Resizing question.... or not....

We started loading for the Colt/Caspian/Kart/Wilson/EGW/Cylinder and Slide/Etc. 9mm Mutt gun that I've cobbled together and have been tinkering with. Bought a used Square Deal and set it up for 9s only. So far, have run only a couple hundred rounds on it. When seating the Dardas SWC, we have been getting a bulge below the base of the bullet. They shoot fine, and run through the gun fine (most of the time). Matt says to use a Lyman expanding die, and that all makes good sense.... but I'd have a hard time getting one to fit in a Square Deal. Looked at some drawings in the manuals, and did some measuring before and after. Looks like the Dillon sizing die is taking them down way too far...I think that's called a "small base die".
  Just for the hell of it, I took out the re-sizer and loaded a couple that were fire formed in the Kart's chamber this morning. Did not change anything else on the toolhead. At the seating station, the flat based bullets dropped down into the flared case up to the lube groove easily, and seated effortlessly. That's a first. They came out of the taper crimp station right at .380".... like the drawings call for. Took a handful out to the backyard to try,and they feed, extract and eject as well as the full length sized batch.
   Thinking there's something good to be learned here....just not sure what. Does anyone else do it this way? What can it hurt? What can it help except being a lot less "stressful" on the bullets as they are seated. (and that is said to be a good thing).
  If it matters, the load is 126 grain Dardas SWCFB sized at .356, 3.2 grains of 231, Remington primers and mixed brass (no two alike).OAL 1.100 and the sized ones are .378ish crimp.  Marvel base under 33mm Sightron, and 9 pound recoil spring, 23 pound main and flat bottomed stop. Can't see where any of that would make much difference other than the light spring running the slide forward to chamber the max sized cartridges that were"t resized.
                                                 Thanks in advance Gentlemen, and MERRY CHRISTMAS to you all;
                                                                                                                                                 Bill

9x19 is well known for case variability and I learned a long time ago that every bullet needs to be tested after seating to be sure there is sufficient tension. I press down on the seated bullet with thumb or finger and ANY movement of the bullet is a reject.
What you have is often called "wasp waist" or "Coke bottle." This is actually a good thing as it shows that not only is the bullet being help with enough tension but that there is actually a very fine "shelf" that will resist bullet set-back.
There real issue is: what is the seated bullet's diameter? If you are seating a 0.356" lead bullet (and that is really the lower limit for 9x19 lead bullets) and, if you pull the bullet, you now have a 0.355" bullet, you will probably get leading and you really do need a larger expander. 
I load 0.357-0.358" lead bullets and use a .38 expander.
Your SDB, with proprietary dies, does not easily allow you to use any other dies.

The sizing die may be resizing the brass pretty small but your neck expander may not be opening the case mouth as much as it should for .356 lead bullets. Thus you have the brass expanded when you seat your bullet and you get the "wrinkle" in the side of the case.
 What really hurts your accuracy if the lead bullet is being downsized when it is seated in the brass. The neck expander on a Dillon 550 is around .353. Their dimension is OK for a Harder and smaller copper jacketed bullet of .355 but not ideal for lead bullets.  If your lead bullet is being downsized to say .354 or .355 then you can loose accuracy plus get leading in the barrel. A larger expander would need to be custom made because Dillon will tell you to go pound sand.
 You may be OK to continue as you are doing because I suspect your chamber is tight compared to other 9MM chambers.

Many thanks for the replies Fellas.....good stuff and what we needed. Took the expander/drop tube out to measure it this morning and come up with .351" every time. Can clearly see what's going on here now, and how to fix it. Dug out a .38/.357 conversion kit and measured it's expander at .355" That would have been the answer except that it's quite a bit shorter.....not enough threads left on the powder die for setting it down low enough to reach into the shorter 9mm casing all the way to the flaring shoulder. 
  Willl load up 50 fire formed and unsized today and shoot them if the range is open till noon. We can set the taper die down tighter for more grip on the bullet if need be.
   And yes, the barrel has been leading bad. Did some reading on the forum here, and the throating reamer would have been the next step. My buddy the gunsmith gave me some stuff called P B Blocker to coat the bore with....it may have helped some but not nearly enough. You both are right about the bullets being squeezed down to bore size or less. As hard as they were to seat, they had to be catching hell from both directions.
                                 Thanks again, and all our best;
                                                                               Bill

Didn't have to touch the taper die Tom...bullets seated snug and STRAIGHT. Crimps are .379-380", and hard as I tried, I couldn't get any of them to move. And every one dropped right into the chamber and spun freely. We used the barrel itself for a gauge. If there's enough tension to let the powder burn clean, this may work out OK. The batch I shot into the ground yesterday all cycled the gun ,and the slide locked back. 
                                                         Best;
                                                                      Bill
  Oh....and no more bulge below the bullet.

Might be on to a fix here. Did a bunch of searching around and stumbled into Double Alpha's webpage. They make a powder funnel/expander for their bullet feeder set ups. Dillon parts manuals show the same number funnel for Square Deal and 650 funnels in 9mm. So far so good. 
  Called them and talked with the tech guy, and he tells me the ball/expander is a gradual taper from .351-to.355" up to the flaring shoulder, and yes, it will work in a Square Deal,and you can adjust it up or down to get the amount of expansion that you need....and they sell them separate form the feeder kits. Have one on the way, and look forward to trying it. Sure can't hurt.
                                                        All our best;
                                                                             Bill
Didn't get to the range to try the unsized rounds Sunday. Shoveled snow instead. Maybe today, and see if it helps with the barrel leading.

The DA 9mm/.38 funnel/expander only has an overall length of .213" including the radius on the end.

The actual length of expansion is .130" up to the flare.

There is an area .055" long just under the flare that is .358" so the bullet has a place to sit when the feeder drops it on the case.

It should work fine on your SDB as I use one in .40 cal on mine.

As for .45 cal, the length of expansion is only .185".

The DA bullet feeders/expanders seem to have the "run and gun" group in mind where they are ultra paranoid about bullet setback so they are setup to give the bullet a place to squarely sit until seated and then jammed into the case as tight as possible.

Thank you for the reply and the measurements Sir....Sounds like less expansion than we really need,but will be a improvement over where we are now. Won't know without trying.
    Might be overthinking this whole cast bullet in 9mm thing anyway...... should just load up a bunch that will cycle and shoot, and go have some fun. And maybe learn something at the same time. Have read on here more than once that most anything will shoot good enough at 25 yards.  We were more concerned about the leading than accuracy, and the leading we can live with. As it is the accuracy is not all that bad.
                                                                                Thanks again;
                                                                                                          Bill

You're welcome!

Cast 9mm may not be a big issue as far as swaging the bullet when seating it. I've pulled a few 115 and 124 and measured them and had very little change in diameter. 147's can be another story though as they get pretty deep into the case.

I am going to try re-grinding a .40 cal Dillon powder funnel/expander for use with 148 HBWC .38 Special.

That way, hopefully, I can end up with an expander that is long enough and large enough diameter to seat them without swaging them when seated.

Great idea.....surprised no one has mentioned it.  My buddy the gunsmith could do that with the tool post grinder easy enough.
                                                                    Thanks DA
                                                                                      Bill

I believe it was this fellow who makes the M style powder dies for the Dillons.

he will make you a custom 38 HBWC funnel... just give him the specs you want. Don't recall what it cost but it works fine.

https://www.ebay.com/usr/gscustom2013?_trksid=p2047675.l2559