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#1906392 - 04/22/11 09:07 PM 243 wssm sizing question
steve154 Offline
Die Hard Member

Registered: 11/28/08
Posts: 601
Loc: Western NY
I am working on starting the 3rd loading on my 1st 100 cases. When setting up the unsized cases in my block to spray lube on them I have noticed that they will not go in to the holes all the way. They are swelled quite a bit. After sizing they fit the holes for the block perfectly. Not a very precise measurement, but it certainly shows the big difference in size. I have had no problems at all with malfunctions. They chamber fine. I am just wondering if it is normal for the body to be blown out so much. A fired case will not rechamber, but they exract every time.

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#1906527 - 04/23/11 12:36 AM Re: 243 wssm sizing question [Re: steve154]
hm1996 Offline
PM Junkie

Registered: 07/23/06
Posts: 16395
Loc: S. Texas
Here is an excellent explanation as to why your 243 WSSM cases are
Quote:
swelled quite a lot
by Mike Milli:

Quote:



Quote:
--------------------------------------------------------------------------------

Actually, dropping one of his cases into an RCBS case mic. will NOT give him the exact dimensions of his chamber. That case is going to be longer than his chamber, and that's why he was having the problems that he was.


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What am I missing, Mike? The case mic would give you the dimensions of the chamber on a bolt gun (minus, of course, the minor spring back of the case). Is it due to the bolt unlocking on the AR while there is still some pressure in the barrel? If so, that may answer one of the questions I asked you in a PM I sent you a few minutes ago. Hope the letter you referred to in your last post explains this.

My 243WSSM upper came in Friday PM and was on the range Sat. morning. Still have some load work to do, but looking real good w/only one ladder test done and the barrel quit fowling even before the five shot strings in your breakin procedure.

Regards,
hm


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



You are correct. If you fire a one of these WSSM's in a bolt-action, you could extract that case, drop it into the case mic. and get a real good idea of the length of your chamber. In fact, you could take that same case and put it back into the chamber and close the bolt on it. Not so with the cases fired out of an AR. The body of the case will stretch and it will no longer fit into the chamber it was fired from.

When you fire your AR, the bullet travels down the bore. When the bullet crosses the gas-port, high-pressure gas is fed back through the gas-tube to begin the process of unlocking the bolt. When the bolt unlocks, there is still some pressure in the chamber. The amount of remaining chamber-pressure and case-stretch is dictated by many things. Bullet weight, gas-port size and placement and powder burn-rate, and carrier weight, to mention a few.

Here's how I use the RCBS mic. to find my chamber length: First of all I measure some unfired cases to get a base-line. Then I measure a bunch of fired cases. I lube up some of the fired cases and set my die up so it doesn't quite touch the shell-holder. As I start to size the case, I drop it back into the case mic. to see what's happening. As the girth of the case is being sized, nothing happens to the length until JUST before the shoulder gets set back. You should see the length of the case get slightly longer JUST before you start setting the shoulder back and the measured length gets shorter. Now that the girth of the case has been returned to spec. the rest of the sizing process for that case will be much easier. When you measure that the shoulder has been set-back .001" from where it was, drop it into the open chamber and see if the bolt will close, extract and open easily. If it doesn't fit the chamber, then turn the sizing die down a little more (trying to set the shoulder back about .001" at a time) Repeat this process until you find the length that fits your chamber. NOW, pre-load your press by turning the sizing die down to the point where your press cams-over quite hard. Measure and compare the cases that are sized this way to the case that JUST fits your chamber. On a WSSM I like to have the case .0015" to .002" shorter than the chamber. If your die sets the shoulder back quite a bit further than that, and you are using standard shell-holders, you can get a set of competition shell-holders from Redding to "dial-in" the amount of shoulder set-back you want, and still get consistent sizing. Unfortunately, with shell-plates like the Dillon presses use, the Redding shell-holders won't work.

Hope this makes sense!
_________________________
Mike Milli,
Dedicated Technology
http://www.dtechsuperstore.com/mili%20Guns.htm


Entire thread located here:

http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=725273&page=1

http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=725273&page=2

Regards,
hm
_________________________
If what's ahead scares you and what's behind hurts you, look up; He never fails you.

If My people will humble themselves, pray, seek My face & turn from their wicked ways, I will hear from heaven & will forgive their sin & heal their land.




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#1906545 - 04/23/11 02:13 AM Re: 243 wssm sizing question [Re: hm1996]
steve154 Offline
Die Hard Member

Registered: 11/28/08
Posts: 601
Loc: Western NY
That about covers it! Thank you, sir.

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#1906635 - 04/23/11 10:37 AM Re: 243 wssm sizing question [Re: steve154]
EJ Reichenbach Offline
Die Hard Member III

Registered: 03/02/10
Posts: 2656
Loc: Wyoming
Never had this problem with my 223 wssm

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#1916056 - 05/10/11 08:38 AM Re: 243 wssm sizing question [Re: EJ Reichenbach]
dzlfarmboy Offline
Seasoned Member

Registered: 01/10/07
Posts: 408
Loc: Maryland
As covered already in an AR that case is getting ejected out so fast while there's still pressure in the chamber so it swells out bigger then the chamber it self.
_________________________
Beanland Custom .243
Beanland Custom .7mm
R-15 18" CS.223
10.5" SBR
CVA Accura .50
Stevens .22LR
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