Fireforming 338 Lapua Improved from factory ammo

Despotes

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Is using 338 Lapua factory ammo acceptable to fireform Lapua Improved cases or should I reload so the bullet engages the lands?
Here's my reamer print if it helps:

338%20LANGLEY_zpsqsxzlgxy.jpg
 

RockyMtnMT

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Factory ammo should fire form fine. I use the cow method or similar so as not to send bullets down the bore.

Go for it.

Steve
 

MudRunner2005

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Step 1, remove ammo from box. Step 2, place into gun. Step 3, shoot.

That's how you fire-form factory ammo.

Unless you are asking about special steps and prep-work. You can't do any of those with factory loaded ammo. Unless you pull the factory ammo apart, prep it, put it back together, but then that defeats the purpose of forming from factory ammo...
 

Despotes

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Step 1, remove ammo from box. Step 2, place into gun. Step 3, shoot.

That's how you fire-form factory ammo.

Unless you are asking about special steps and prep-work. You can't do any of those with factory loaded ammo. Unless you pull the factory ammo apart, prep it, put it back together, but then that defeats the purpose of forming from factory ammo...

I was asking which was better, using factory ammo or reload 338 Lapua with the bullet in the lands. I read that land engagement is best for fireforming.
 

MudRunner2005

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I was asking which was better, using factory ammo or reload 338 Lapua with the bullet in the lands. I read that land engagement is best for fireforming.

Any non-belted case, it is best to fire-form with a bullet jammed into the lands to ensure the case is properly seated against the bolt-face while it's forming. That way the case properly fills the chamber while expanding.

You will want to run a light load and not a full load when you jam a bullet into the lands. I'd run about 15gr LESS powder than a full load to ensure of no pressure spikes while forming.
 

Earl Fouraker

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Your reamer is cut with a -.004 headspace. That will cause a slight "crush" on the shoulder of factory ammo if the barrel is chambered correctly. You should have no problems shooting factory ammo through it.
 

RockyMtnMT

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Your reamer is cut with a -.004 headspace. That will cause a slight "crush" on the shoulder of factory ammo if the barrel is chambered correctly. You should have no problems shooting factory ammo through it.

Also means that he can fire form unloaded brass with the cow method in the future.

Steve
 
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