From: schuette@roadkill.nrl.navy.mil (Larry Schuette)
Newsgroups: rec.guns
Subject: summary - chamber casting
Date: 12 Nov 92 14:57:45 GMT

Hi,
	Thanks to all who responded to my question about chamber 
casting.  I initially asked this question due to the nature
of the round.  I'm firing a necked down .348 Winchester round.
This is a .30 - .348 round with an improved case type.  Sample
bullet / powder /speeds are 130 grain bullet, 66 grains of 4831
moves out at (chrono-noed) 4000fps.  I had an excessive chamber
pressure event (what fun!) where a case would not extract.  I 
wanted to know for sure what the maximum case length was, so that
I could trim accordingly.  

What follows is just some of the responses.  I plan to follow the
plan outlined below by bart at h.p. to measure the maximum case length.

Many thanks to all.

-------------
#From rcower@deadend.intel.com  Tue Nov 10 18:26:02 1992

it's pretty easy to do. the tricky part (as i remember it) was that stuff
cools strange. i think it's at the right size when not fully cool (15 mins).
anyway...just follow the instructions. 
if the brownell stuff is too much, maybe some carbon (lipstick works too)
on the cases...and see where they touch. i think the casting is about the
best you're gonna do...
do the casting. then get one of those new bullet seating gizmos from
sinclair and you should know everything you want to know about the inside
of your chamber...

..rich
----------------
#From gus%onodrim@gatech.edu  Tue Nov 10 13:53:33 1992

word of warning - improved cases do not show some of the usual
pressure signs. i was WAY overpressure with my 257 imp and
didn't realize it.  mike case heads for pressure indication:
i try to stay under 0.002 expansion.  avoid CCI primers 
because they're so damned hard you won't get pressure
sign there (that's what fooled me on the 257).
your extraction won't get hard as quick nor will you show
pressure via bolt thrust like you do on tapered cases.

if you have trouble extracting an improved case you're into 
the clag for sure.  i went to winchester primers, but
remington are soft enough, too. feds tend to be hotter
------------------

From: K. Karcich <kkrh@troi.cc.rochester.edu>

Using Cerrocast or other similar alloys this is simple can't harm your gun.
Cerrocast shrinks initally so you can remove the cast. After about 1 hour
it expands to the measuring point and you use your calipers and mikes. After 
that it expands more and will give you oversize readings but you can recast
it again. The only thing I'd recommend is to remove your action from the stock.

I'm curious about your 30/348. Is it on a Siamese, Winchester 71 or single shot
action. I've been interested in wildcats based on the 348.

regds,

Ken Karcich

-------------------

#From bartb@hpfcmgw.fc.hp.com  Tue Nov 10 21:15:00 1992

If you need to see what the chamber's length is, that is head to the
end of the mouth of the chamber, try this:

  1.  Take a fired case, and resize it.

  2.  Trim the case neck back about 1/4-inch.

  3.  Do steps 1 with another case.

  4.  Cut about 1/8-inch of the second sized case's neck off.

  5.  Press a bullet into the 1/8-inch section of cut off case neck; enough
      so the bullet's base is sticking out of the neck section about 1/16-in.

  6.  Press the bullet, point first (backwards) into the mouth of the first cut
      off case.

  7.  Insert the case with ringed bullet into the chamber and close the
      bolt completely.  

      What this does is force the bullet into the case and the brass ring's
      front end should be pressed against the chamber mouth front end.  

  8.  Eject the reverse-bulleted case from the rifle; slowly.

  9.  Using a caliper, measure the distance from case head to the end of
      the cut off brass ring on the bullet.  This is what your rifle's
      chamber length is.

 10.  Subtract 0.20-in. from that length and the answer is about what you
      should trim your cases to.

I've done this with bolt guns with good success.  I suggest you repeat this
three times to be sure your process is repeatable; then your answer is good.

I've made chamber castings (years ago) using plastic steel like Devcon or
Duro.  Be sure to coat the inside of the chamber with a release agent; I
use Simonize car wax.  Then push an eraser into the bore about 1/4-in. in
front of the chamber to seal it off.  Mix the epoxy and carefully pour it
in slowly to be sure there's no air bubbles.  If you can't easily remove
the barrel first, use a funnel with a tube on it to get the epoxy only in
the chamber, then stop when the chamber is full.  But this was only for
measuring chamber neck diameter and length; not case length.

Remember that chamber casting will not tell you what length cases need to
be trimmed to.  Chamber casts do not provide dimensional information on the
back half-inch or so of the chamber; you can't make a chamber case with a
closed bolt, at least not without great difficulty.

Hope this helps.........

--------------------------------

#From UCSD.EDU!btree!hale  Wed Nov 11 15:38:02 1992
There was a good article about making chamber castings in American
Gunsmith a few issues ago.  You might want to find a copy of this
magazine and check it out.

Best regards,

Bob Hale                                      ...!ucsd!btree!hale
...!btree!hale@ucsd.edu                       ...!ucsd!btree!hale@uunet.uu.net



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Lawrence C. Schuette			  schuette@roadkill.nrl.navy.mil
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Naval Research Laboratory		  (202)767-5561 (fax) 	
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