Questions.. Loading Dies..Lee?? FCD??

[hobbit99]

4 hours ago, N3WWN said:

 

 

Sorry for the bad math... 

 

Attached is an image (from another forum about sizing dies, so ignore the measurements) which shows the tapering of the walls themselves.  A Google image search for '9mm case wall thickness' returns some other examples of varying value.

 

I seat the Acme 145gr RN-NLG bullets to 1.102", so it's a fairly short COAL, but that's what I had to do to get it to work in all of our 9mm firearms.  The tapered wall thickness means the bullet meets more and more case thickness until the base of the bullet.  My short COAL exacerbates the issue.

 

I don't know if the thickness increases by 3.7x or not, but it doesn't seem unreasonable from this image.

 

I wasn't ever able to reclaim a tumbled bullet, so I can't do any root cause analysis... wish I could have, though!  

 

But, as you said, "...it doesn't matter. If a bullet tumbles, the load needs to be fixed."   For me, culling stepped brass all together and rejecting rounds that require excessive FCD force into the practice ammo bin resolved the tumbling bullets at matches.  I couldn't have done that without feedback from the FCD.

 

 

Tres interresant.!!  Thanks for the image... That explains a lot.!! 

 

Some things I was not aware of (bad English..), I had no idea you were loading that short. That definitely makes a difference. How many different guns do you try to use the same load in.??  Admittedly, there is more thickness variation in the walls than I had imagined. I knew there would be some..(all cases are somewhat thicker near the web..). So, the deeper you seat your bullets the more potential swelling of the case and the more swaging that would occur in the FCD...depending on how it is set up.

 

I stopped writing for a moment and did some quick checking... Have to go find my slide rule... I'll be back after I do some checking and some calculations...

 

 

Edited July 14, 2017 by hobbit99
STUPID auto-correct!!!

[hobbit99]

On 7/11/2017 at 3:35 PM, N3WWN said:

 

...See following...

 

 

N3WWN...Your image in the last post made me think. I went back to your post of the measurements and read more thoroughly. I also reviewed the "net" and found some more images of sectioned brass much as you said. After reviewing and thinking I believe that your measurements are probably very close.... but I think you may have moved a little off track in a couple of places. This is really easy to do on a computer, especially when you are working quickly. In any event, here is what I discovered.

 

You said:  .... 

 

"... the "good" range brass  shows about 0.009"-0.011" for the top ~1/4" of the wall..." Okay, this sounds plausible. 

 

"... brass culled out has walls 0.013"-0.015", with 0.0135" being the most common (same top ~1/4" of the wall)..." Okay here too, sounds likely.

 

Here is where things start to go a little "off".

 

"...If I have the FCD set to just remove the flare from my "good" range brass, let's call that 0.010" for each wall + 0.3565" for the bullet, or 0.3585" at the case mouth...."  Not really... Your numbers allow for only an additional .002 (two thousandths..) for the case walls instead of .020 (twenty thousandths..). The correct number here should be .3765 not .3585. 

 

"...If we throw in the worst case reject brass, that's 0.015" for each wall + 0.3565" for the bullet, or 0.3595..." Again, not really. The number here should be an additional .030 (thirty thousandths..) for a total of .3865 not .3595. 

 

"...BUT, the FCD is set to 0.3585", so the bullet is getting swaged 0.0010", resulting in a 0.3555" bullet at the case mouth..." The errors up there ^ start compounding... The FCD would be set to .3765 resulting in a swaging effect of .010 (ten thousandths..) not .001... resulting in a bullet diameter at the case mouth of .3465 not .3555.

 

It is now easy to see why there could be a problem. Your original "good cases" would allow the bullet to leave the case at approximately .3565 which is very close to groove diameter and with a little obturation should fit the barrel very well. The "bad" cases would close the bullet down an additional .010 (ten thousandths..) which would make them undersize for the bore at .3465. Now, depending on the amount of internal taper in the case, the "driving" surface of the bullet could be a bit smaller than that.!!! Undersize = yes.!! Gas leakage = yes.!! Gas cutting = probably.!! Deformed bases = probably.!! Squeezed like this, it is conceivable that the bullets may not have even touched the lands..... Remember the potential diameter of the lands is around .348, depending on the type of barrel and the QC by the manufacturer, and whether or not they hold tight to SAAMI specs.

You could probably use these cases, but you would have to back your FCD off to just straighten out the case at the mouth without swaging them down.....

 

This puts a whole new light on this issue.....