375 H&H chamber cast

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mtngun
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375 H&H chamber cast

Postby mtngun » Fri Mar 05, 2010 4:17 pm

I received a chamber cast today, from a Remington 798 375 H&H. BTW, I enjoy looking at chamber casts or chamber impressions, it is educational.

Here are the raw measurements. Contrary to what some sources claim, cerrosafe expansion is not 100% predictable. In my experience an old casting is probably 0.0015" - 0.0020" larger than the true diameter, so let's subtract 0.0017" from the cerrosafe diameters.

groove diameter, 1/2" beyond chamber neck: 0.3789", 0.3790", 0.3791" cerrosafe, 0.3773" true diameter.

bore diameter: 0.3690" cerrosafe every time, 0.3673" true diameter.

length between chamber neck-to-rifling: 0.220"

throat diameter: starts out 0.389" and tapers to groove diameter, 0.3873" true diameter

chamber neck diameter: 0.4110" cerrosafe, 0.4093" true diameter.

The customer proposes a 0.378" diameter bullet. I neither agree nor disagree, since only trial and error can determine the most accurate cast bullet diameter.

It is typical for the 375 H&H to have a very sloppy throat. Since It is not practical to size the bullet to fit the 0.387" throat, the bullet must take an unsupported flying leap. Not the end of the world, but don't expect to set a new benchrest record, either.

Pic later.

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mtngun
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Posts: 1632
Joined: Fri Feb 01, 2008 5:45 pm
Location: Where the Salmon joins the Snake

Re: 375 H&H chamber cast

Postby mtngun » Sat Mar 06, 2010 11:19 am

Image

Was told the neck of a round loaded with a .375" jacket bullet is 0.399" diameter. Allowing 0.003" clearance at the neck, bullet diameters up to 0.382" should chamber reliably.


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