difference in case body length, the shorter 270 WSM’s case shoulder got to be blown forward .038” all the while the projectile is seated out far enough to put its ogive into the lands with force enough to keep the case base backed up against the bolt face.

 

[swd]

Dennis you need to be jamming your bullets .030"-.040" in to lands not off them to get the case head back against the bolt face to fire form and this doesn't always work well. The best way is to expand the necks to 30 and then back down to 7mm with light bolt drag. I would toss all your cases with flat primers and look over the rest very carefully for case head separation. I have a wildcat that blows the shoulder .040" forward and learned all this the hard way too.

 

[expiper]

OP,,,,reply #9 is correct in advising to make false shoulder from 30 cal neck,,,,and I have always found Nozler bullets to cause higher pressure than any other brand (esp in hunting rifles ) because they generally have a longer bearing surface and the jackets "usually" are thicker and made from harder material,,,,so you can pretty well expect a 168 gr (or any equal size) Nozler to make more pressure than a 168 gr. Berger or Sierra,etc,,,,Roger

 

[Fire306]

I am currently having a 7WSM build on a Sako 75 action. My plan is to use it as my go-to hunting rifle. I have 270 WSM Norma brass as well that I plan to fireform. The rifle isn't back yet, but I think I have read everything there is to find about the 7WSM and forming brass for it.
This is just my opinion, so take it for what it is, but I see it does line up with what several others are saying.

The 270 WSM shoulder a shorter length from the base of the cartridge that the 7 WSM. Therefore when fireforming to 7 WSM you must have some way of keeping the base of the cartridge pressed tightly against the bolt face. So like others have said, you must either seat bullets out so they jam tightly into the throat, thus keeping the base against the bolt, or form the false shoulder to achieve the same result.
I can't remember currently which cartridges I have had to used these method for before, but I have done it. (243 up to 260 Rem possibly??)

From what I remember reading loading manuals over the years, flat primers can be caused (not only from high pressure) by improper head spacing. (Which you have by firing a 270 WSM case in the 7WSM chamber) When the firing pin strikes the primer, it shoves the case ahead away from the bolt face. When the powder ignites it can then push the primer out of the pocket somewhat before the case head gets shoved back to the bolt face again. This can result in the flat primer, and not necessarily mean high pressure.

You need to inspect your brass as others have said, improper head spacing can cause case separation, or just weakened cases.

 

[savagedasher]

The load you described should be good for FF. But you should be jamming the bullet .030 or more. The reason for the flat primers is excessive head space. Larry