Long .40S&W experiment results

[Turo]

I'm sure most people have read my thread about my long loaded .40S&W ammo experiment.  (If not, here's the link http://10mm-firearms.com/10mm-semi-auto-handguns/glock-20sf-got-a-new-barrel-(kkm)/)

The idea was to be able to load a .40S&W case with a 10mm equivalent charge and OAL in order to not only make practice cheaper, but to explore something I found interesting.
The rounds fired were all made to an OAL of 1.228 inches, using .40S&W brass (most so far have been reloaded a few times).  I used CCI spp No. 550 primers.  Yes, magnum primers, but they served me well while loading .40S&W.  All powder levels are in grains, and powder used was Hodgdon Longshot. Bullets were 180gr Precision Delta (length of bullet is important here.  Bullets used are .592" long, with a bearing surface about .400" long.) I may attempt to do this with lighter bullets in the future, but I will need to do more research before I try it.  Barrel length is 6.02".  KKM 10mm-.40S&W conversion.

Powder Charge (gr)	Velocity    (fps)
7.1	1063
7.5	1139
8.0	1179

All velocities are averages of 5 shot groups except for the 8.0gr load, which had a chronograph malfunction during testing leaving 3 rounds with viable data.

So far, this data is still within .40S&W book values, except the OAL, and I haven't seen any pressure signs on any of the brass.  I wouldn't expect to though, as these rounds would be sufficiently low pressure enough to be fired in any .40S&W chambered pistol.

Here's a little video I made of the shoot:

I'll update when I have successfully loaded more.  Next up is 8.2gr, but they'll have to wait until the weekend.

[sqlbullet]

Interesting data so far.  Anxious to hear what happens as the loads ramp up.

You don't happen to have case head measurements do you?

[cwlongshot]

Interesting data so far.  Anxious to hear what happens as the loads ramp up.

You don't happen to have case head measurements do you?

FYI, Measuring case heads is useful in determining pressures. BUT you need to be above 40K for any measurable expansion. As you likely know, MOST hand gun callibers fall below this.

CW

[sqlbullet]

Yes, but I really regard it as the only reliable indicator of pressure, especially for rounds like 10mm.  Primers can get flat for a variety of reason, not all pressure related.

So, establishing where he is with case head at these  loads will help indicate when he starts to flirt with the low 40's in pressure.

[The_Shadow]

This is not all that bad being a long loaded 40S&W being shot in the conversion barrel whih has better support than the factory 10mm barrel.  The longer barrel helps the velocity even though he has less bullet tension.  Pressures should track fairly well only slightly higher than 10's due to the less case capacity at that load length.

[Turo]

No case had measurements yet, I'll grab those when I have some time this weekend.  This is a new barrel for me though, so these numbers will set the baseline for this brass/barrel combo.

Thanks for the interest everybody!

[Turo]

Had some time and measured the case web.  These measurements are taken at the widest point close to the extractor groove on the side the holds the bullet.  I'm not 100% sure on the terminology, but it's pretty much where the maximum expansion is.

The 7.1gr loads (what I consider mid range .40) gave .425"-.426"  My calipers measure to the thousandths, and the average measurement was right in between those.

The 7.5gr loads gave a solid .426".

The 8.0gr loads gave between .426" and .427".

I fired some normal OAL Winchester Ranger T 180gr ammo, which I would consider medium-mild loads.  They averaged 850fps out of a short (3.5") barrel, but unfortunately I didn't chronograph them out of the long (6.02") barrel.  The case web measured .426" on those.  They were nickel plated brass.

The chamber of the KKM barrel seems to be slightly conical with the front of the chamber smaller than the rear.  The front of the chamber measured .426" and the rear was .430".

I'm not sure what this says, but those are the measurements I got.  Keep in mind that all of these loads are within the listed "safe" loads Hodgdon gives for 180gr bullets and Longshot.

[REDLINE]

FYI, Measuring case heads is useful in determining pressures. BUT you need to be above 40K for any measurable expansion. As you likely know, MOST hand gun callibers fall below this.

CW

Interesting.  Never seen that brought up before.  Do you know of any online writeups on the subject that talk about that more indepth that you could link me to?

Please don't take it that I'm judging what you're saying, I'm just always searching for the "how and why" type explanations.

[cwlongshot]

FYI, Measuring case heads is useful in determining pressures. BUT you need to be above 40K for any measurable expansion. As you likely know, MOST hand gun callibers fall below this.

CW

Interesting.  Never seen that brought up before.  Do you know of any online writeups on the subject that talk about that more indepth that you could link me to?

Please don't take it that I'm judging what you're saying, I'm just always searching for the "how and why" type explanations.

I have read it by a couple authors... I need to look back to see just where.. BUT a quick Google serch revealed a article written by Ken Waters about 10 years ago. You will notice his charts on expansion start at 50K...

http://yarchive.net/gun/ammo/pressure_signs.html

CW

[REDLINE]

FYI, Measuring case heads is useful in determining pressures. BUT you need to be above 40K for any measurable expansion. As you likely know, MOST hand gun callibers fall below this.

CW

Interesting.  Never seen that brought up before.  Do you know of any online writeups on the subject that talk about that more indepth that you could link me to?

Please don't take it that I'm judging what you're saying, I'm just always searching for the "how and why" type explanations.

I have read it by a couple authors... I need to look back to see just where.. BUT a quick Google serch revealed a article written by Ken Waters about 10 years ago. You will notice his charts on expansion start at 50K...

http://yarchive.net/gun/ammo/pressure_signs.html

CW

Thank you!