Case Neck Prep

[Doug Brownlee]

I am trying to take the variation out of the case neck to achieve equal bullet tension on my 270 loads. I read on line the new Winchester brass was .015 thick all my brass mikes out to .012. The author also stated he trims down to .0135 mine clean up at .011+or- .0005. I guess it boils down to how much clearance is acceptable between your chamber neck area and your loaded cartridge, and how can you figure out what your chamber was machined to.

 

[Mikecr]

It dosen't matter what you read when you know what you have. Right?
If your unturned & loaded necks chamber ok, your turned necks will be fine.
Seat a bullet & check chambering.
You'll find out better about your chamber necks/clearance once you've fired a case and measure a neck as sprunback from chamber neck.

 

[Doug Brownlee]

Thanks Mikecr: All cases were fired from the 270; I am putting together test loads to find the best setback and wanted all the cases to be as close as I could get them. I was worrying about the neck wall being too thin and the clearance so great that I would encounter neck splitting. When the snow stops I will go to the range and post my results.
Thanks

 

[boomtube]

"...how can you figure out what your chamber was machined to."

Mike a fired case neck and add 1 thou. The springback on most necks is so close to a thou that any slight difference won't matter. Or you could make a chamber cast to measure but it would only prove what a fired case will show you close enough.

Bullet tension typically varies by metal alloy and temper variations as much as any tiny thickness variations, and the temper - metal hardness - changes with every cycle enough you can feel it when you seat bullets, so precisely turning factory cases for a factory chamber is meaningless for most rifles. Most of us settle for skim turning enough to clean up something like 60-70% of the neck circumference and let it go at that. It's hard to see any accuracy difference attributable to neck turning alone, most of us who do it know we aren't helping much but it's something we can do to improve overall consistancy and doing it doesn't cost anything.