Questions about 9mm luger data

[Grunt81]

Using the technique I described above, I figured that bearing surface/shank of my 147 grain copper plated round nose is 0.290'' long. 80% of 0.290" is 0.232". I marked that part of the bullet and made a dummy round. I realized that the OAL that I'm using of 1.152" is right on the money at seating 80% of the bullet shank.

[J-cat]

Hmm, very helpful info. I've read before that a 0.355 diameter bullet in 9mm should be seated at least 0.355" deep into the case. I'll go ahead and measure my bullets from ogive to base, and try to calculate what OAL 80% seated will give me.

What do you think about this technique? In order to determine where the ogive is, I've resized a 9mm case and attempted to bullet in upside down. Wherever it sits, I mark it with a pen and consider that the ogive.

That's a good technique. I eyeball it myself, but yours is more scientific.

[ReadySteadySmash]

I have been researching 9mm loads and started asking around about the data differences. For example:

Powder Vihtavuori, Bullet Hornady 115gr HP XTP (35540).

http://www.vihtavuori.com/en/reloading-data/handgun-reloading/9-mm-luger.html

Hornady Reloading Handbook: 9th Edition

So I emailed Hornady support about the differences via email and got the below:

[CSACANNONEER]

Different manuals use different methods of testing. Length of barrels, etc. are all part of the final equation. Also, just because two bullets are the same weight, it doesn't mean they have the same bearing surface. So, cross referencing and asking questions is recommended every time you work up a new load. I commend the OP for asking about this.

[J-cat]

But the main reason for the OP cited discrepancy is the OAL.

Alliant used 1.125" and a Hornady used 1.090". Different OAL, different internal volume, different pressure.

[BLR81]

Hmm, very helpful info. I've read before that a 0.355 diameter bullet in 9mm should be seated at least 0.355" deep into the case. I'll go ahead and measure my bullets from ogive to base, and try to calculate what OAL 80% seated will give me.

What do you think about this technique? In order to determine where the ogive is, I've resized a 9mm case and attempted to bullet in upside down. Wherever it sits, I mark it with a pen and consider that the ogive.

I believe the rule about seating the bullet to diameter length relates to rifle bullets. An Extreme 124 gr plated round nose measures .590 in length. If you seat it to its diameter of .355 that only leaves .235 outside the case mouth and since the case is .750 your OAL would only be .985.

I'd say that would be too short, and possibly a high pressure situation. Using the 80% method, I came up with a total bearing surface of .290 appx. so 80% is .232 seated. That leaves .358 beyond the case, so the OAL with a .750 case would be 1.118. I normally would load them to between 1.115 to 1.125 so the 80% seems pretty close.

Of course, judging the actual bearing surface or where the shank starts to curve isn't exactly a perfect measurement but I'd guess that I was within .010". The 147gr Xtreme RN was .080 longer with appx. the same shank length, which put the OAL at 1.118 plus .080 or 1.198 which is quite a bit over the SAAMI max of 1.169.

The danger here is that the case seats based on the rim. If you load too long and the bullet touches the lands before the case mouth seats, you may end up with the case not totally supported so I wouldn't load past the SAAMI max OAL.

[BLR81]

After giving it some thought, I decided that I could get a more accurate measurement than I did the first time by sizing a case and inserting the bullet nose into the case and measuring from the bottom of the cast to the bottom of the bullet. What I got was that the 124gr measured 1.05" minus the .750 case length for a bearing surface of .255 instead of my original guess of .290. The 147 gr measured at 1.085 minus the case length so .335, and 80% of that is .268.

Taking 80% of the 124 gr shank of.255 you get .204, so using the bullet length of .590 minus the .204 seating depth would leave .386 extended out from the mouth, plus the case length of .750 equals 1.136 OAL. The 147gr length of .670 - seating depth of .268 leaves .402 beyond the mouth. Add the case length of .750 and it's OAL is 1.152.

Again there is some error in measurements, but I found it interesting that using the 80% method both Xtreme bullets calculated out to around the 1.140-1.150 range. That means that the 147 gr which is .080 longers would be set considerably deeper than the 124 gr at similar OAL.

I usually load the 124grs a little shorter than the 1.136 more in the 1.125 range but I usually load the 147grs at 1.150 so that's really close to the 1.152 I got from the calculations. But, I do load slightly on the light side so I don't have much concern there. So, the 80% rule of thumb seems to work, but starting low on you powder weight and working up still seems to be the prudent method for finding your max safe charge weights.