Least amount of seating depth? 9mm/124 at 31mm (1.220")

[Whistler]

I have a 9mm STI chamber that will take a 31.0 mm / 1.220" OAL with a 124 gn RN.

I have loaded 9.0 gn N105, similar to what I worked up for a friend's .38 Super with the same bullet and load.

 

The seating depth is a mere 2,54 mm / .100".

So far everything actually seems fine, I have no bent cartridges and it seems to hold for the recoil forces.

 

If it would have touched the lands I would have been worried that the case tension was not enough to eject the case without having the bullet stuck in the chamber on unloading, but this OAL passes all plunk tests on the barrel.

 

Anyone else have any experience with shallow seating depths with 9mm? All references I find are about bench rest shooting where they seat to the lands.

[yoshidaex]

What’s accuracy like with the loads you currently have?

 

[Whistler]

Haven't benchtested it yet, but it holds roughly 1" steadily at 20 yards offhand.

[Hi-Power Jack]

22 hours ago, Whistler said:

 Anyone have experience with shallow seating depths with 9mm?

 

WOW !!!!

 

1.22"    I backed off at 1.175", thought that left too little bullet in the cartridge   .....

 

But, I was using a 124 gr. JHP - not a RN.    Don't know how that would equate.

[racer-x]

I shot Montana Gold 124 JHP's at 1.200 for my first few months with 9major. Had a few bullets fall out of the case (recoil) while in the magazine during matches and decreased OAL. That was in 2008... have not had that happen again since changing to a max of 1.185 with MG124JHP or 1.165 with MG115JHP's.

 

Either of these loads equate to about .130" of bullet pressed inside the case. Much less that that is asking for reduced reliability. 

[Whistler]

Allright, so it is time to wake this thread.

 

I have run about 250 rounds of the 1.220" ammo, about half of that was on a club match to try it under competition conditions.

I've had one nosedive on the feedramp, apparently related to that magazine. Can be recreated by filling it up and just letting the slide go, the bullet will dive and jam the slide. Will try bending the spring.

 

One round got caught halfway into the chamber. When racking back the slide with force, the bullet was lodged slightly into the lands. Since the bullet cannot reach the lands when inside the case, I gather the jam must have acted as a kinetic hammer, forcing the bullet forward until it let go of the case. There are two considerations here:

 

1. The case tension was too loose.

1A. Was the case tension specific for this cartridge? Was it caused by being in the bottom of the mag for several stages, shaking the bullet loose?

1B. Is this true for all the cartridges? If so, a deeper seating may be required.

 

2. What caused the jam? Was the tension enough for regular shooting, but the jam was more force than the cartridge would withstand even under normal circumstances?

 

After returning home from the match I tested all cases in the 9mm case gauge. They are too long (of course), but otherwise most went in fine. Some have a resistance, I wonder if this is due to the chamber of the previous firearm (I use once fired Speer +P range brass only). It could also be due to the heavy compression of the powder, making the case bulge.

 

I had the opportunity to test the ammo in a chronograph.

Velocities were not very even, but accuracy is good and I can tell no difference in dot tracking.

Average velocity was 1337 fps. Lowest factor was 166 and highest 178.

 

Next plan will probably be to lower the charge with about 0.2 gn and see if the cases will have less bulge and still function.

[Hi-Power Jack]

Why are you loading so long ?

[Steve RA]

I load all my 9mms to 1.171.  Had the throat lengthened so any fit - LSWC, tapered cone - whatever.  Some could be loaded longer but at this length they all feed and present no problems.

[Flatland Shooter]

I used MG 124 gr JHP at 1.195" for many years.  Reliable and accurate.  Much longer might make me nervous.

[jcc7x7]

Old School Thought Process

Was

Load the bullet to at least it's diameter.

I've held to the thought of at least 3/5 dia. for good neck tension

Not saying you have to just some old school thoughts to share with you

[JRM83]

I had an STI 9mm barrel with a throat as long as yours. Instead of trying to load common bullets to accommodate the throat, I just bought some 170gr 9mm that would allow me load super long and still have enough bullet in the case to avoid issues. Since 2011 9mm/38S mags are identical the extra length is not an issue there either. 170gr bullets with 2.7gr of powder are very soft shooters. 

 

Edit - just saw you are loading for 9 major. Disregard!

Edited March 25, 2018 by JRM83

[Hi-Power Jack]

11 hours ago, JRM83 said:

 170gr bullets with 2.7gr of powder are very soft shooters. 

 

Where do you get 170 gr bullets ?

 

Pls let us know what results you have with them - very interesting     

 

Little over 740 fps ?   stable ?  accurate  ?   feed okay ?

[JRM83]

1 hour ago, Hi-Power Jack said:

Where do you get 170 gr bullets ?

 

Pls let us know what results you have with them - very interesting     

 

Little over 740 fps ?   stable ?  accurate  ?   feed okay ?

 

I was getting right at 125 power factor with that load, but I suspect there would be a lot of variability on the velocity if you ran a 170gr in a different gun due to differences in seating depth and barrel. My STI was a slow barrel with a long throat. No issues with feeding or stability, accuracy was a bit less than with a 147 running at 130 PF, but still acceptable. Sadly I can't run that load anymore because when STI rebarreled my gun they gave me a 9mm with a MUCH shorter throat. I haven't got around to playing with new loads for the new barrel. 

 

Sourced the bullets from BNB casting. https://www.bnbcasting.com/9MM/cat1287790_2140749.aspx

 

The bullets themselves are pretty large. For reference: 

9mm casing - 0.75"

147 Acme FP - 0.6480"

170 BNB RN - 0.7650"

Edited March 26, 2018 by JRM83