Neck getting thicker

[Ritterbruder]

I am using Redding Competition Dies with a 0.290" bushing to reload Lapua 6.5 CM brass. My loaded rounds measure 0.292-0.293" on the outside of the neck, so the 0.290" bushing should be fine.

This worked fine for the first two reloads. On the third, I noticed a lot of neck tension and copper shaving. I measured the necks again. The middle of the neck still measures 0.292-0.293", but the mouth of the case measures 0.296". It looks like the neck is getting thicket at the top of the case mouth, which causes the 0.290" bushing to put too much neck tension.

Am I doing something wrong here?

 

[McCrazy]

It's difficult for me to guess what is going on here based off only your outside measurements of the neck.

How thick is the brass at the mouth of the brass?

How long are the brass now after multiple firings?

Have you trimmed the brass to length after these multiple firings?

Did you deburr and chamfer after trimming?

When you fire, brass will stretch out and expand under the pressure induced. This means the brass gets thinner in some places. When you resize the brass and bump the shoulder the displaced brass has to go somewhere and it ends up as being additional length to the neck which needs to be trimmed off. After trimming you then need to chamfer and deburr the mouth of the brass.

 

[V-Ref]

You're not necessarily doing anything wrong.

You've discovered why some neck turn...to uniform the neck wall thickness.

Are your reloads what you would describe as "higher pressure" reloads...brass will tend to "flow" forward at a quicker rate when you push pressures. Sharper shoulder angles do a better job of controlling that (think saami 243 vs 243 ai) than shallower ones.

How much are you pushing the shoulder back from a case that's fully formed to your chamber (usually takes 3-4 firings)?

 

[Ritterbruder]

I believe I fixed the issue. It seemed like a QC issue where the case mouth was a bit thicker than the rest of the neck. I used a 0.261" mandrel to uniform the neck and use a chamfer/deburr tool to trim off the excess. Took 2 firings to get it uniformed.