How much can you safely trim down a 308 case ?

M

Metal god

New member
I have some R.P. cases that have some neck/mouth deformations . Not sure what it is but If I had to guess I'd say it's from a crimp or something . The issue in that I'm unable to size it out . The sizing die and expander button does not remove the deformation . I trimmed it out of a few but that will leave the cases at a case length of 1.990 or so . How short can I really go ?

My question is would these still be safe to use ? My thinking is yes because that .015 less of neck material is not going to reduce the bullet hold all that much . That is of course assuming I don't size them to have minimal neck tension . They will not be used for any meaningful loads . Likely just sized and saved for the zombie something or other :rolleyes: . I don't want to cut them down and save them if they're ultimately unusable ? I'll add that there is a possibility they may be loaded for a semi auto some day .
 
How close are they to the trim to length? I don't have access to my manuals at the moment or I'd look it up. If it's within a few thou I'd call it good. Shoot and reload them a few times and they'll grow
 
I trim all mine to 2.000. I've ran into some factory cases coming in at 1.990". If it was me and I was looking for top notch accuracy, I'd trim all to 1.990", then 2.000" thereafter


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The M14/M1A service rifle match shooters had a rule of thumb not to reload a case more than four times. That platform isn't easy on brass, and they considered there was too much chance of a head separation not only jamming your gun, but possibly delivering a sharp object into the cheek of the shooter on the next firing point. A number of them would trim down to 1.975"-1.985" on the premise that was enough that they'd never have to trim it again before tossing it. I don't know of any issues that result from doing that. But then, service rifles aren't asked to produce benchrest accuracy, either.
 
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Thanks guys , i'll go ahead and trim them back go 1.990"

EDIT : To confirm SAMMI minimum is 1.995 correct ? There blue print shows 2.015 - .020 . I don't think I'll have issues going .005 more but what are the issues that could come up with a case that short . I'm asking because this really came to mind when I read the 270 and 30-30 trim to lengths . Those two and I'm sure many others still have A LOT of neck left . I'd had always figured you could trim those types of cases way back with out issue . How ever the 308 has a much shorter neck and thought it would be best to ask first .
 
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Metal god said:
Thanks guys , i'll go ahead and trim them back go 1.990"



EDIT : To confirm SAMMI minimum is 1.995 correct ? There blue print shows 2.015 - .020 . I don't think I'll have issues going .005 more but what are the issues that could come up with a case that short . I'm asking because this really came to mind when I read the 270 and 30-30 trim to lengths . Those two and I'm sure many others still have A LOT of neck left . I'd had always figured you could trim those types of cases way back with out issue . How ever the 308 has a much shorter neck and thought it would be best to ask first .
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You're talking less than the height of two human hairs stacked on each other to put it in perspective.


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The 308 Winchester Cartridge Dimensions reflect a maximum case length of 2.015" -0.020" giving a minimum of 1.995". As mentioned it really won't matter if you go a little under the minimum, even 0.005" getting it down to 1.990".

If you trim back to the SAAMI minimum once you fire the cases they should conform to the chamber you fire them in and be more easily re loadable but have a slightly shorter life. Anyway, the link gets you to the SAAMI specifications for the cartridge and chamber.

<EDIT> Fixed my math. :) </EDIT><EDIT> Changed Maximum to Minimum</EDIT>

Ron
 
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Ron,

you missed a couple of "9's" there, right after the decimal point.


MG,

SAAMI .308 Win standard calls for case length of 2.015-0.020", and the NATO 7.62 standardization spec (M80) calls for 2.015-0.015". SAAMI headspace standard is 1.634" -0.007", while NATO uses 1.634-0.006". SAAMI COL standard is 2.810"-0.032", while NATO is 2.800"-030". But those specs are premised on considerations not affecting individual handloaders. You always have to keep in mind these standards are for large scale manufacturing of ammunition that may be handled roughly and that has to operate adequately in all guns stamped with that chambering, regardless of type. It is not for ammo hand-tuned and carefully worked up and tested in the individual gun that will fire it. Because those specs are known to be universally adequate, they make a very good starting point for the handloader, but if you find your equipment is happy with something else, the departure is reasonable. Probably the most common such departure is neck-sizing-only. It works in your gun, but maybe in no other. Certainly a manufacturer isn't going to make cases that size. They'll be smaller to assure feeding in all guns.
 
For reference the .300 Win mag's Trim length is 2.610 -.020. When I was new to reloading, I once bought some brand new Remington (RP) brass to make some elk hunting loads. I over trimmed them down to about 2.580 when my trimmer setting moved and settled because I didn't tighten the fine adjustment enough. I caught the mistake about 20 rounds in and re-set the trimmer, but I went ahead and loaded the 20 rounds but kept them separate from the other 80 rounds that were trimmed to the recommended SAMMI.
I found that the point of impact on the "over-trimmed" brass was un-noticeably different at 200 yards. The average group for this load was around 1/2 MOA, not only did the overtrimmed brass maintain this spread, but the POI remained at least close enough that for hunting purposes they could be mixed in with the other lot.

As has been said, for the bench/long range competition shooter the difference in POI may be far enough apart that the brass isn't useful as match brass. But for hunting "minute of elk" or for destroying pumpkins/watermelons at 200 yards you likely wont see much difference.

Also, like others have said, after a few firings those short necked cases will catch up to the other cases.
 
The 308 Winchester Cartridge Dimensions reflect a minimum case length of 2.015" ...
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I'm sorry, but this is incorrect. 2.015" (+/-) is the MAXIMUM case length, not minimum.

Neck length only really matters when it is too long. Too short is usually not an issue, until its too short to securely grip the bullet. Generally a 1/2 caliber neck is considered the minimum to provide proper neck tension. For a .30 cal bullet that would be a neck minimum of 0.15" (contact with the bullet). More than that is even better. Some people think at least a full caliber's worth of neck is important and a half caliber isn't enough.

The .308 doesn't headspace on the case mouth or the neck, so a little shorter NECK than usual doesn't matter. Might make a difference in a benchrest score, but I've had lots of rounds in different calibers (not headspacing on the case mouth) where cases got trimmed a little too much, and the rifle never noticed.

Cases a few thousandths too short in the neck make an important difference in your crimping adjustment, never found them make any difference in FIRING. (bottle necked cases, or straight rimmed)

I once had an OOPS that trimmed nearly a full case of .223 noticeably "too short" in the neck (though still plenty long enough for proper bullet hold). Loaded them anyway (after proper die adjustment), put them in the pinking stash. All shot equal to regular length cases, in all aspects, in two different rifles.

Don't sweat it.
 
…And I expect crimping has a lot to do with the specs being as narrow as they are, to make sure the case mouth overlaps a crimp cannelure when the bullet is seated to proper seating depth.

I've explained this before, but I'll go through it again: Standard engineering practice is to use bilateral tolerances (± tolerances) when error in either direction has equal same consequence. But when one direction makes for sloppy fit while the other stops the machine from working at all, then the latter is called the critical dimension and the dimension is given as that critical limit number with a unilateral tolerance away from it in the direction of sloppy fit, whether that direction happens to be positive or negative. For ammunition specs, like SAAMI or NATO STANAG drawings, a loose cartridge will still fit a chamber and usually fire, but one that's too big won't chamber at all, so the biggest numbers are the critical limits (except for an an inside radius, where small fits better than large) and are maximums and those are what are given with a minus-only tolerance in the direction of sloppy fit. For the chamber it is the other way around. Too big still accommodates a cartridge, but too small won't, so too small is the critical limit and they give you the minimum (critical) dimension with a unilateral plus-only tolerance.

The only thing the user has to watch out for is that with a ± tolerance, the value given is the middle value that you want to aim to achieve. With a unilateral tolerance, the middle is half the tolerance away from the critical value.

Incidentally, while that middle value is used for trim length, it isn't always ideal. You'll find cases are made much closer to the minimum value, as far from the maximum value as the manufacturer can go without being too small. This is because that will be guaranteed to fit the most guns. It is also because the maximum case length from head to shoulder datum, is larger than minimum headspace. This is possible because the chamber is enough wider than the case than a bolt can compress and widen it and still force it into the chamber. But most people want smoother operation than that. In other words, that case maximum is truly the critical, won't-even-operate-with-force value, and not a smooth operating value. So you have to look at these things closely to see what they are telling you.
 
Jeez ron , is there anything you did write that was correct lol
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Yeah, about the only thing I got correct was my link. Anyone who followed the link then could easily figure out my actual post was one huge error. Really, just about everything was screwed up from math to maximum and minimum. Took some effort to screw it up that bad. :)

Ron
 
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