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Shoulder bump problem? Not far enough?

 
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  #50  
Old 10-21-2013, 11:11 PM
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Re: Shoulder bump problem? Not far enough?

That gage looks dang familiar. Think I have one too........ Bart, tell them how you check the shoulder in relationship to the chamber using the shoulder datum and the gage or machinist blue...

Remind me never to get a caliber with a belted case......
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  #51  
Old 10-22-2013, 07:56 AM
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Re: Shoulder bump problem? Not far enough?

Quote:
Originally Posted by BrentM View Post
Pardon me again guys. Trying to understand this thread and Learn. I measures a 6.4x284 case using a OAL comparator Guage for a .30 cal. The new lapau brass measures 1.884 and my 6th fired case measured 1.914. Difference is .03.

How do you know how far to push the fired case or this case junk?
I and most folks think "OAL" in reloading and ammo stuff means the Over All Length of the cartridge; includes both the case and loaded bullet; it's the case head to bullet tip. Case length is the dimension from the case head to the case mouth. I think what your comparator gauge measures is the distance from the case head to a reference point on the case shoulder, and that's a good thing to measure when setting a die in a press to full length size cases. This dimension's often called case headspace.

That .030" difference in case headspace your gauge is measuring is quite a bit excessive, in my opinion, even on a case fired 6 times. If there's that much spread between new cases and fired ones in your chamber, I think either the new brass is a bit short in headspace or the rifle barrel chamber is way too long. I would expect no more than about .005" or so difference. Which leads me to think your gauge is not repeatable in its contact with the cases for both new and fired ones.

I think the 6.5x.284 had the same headspace specs as the .284 Win. Case specs are 1.814" -.007", chamber headspace is 1.810" + .010". The most spread from a minimum case in a maximum chamber would be .013". That a lot less than the .030" you mention. My concern is where you're measuring on the case. I think the gauge contact point's at the neck-shoulder junction on the case and that dimension on new cases is about right. Your fired cases shouldn't be more than about 1.890". That 30 caliber comparator gauge may not be best for the 6.5x.284 case as it may not be contacting the same diameter point on both new and fired cases. I suggest you get a nylon bushing at a hardware store with a 3/8ths inch inside diameter and 1/2 inch long. Use it to measure your cases headspace with the caliper as it's contact point will be about halfway up the shoulder at a .375" diameter reference. The numbers will be different but its the difference between them that's important.

Normal setback of fired case shoulders is about .002" to .003" for general use. Some competitors prefer no more than .0005" to a max of .0010".
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  #52  
Old 10-22-2013, 08:56 AM
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Re: Shoulder bump problem? Not far enough?

Sounds good. I have this Hornady OAL kit for mesauring the seating depths via the ogive and thought it might work OK. I measured about 15 cases from this reference point and they went from 1.914 to 1.917 The 917 cases were hard to chamber and the 914 cases had resistance but not too bad. After sizing the cases measured 1.906 to 1.908. The 908 cases were harder to cycle and the 906 cases were relatively easy. From what I could tell the 908s grew as the case was squeezed, these cases were the ones that suffered the most pressure I believe.

I might use this set up but drill one of the guages to the 3/8ths dimension. I like how this set up clamps on to the calipers securely and is easy to get repeatable results since it doesn't move around.
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  #53  
Old 10-22-2013, 09:04 AM
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Re: Shoulder bump problem? Not far enough?

I looked at this site Cartridge Diagrams
and see the case shoulder and neck joint measurement is 1.9059.

This is very close to my measurements. .294 to .295 is fired case neck diameter and .292 is sized. So the .308 guage has .016 slop at the neck junction.

Last edited by BrentM; 10-22-2013 at 10:59 AM.
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  #54  
Old 10-22-2013, 10:04 AM
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Re: Shoulder bump problem? Not far enough?

SF, I prefer belted cases. They have many fine attributes.
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  #55  
Old 10-22-2013, 11:38 AM
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Re: Shoulder bump problem? Not far enough?

Brent, if your case measurements as you do them grows a few thousandths after full length sizing them, I think the shoulder's being move forward as the case body gets sized down in diameter. This is normal when the die's not set low enough in the presss and its shoulder's not touching the case shoulder at all.

Loosen the die's lock ring, turn the die down such that its circumference moves 3/10ths inch relative to the lock ring. That should lower the die about .003" and make your measurements that much shorter.

Here's drawings of the .284 Win case and chamber showing how they're typically measured for headspace. These dimensions are not shown on the case diagrams you referenced. The ones measuring .420" diameter are the reference ones.

http://www.saami.org/PubResources/CC...Winchester.pdf

I think most 'smiths chambering for the 6.5x.284 use .284 Win headspace gauges.
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  #56  
Old 10-22-2013, 12:23 PM
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Re: Shoulder bump problem? Not far enough?

I hear ya. I moved the die down to the point the press was just barely able to cam over. I don't think I can get it any tighter than that. The cases shoulder moved from 1.917 to 1.908. If I loosened the die the measurement would grow accordingly from 1.908 to 1.910 etc until no bump was achieved. Perhaps a bit more playing is in order. I will fire a new case and start from there to see what the scoop is.

6,5x284 Norma - Norma
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