Case length question

[Vern94]

I'm in the process of reloading some 7mm-08 rounds (first time reloading) and had a question regarding case length. According to the Speer Manual the Max case length is 2.035 and trim length is 2.025. How critical is it to be right at the trim lenght of 2.025? What would happen if I used a case that was 2.015 or 2.026? So far I have trimmed my cases as instructed except for one that I over trimmed and don't plan on using.

 

[Jasper1573]

If you are a bit below the recommended length, say 2.020, there is no issue. I wouldn't use above the recommended length...might cause chambering issues.

 

[Robert101]

The trim length is really a guide to successful chambering. It really is chamber specific as manufacturers will have varing degrees of these dimensions. It is a very good rule of thumb to start with. My 308 chamber in semi-automatic is forgiving in case length therefore I trim when the maximum is approached to maximize reliability. You can test for propert case length by inserting various length cases into your rifle and test for function. The ejector might cause you some problems depending on tension.

 

[dmazur]

There is also the concern of "crimping" the case mouth in the rifling if the case is too long, which can cause dangerous overpressure even if the load data is otherwise correct.

With bottleneck cartridges, increases in the head to shoulder dimension after several firings is quite common, especially if neck sizing is used. This can cause chambering difficulties unrelated to overall case length.

One relatively easy solution to the problem of checking case lengths is to use a Wilson case gauge. The gauge can be used on one end to check the distance to shoulder datum to make sure it is in SAAMI spec, and the other end to check trim length.

So, there are two length dimensions involved in chambering safely and reliably - one is head to shoulder datum (sometimes called "cartridge headspace") and the other is shoulder datum to case mouth.

 

[jwrowland77]

Below isn't any concern, but as stated above longer could cause chambering issues. The the big thing is consistency in trim length if you want constant ammo.

 

[45lcshooter]

"Below isn't any concern, but as stated above longer could cause chambering issues. The the big thing is consistency in trim length if you want constant ammo. "

jwrowland77- i couldn't have said it better myself. haha. +1 for ^^^^^^

 

[ranger335v]

"How critical is it to be right at the trim lenght of 2.025?"

It isn't. Book "trim to" length is commonly 10 thou less than max, that's all there is to it.

 

[Vern94]

I've got nine cases trimmed to 2.025-2.026 inches, primed and ready to charge. Hopefully in the next day or two I'll charge them (IMR 4350) and seat Speer 145gr BTSP. The proof will be at the range. I appreciate the comments, and one of the things that sticks out for quality reloading is consistency. This is my first time using my reloading equipment and I can see how this can be addicting and lead to more shooting...which is a good thing.

 

[gamestalker]

Other than consistency of reload performance, exceeding the maximum case length is a serious concern regarding what is often referred to as mouth pinching, which is fact can result in an explosive out come. Unfortunately many reloaders are unaware of this well published and documented fact which more often than not results in premature throat erosion.

GS

"When seconds count, the police are only minutes away"

 

[GLOOB]

I know some people (including me) purposely trim up to 0.02" below maximum, so they don't have to trim as often. I don't do that in this caliber, though, because the neck is so short to begin with. I'm sure you'll also find the occasional factory case that's way shorter than normal.

I shoot reformed 243 and 308 cases in my 7mm-08. The necked down 308 cases usually measure as short as 2.014". No problem. The shiny new O.F. 243 cases that I find in lots of 18-20 have been measuring in at around 2.020-2.025". I love hunters that don't reload.

 

[FiveInADime]

I shoot reformed 243 and 308 cases in my 7mm-08. The necked down 308 cases usually measure as short as 2.014". No problem. The shiny new O.F. 243 cases that I find in lots of 18-20 have been measuring in at around 2.020-2.025". I love hunters that don't reload.

Do you have to turn necks or worry about shoulder brass flowing into the neck when you resize from .243 or .308 to 7mm-08? Once fired .308 brass is very easy to come by, as you know, so resizing it to 7mm-08 would be a boon for me since I don't have a .308 to mix up the brass with. 7mm-08 brass is extremely difficult to find new right now.

 

[GLOOB]

Do you have to turn necks or worry about shoulder brass flowing into the neck when you resize from .243 or .308 to 7mm-08?

I've converted primarily two kinds of 308. FC and some military kind with headstamp I can't remember.

The FC comes out with an OD neck diameter about 5-6 mics larger than my Winchester 7mm-08 brass. They have been working fine in my particular rifle, with both jacketed and even oversized cast bullets. There's no resistance on my bolt or pressures signs, yet, anyway.

The other military headstamp comes out only 2-3 mics larger. And the one BHA MATCH 308 I reformed measured only 1-2 mics larger.

So do I have to neck turn? Not yet. I think it was Clark that recently declared you can neck down to 7mm without neck turning as long as your chamber is in spec. You can neck down to .260 90% of the time. And to neck down a 308 to 243 would always require turning.

I have not checked for donuts in my 243 cases. I have only tried a handful with jacketed bullets, and only after the first sizing, so I don't know if they'll appear later. I use my 243 cases for cast bullets, which I seat above the bottom of the neck, anyway. I assume a donut wouldn't affect pressure unless you seat past the shoulder. And it would logically only form while you chamber the case (a FLR expander ball would push the extra brass to the OD of the neck until you cram it into the chamber; even if you neck size, the bullet would bulge the brass back out until you crammed it into the chamber), so I would think you should be able to feel it as significant stiffness on your bolt by the time it was dangerous. So I don't really worry about donuts, but that probably doesn't answer your question.

FWIW, I find reforming 308 cases is a little easier than 243. (I do the 243 on the press, too; no fireforming). All I'm using is Frankford Arsenal spray lube, like normal, but I always apply some inside neck lube for both up and down sizing. (It's getting the expander ball back out of the thicker 308 cases that's the only real aggravation.)

 

[AABEN]

I'm in the process of reloading some 7mm-08 rounds (first time reloading) and had a question regarding case length. According to the Speer Manual the Max case length is 2.035 and trim length is 2.025. How critical is it to be right at the trim lenght of 2.025? What would happen if I used a case that was 2.015 or 2.026? So far I have trimmed my cases as instructed except for one that I over trimmed and don't plan on using.

I like all brass to be the same length! more accurate.