9mm Neck Tension

[justindad]

Making some rounds for the wife’s new piece, and I am having an issue with low neck tension. The boolit is a 124 grain truncated nose, cast from 92-6-2 hardball, sized to 0.356. The brass (Starline) was expanded with a Redding neck expander for lead. I crimped with a Redding taper crimp die. Problem: if I did not crimp so tightly that the lead swayed in, then I could press the boolit into the casing by pinching the round with my fingers. Even then, cycling the round through the pistol would reduce the OACL by 0.004”. Cycling the round multiple times does not result in more than 0.004” set back.
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I’ll try 0.357” & 0.358” sizing, along with omitting the neck expander. However, is low neck tension an issue with 9mm and it’s tapered case? I’ve never paid any attention to 9mm issues before, so I am relatively ignorant here.

[zarrinvz24]

I size my 9mm Boolits to .3575, for use in Glock 17 &19 with factory barrels. With the tapered case of 9mm you have to be careful not to over expand the neck. Use the absolute bare minimum amount of flare you can get by without shaving lead. It takes some patience to get adjusted, more than is required for straight walled cases. Keep at it.

[mdi]

I use a Lyman "M" die with just enough flare after sizing with a plain Lee die set and "deflare"with an RCBS taper crimp die (mixed Brass). My cast bullets run .357"-.358". Prior to using the M die I used a Universal Flaring tool from Lee. I have not experienced any setback. Perhaps ther Redding die is opening the case too much. Measure the "expanding" portion of the die. I would want the expander to be about .003"-.004" smaller than the bullet diameter. Also, too much crimp can bulge cases and loosen neck tension. I don't "crimp", I just "deflare"...

[Outpost75]

In 9mm the expander plug should be 0.002" smaller than bullet diameter. For jacketed bullets .353" and for lead .355"

[zarrinvz24]

It should be noted that the OP is using the Redding neck expanding and flaring Die. This is the same as Lyman’s M-die.

[243winxb]

Bullet set back is a problem. First make sure the sizing die is doing its job & the expander measures .352" The larger diameter bullet has to fit the barrels throat. My maximum is .3568" diameter, to fit barrel.

https://www.amazon.com/Lee-Precision.../dp/B00MO4SKE8

Lee Precision Reloading Undersize Sizing 9mm Die

[fredj338]

Starline brass is pretty thick, so odd you are losing neck tension. Size of the expander? It should be no bigger than 0.355.

[justindad]

The small diameter of the expansion plug is 0.3528” and then there is a short step up to 0.3579” just before the flaring portion (see two arrows below). The total length of the flare plus the 0.3579” section is about the length of my front driving band, and the the rear driving band is deep enough in the tapered case that the boolit is not squeezed by the case at its rear driving band. So either my taper crimp has to be longer than this flange + step, or I can’t use the flaring portion of this plug.
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Does the Lyman M Die have this same step?
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[243winxb]

Yes,
The Lyman "M" die works the same, with the step.

The short step of .3579" should just enter the case mouth of the shortest case of the lot. The flare part should not be needed with the correct bullet diameter.

The small diameter of the expansion plug @ 0.3528” should provide lots of neck tension/bullet hold. But the FL die has to size brass small enough.


The taper crimp die should just close the mouth of the case. At most, the mouth should be .001" smaller then the rounds body.

* FIRST- Make sure your Sizing die makes light contact with the shell holder, for proper sizing.*

Photo of my RCBS 9MM expander.

[justindad]

Thanks 243winxb. I did that last night with much better results than before. I slowly moved the sizing plug deeper into the casing while measuring the case OD, until just slightly after the step entered the case. The case mouth OD got to be 0.378” when the 0.356” boolit would just barely enter the case without shaving lead during the seating process (case OD was 0.374” just before the step entered the case). Hopefully this works with 0.357” (0.379” case OD) & 0.358” (0.380” case OD) sized boolits, without the case going on the tapered flaring section. Strange thing is - the Redding literature says to use the tapered section of the plug.