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Decrease in velocity with increase in powder? Any explanation?

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Hi all,


New to the Forum; just registered today. I've been reading these forums and hoped I could get some help from someone more experienced than myself


I'll start this off by saying I'm relatively new to reloading (been reloading rifle for around 3 years), newer to pistol reloading (been reloading pistol for around 1 year), and I just bought a 10mm 3 weeks ago so I'm very new to reloading 10mm. Like most here I didn't pick up a 10mm to shoot .40 s&w power loads; I want the hot stuff (within reason).


I decided last week to see how fast I could push a 180 grain XTP with Power Pistol. I intended to load the 180 grain XTP over 9.4 grains PP @ o.a.l of 1.26", then increase by 0.1 grain increments until I either saw pressure signs in the brass or achieved 1400 fps, whichever came first (I had previously safely loaded up to 9.4 grains PP). I am using new starline brass and Winchester primers, firing out of a Rock Island Armory 1911 5". Below are my results:


180 grain XTP @ 1.260" O.A.L. (5 shots each)


9.4 grains Power Pistol

Average velocity: 1292 ES: 57


9.5 grains Power Pistol

Average velocity: 1308 ES: 48


9.6 grains Power Pistol

Average velocity: 1319 ES: 21


9.7 grains Power Pistol

Average velocity: 1290 ES: 35


9.8 grains Power Pistol

Average velocity: 1292 ES: 66


I stopped at 9.8 grains, although my brass never showed signs of over pressure aside from slightly flattened primers. No case bulges, excessively flattened primer, primer piercing, etc. I loaded up to 10 grains, but did not fire past 9.8 as the dropping velocities made me nervous. I also note the relatively large ES.


This brings up several questions:


1) Why would my velocities decrease as my powder charge increased?


2) I am more experienced in long range rifle reloading and have never crimped rounds on my bolt guns. These 10mm rounds were all without a crimp. Could that be affecting my ES and velocities? Is crimping mandatory when developing hot loads?


3) Are there any suggestions on how I could get to 1400fps? change powder? different crimp? etc. Is it possible that ~1300fps is the limit with my gun for a 180 grain XTP?


I realize that these are very hot loads, but the thing that makes me want to keep pushing it is the brass seems fine. I've read several of the posts on this forum with some reaching velocities into the 1400's (albeit they were probably using 6" barrels). I'm not trying to push my luck too much, but just cant wrap my head around why my velocity would decrease as my powder charge increases.


your responses will be appreciated!






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That looks like the powder is not fully burning at the higher charge weight.

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Thanks for the reply Flesh Wound!


Any way to fix that? Or would I just need to try a different powder?

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You can live with the better performing loads with Power Pistol (Which is a powder I love in semi pistols) or you can try other powders. I'd spend some time looking at *published* load data and see what other options you have. Pushing a 180 grain pill that fast is pretty dang impressive from any handgun. You usually see those sorts of speeds (and faster) from Magnums and much smaller lighter pills like 30 caliber.

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I think you are going to have a hard time getting to 1,400 fps. Here's some data from Hodgdon.




Sorry the stinking table would not display


The hottest load using Hodgdon powder was 9.5 grains of Longshot for 1,287 fps, 34,600 PSI

Edited by Flesh Wound

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TJ beat me to it.


You may have the powder in to a density that a standard primer is not igniting as much of the powder at the same time as it would with increased surface area to ignite more powder at once. A hotter primer may be able to ignite more. You would have to back down the load and work your way up again


A faster burning powder would seem to be the other option, or a longer barrel to allow more burn time.

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Thanks for the replies!


I'll go pick up 100 magnum primers to see if that fares any better.


I've read several posts from Taosglock who seems to be achieving these kinds of velocities, maybe I'll get lucky and he'll post here to let me in on how he does it.

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Ok I've got an update with magnum primers


Following results were with CCI 350 large pistol magnum primers. Brass was new starline, using 180 gr XTP over Power Pistol at OAL 1.260. Fired from a Rock Island Armory 5" 10mm.


(5 shots per)


9.1 grains PP

Average velocity: 1299 fps ES 26


9.2 grains PP

Average velocity: 1306 fps ES 16


9.3 grains PP

Average velocity: 1328 fps ES 48


9.4 grains PP

Average velocity: 1327 fps ES 32


9.5 grains PP

Average velocity: 1325 fps ES 46


9.6 grains PP

Average velocity: 1337 fps ES 52


9.7 grains PP

Average velocity: 1332 fps ES 22


9.8 grains PP

Average velocity: 1342 fps ES 70


9.9 grains PP

Average velocity: 1359 fps ES 73


10 grains PP

Average velocity: 1327 fps ES 82


Again, the velocity decreased as the powder charge increased with the magnum primers as I reached the higher powder charges, but accuracy was substantially better after switching to the CCI 350 magnum primers. I had two 5 shot groups (9.2 grains and 9.6 grains) which hovered around 1 inch @ 15 yards ( .98" and 1.03" respectively). My loads with the standard WLP primers hovered around 2-2.5 inches @ 15 yards.


Starting at 9.8 grains PP I began to see mild cratering of the primers. I see no reason to push velocities any further and I'm happy with an accurate load that is still averaging 1337 fps. Of course, I can't be confident with a 5 shot group. Time to load up more batches of 9.2 and 9.6 to test 10 shot groups!


Thanks to everyone who contributed and hopefully someone besides just me can learn something from this.

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Ok, there's only three options.


No 1, you tried incomplete burn. That's powder doesn't burn, not in the shell case but its still burning as it leaves the barrel. This you will notice a bigger than normal barrel flash, quite pretty at night.


No 2, You still have an incomplete burn after using a magnum primer then its your powder choice is too slow. Choose a faster powder from the powder charts that's rated for pistol and there's a load data for your bullet weight. Pistols are not rifles where slower you go the better because they have very short barrels. That's why there's pistol powders instead of one powder does all, though arguably Clays works pretty well in handguns and shotguns. Now the exception to this is shape of the powder. Longshot actually is a very slow burning powder but burns quicker when under a compression load due to its long rod shape. Compression load is if you listen, you can hear it crunch when you seat the bullet.


No 3, Your bullet is out of spec allowing it under more pressure to either deform or tilt (too small a diamter for your barrel). This causes drag, more friction coming out. They would cause more recoil than normal. Pretty much that means the bullet you are shooting is not rated for the pressure. Lead bullets for example, tend to deform at hgher pressures. Too much play in a bullet, you can use your micrometer at the widest point and get an idea, however deformation you can't tell really because its after the fact.


Now i can't help you much on powder selection. I don't do 10mm. Though I'm damn certain I would love the caliber, there's a few like that, I don't want to add anymore calibers unless I have to. I have too many as it is. I do load the two traditional magnums .44 mag, .357 mag, and .45 acp in the same weights. What I can tell you is my powder selection, other than the slow burning long rod Longshot, is radically different. The revolver magnums especially 44 mag are rated for a lot more pressure. What I look for then on a pistol load is fastest powder with the best velocity to pressure ratio I can find. Though not important on say a .44 mag, it is very important on a semi because that controls recoil so you want a fast burner, more pop than shove recoil, so your back on target is quicker. Too often people look at load data then simply pick the one with the highest muzzle velocity and don't realize that muzzle velocity is for a given barrel, their test barrel, and a given bullet, their bullet. The better data gives you that information, test barrel and brand type of bullet so you have a better idea. Lacking that, you want the fastest burning powder, highest muzzle velocity, at the lowest pressure to insure a faster recoil thus faster back on target. Burn charts will simply rated by numbers fastest to slowest. You can find many either by powder manufacturer or general on the net.


Other than the basic rule, don't overload a lead bullet, that's about the order of priority, primer, powder, and bullet. I only put bullet last because by the time we find something like that out, we already own the bullets.


In general for handguns its not any different than rifles. Our priorities in loading are the same and its not go as hot as we can go. Its a balance between speed, what hits the target (accuracy), and recoil back on target. Too fast is as bad as too slow. 1,300 fps for a 180 grain pistol bullet is very respectable. Its on a mathmatical average 300 fps faster tan a .45 and 300 slower than a much larger case and way more pressure .44 mag.


Hope this helps.



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Ok thought of some stuff I forgot. I believe its Hornady that has a great explanation of bullet dynamics. It explains the importance of things like bullet position, jumping the gap to the opening, and the hunting and finding a bullet does before settling into the grooves. That last part is real important on a handgun because its so short. If you are so fast for a given bullet the grooves aren't grasphing it, it will be all over the target because there's no predicting what angle they come out.


Handguns are not like rifles, unless the bullet is a known entity, we can't just chrono them, we need to see how well they hit the target. Though the brass part of the loading is more forgiving, the actual ballistics are harder due to our shorter barrels.


There's theory and practical application. If theory was king then we'd see sniper rifles with fat 5" or less barrels. It doesn't work that way. The Hornady site will give you a good understanding of why. There's a lot more going on than bullet takes off and grooves add the spin.



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One other thing to consider is using a magnum primer can dislodge the bullet and start it moving before complete ignition of the powder. This can be effected by several factors.

The semi auto relies a lot on the case to bullet tension in the effort to secure the bullet. Proper taper crimp can add to the hold and improper crimp can be detrimental to the point of being loose. As the case lengths can differ, it will change the crimp strength and effectiveness.


Faster burning powders can snap the case expansion faster which can cause case splits.

Slower burning powders usually yield better velocity with lower pressure.

Finding a balance of burn rate and performance is key! Alliant BE-86 is showing good results in addition to 800X, LongShot, Blue Dot, Power Pistol, AA#7, AA#9.

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It has been a while, but i used to reload for pistols.


I would consider a taper crimp, may help with those ES fluctuations.

Although I have not loaded 10mm, I had great luck using a taper crimp with 9mm

when I was trying to duplicate the ISP 9mm +P+ load in a Browning Hi Power, and later a Glock 19.


But You need to check with the experts here before trying the taper crimp on non cannelure bullets

to make sure I am not steering you wrong with the 10mm.


A faster burning powder seems like the next step, but I would start over without the magnum

primers. (unless they are called for normally in the 10mm, IDK.)

As someone mentioned, I would spend more time looking at published data from the tried and true major reloading manuals.


I understand your wanting to get the most velocity out of a load,

but please also consider the wear and tear on your pistol.


A hot 10mm with the right bullets is at the lower end for something you can always have on your belt for bear medicine.

Is that you goal?

Are you trying to load for a self defense round for 2 legged varmints, or are you climbing this mountain because it is there?

All reasons are GTG, IMO.

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A taper crimp is exactly what you want on non-cannelured bullets. Roll crimp is bad and no cimp is..NOT GOOD..LOL



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