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How much Case Expansion after Fireforming

 
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  #1  
Old 07-22-2005, 08:48 AM
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How much Case Expansion after Fireforming

I was breaking in the barrel on my new 25-06 yesterday and I compared a fired casing to a factory federal casing. Just by eye balling it I could see the shoulder looked dramatically wider. I used caliper on the shoulder line and I came up with .433 for the unfired and .443 for the fired brass.

I am just curious as to what is normal for case expansion in a factory chamber. I was also wondering how much difference this will make in case capacity as I will be partial full length sizing this brass.

Thanks
Steve
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Old 07-22-2005, 01:19 PM
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Re: How much Case Expansion after Fireforming

Steve,

This is typical with a factory chambering, especially one based on the '06. For some reason, brass makers and rifle makers can't seem to get on the same page with the '06 cases and chambers. The standard head size for the 06 is not what the brass makers or the rifle makers use to build their products, don;t know why??

Case capacity increases will be there but not dramatic. Maybe a grain or two at the most, in a case this size, not really enough to worry about.

I'm tellin ya man, just have her opened up to the 25-06 AI!!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

Kirby Allen(50)
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Old 07-22-2005, 01:32 PM
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Re: How much Case Expansion after Fireforming

Trust me Kirby I would love to.

I just have too have a factory gun so I can kick ass at local competions. After that I will break out my Allen mag to really stomp people in the open class.

Take it easy
Steve
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Old 07-22-2005, 05:34 PM
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Re: How much Case Expansion after Fireforming

Lerch,

Are you limited to factory chamberings???

Most factory classes I am aware of allow rechambering as long as you use the factory barrel??

Just curious, not pushing for the job by any means, or Hawking as it has been called in past posts [img]/ubbthreads/images/graemlins/grin.gif[/img]!

Kirby Allen(50)
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  #5  
Old 07-22-2005, 06:18 PM
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Re: How much Case Expansion after Fireforming

Lerch, Fiftydriver,
That's an excellent question and answer. My 300 RUM, when I was shooting it with brand new remington brass 94.0 grains of Retumbo with 200 grains Accubond was giving me 3222 f/s muzzle velocity; after the brass had been fire formed and just resized enough with FL dies to hold the bullet, my MV droped to 3159 f/s. At first I thought my chronograph was messed up but when shooting the .22 throught it, the consistency was there. Is possible that would make a difference of 63 f/s? Looks like it! That would go along with what Kirby is saying, maybe 2.0 to 2.5 grains more would put me back to 3222 f/s!
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Old 07-23-2005, 05:42 PM
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Re: How much Case Expansion after Fireforming

Lerch, Like Kirby I have also discovered that the factory new brass often seems to be undersize compared to the chamber dimensions, as an example, I will give you a comparison to yours with several of the 25/06 rifles I have owned.

In 1986 I purchased a new Sako AV 25/06 sporter. The Remington 25/06 new brass measured .464 at the head, .435 at the shoulder, and had a capacity of 65.5 grains.

After firing, full length sized cases were .4675 at head, and .4385 at shoulder, while neck sized cases where .469 at the head, and .4435 at the shoulder. The capacity of fired cases were 68.2 grains. After about 300 shots, the barrel was set back and rechambered to the 25/06 AI, and Remington fireformed cases were .469 at head, .455 at shoulder and had a capacity of 71.2 grains.

Three years ago, I purchased some new brass for a custom 25/06. This time the Remington new brass measured .467 at the head, .439 at the shoulder, and had a capacity of 65.3 grains. The Winchester new brass measured .4665 at the head, .4395 at the shoulder, and had a capacity of 67.6 grains. On this occasion I did not measure the fired head and shoulder dimensions of these cases. However, after about 100 shots the barrel was set back and rechambered to 25/06 AI, and the capacity of the Remington fireformed cases increased to 70.1 grains, and the Winchester cases measured 71.1 grains.

I also endorse Kirby's suggestion of considering rechambering to the 25/06 AI, as my experience in the above 2 rifles suggests that you can expect an increase of about 225 fps with bullets of 100 grains and more. Hope the above information helps. Brian.
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  #7  
Old 07-23-2005, 06:17 PM
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Re: How much Case Expansion after Fireforming

Not sure of lerches local competitions but the VHA factory gun class only allows factory chambers.
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