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Old December 3, 2009, 01:30 PM   #1
bkhann
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9mm Hot Loads?

I got a recipe for a 9mm load off of Handloads.com website. 9mm---124gn FMJ --- COL 1.142” --- 5.7 gn VV N-340 --- 1227 FPS

I loaded a bunch of these and it feels like a good strong load, however, when I ran these past my new Shooting Chrony Beta Master my average speed was 1751 FPS. None of the cases show evidence of overpressure and my pistol is rated for +P+ rounds, but I am concerned that I might be shooting seriously too hot a load.


Your thoughts?
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Old December 3, 2009, 01:46 PM   #2
bozhoz
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I would guess chrony error- buy some regular rounds with stated velocity on the box and double-check the accuracy of the chrony. 1700 fps sounds REALLY fast in a 9mm 124 gr. I would think if it was truly that fast, the gun would blow up. I know the relationship is by no means linear, but just some napkin math using IMR powder and 124 grn, velocity 1015, pressure, 27,700 PSI; velocity 1115, pressure 32,700 PSI- starts to put us in the 50,000 PSI range at 1700 fps. I would really think something at that PSI would feel a lot more substantial than just a stout load and should probably be causing some major damage to the firearm. Again, numbers seem way too high to be real, so I would really double check the chrony.
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Old December 3, 2009, 02:00 PM   #3
Jim Watson
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Depending on the exact bullet, that load is at or above the Vihtavuori maximum. But 1700+ fps is not realistic.
How close are you to the chronograph? Ten feet to the start screen is usual. Closer will get you strange numbers from shockwaves.
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Old December 3, 2009, 03:16 PM   #4
bkhann
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10 feet from the chrono. This was my first day with any chrony and a cloudy day to boot. I will try again on a little brighter day.

Is there a mathamatical formula for calculating pressure when you know bullet weight and speed?
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Old December 3, 2009, 03:58 PM   #5
bozhoz
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I am not aware of any mathematical formula. Every powder produces different pressure curves with too many variables to lay down a firm formula. There is some software out there that can approximate the pressure based on many variables that you put in, but again, WAY too many variables to apply a cookie-cutter approach to bullet weight/velocity/pressure. Suffice to say, I think you are probably at or near a max load, but by no means approaching 1700 fps. When you get the chrony working right, you'll probably see it's more like 1200-1250. When in doubt, back it down a little on the powder charge. Maybe take it down to 5.5 grains until you are sure you are not too hot.

Last edited by bozhoz; December 3, 2009 at 04:01 PM. Reason: spelling
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Old December 3, 2009, 04:50 PM   #6
Foxbat
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The QuickLOAD sez you are lucky you brought back your eyes. Of course 1700fps is just a joke, but depending upon the exact bullet type you are in the red pressure zone.

For instance, for 124, Speer TMJ 3993 bullet the program gives the max pressure of 46,096psi - this versus the limit of 35,000.

What bullet did you use? Just to say 124 grain FMJ is not saying much.

The program also indicated the velocity of 1277 for a 4.5" barrel.

Substituting the 125, Speer TMJ 4362 bullet results in peak pressure of about 32,000 - something that might still be too close for comfort.

The difference is in different length of the two bullets. The longer one, for the same COL, leaves less internal space, hence higher peak pressure. The first bullet is .595" long, the second - .525".

The difference in internal space using these two bullets is over 20%!!!!!

THIS is the big problem with the Internet site recipes... you can take very similar components and end up with a VERY different result. Especially for the small case ammo, like 9mm.

Last edited by Foxbat; December 3, 2009 at 05:01 PM.
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Old December 3, 2009, 05:03 PM   #7
Foxbat
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Quote:
Is there a mathamatical formula for calculating pressure when you know bullet weight and speed?
There is no such "formula", but there is the program called QuickLOAD that does that, while considering whole host of parameters. You can buy it for around $160. It is an absolutely marvelous tool if you are considering leaving the beat path of book recipes.
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Old December 3, 2009, 05:07 PM   #8
edward5759
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Are you sure

The chrono my have said 1251
The bottom of the "2" may have been blocked or you didnt see it.
1251 is about right with that load.
also the LCD, LED on the bottom of the "2" could be out that will give
you a "7".


and if you had a 3 though 6 you would have had a straight

Ed
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