250 Sav Don

[455]

I received about 200 rounds of new 250 Sav brass from a friend who was a great BR shooter for many years. He has passed now. When I measured the length of the brass they read on the package trimmed to 1.902" they were in fact trimmed to 1.892 .010" undersize. I believe he read his caliper wrong. Are these cartridges usable ? Sorry for the original post that read 6mm ppc should have been 250 sav.

[FrankenMauser]

They're fine.
Cartridge overall length matters. But neck length isn't much of an issue - especially with cartridges that typically do not get crimped.

[hounddawg]

it means you have 3 human hairs thickness worth of case neck is holding your bullet in place. In other words if you had not measured it you would never know.

[reynolds357]

Get a set of RCBS x dies and they are trimmed to the correct length for them. They are fine anyway.

[Unclenick]

455,

Welcome to the forum.

Your problem isn't with reading the caliper, but with reading the SAAMI spec. That spec calls for the case to be 1.912" maximum length with a tolerance of -0.020". So any case between 1.892" and 1.912" is acceptable for standard factory loading. Most manuals will give you a "trim-to" number halfway between those limits, figuring that gives you ±0.010" of error margin in your measuring or trimming. Manufacturers often aim at that midpoint for statistical reasons, allowing for the maximum number of standard deviations around the mean before going outside those two limits.

The reason SAAMI gives 1.912" -0.020" instead of 1.902 ±0.010", is they are following an engineering practice called critical dimensioning. This is where one end of the tolerance range is a more critical value than the other. The dimension given is at the critical, not-to-exceed end of the range and the tolerance is in the direction of the less critical end. This is called a unilateral tolerance. All SAAMI drawings follow this practice, though persons not familiar with engineering drawings often find this confusing.

For the 250 Savage, a case that is over 1.912" after resizing must be trimmed, as 1.912" is considered a critical upper limit to prevent the case mouth wedging against the bullet at the end of the chamber's neck area, thereby raising pressure. A case that is under 1.892", however, is not considered a critical problem as all it does is cost you a bit of grip on the bullet. Depending on how long your bullet is, that may or may not affect the cartridge's ability to stay straight during feeding, so it might affect your load accuracy in some instances. What it won't do is stop the gun from shooting or affect pressure in dangerous ways, so it is not considered critical.

Having your cases on the short end of the range means you will be able to load them more times before you need to trim again. You determine that need by measuring them AFTER they have been resized (resizing squeezes cases out longer), and trimming them when that number gets longer than 1.912".

[std7mag]

455,
It is as they have said. It won't affect COAL at all. Maybe eventually you may actually need to trim them again. Lol
Are you shooting 250 Savage? And if so, what type/make/model?

I re-barreled my Stevens 200 with a 24" E.R.Shaw barrel in 250 Savage.
Seeing as to it being a "modern bolt rifle" i've been shooting what some may call +P.
Nothing crazy, but really brings the old cartridge alive!

[RC20]

You just have to love Unclenick. I am a technician mechanic and I don't know what he just put out in the terms (I know about staying under)

I have taken to taking my cases down another -.010 (per a previous post) to avoid a few going over between annealing g(when they all get trimmed regardless)

[hounddawg]

Since it looks like the OP's question has been answered I 'll go into the weeds a bit and if I may I'll try to interpret a couple of terms into common speak

Critical dimensions on a drawing are subjective in nature and are dimensions which are most likely to come into contact with another part of the assembly. In this case, no pun intended, it would be the case neck intruding into the freebore area of the chamber. Having a case neck too long would affect the functioning of the assembly. A case neck that is too short within a reasonable amount would not interfere in the functioning of the assembly so the short end of the measurement would be considered non critical.

In a unilateral tolerance the dimension of the part is allowed to vary on one side only so it would have either a plus or a minus to it's dimension but not both, in a bi lateral tolerance you will see both plus and minus signs tolerance

I think I have that right, if not please correct me UncleNick

[455]

Thank you very much, one of the Fathers to success. I will read the Sammi specs, big load off my mind. Thanks again

[455]

Yes my Savage was bought years ago and stripped down and redone. Hart barrel, Mouser action, glass inlayed, Kevlar stock, 12 power Léopold scope. Shoots great thanks for asking.

[Unclenick]

455,

You'll be fine with it. A lot of M14/M1A match shooters used to trim their cases even shorter than SAAMI spec, down another -0.020". They were using mostly 168-grain Sierra MatchKings which seated deeply enough that the shorter neck still gripped them well. Since those guns tended to wear out FL resized military cases after about four reloads, these guys were simply figuring to trim just once in the life of the case, then scrap the brass after four reloadings, when the most noticeably grown cases would be nearing maximum length.


Hounddawg,

You are right except for the "subjective" part. A critical limit is one that objectively can prevent the device from being assembled or operated. You'll notice that a lot of SAAMI rifle cartridges have maximum shoulder datum locations that are longer than their minimum chambers are. That is because the minimum chamber is wider than a maximum cartridge case so that if you use the bolt to jam the case in, it will have room to be squeezed out fat enough to allow the gun to be put into battery and fired, albeit with extra difficulty. Make the case any longer, and you cannot count on being able to get the bolt closed on it, so you can't count on being able to fire it at all. That's why that length is "critical". Critical for function.

That same tight fit is too much for many self-loading guns to operate with reliably, so the manufacturers of new ammunition almost always make cases shorter than a minimum chamber. Just another example of how, just because something can be made to work, doesn't mean it is optimal.

[hounddawg]

@ UncleNick I was attempting to give a general definition of what critical and non critical dimensions are, not whether it is a subjective decision to classify the maximum neck length as a critical dimension and minimum neck length as non critical. But even at that someone had to designate the maximum length as a critical dimension

At some point in a design decisions have to be made to decide which dimensions are critical. Then the design team communicates to the manufacturer which dimensions are critical and which are non critical for tooling decisions. That is where the subjective part comes in. "Will this dimension interfere with the proper functioning? Yes or no" Obviously too long a neck length will prevent proper chambering whereas too short will just mean a little less hold on the bullet

[std7mag]

455,

I've been playing with RL17, RL16, PP2000, with 115gr Berger VLD Hunting.
Good results from all so far.