Die Squeezing Bases Too Much

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ozfclass

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I've had some very good advice from this forum in the past, so am hoping for the same with this little problem.

I bought a $200 FL sizing die for a 7mm Shehane, and believe it is squeezing the base about 0.001 too much, so am looking for a way of opening it out by about 0.0005 all round. I'm considering putting some lapping paste on a fired case and rotating that in the die, with the die in a lathe, and holding the brass with a shell-holder. I'm not a machinist, so there's probably a much better idea out there?

Thanks for any help.

Alan
 
ozfclass said:
I've had some very good advice from this forum in the past, so am hoping for the same with this little problem.

I bought a $200 FL sizing die for a 7mm Shehane, and believe it is squeezing the base about 0.001 too much, so am looking for a way of opening it out by about 0.0005 all round. I'm considering putting some lapping paste on a fired case and rotating that in the die, with the die in a lathe, and holding the brass with a shell-holder. I'm not a machinist, so there's probably a much better idea out there?

Thanks for any help.

Alan
Click to expand...
Spinning th die in a lathe is the best way to go. But I would use some wet-or-dry at about 600 grit wrapped around a split dowel, then finish with 800 grit, wet.

Using lapping paste does not allow the control that an abrasive on a dowel. Plus, cleaning out the lapping compound each time to check your progress is a pain. With the wet-or-dry, just patch the die clean while it is spinning.
 
Thanks Jerry, exactly the detailed instructions I was hoping for. Once again, experience matters.

Alan
 
To add to what Jerry said, the lapping compound would not leave the finish that you really want in a die. The wet dry on a dowell is a simple and affective way to remove the stock, and keep it slick....jackie
 
A 200$ die sounds like a custom die to me. Are you sure its sizing the case to much? I am sure you are or you wouldnt be asking, it just seems to me like a die that cost that much should be a perfect match. Whats the scoop on the die? Lee
 
The die is a Redding S-Type FL die for the 7mm Shehane which is sold (exclusively I believe) by Bill himself. Bill's intention is for the die to squeeze the case by 0.002 all the way from base to shoulder. Using this die, I have been getting loose primer pockets after a couple firings of 180gn VLDs at anything over about 2880 fps. If I use just the Wilson neck sizer, things are okay - however at these admittedly quite high pressures, I need to bump and squeeze the shoulder each firing, which the neck sizer won't do. I've had some advice from Jim Hardy, who virtually pioneered this chambering's recent popularity in the US, saying that 2950fps is obtainable with his custom dies without primer pocket problems. He advised that he's heard reports that the Redding-Shehane die squeezes the base too much. Now that's counter-intuitive I know, but strange things seem to happen in rifle chambers. How about this as a possible explanation : you squeeze the base so much that it doesn't grip the sides when fired, putting a huge force onto the boltface, which tends to spread the case head. If Alinwa is there, he would no doubt have an opinion on this.

Alan
 
I would have thought that if things work OK with the Wilson, then your issue is that you atr knocking the shoulder back too far with the FLS die causing more "headspace" than necessary. A consequence of that is likely to be in sequence:

  • Firing pin pushes the case fully into the chamber, then ignites the load
  • As pressures build, the primer backs out into contact with the bolt face & mushrooms somewhat
  • Further pressure causes the case to expand to fill the chamber fully, driving the case head back onto the primer
The outcome you're seeing could well be a consequence of that process.

Of course, that's not the only possibility, just another to consider.
 
John Kielly said:
I would have thought that if things work OK with the Wilson, then your issue is that you atr knocking the shoulder back too far with the FLS die causing more "headspace" than necessary.
Click to expand...
Good point John. I'll take a bit more care with the bumping i.e. only do exactly what's needed and see if it helps. I have a set of Redding competition shellholders which should help with that.]

Alan
 
The head space gauge from Sinclair will tell you how much you are bumping the shoulder. Most of us adjust our dies in or out in relation to the bottom/topping out of the shell holder to attain the right amount of bump for the shoulder.
Some use Shims others just adjust the die the hard way.
 
Either way, i really hope you get it all figured out. I hate having problems myself. On the other hand, learning from our problems keeps us from repeating them in the future. or in better words, they teach us what to look for or avoid in the future. Good luck man!! Lee
 
Alan, if the brass is squeezed down .002" it will not remain there when removed from the die because it springs back a bit. I believe .003" keeps a sizing die working without trouble. Perhaps .002" at the base is what they are after allowing for .001" springback. If your chamber is .001 too big at the base then you will be sizing too much if the die is perfect. Cutting a chamber .001" too large is easy to do if the reamer holder / technique is not perfect.

I just received my reamer print for my 284 Shehane carbide resizer and I am more than worried about it. Besides the neck diameter, the only difference I see on the print is less than .001" reduction at the base, from .5009" for the chamber reamer and .5000" for the die resizer. My shoulder diameter on both the chamber reamer and die resizer prints is .485". I was under the impression my resizer was going to be .002" smaller the length of the case and .003" for the neck. I think I will have trouble.
 
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