Necks splitting with Factory Ammo?

Potshot21

Potshot21

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Moose Country, Ontario
Hey fellas!

So I recently bought a nice Ruger M77 tang safety in 7mm Remington Magnum. Really like the rifle, find it balances and shoulders well, just need to find a scope either long enough or with enough eye relief so I can shoot it comfortably. It is however equipped with iron sights!

When I purchased the rifle, it came with about 50 rounds of Remington Core-Lokt 175 gr. ammunition. Naturally, this is what I used when I took it out for test firing. Messed around with it a bit and fired about 10-15 rounds in total. When policing up my brass to be loaded later, I noticed I had about 3 or 4 cases that had the necks split on them. Does anybody know what would cause this in factory ammo? All the research I've done points to neck cracking being an annealing issue or from excessive brass drawing from full length sizing and leaving the neck walls thin and soft.

Thanks!
 
I can't speak to the age of the ammo as it was included in the sale of the rifle that took place only a month ago. I'm glad that it is a factory problem and not the rifle. I wasn't sure if excessive headspacing or a worn out throat would cause it or not. The rifling looks good to me, but still not sure what the round count is through the old girl. But I imagine a big magnum case pushing a small .284 bullet would wear the throat faster than other calibres would.

Thanks guys!
 
Are you sure the ammo is not reloads?

Measure the neck diameter of the fired cases compared to the unfired. It will tell you how big the neck is in the gun and how much they are expanding. Unusual for factory ammo to crack, or age on the shelf. I have 7mm ammo that is 50 years old and it does not crack.
 
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I've seen this a few times with factory WSM ammo, I think it was Remington or Winchester brass. About half cracked on the first firing and almost all the rest cracked on the 2nd. In that case, it was definitely the brass as changing manufacturer eliminated the problem.
 
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