"coke bottle" shape when reloading 9mm: good, bad, ugly?

I think the short version is that for most cartridges it doesn't matter, in that it doesn't hurt anything or cause any problems. So for most cartridges I don't worry about it either way.

In bigger cartridges - .357 Magnum on up - I want to see that "wasp waist" and if I don't, I fix it. Seeing a little bit of hourglass ensures that I have good bullet pull and usually results in increased consistency and accuracy along with complete powder burn.

 

The "coke bottle" shape tells me that I have good neck tension on my semi auto rounds, helping to prevent bullet setback and insuring a good complete burn of the powder. It may also help prevent bullet pull in revolvers, along with a good roll crimp.

chris

 

But does the absence of the shape indicate poor neck tension? Seriously, since I don’t get the shape (test loaded 10 this AM just to confirm) I’m feeling unloved.

 

I don't believe the absence of the "coke bottle" indicates poor neck tension. I do believe the presence of it indicates good or high neck tension.

If your loads don't show this trait, and they function without setback, then you have no problems. I tested setback when I started loading by making a few dummy rounds, and chambering them.

Process I used:

1) Measure and record dummy round OAL
2) Load magazine with dummy round
3) Chamber dummy round using slide release
4) Measure and record dummy round OAL
5) Repeat ten times and record OAL each time
6) Any change in OAL is your bullet setback

I did this with several dummy rounds, and repeated the above process ten times for each round, recording OAL each time. After ten chamberings, my rounds had a shorter OAL by .002" ~ .003" total. Some had less than .002". I figured that was good enough for me.

chris

 

Thanks I’m going to try that in my 1911
What type of of pistol is yours?

 

I have a Kimber Ultra (3" barrel) 1911. It doe's have a tight chamber, and I have to crimp to a .468 or so for rounds to feed reliably.

FWIW, I size with an RCBS die. I don't know if that makes a difference, but it works for me. I'll take a few pics of my rounds and post them for you.

chris

 

I really appreciate your effort here!

 

I think ultimately what ends brass life is work hardening that leads to split case when brass becomes brittle and loses maleability from repeated firing and resizing ... flaring of case mouth and reducing/taper/roll crimping.

"Coke bottle/hourglass" shape that happens with 9mm case is more pronounced than what is happening with 40S&W/45ACP cases but nonetheless, it is still happening, to a lesser agree, especially with slightly larger sized .401"/.452" lead/coated lead bullets.

 

Since most of my reloads get chambered only once, I test neck tension/bullet setback only once or upto few times.

Lee resizing carbide ring will often reduce case neck to smaller OD and further down towards case base than Dillon/RCBS dies. Depending on bullet sizing and thickness of case wall/headstamp, I usually get no bullet setback to miminal setback of .001-.002" - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

Since factory new ammunition made with new brass will often produce some bullet setback, I consider one time bullet setback of few thousands acceptable but prefer no bullet setback for accuracy/match grade loads.

 

So I took a dummy round and measured the OAL. Bullet is an Acme 185gr coated swc.



I then chambered it three times from the slide release, and measured. I repeated this three times, for a total of nine chamberings.



.0005" setback after nine chamberings. The bullet nose is getting beat up a bit.



And you can see the "coke bottle" effect in this pic.



chris

 

I have factory ammo that is wasp shaped.
Nothing in life is perfect…..

 

40S&W (Especially 180 gr bullet) and most 45ACP bullets have long bullet bases that produce good neck tension and minimal/no bullet setback.



It's 9mm bullets with shorter bullet base length, especially 115 gr FMJ/RN that is particularly susceptible to neck tension/bullet setback issues. And since 9mm case is tapered, at some point, seating deeper will actually start to decrease neck tension and bullet will simply fall into the case.

I believe that's why Cone Nose/SWC/HP profile bullets tend to produce greater accuracy than FMJ/RN profile 9mm bullets and manufacturers like MBC switched from "Pointed stepped RN" to "Rounder shorter RN" bullets to increase bullet base length.

Compare the bullet base of following 9mm bullets and notice the difference in bullet base lengths ... The longer bullet base bullets seated deeper when loaded will produce greater neck tension and less bullet setback for more consistent chamber pressures ... which will produce smaller groups on target (Barring other reloading and shooting variables).

 

I can see where with a tapered case like the 9mm (which I don't load, yet) the deeper the bullet is seated the lower the bullet tension is due to the inside diameter of the case becoming larger. At some point the ID of the case exceeds the OD of the bullet, thereby letting the bullet "fall" into the case. That makes perfect sense to me.

However, if the die sizes the case ID to .354 most of the way down the brass, and the bullet is .355 OD, wouldn't that increase bullet hold/tension? I may be wrong on this and would appreciate your thoughts. Thinking of a modern carbide die, not an older tapered steel die.

chris

 

Yes, "modern" carbide resizing dies like Dillon/Lee use "tapered" carbide sizing ring. And this notion was tested in this myth busting thread.

Case wall thickness measurement was made .200" below case mouth where bottom of 115 gr RN bullet was seated down to where neck tension would be greatest due to thicker case wall - https://www.thehighroad.org/index.p...nd-bullet-setback.830072/page-3#post-10713822

And 9mm bullets sized .354", .355", .3555" and .356" were tested for bullet setback using various case wall thickness cases to measure bullet setback - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

I load different 115 gr FMJ/RN bullets from 1.130" down to 1.110" to increase neck tension but not shorter than 1.100".

 

Thank you for all your efforts.

I've read both of those threads in my research here and would say that I and probably many others appreciate the work you've done.

chris

 

Often depends on brass thickness.

 

Nope, not how sizing and expanding tapered cases work! It's mainly a Dillon "thing" due to the engineering of their dies. Same in their straight 45ACP dies!

 

On your last point, for 9mm, I decap/size, then drop in gauge. If it passes fine, if not, through the Makarov bulge buster it goes and into the gauge. If it passes the gauge (which it always does) I don’t run it through the decap/sizing die again, would you?

 

In response to "why aren't carbide dies tapered" the response was:

but then the following is posted:

There seems to be a disagreement here?

 

Not really and you can see the difference on resized brass.

With non-tapered carbide sizer ring with sharp die opening, you see scrape marks on resized brass like these, especially with overly expanded brass shot in generous chambers with higher powder charges or 9mm Major brass - https://www.thehighroad.org/index.php?threads/9mm-resize-die.863126/page-2#post-11381953



With tapered carbide sizer ring with radiused die opening (Hallmark of Lee carbide sizer dies), you do not see scrape marks on brass as round radius smooths out the expanded brass with the taper of the carbide ring. I like my Lee carbide sizer dies.

 

I was referencing the fact that you indicated that Lee dies have a tapered carbide ring but it was my impression that @9mmepiphany said they did not. Perhaps I misunderstood one of you?

 

I don’t bulge bust any cases of any caliber. If they don’t gauge correctly after resizing, I toss them or recycle them or give them to the range in Micanopy to sell to the scrapper. I don’t trust a case that’s been blown out not to rupture in my guns. Brass is cheap. My guns aren’t. However, that’s me and I do tend to march to the beat of my own drummer - who happens to sound a lot like Gene Krupa - so don’t anybody take any offense. I’m not criticizing anyone, just saying it’s an issue I have encountered and always just figured maybe my old, cheap Lee dies are the reason. My loads are at least as reliable as any factory ammo I’ve tried and much more reliable than most. So the wasp things not really a problem worth solving for me.