Thread: neck die may not be sufficient??

In the early stages of load development for my Sendero 7mm Mag.
First Norma brass I full length sized, went to the range and used them.
Now they're fire formed it's my understanding I only need to neck size. I do this only to find the projectiles go in alot easier than the first time. That worries me that the velocity/POI will be affected.
So I measure unused case neck outside 7.86mm inside 7.09mm
Fire formed and neck sized ones neck outside 7.92mm inside 7.14mm. About 0.05mm difference
Projectile (162gr Hornady SST) diameter is 7.18mm
Stem of neck sizer is 7.14mm
As this gun is for LR I'm thinking this is critical.
A)Is it fine like this and don't need to do squat.
B)Put the stem in a drill and sand it down 0.05mm

What dies are you using? Collet, bushing or expander ball ?

Take one of the the fireformed brass and full length size it, what neck dimensions do you get ?

If you are using collet dies wind it down a bit more.

I'm using the Lee Deluxe set i.e. three dies neck, full and bullet seating. Inside stem is parallel

Must not be collet. Doesn't seem possible to neck down less than diameter of stem

Originally Posted by Toby

If you are using collet dies wind it down a bit more.

Ok, so that is a collet neck die.

Try turning the die down further, maybe 1/8 turn at a time. Use light pressure on the press handle, the collet dies have a sweet spot, it's not about applying more force.

Uh ok thanks. I'll try it in the morning. I'll also send an image of the die to confirm. Cheers guys


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The other thing with the collet dies is that the collet sometimes gets stuck. Use a bit of 1500 or 2000 sandpaper and polish the outside cone part of the collet, and apply a TINY amount of lithium grease to that area.

Have a look on youtube, on the ammosmith channel he has 2 vids about the lee collet neck sizer.

If all of that still does not sort out the problem, then yes, sand down the mandrel, but whatever you take off is gone forever 0.05mm is only 2 thou of an inch, so go slow...

Cheers. Yep def a collet sizer. Tried screwing in further, zero difference. Will check out ammosmith etc. thanks


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Lee advise you can order a custom (ie smaller diameter) rod from them, or you can turn/polish it down yourself to a slightly smaller diameter.
I also anneal the neck of my cases and that helps with the neck tension.

In fact for my bolt actions, I don't use the full size die anymore, I only neck size with the Lee Collet and every 4-5 firings (depending if it was a hot load) use my Redding Body die and Lee Collet combo.
So you don't get the variation in neck tension from using a full size die.

Originally Posted by dogmatix

In fact for my bolt actions, I don't use the full size die anymore, I only neck size with the Lee Collet and every 4-5 firings (depending if it was a hot load) use my Redding Body die and Lee Collet combo.
So you don't get the variation in neck tension from using a full size die.

+1, best of both worlds

Dogmatix, when you do body/bump + collet, when do you trim, before or after sizing ?

Other option if you already have the full deluxe set, is to take the FL die, remove the decapping pin/expander ball, and then drill out the neck part, turning it into a Lee body die

I ended up putting the neck size die mandrel in a drill and lathing it down 0.04mm with sandpaper and polished with aerosol. made up five bullets and the projectiles had the same tension as the original cases. Much happier now. Hopefully means consistent POI and velocity. Thanks for the help.

This sounds like a good solution. I've had a similar issue with my 223 Collet, I'll give this a crack.

Same with my 6.5 Mauser neck die. Now I know I'll do the same to that

Projectile (162gr Hornady SST) diameter is 7.18mm
Stem of neck sizer is 7.14mm

so 0.04mm....some articles and info out there saying any more than 1~2thou and the bullet resizes the neck anyway and you have about 2.

If its for hunting try a light crimp off a Lee collet die