Thread: . 284 Winchester

Originally Posted by Puffin

Further to my earlier post, I've since cross-checked several dimensions on the Manson and JGS regular SAAMI reamer drawings.
The neck diameter runs from 0.323" to 322". Necked up but unturned 6.5-.284 Lapua brass measured 0.3120 - 0.3126" loaded, so that is already 10 thou expansion on firing. If the brass is then turned and tidied up for a donut then 0.310 is about right. That is quite a lot of to-and-fro for each firing/resizing cycle. Online reports indicate that the Norma .284Win brass has thicker neck walls than either the Winchester or necked-up Lapua brass at 0.316" give or take. This might be reason enough to use Norma brass in a standard chamber, but also a potential safety issue if the chamber is cut with a non-standard neck.

The SAAMI profile does NOT include parallel sided freebore. It tapers down from 0.290" ahead of the neck at 47' 33" (0.7925°) in one continuous freebore/leade. At that angle is narrows to the nominal bullet diameter 0.284" at 0.217" ahead of the commencement of this profile, so this figure can be substituted roughly for freebore. It looks like many here are getting good accuracy from their .284s, but based on this I don't imagine many of those bullets that aren't 180gr are out near the lands.

Yes that all sounds about right.

My M595 was rechambered a long time ago before my ownership.

It has a .322 neck, I'm running new WW brass in that which measures .313 on a loaded round. So yeah it will be working the necks alot, very important to annual.

When I first got the rifle it came with some fired WW brass I noticed some of the necks were split or split after I fired them once or twice.

When I got my t3 rechambered I got gunworks to use their other reamer with a .317 neck and a different lead angle.

In this rifle I have used necked up 6.5-284 Lapua brass which I neck turn to remove the donut that forms after expanding. A loaded round of this measures .311

I always remember reading that the 284 win doesn't like too tighter neck clearances.

In loading for both rifles I've always found that I cannot run the powder charges that I believe I should be able to in the barrel with the .317 neck.

I don't know if it's due to the lower neck clearance or the different lead angle.

Whereas the old M595 with the big sloppy neck has always been able to run the charges that Quickload tells me I can without seeing pressure signs too soon on a ladder.