Mandrel question

[NJRaised]

Running a FL bushing die on 1x fired, annealed brass and then mandreling it after.

I know I don’t want to overwork the neck by squeezing it too much with the bushing and then mandreling it back out. But is there is a minimum or correct amount that I should re-open that case mouth? I’ve heard (online rumors) that the mandrel needs to open the case mouth at minimum 2 thousandths to “properly” work, apparently due to springback.

 

[straightshooter1]

Running a FL bushing die on 1x fired, annealed brass and then mandreling it after.

I know I don’t want to overwork the neck by squeezing it too much with the bushing and then mandreling it back out. But is there is a minimum or correct amount that I should re-open that case mouth? I’ve heard (online rumors) that the mandrel needs to open the case mouth at minimum 2 thousandths to “properly” work, apparently due to springback.

How much to squeeze the neck depends on the thickness of the case's neck. You'll probably have to experiment with different bushings to see what you're getting after running the mandrel through the neck. And keep in mind that springback doesn't happen all at once. Like, 24 hrs later, their can be a substantial difference from when you first ran the mandrel through. .002 for an annealed neck can indeed work just fine. I prefer .003 for my annealed necks that are turned to .014 thick, as I've found that gives me good consistent results, but that's just me.

 

[CK1.0]

I did quite a bit of experimenting, and in 6mm, I've ended up settling on a .266" bushing followed by a .241" mandrel (I actually prefer a custom-honed FL die instead of a bushing die these days, but a bushing die is fine too). I used a .268" bushing followed by the same .241" mandrel for a long time, and it made great ammo, but I found having the mandrel get a bit more engagement when opening up the necks works even better (better groups, better vertical downrange).

You'll likely have to experiment due to your brass thickness, but there seems to be a "goldilocks" point where the mandrel gets enough engagement to have a more profound effect, but not so much as to overwork the brass... (FWIW, I anneal on an AMP every firing.)

 

[Luckyshot]

I have a 0.263 mandrel and bushing dies for one cartridge

Necks are about 0.0145" thick, or 0.029" extra diameter

For your reference, a 0.289" bushing was the largest bushing I could use prior to mandrel that gave enough neck tension to seat bullets. Its probably 0.0015 neck tension.
Any less and I would have problems with bullets staying put, so I would consider this the minimum-brass-working you could achieve

0.291 bushing and 0.290 bushing had almost no neck tension

 

[straightshooter1]

I did quite a bit of experimenting, and in 6mm, I've ended up settling on a .266" bushing followed by a .241" mandrel (I actually prefer a custom-honed FL die instead of a bushing die these days, but a bushing die is fine too). I used a .268" bushing followed by the same .241" mandrel for a long time, and it made great ammo, but I found having the mandrel get a bit more engagement when opening up the necks works even better (better groups, better vertical downrange).

You'll likely have to experiment due to your brass thickness, but there seems to be a "goldilocks" point where the mandrel gets enough engagement to have a more profound effect, but not so much as to overwork the brass... (FWIW, I anneal on an AMP every firing.)

Likewise, I prefer a honed FL dies instead of a bushing die. I use honed Forster FL non-bushing dies that for $15 Forster will hone a die to your spec. But if one is using various brass with various thicknesses, this probably won't work out as one expects, where a bushing die can more easily manage such variations.

 

[TheMarkm87]

Have you thought about/tried the Lee Collet neck die? I FL size with a body die and then run the Neck collet die for minimal neck working.

I tried Bushing dies, but got a lot of runout no matter if I floated them or tightened them down. The Lee die gives me .001" or less runout.

 

[straightshooter1]

Have you thought about/tried the Lee Collet neck die? I FL size with a body die and then run the Neck collet die for minimal neck working.

I tried Bushing dies, but got a lot of runout no matter if I floated them or tightened them down. The Lee die gives me .001" or less runout.

I've used the Lee collet die a lot and it does a good job as long as you've got the mandrel that give you the neck tension you're after. Also, had to follow up with the neck sizing by bumping the shoulder back to get the case headspace where I want it using a Forster Bushing Bump Neck Sizing Die without the bushing (another step in the brass prep process ).

 

[TheMarkm87]

I've used the Lee collet die a lot and it does a good job as long as you've got the mandrel that give you the neck tension you're after. Also, had to follow up with the neck sizing by bumping the shoulder back to get the case headspace where I want it using a Forster Busing Bump Neck Sizing Die without the bushing (another step in the brass prep process ).

I actually spun my .308 mandrell down a thowie or two with 400 grit and my Drill press. Gives me a little bump in neck tension. I've not done the same with 6.5cm or 300wm.