Subject: Re: Big guns in storage?
From: norton@ASYNC01.ACM.Org (Scott Norton) 
Date: Dec 22 1995
Newsgroups: sci.military.naval

In article <1995Dec14.233303.1@bsuvc.bsu.edu> 00jegroves@bsuvc.bsu.edu writes:

> The official designation of an Iowa's guns is 16"/50 cal Mk 7 Mod 0.
> I never heard of a turret having a Mark number, but it wouldn't surprize
> me if it did.  There was a lubricant for the guns, which was called
> "Swedish Additive", which was added to the powder.  
> 
> Changing a liner also meant removing the gun from the turret.  The guns
> were made by heating tubes and allowing them to cool onto the inner layers.
> I think there were actually eleven components to each barrel, but I'm
> going off of memory here.  To change a liner, the barrel would have to be
> heated to allow it to expand from around the liner, and a new liner
> inserted.  The New Jersey had a gun replaced due to barrel wear in 1983
> or '84.  Only time I know for sure a gun was replaced after the last
> reactivations.  I don't know if the barrel was re-lined, or if they just
> stored it.

The need to replace guns or liners in the battleships was not as much
trouble in more modern times as it was in the era when the gun was
designed.  Two things helped the barrels last much longer:

- The afore-mentioned Swedish Additive, which entered service after WW II

- The shift in planned use from a surface battle, where the ship fired
heavy armor-piercing rounds at the highest possible charge, to shore
bombardment, which used the lighter HC projectiles and smaller
charges. 

I don't recall the exact numbers, but a HC round was only 75% or so of
an AP round (using the approach of Full Service Equivilent Rounds as a
way of comparing wear).  But the real improvement was the Swedish
Additive.  The combination of the two was about a factor of ten in
barrel life extension.

Someone else asked what autofrettage was.  It is a technique of
locking the liner into the barrel by driving a mandrel through the
barrel.  The stress increases the outside diameter of the liner,
placing it in compression inside the barrel.

-- 
Scott Norton
Norton@ACM.org
Defense Technology, Inc.
2361 Jefferson Davis Hwy, Suite 500
Arlington VA  22202-3876
(703) 415-0200, fax: (703) 415-0206


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Subject: Re: autofrettage, was Big guns in storage?
From: norton@ASYNC01.ACM.Org (Scott Norton) 
Date: Jan 22 1996
Newsgroups: sci.military.naval

I wish I could consult a written source, but my knowledge of the
autofrettage process comes more from discussions with NSWC Dahlgren's
gun barrel experts than from a document.  As I recall, the pressure
certainly comes from hydraulics, but I'm almost certain there's a
mandrel involved.  It is possible to have either fully autofrettaged
or partially autofrettaged barrels; without a mandrel, would you just
put a plug half way down the bore to make a partially-auto-f barrel?

Also, key to the process is expanding the liner radially, not making
it expand linearly.  With a mandrel, the force is applied is enough to
strain the liner radially, but the mass of metal ahead and behind
prevents lateral movement.

Maybe I confused the issue by calling the device a mandrel.  Its not a
rod as long as the barrel; its a short plug.

The auto-f process is done after the heating-shrinking of the outer
layers over the liner.  It provides an even greater amount of stored
compression. 

-- 
Scott Norton
Norton@ACM.org
Defense Technology, Inc.
2361 Jefferson Davis Hwy, Suite 500
Arlington VA  22202-3876
(703) 415-0200, fax: (703) 415-0206