Pre-Mandrel Neck Size

[Patrick Comte]

I'm starting to use a mandrel to expand necks after FL sizing them. How small should the internal diameter of the neck be before expanding back out? I'm expanding to .242 I'm thinking .004 smaller, so .238. What have you guys used? What has seemed to work? Thanks in advance.

 

[Dusty Stevens]

Why overwork your brass that much? Why not go .001 and see how that works? Are you doing it due to unturned necks or runout? The expander from porter precision products is a great tool for this job but i recommend doing as little back n forth as you can get away with.

 

[McHaggis]

Sounds like you’re thinking you need to size it down enough so that when you push the manderel through it, it’ll move it enough to overcome spring back? The best way to get consistent neck ID with a mandrel is to have consistent brass malleability. This = consistent spring back. This simply means annealed brass. Work hardened brass can spring back enough that you’ll end up with the neck ID smaller than expected.
Start with annealed brass sized .001” under then run the mandrel thru it. This should give you the results you’re after.

 

[Mikemontminy]

I agree .001 under is what I resize my neck to before running a mandrel in to open it back up. I also check each one after with a guage pin to make sure the bullet seating will be consistent. Sometimes a donut starts forming and the mandrel won’t push it out all the way. The guage pin will show you this. You can buy these in single packs on eBay pretty cheap. I shoot for a half thousand less than the mandrel size. Just type in the size your looking for on your search. If there is a donut forming I cut it out with a K&M carbide pilot installed in a drill. After this step check again with the guage pin. Good luck.

 

[muleman69]

Sounds like you’re thinking you need to size it down enough so that when you push the manderel through it, it’ll move it enough to overcome spring back? The best way to get consistent neck ID with a mandrel is to have consistent brass malleability. This = consistent spring back. This simply means annealed brass. Work hardened brass can spring back enough that you’ll end up with the neck ID smaller than expected.
Start with annealed brass sized .001” under then run the mandrel thru it. This should give you the results you’re after.

So let me get this straight, you take fired brass and size it .001 under then anneal it then run over mandrel, my question is what size would mandrel have to be to get correct neck tension? If it were .001 over there would be no tension? Just asking as I just bought a mandrel

 

[PatMiles]

The expander from porter precision products is a great tool for this job but i recommend doing as little back n forth as you can get away with.

The beauty of Porter Precision's mandrel expander is that you can use many different pin gauges in the same collet, thus you can find the pin gauge that expands the neck, including spring back, that you want. If it turns out that you want more or less expansion, you just install a different pin gauge in your existing collet. I use a 9/32" collet for 6.5 Creedmoor which will take pin gauges from .242-.281. The same Porter die will take any ER 16 collet, so just buy a different collet for different calibers. In the case of 223/5.56 and .243, 6mm, a 1/4" collet will work for both as it will accept .211"-.250" pin gauges.

 

[BenPerfected]

After full length sizing my 6 Dasher thin neck brass, my necks are .242. I immediately follow up using a K&M .2435 expander mandrel and the necks are also annealed every 3rd firing. On my force gauge, this gives me a very consistent 10-15 lbs seating force. Before bullet seating, the necks are brushed & dipped in dry lube.
Ben

 

[McHaggis]

So let me get this straight, you take fired brass and size it .001 under then anneal it then run over mandrel, my question is what size would mandrel have to be to get correct neck tension? If it were .001 over there would be no tension? Just asking as I just bought a mandrel

I'd anneal it first then FL resize then run the mandrel into it. As to what size mandrel I couldn't say for sure as spring back is going to be different due to many factors such as case size, neck thickness, bass make, etc. A good size to start with would be 0.001 -0.002" under but you'd have to try and see what's going to work with your brass.

 

[muleman69]

I'd anneal it first then FL resize then run the mandrel into it. As to what size mandrel I couldn't say for sure as spring back is going to be different due to many factors such as case size, neck thickness, bass make, etc. A good size to start with would be 0.001 -0.002" under but you'd have to try and see what's going to work with your brass.

Gotcha,thanks

 

[mikecr]

I'm starting to use a mandrel to expand necks after FL sizing them. How small should the internal diameter of the neck be before expanding back out? I'm expanding to .242 I'm thinking .004 smaller, so .238.

Every bit of this is way over-sizing.
Normal tension is about a thou of spring back gripping seated bullet bearing. Any more interference fit is just expanded by seating of bullets -to that same value. So it's overworking necks.
That's normal.
FL sizing of necks (sizing length beyond normal seated bearing) is different in that the bullet is not expanding this much, unless seating bearing FL or beyond of neck length (even worse condition).
With this worse case condition, even constant annealing won't provide consistent neck tension unless you also anneal shoulders (contributing here).
When FL sizing of necks, and seated bearing less than FL, you still establish binding against bullet bases. With any donut amounts (varying), even annealing won't help here.
So unless you need extreme neck tension, for extreme starting pressures, it's best not to FL size necks.