Howdy,

This weekend I spent an enjoyable afternoon sizing down .30'06 brass into .257 Roberts. My neck thickness increased only an average of .003" per side, .006" overall. As this is the first time I've done this, my question is simple.

Is this amount of neck thickness increase (.006") about normal for such a proceedure???

Thanks

Coach

It's totally dependant on the thickness of the body where the neck ends up. When it's the same length and the neck is sized down there is very little increase in the wall thickness. In taking '06 down to say 22-250 where the neck ends up half way up the body, the increase can be as much as .020", depending on the wall thickness. I did that one to reduce neck clearance to .002" after turning, believing that would improve accuracy. No difference in accuracy but it sure was a lot of work.

Coach, the problem comes if the neck thickness will not allow enough spring outward to release the bullet within specs. The neck must spread to allow the bullet to exit the neck else high pressure & other unpleasantries result. I had problems with GI brass necked down to 7mm - same length as 257 - because the mid-case wall was thicker, especially after forming the new neck. If you form brass, measure a loaded round with your caliper/micrometer and compare it with a factory - but it depends on your chamber whether it is o.k. If the formed round is thicker by .006, I would be very cautious. If your neck chamber is generously sized it may not be a problem but if it's on the tight side (good for accuracy/brass life etc), you may be setting yourself up for pressure problems. Approach these things like you're laying charges on a bridge, and you're in the middle...
"The Voice of Experience and Incredibly Lucky Survivor of Untold Ignorant Moves"
Maj Dad

Howdy,

Thanks Maj Dad. My chamber will allow for quite a bit larger necks than even these!!! I think that this might tend to be much ado about nothing. It is a lot of work, but I hadn't anything better to do; but, I am not sure the ammo will be any better than normal. With good ammo, this particular rifle will keep all its shots inside a half inch at 100 yards.... provided I do my part and its not windy!!! With better ammo, I was just wondering what it would do. Any other comments???

Coach

As you've found, most rifles have overly generous throat dimensions, so you are just making a better-fitting case by using the '06 brass. I used to make some .257 from '06 many years ago. You probably need to anneal after reforming to prevent early case neck splitting. Be careful with the annealing -- heating the case to "cherry" red is too much. You may also find some neck wall thickness variances which can be taken out with a neck turning tool, if necessary.

There's an additional point to consider: Sizing brass down considerably may also produce the "dreaded doughnut" after the first firing. See if your .257 bullets will enter these reformed cases after you've fired them. If they resist or just plain won't fit, then you'll have to ream the [inside of] case necks.

Howdy,

And thanks for the replys.

Neither neck turning nor inside reaming will be a problem with these cases. I've done both operations many times. My intent was to produce better fitting brass for the chamber.

I am intrigued by the gentleman mentioning annealing. I will investigate further and inform you of results.

Oh, by the way. Five shots at 100 yards with 7 mph fairly steady cross wind.... group size .56"

I'm fairly pleased, although this rifle has done better. Too much wind to be super.

Thanks again,

Coach

I have just started reforming .300 WM brass for my 7RM and found that annealing the neck/shoulder of the .300WM makes it a lot easier to reform the cases, and reduces the amount of crumpled cases to zero. Without annealing them first the reformed cases are very hard. By the way, I use virgin brass for reforming.

Tron