Neck tension and NOE expanders - what is "right"

[RogerDat]

I was loading some cast Lee 158-SWC TL and Lyman WC that were sized to .358 and being loaded in Federal brass.
I decided to put in a 360 x 356 NOE expander I had tried in 38 specials. Right away I notices the bullets were hand seating much easier and deeper than the Lee Powder Through expander which just flares the case mouth. What I couldn't tell is if they bullets were going in a bunch easier than they did with the 38's.

My understanding is that in a 360 x 356 the larger number (360) is the top flare portion of the expander. The main body of the expander would be the smaller size listed (356). Thus I think at .356 I have expander of .002 under bullet size of .358

Would that .002 under be pretty much a press fit that I could do fairly far into the case by hand? Or would that ability to press bullet in by hand be an indication of too little neck tension?

I really liked how these worked with .223 but that expander plug arrived with only the one size on it. And I just don't recall the "feel" of seating those bullets, or the 38's I'm really sure I'm not swaging these down that is for sure!

[OS OK]

The brass elasticity is different from case mfgr. to mfgr.
The way I understand it is that an expanded case will shrink back generally about .002".
If your expander mandrel is .001" larger than the sized casts then the case will exert .001" tension on the cast.
Follow it up with the correct for caliber crimp for good start pressure and you should have it.
RCBS sent me for free...all the expanding mandrels for cast boolits of the various die sets I've bought over the years.

You still have to disassemble a few to see if the cases are trying to swage your soft casts.

[RogerDat]

The brass elasticity is different from case mfgr. to mfgr.
The way I understand it is that an expanded case will shrink back generally about .002".
If your expander mandrel is .001" larger than the sized casts then the case will exert .001" tension on the cast.
Follow it up with the correct for caliber crimp for good start pressure and you should have it.
RCBS sent me for free...all the expanding mandrels for cast boolits of the various die sets I've bought over the years.

You still have to disassemble a few to see if the cases are trying to swage your soft casts.

So there will be some tendency for the brass to snap back after the bullet is seated?
I'm doing a very moderate roll crimp, two bullets get rolled into a crimp or lube groove, one the smooth side ( I leave about 1/16' of WC above case)
My Lyman WC mold if I crimp in the top groove the bullet base extends into the case the same amount as the Lee SWC so pressure/velocity should be close to same for both.

I'm trying out plain base gas checks and 2400 powder @13 grains and laddered down. I know 2400 has a tendency toward unburned powder if the pressure is not high enough. And I just do not recall bullets going in this easily. But I sometimes don't recall where my coffee cup is when standing in front of the microwave so ....

Thanks for the reply I take it by disassemble you don't mean the fun way at the range but the un-fun way at the bench.

[OS OK]

Yeah, the un-fun way.
If you get a wide variation from low velocity to high velocity when you run a batch of test rounds over the chrono...sometimes it's the crimp not being substantial enough to let them develop quick start pressure.

"Recall...let's see, that's when something gets called back by Ford or some-such, right? I know that word sure doesn't pertain to my memory!"

[BK7saum]

I think you are close with expander size. I expand cases with an expander 0.001 under to same size as the boolits I'm using. No problems in the .357 and .41 magnums I have used them in. My opinion, using an expander more than 0.001" under is inappropriate for the soft cast boolits I use. The cases swage the boolits during seating if too small an expander is used. For jacketed bullets, any expander works fine as long as there is enough flare to not crumple the case. I think brass has an elasticity of 0.001-0.002" before permanent deformation takes place. Using too small an expander makes the boolit a second expander and there is only 0.001-0.002" of neck tension available. There is no such thing as 0.004 0r 0.005" of neck tension.

Don't believe it. Seat a jacketed rifle bullet using factory expander/die. Note the seating pressure. Then pull the bullet and seat it a second time. There is less seating force the second time because the bullet expanded the case neck and then was held by the 0.001-0.002" of springback.

[fatelvis]

Seat a jacketed rifle bullet using factory expander/die. Note the seating pressure. Then pull the bullet and seat it a second time. There is less seating force the second time because the bullet expanded the case neck and then was held by the 0.001-0.002" of springback.
Very good point. Nicely illustrated.

[No Blue]

OP, time to tool up! You need a dial or digital caliper so you can actually measure what you've got. A set of small hole gauges and a 1" micrometer would also be valuable.

The small hole gauges are a split ball on a handle that you insert into the case mouth, spin the adjusting handle to expand the ball until you get a barely felt drag while moving the gauge up and down. Then measure the diameter of the gauge with your mic.

You being in Lansing should be able to find everything on Craigslist; all the widows and children selling Dad's machinist tools. Me and my brothers got our Dad's tools, he was a wood model maker at Fisher Body for 32 years. You might of heard of Fisher....

[gloob]

Would that .002 under be pretty much a press fit that I could do fairly far into the case by hand? Or would that ability to press bullet in by hand be an indication of too little neck tension?
If you can put the bullet in by hand, you probably won't have enough neck tension. But as others have pointed out, you're not even close to that point.


Seat a jacketed rifle bullet using factory expander/die. Note the seating pressure. Then pull the bullet and seat it a second time. There is less seating force the second time because the bullet expanded the case neck and then was held by the 0.001-0.002" of springback.
Also, I think it is significant that the jacketed rifle bullet will have pretty close to full neck tension, even after pulling it and reseating it, IME. Another way to illustrate this is:

Take sized pistol case. Notice how much force it takes to press the expander in. Notice how much force it takes to withdraw the expander out. Now pull the lever again, and note how much LESS force it takes to push the expander in the second time. BUT notice that the force to withdraw it feels exactly the same (within any human ability of perception). Keep on doing this... the force of insertion/withdrawal does not perceptibly change after the first insertion, no matter how many times you do this. To me this is proof that the expander does not need to be smaller than the bullet to get good neck tension. When the expander is exactly the same size as the bullet, you can get it started by hand, but only a tenth of an inch or three before it gets stuck and you can't get it in any farther (nor pull it back out). Yeah, this "oversize" expander will make seating feel easier, because it is doing all the "permanent deformation" of the brass so the bullet doesn't have to. But neck tension will be fine, IME.

Because a bullet has varying degrees of hardness/elasticity, you might theoretically lose a tiny bit of neck tension by not going under by a mil, particularly with softer and/or more elastic bullets. But the brass is doing 99% of the "giving," not the bullet.

[RogerDat]

OP, time to tool up! You need a dial or digital caliper so you can actually measure what you've got. A set of small hole gauges and a 1" micrometer would also be valuable.

The small hole gauges are a split ball on a handle that you insert into the case mouth, spin the adjusting handle to expand the ball until you get a barely felt drag while moving the gauge up and down. Then measure the diameter of the gauge with your mic.

You being in Lansing should be able to find everything on Craigslist; all the widows and children selling Dad's machinist tools. Me and my brothers got our Dad's tools, he was a wood model maker at Fisher Body for 32 years. You might of heard of Fisher....

Have a digital caliper and 1" micrometer but no small hole gauges. I did check bullet with calipers and they are a consistent .358 the cases after decap & size run .355 to .354 after NOE expander they are .360 at the mouth but .356 to .357 down further in the case.

I'm thinking based on those measurements that I have been putting some swage action on those bullets without the NOE expander. When I say push in by hand I don't mean seat them all the way in but they are much easier to start and I can push them in deeper and seat with little force. I could if I had to push them in by hand with a block of wood.

I did provide a bit more crimp to help keep pressure consistent with what I had been getting. Will be interesting to see how WC in front of 13 grains of 2400 performs. These are ones with plain base gas checks.