lee undersize decapping/resizing die 9mm

bullseyewannabe · March 6, 2016, 08:56 PM

Hi all. I began reloading some 9mm and starting decapping/resizing with a lee 9mm undersize resizing die. It occurred to me that I could be creating a problem with too much neck tension. I know that 9mm can be effected by to much crimp and want to make sure that I'm not creating an unsafe ammo. Any thoughts on this?

454PB · March 6, 2016, 10:21 PM

It depends on how you plan to load them. Are you using commercial jacketed bullets? If so, you won't have a problem.

If you're using cast or swaged bullets that are larger in diameter than standard (usually .355" to .356"), you can have some problems. Typically that includes damaging the bullet while seating and crimping, or a bulge in the loaded round that prevents proper chambering. I always seat and taper crimp in two separate operations.

As a very high intensity cartridge, 9mm is quite sensitive to seating depth, and that can get you into trouble regardless of the bullet diameter.

I use home cast bullets almost exclusively in my 9's, and size them to .357". With all the above in mind, I've never had a problem. If you are casting and sizing your own, you need to know what groove diameter you have.

LE-28 · March 7, 2016, 06:33 AM

My standard 9mm RCBS dies make 50lb+ stress with my Extreme and RMR plated bullets. I use a strain gauge that pushes straight down on the bullet. My gauge only go to 50lbs so I don't know how well the calibration would be after that amount.

Plated and lead are just half to .001 larger in diameter than the jacketed bullets are. My jacketed bullets slip at 43lbs which I feel is more than adequate for 9mm luger loads.

I checked some of my .357 loads, uncrimped, with lead bullets and they also maxed out at 50lbs.

At 43lbs I never see any bullet setback in my loads. I can't imagine why you would need undersized resizing dies. They would have to be hard on your brass but unless you splitting your cases or bulging them, they should work ok.

**Unclenick** · March 7, 2016, 08:08 AM

Bullseyewannabe,

You don't need to worry about it. In order to expand and stretch permanently at all (plastic deformation), brass has to exceed it's yield point in pounds per square inch of cross-sectional thickness. Whether the expander die or your bullet causes it to do that, once the yield point is reached there is relatively little additional force required to stretch it further. It's almost like reaching a force threshold.

Most cases can and do deform elastically for half to a thousandth of an inch, but once you go beyond that point you have surpassed the brass yield, so the force needed doesn't grow much. This is why we have to resort to crimping to get added bullet pull. No amount of narrowing the brass further by sizing it can provide enough additional hold.

March 6, 2016, 08:56 PM	#1
bullseyewannabe Junior Member Join Date: January 1, 2016 Posts: 4	lee undersize decapping/resizing die 9mm Hi all. I began reloading some 9mm and starting decapping/resizing with a lee 9mm undersize resizing die. It occurred to me that I could be creating a problem with too much neck tension. I know that 9mm can be effected by to much crimp and want to make sure that I'm not creating an unsafe ammo. Any thoughts on this?

March 7, 2016, 08:08 AM	#4
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Bullseyewannabe, You don't need to worry about it. In order to expand and stretch permanently at all (plastic deformation), brass has to exceed it's yield point in pounds per square inch of cross-sectional thickness. Whether the expander die or your bullet causes it to do that, once the yield point is reached there is relatively little additional force required to stretch it further. It's almost like reaching a force threshold. Most cases can and do deform elastically for half to a thousandth of an inch, but once you go beyond that point you have surpassed the brass yield, so the force needed doesn't grow much. This is why we have to resort to crimping to get added bullet pull. No amount of narrowing the brass further by sizing it can provide enough additional hold. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

March 6, 2016, 10:21 PM	#2
454PB Senior Member Join Date: February 23, 2005 Location: Helena, Mt. Posts: 122	It depends on how you plan to load them. Are you using commercial jacketed bullets? If so, you won't have a problem. If you're using cast or swaged bullets that are larger in diameter than standard (usually .355" to .356"), you can have some problems. Typically that includes damaging the bullet while seating and crimping, or a bulge in the loaded round that prevents proper chambering. I always seat and taper crimp in two separate operations. As a very high intensity cartridge, 9mm is quite sensitive to seating depth, and that can get you into trouble regardless of the bullet diameter. I use home cast bullets almost exclusively in my 9's, and size them to .357". With all the above in mind, I've never had a problem. If you are casting and sizing your own, you need to know what groove diameter you have.