New Lapua brass bulged after first shooting in M39

[hardwood34]

Just got 100 new unprimed Lapua 7.62X53 R to shoot from my M39. Carefully prepared them (cleaning, FL sizing, another cleaning) and load 50 of them with Rem 9 1/2 primers,19 gn of #2400 and Lee 160 gn (real weight 168 gn GChecked) and went to the range. And see what I got after shooting:

From left to right: 1 - old PPU (19 reloads) and the rest all Lapua. I shoot 104 rounds that day (54 PPU and 50 Lapua) from same gun, same primers/powder charge and same bullets, but 35 Lapua cases got bulged on the shoulders. The rest of Lapua looks like second one on the picture. And everything okay w/PPUs. I checked that load in M39 many times (from 16 gn to 22 gn of #2400) w/PPU brass and nothing similar. What is that? Too short to ogive brass? And BTW new brass length is 2.087" and once fired - 2.076/2.077".
Is it safe to reload and shoot again?

[Frank46]

The ppu looks ok. however the lapua with the weatherby shoulders were too short for your chamber. Never saw anything like that. your loads aren't really hi pressure compared to full on mil surp ammo. So I'm thinking in your case you will have to one of two things. Find a fireforming load or reload again with your CB load. Just need the shoulders blown out. Frank

[Scharfschuetze]

I think that Frank46 is on it. A few more loads and they should be fire formed to match your chamber assuming the rim is properly headspacing the case in the chamber.

[hardwood34]

Thank you guys! Should I do FL sizing or just neck?

[Paul Tummers]

When neck sizing is good enough to get your rounds chambered, I would neck-size them. When full sizing you destroy the part of the job that already has be done by partially fire forming at the first shot.

[texassako]

By the way, there is a reason for the different headstamp on Lapua brass. It really is slightly different in length and there are rifles with chambers that will only chamber 7.62x53r brass.

[country gent]

You need to fireform the cases to your chamber first, blowing out the body shoulder will shorten the case some also. a charge of unique or medium fast pistol powder with cream of wheat filling the case and fire. Another way is to seat bullets out to solidly touch rifling so case is held back in place and fire.As to neck versous full length sizing neck sizing will work and allows for some added alighnment at the neck and body due to cases not being sized down from chamber sizes. Draw back is that at some point brass will get sticky requiring full length sizing. The trick to full length sizing is to just kiss the shoulder and bump it back .001-.002 from chamber dimension. This allows easy chambering of the round slightly sizes body and all of neck, but dosnt over work the brass. A gage can be made to use for measuring this easy enough, have a hole drilled in a 1" rod 3/4" dia. Hole needs to be mid point between neck and shoulder dia, Datum line of shoulder is mid point of angle. You can use this to measure the datum line comparatively to see how much shoulders are moving with calipers.

[tomme boy]

NEVER FL size new brass. All you want to do is make sure the neck is round. I have seen new brass have a case separation because the person FL sized the brass. If the brass chambers, load it.

[Frank46]

The lapua 7.62x53r is actually one milimeter shorter than the standard 7.62x54r. So in your case I'd just neck size until they are fully fireformed. And yes there are Finnish rifles so chambered for the lapua case. The 28-76 Finn moisin nagant target rifle I believe is chambered for the lapua case. I have heard stories about hard feeding into the chamber of these rifles with the standard 7.62x54r ammo. Frank

[mannyCA]

NEVER FL size new brass. All you want to do is make sure the neck is round. I have seen new brass have a case separation because the person FL sized the brass. If the brass chambers, load it.

+1
Thats how I treat ALL brass, new or once-fired.

[DeanWinchester]

I was under the impression that the brass is a hair shorter because as has been said there are rifles that will only chamber the 53R and those rifles had .308 bores. In an effort to keep the bigger diameter out of the smaller bore, they shortened it .039 or so.

[texassako]

Here, this will clarify things a bit on the difference: http://en.wikipedia.org/wiki/7.62%C3%9753mmR . You are fine with the Lapua brass. A hotter load would have moved the whole shoulder forward and you might never have noticed.

[hardwood34]

Thank you, guys! And any suggestions what is the best way to finish fireforming: reload them w/jacketed bullet or just use COW? If COW fire forming any powder's suggestions? Or, may be anneal the cases beforehand also?

[Scharfschuetze]

As the case headspaces on the rim, you can probably just keep shooting your current load and the shoulder will fill in (fireform) within a few more loads.

Option two, in my view, would be to up the chamber pressure with a jacketed bullet and get it all done in one shot per case.

[Larry Gibson]

I disagree, that brass is toast.....he needs to send it to me for proper disposal.............

Larry Gibson

[MostlyLeverGuns]

Not unusual for Rimmed cases to have a 'short' shoulder. Mostly it is never seen because it is moved forward when pressures are high enough to move the brass, filling the chamber. If you full-length size new brass and get head separations, your sizing die is not properly adjusted, headspace on the rifle is excessive, or your new brass started with the shoulder too 'short' (I found this with some Winchester .358 Win brass.) Just keep reloading that brass, the shoulder will eventually move to fill the chamber while the rim controls headspace. As long as it chambers to your satisfaction, neck sizing should be all that is needed for your modest load. With that load and neck sizing that brass should last a very long time.

[tomme boy]

Ah, Larry, since I posted first before you. It has to go to me. Just to make sure, send ALL of the brass to me and I will make sure to dispose of it for you.

[Larry Gibson]

Just posted in case he missed you two......can't blame a guy for tryin'..........

Larry Gibson

[Gunor]

I remember reading somewhere of placing a o-ring on a 303 case in a SMLE (or No. 4) action - first firing - to make sure the shoulder fills the chamber shoulder - Cast Boolits wise/pressure....I think that was to help with generous head spacing...and getting a brass case to properly fill the chamber. And these loads, probably where not to hot enough to fire form and match the chamber.

Seems to make sense on 7.62x54 (or 53) Rimmed case. Also, did Mr. Harris propose a larger flash hole for these types of reduced loads? I should probably re-read the article.

Geoff in Oregon

[EDG]

The data on the two cartridges does not tell the entire story.
In fact it can lead you to make some wrong assumptions.

You need to get a copy of the CIP standards for the 2 rimmed rounds.
What you will find is the Finn cartridge is slightly shorter than the Russian round
BUTT<<<<<<< and it is a big BUTT

The Finn chamber is a little longer than the Russian chamber.
The best fitting ammo is the Russian ammo in a Russian chamber - bigger ammo - smaller chamber
In engineering parlance this is the maximum material condition of the ammo and of the chamber

The worst fit is the Finn ammo in the Finn chambers smaller ammo - smaller ammo - longer chamber
This is the minimum material condition of the ammo and chambers.

Kind of wierd.
I guess close enough counts with horse shoes, hand grenades, nuclear weapons, and mixing Russian and Finn rifles and ammo. And add .303 British ammo and chambers - about the worst there is.