RESIZING .308 BRASS TO 7MM-08 ?

[mobertok]

HI EVERYONE, I AM RELATIVELY NEW TO RELOADING. I JUST TRIED TO RESIZE SOME .308 BRASS TO 7MM-08 AND THEY COME OUT TOO SHORT AS MY BOOK SAYS 7MM-08 2.025"-2.035" AND THEY ALL ARE COMING OUT TO ABOUT 2.015 OR THERE ABOUTS. AM I SUPPOSE TO RELOAD THEM AND SHOOT THEM AND RESIZE AGAIN FOR PROPER LENGTH? OR AM I DOING SOMETHING ELSE WRONG?
THANK YOU ALL VERY MUCH, MARK.

 

[nastynatesfish]

It'll work fine. Shoot them, form them, then recheck your length. I made a bunch of 7-08 from lapis small primer brass. Ohh welcome!! TAKE YOUR CAPS LOCK OFF!!!! Lol

 

[mobertok]

Thank you.

 

[fguffey]

I JUST TRIED TO RESIZE SOME .308 BRASS TO 7MM-08 AND THEY COME OUT TOO SHORT

If I wanted to know the effect of necking down a case I would measure first and then again after.

Directions always start with "All you got to do is etc..". When I form cases to some wildcats the case shortens .035", others shorten as much as .045". Then there is fire forming, there is the illusion the case shortens when I fire form cases to wildcat chambers. When discussing case length most reloaders are thinking from the end of the case neck to the case head.

When forming cases start with a longer case, I use 280 Remington cases when forming cases for long 30/06 chambers, when determining the length of a 30/06 chamber from the shoulder to the bolt face I use 280 Remington cases or cases that have been fired in trashy old chambers.

F. Guffey

 

[Laurie]

The parent 308 has a slightly (0.020") shorter case than the 7-08 variant, hence a reformed 308 will always be on the short side initially.

More to the point, many makes of 308 brass have thicker necks than you find on the 7-08 and necking them down makes them a little thicker again (adds around 0.001" to Lapua, so 0.002" overall). In my custom 7mm-08, the chamber neck diameter is minimum SAAMI 0.316", so whilst factory Winchester brass is fine in it, the reformed Lapua 308 is tighter than I'll live with in an F-Class rifle at 0.314- 0.315" O/D for a loaded round's neck. So add another task - a light neck-turn.

 

[bobm]

Your looking at a magnified photo of my sectioned 7-08 Remington 700 chrome moly barrel. It stopped shooting good at 4655 rounds. Went from 2 inches @ 200 yds to six inches @ 200 in as few as 10 shots. More than half the brass used in this barrel started as .308 win. Note the lack of erosion at the chamber end. Just a light carbon coating band there. All the erosion starts at the leade. Your shorter brass will grow longer as it is fired with no harm to the chamber neck area.

 

[Brians356]

You didn't mention how long the 308 Win cases were before resizing them! So we cannot know just how the resize affected them.

SAAMI Max Case Length for 308 WIn is 2.015", but few cases in use are ever that long. Yours could have been considerably shorter, e.g. Trim To Length 2.005", or even Min Case Length 1.995". That's a .020" swing - not chopped liver.

If we knew how long they were to start, we would have a better chance of usefully analyzing your results.

 

[mobertok]

Before resizing they were about 2.005" and after they are 2.015"

 

[Brians356]

Before resizing they were about 2.005" and after they are 2.015"

Ok, so as expected, when sized down in the neck, the cases grew somewhat, to wit 0.010" longer. Mystery solved - they didn't shrink.

As it happens, it is still within SAAMI spec for 7mm-08 Rem - it's spot on Minimum Case length. So while it is not ideal, it's certainly not a cull situation, unless you are shooting the lightest/shortest bullets, and need more neck length to seat bullets near the lands.

So if you started with 308 Win cases which were at SAAMI Maximum Case Length (unlikely!), and formed them into 7mm-08, they would finish up right at 7mm-08 Trim To Length.

So while it's true "7mm-08 is just necked-down 308", that's really just how the original wildcat was made; the production cases are longer than that.

 

[mobertok]

Thank you, to all of you!

 

[fguffey]

Before resizing they were about 2.005" and after they are 2.015"

Ok, so as expected, when sized down in the neck, the cases grew somewhat, to wit 0.010" longer. Mystery solved - they didn't shrink.

There was never a mystery to solve, when the neck is necked down the neck gets longer. When the neck is necked up the neck gets shorter.

The mystery: reloaders claim the neck gets thicker and or thinner. When necking 30/06 to 35 Whelen my case necks shorten .035".

F. Guffey

 

[Brians356]

Before resizing they were about 2.005" and after they are 2.015"

Ok, so as expected, when sized down in the neck, the cases grew somewhat, to wit 0.010" longer. Mystery solved - they didn't shrink.

There was never a mystery to solve, when the neck is necked down the neck gets longer. When the neck is necked up the neck gets shorter.

The mystery: reloaders claim the neck gets thicker and or thinner. When necking 30/06 to 35 Whelen my case necks shorten .035".

F. Guffey

It was never a mystery to me, and I could have worded that better. I was referring to the OP implying was wrong:

>> I JUST TRIED TO RESIZE SOME .308 BRASS TO 7MM-08 AND THEY COME OUT TOO SHORT

He didn't say in so many words, but the implication was that the cases might have been shrinking unexpectedly. My mistake for putting words in his mouth as it were.

Ken Howell in his book lists two ways to form 7mm-08 from something else, and he always presents them in preferred order:


1. Fireform 243 Win in 7mm-08 chamber using inert filler.

(I note with interest that 243 Win, with SAAMI Max Case Length of 2.045", is .010" longer than 7mm-08 Rem.)


2. Form 308 Win in an RCBS "7mm-08 Rem from 308 Win" Form and Trim Die.

(Howell specified "Form and Trim Die" rather than a regular 7mm-08 FL die. There is unlikely to be any neck protruding to trim back, though.)