"Setting the shoulder back too far" - How???


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Navy_Guns
July 27, 2007, 12:49 PM
I have read a couple times now about screwing up bottleneck cases on resizing by "setting the shoulder back too far". How can you do this? I thought the proper way to set up a sizing die for a full-length resize was to put the shell holder in the ram, raise the ram fully, and thread the sizing die down until it makes firm contact with the shell holder.

How can a standard sizing die set the shoulder back too far?

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Walkalong
July 27, 2007, 01:57 PM
Mechanical tolerances. Everything is machined to a standard plus or minus a reasonable amount, and then some, sometimes. Chamber cut a bit long, die cut a bit short, etc. You get the idea.

ReloaderFred
July 27, 2007, 02:23 PM
Walkalong is correct. When tools are manufactured, they are made within certain parameters, i.e.: maximum and minimum acceptable measurement. When two manufactured parts are put together, you get what is referred to as "tolerance stack", which simply means the sum of the variation between the two parts.

If your shellholder is made to maximum thickness, and your sizing die is also made to maximum length, that will give you a longer sizing length for the case when the two are set up to mate together, and the shoulder of a bottleneck case may not reach the shoulder of the sizing die.

Conversely, if each part is made to the minimum specifications, then you'll get a shorter sizing length and the shoulder of the same case can be set back too far and cause excessive case stretching when fired and lead to case head separation. All the parts are "within spec", but at opposite ends of the parameters.

Add into this equation chambers that are at the minimum SAAMI spec, or maximum spec, and you can end up with quite a distance, all within spec.

This is why it's important to set up your sizing die for the chamber the bottleneck case is going to be fired in.

Hope this helps.

Fred

Walkalong
July 27, 2007, 02:40 PM
Fred said that so well. Thanks for helping Fred. :)

USSR
July 27, 2007, 09:53 PM
I thought the proper way to set up a sizing die for a full-length resize was to put the shell holder in the ram, raise the ram fully, and thread the sizing die down until it makes firm contact with the shell holder.

The proper way to set up a sizing die is to use a RCBS Precision Mic or similar tool to check how far you are bumping the shoulder back.

Don

RavenVT100
July 27, 2007, 11:21 PM
I can see where you might be getting confused here.

Even though it will stop, and cam over, when it contacts the die, it will continue to knock the shoulder back if you screw the die down further.

That's why it's a good idea to get a cartridge headspace gauge and measure how much you're knocking back the shoulder vs. how much the cartridge expands during firing. That way, you can knock it back one or two thousandths of an inch and not have the brass grow that much.

ReloaderFred
July 28, 2007, 12:46 AM
The RCBS Precision Mic is what I use to set up .223, .308, .30-06 and 8X57 dies with. All the others are done by trial and error with fired cases and sizing them in steps until I get the shoulder setback I'm looking for, which is usually about .002" for most calibers.

I do have headspace gauges for several calibers, but they also happen to be the same calibers I have Precision Mic dies for......

Hope this helps.

Fred

OKIE2
August 14, 2007, 04:29 PM
here is how I check my shoulder set back to match my chamber.
I take a 357 case and insert the neck of your fired round it will hit on shoulder of case measure over all length from primer to primer with calibers
then resize one of your fired rounds in your die and measure to see if they are the same length if not ajust die.
Also if you want a free way to tell where to seat your bullets to touch the lands write me
ROBERTL@CIMTEL.NET

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