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Sizing down 308 brass causing tight neck issues.

6.5 GUY

Be careful what you wish for….
Full Member
Minuteman
Dec 19, 2013
285
93
Northern ID
I've lately had to necking down Lapua 308 Winchester brass to form 7mm-08 Rem. due to no 7mm-08 Winchester brass available, and now seem to have a tight neck situation due to the extra brass increasing the thickness of the neck.

The 7mm-08 Federal and Winchester brass I've used in the past of a loaded round tends to measure around .3110", but the neck sized down Lapua brass of a loaded round measures .3150"-.3155". Which according to SAAMI is right at the case neck dimensions of a case (.3150"), the chamber dimension is .3170" at the neck shoulder juncture and .3160" at the end of the chamber. Which in this case is rather tight for neck expansion to release the bullet upon firing. These loads have also not produced the same bug holes as the previous loads with the other brass leaving me to think I'll need to turn down the necks. I also think for a tactical comp gun that could give me a head ache in a match if a case were to get stuck in the chamber after a far number of rounds being fired, or am I incorrect in my thought process?

Which reminds me why I went with a .300 neck on a 6.5/300 WSM I had built years ago in the first place? Honestly at the time I was swamped with building my house and then to find the gun's chamber cut too long, and having to ship it back, then not doing anything with it until two years later I spaced out why I came up with that number in the first place? But I had read the WSM's don't seem to shoot all that well with tight neck chambers.

But now I realize why? Necking down a 300 WSM to 6.5 mm and not wanting to turn the neck left me with using that number. Although somewhere along the interim I traded the Norma brass to a friend for work since I thought why not neck down a 270 WSM brass instead since it was such a pain in the ass using the 300 WSM brass. Either way I was kinda dumb founded by why my numbers weren't coming together until now? I was using a number from a dummy round made from a 300 WSM I made up before I ever built the gun. If my 6.5/300 WSM runs so well with a sloppy neck and so did this gun, a Wby. Vanguard with a Heart barrel, something is wrong with the "tight neck theory" in my opinion.

So I ordered a .308 pilot for my neck turner so I suppose I'll see if turning the necks before sizing them helps with running them over the expander ball. Or should I turn them after sizing down? I've ask this question to even the owner of K&M and he still wasn't sure which was better? To me it seems if the brass has moved after neck sizing down that is when it should be removed?