9mm 124 gr. FP Reloading Question

[dleong]

Hello, all.

I have a quick 9mm reloading question that I wish to pose to the experts in this forum.

But first, a little background: I recently acquired some Rainier 9mm 124 gr. FP projectiles to handload 357 Sig cartridges for a SigPro SP2340.

I have handloaded tens of thousands of 9mm cartridges using 124 gr. RN projectiles with great success, and thought it would be interesting to see if I could duplicate or improve the results using FP projectiles instead. And since I had several hundred of the FPs on hand...

The COAL of my usual 9mm 124 gr. RN loads is 1.140". The lengths of the RN and FP projectiles are 0.584" and 0.534" respectively, for a difference of 0.05". This would mean that, in order to maintain the same case volume, I would have to size the FP cartridge at a COAL of 1.140" - 0.05" = 1.090". When I loaded a dummy FP cartridge to this length, I immediately noticed that the straight-walled portion of the projectile extended significantly beyond the case mouth and was engaging the rifling before the cartridge could chamber fully and headspace correctly in all of my 9mm pistols. Only when I reduced the COAL to about 1.055" did it fully chamber in all of them. This also means the case volume is now 1.090" - 1.055" = 0.035" less than that of my usual RN load.

Now the question: assuming I use the same powder charge in the FP cartridge as I do now in my RN ones, will the reduced case volume drive pressures in kaBOOM! territory? Rainier's website does not provide any load data for this projectile.

If it helps, my current 9mm target load is as follows:

124 gr. 9mm Berry's TCJ-RN projectile
4.4 gr. Universal powder
WSP primer, mixed cases
1.140" COAL, light taper crimp
Approx. 1100 fps out of a 9mm CZ 75B

Thanks in advance.

 

[bill in IN]

The normal routine I subscibe to is when changing any component or dimension is to reduce the charge by 10-20% and work back up. This should work in this instance. If it is a load that you have used quite a bit you should have an idea how much to reduce. Usually I do one round down then step bakc up- but I only need walk about 25 feet to find the answer, if you need to go to a range it could be a problem.

 

[robertbank]

I am confused! If the FP bullet is shorter than your RN and you load it out to 1.114 the case volume should increase not decrease. If this is true then you can reduce the OAL of the cartridge by the difference and still maintain the same volume within the case for powder. Assuming the ogive does not interfere your cartridge OAL would fall to 1.09 to maintain the same internal case volume. If the OAL of your cartridge, to seat properly, has to be 1.09that represents only a 5/100th reduction in case capacity. FYI Hornady lists FMJ - FP with a COL of 1.050. I have to think you will be OK with the OAL you have quoted.

Take care

 

[dleong]

Bob,

The FP projectile is shorter than the RN one. If the FP projectile is seated to a depth that maintains the same internal volume as with the RN projectile, the COAL is reduced by the difference in the lengths of the two projectiles (i.e., 0.05"), to 1.090". However, at this COAL, enough of the straight-walled portion of the FP projectlle is exposed to prevent the cartridge from chambering fully because the projectile is butting up against the rifling.

The FP projectile needs to be seated deeper for the resulting cartridge to be able to fully chamber--in this case, the "magic" COAL is 1.055". This means the bottom of the FP projectile now rests 0.035" deeper in the case than the bottom of the RN projectile. And I am sure the difference is more than 5/100th, as the space in the case for the powder does not extend all the way to the rear of the cartridge.

Gotta love the experimentation that comes with reloading!

 

[HSMITH]

Set your seating die with a known good combination and/or a factory round that you KNOW feeds well. Leave the seating die alone after that!!! Load your new bullet, check OAL and adjust charges accordingly. A lot of times we make this stuff a lot harder than it needs to be. If the OAL is short of data reduce charges by at least 10% and work up. If OAL is longer than data start with starting data and work up.

 

[GunAdmirer]

The Hornady manual gives an OAL of 1.050" for their 124 grain flat point. A friend and I use the Berry's (near identical) version of the flat point bullet at that OAL with great success.

There is more to seating depth than the difference in the length of the bullets. I don't understand it, but the OAL I found in the Hornady works well in my application.

 

[dleong]

The Hornady manual gives an OAL of 1.050" for their 124 grain flat point.

Thank you for that information, sir! I do not have the Hornady manual, so I appreciate the numbers.

So it looks like I should not have much to worry about with a COAL of 1.055" then.