10mm Short barrel / Derringer loads

[Forrest]

So I did the prerequisite searching and read a few really good threads that contained some great ideas about 10mm loads. I'm trying to come up with the most effective load I can have out of really short barrels. I'm going to have a 3" barrel as measured from the muzzle to the breech. That gives me essentially 1¾" of rifling to affect the bullet and same to accelerate the bullet.
I have the following questions about this:
What kind of accuracy are people getting with resized .41 magnum bullets?
Do I have sufficient velocity to make use of the .41 bullets or would they require even more than lower 10mm velocities to work?
Should I look to another powder besides Aa#7 or 9 for the short barrels?
Staying in 10mm bullets should I stay on the lighter end in JHP to keep velocity high or opt for a hard cast on the heavier end of the spectrum for more retained energy and give up on expansion all together?
I found the following threads very interesting during my search:
http://10mm-firearms.com/reloading-10mm-ammo/41-magnum-bullets-in-a-10mm/45/
http://10mm-firearms.com/factory-10mm-ammo/underwood-xtreme-hunter-150gr-defender-100gr-hardcast-and-grizzly-155gr-xtp/

As always thanks for the input.

[sqlbullet]

The good news is you actually have a bit more space for acceleration.  This distance is measured from the where the base of the bullet starts until it clears the barrel, so it will be closer to 2.25".   

This barrel is .75" shorter than a Glock 29.  Ballistics by the Inch tested a variety of 10mm loads down to 3" measured breech to muzzle.  The full power Buffalo Bore 180 grain clocked at 1250 fps.  That is plenty effective.

In general the same powder that gives the best performance in one barrel length will give the best performance in all barrel lengths.  Reloader has done a couple of articles on this topic over the years.

It is a pretty common mis-conception that slower powders work better for longer barrel.  You see it all the time in forums.  Comments like "It has a 26" barrel so I thought I would start with the slower powders".  The idea is that a slower powder provides better pressure down the tube.

But that isn't really what is going on.

Powder burn rate is really a measure of its gas expansion rate.  Fast powders expand faster, slow powders expand slower. 

With that in mind, think about the cartridge/chamber/barrel as a pressure vessel, and the bullet as pistol that adjusts the volume of that chamber.  As the bullet moves down the barrel, the volume of the chamber increases.  We want a powder that has an expansion rate such that it keeps the pressure at or near the maximum pressure for the system or at least as close as possible.

If we use too fast a powder, then at some point the expansion rate of the gas will exceed the expansion rate of the chamber and pressure will spike above the limit.  If we use too slow a powder, then the expansion of the gas will lag so far behind the expansion of the chamber that we never reach maximum pressure.

If we use this model as a hypothesis and start making predictions about what this would mean in real world use, we get a couple of testable use cases.

One, we know that bullets of higher mass will accelerate more slowly given the same pressure.  This means the volume of the chamber will increase at a slower rate, which would indicate a slower powder would be better for heavier bullets.  This is confirmed in load data and in real world tests.  As bullets get heavier in any cartridge, but powders that deliver the best velocity get slower.

Two, we know that the larger the initial case volume relative to the bullet diameter, the slower the expansion ratio.  The 444 marlin has twice resting case capacity of the 44 special.  This means a 444 marlin bullet has to travel twice as far each time it wants to double the inital case capacity.  It's expansion ratio is half the 44 special, which would indicate slower powders.  And we find that is true in the load data and real world tests.

Since the final volume of the expansion chamber is NOT a factor in the expansion rate or expansion ratio, we would predict it would not impact which burn rate of powder would be ideal. And in general testing, this also holds true.

I would certainly start with your best loads in other 10mm guns.

[The_Shadow]

Forrest, sglbullet brings up some good points.
A derringer is what they call a belly gun...you stick it in the perp's belly and squeeze one off!  If it moves squeeze off another.

With that said, you might want to use BE-86 (a flash suppressed powder) 8.8 grains under a 155 grain Gold Dot.  It should be about the right burn rate to get you a proper head of steam...
The 155 or 165 grain Gold Dots would probably yield good expansion in the velocity range you would get for the shorter barrel pistol.

AA#7 or LOVEX D037-01 or the Shooter's World "Major Pistol" would be other choices using AA#7 data

[Forrest]

Thank you both for your highly informative responses. I feel a little better about it now. Apparently I just need to get the gun made and then get some ballistic gelatin and go from there.
I'm running a 180 JHP xtp clone over 14.6 of #9 or 12.5 of #7. It was trucking out of my 5" DE somewhere between 13&1400. I don't recall exactly and don't wish to exaggerate.
For practice loads I'll just shoot American Eagle because it's pretty weak and won't cycle the DE.

I'm working off the range hot article and have communicated with Hunter, who has been as accommodating as can be in recalling the details of his test some several years later. It was based on vanilla factory loads. I am going to try my favorite Aa#7 and #9 loads which should be quite stout, but provide the necessary velocity for the expansion.

With regard to derringer accuracy it would appear that the common misconception is that they aren't very accurate. I feel like this is perpetuated by the .45/.410 crowd that has free bore to high Heaven and not a lot of rifling to stabilize the projectile. As a result some of the bullets tumble badly. After all they are only putting the grooves to get around a regulation. Secondly, it would appear that people are comparing two unregulated barrels and the common group they produce to a single barrel with regulated sights. If we figured the offset or inset that the barrels would need to be collimated at 20 yards or so then folks would be singing a different tune about derringers and their accuracy.
I've actually read about folks that tested the mechanical accuracy of the barrels individually and found them to be on par with the handguns of similar barrel length.
Any how I am just looking at a toy in my favorite caliber.

[sqlbullet]

I would have no reason to doubt their accuracy.

People tend to blame the gun, and it has gotten worse over time, not better.

Small gun, short sight radius, heavy hitting caliber and short grip all make for a gun that is hard to shoot accurate.  Especially twice in a row.   

Up until about a year back I didn't own a handgun more powerful than 10mm, so I rarely practiced with true "big bore" power in the 44 mag range.  I have a friend and shooting buddy who has a 629 with a 6 or 7" barrel.  Every time I would shoot that gun the first round would be in the X ring, and the second would be wild, often off the paper.  Rounds 3-6 I would settle down, get my head in the game and usually put up 10's and 9's.

Thats gotta be worse with a derringer.  And it is easy to blame the gun, rather than look at the man in the mirror who flinched.

[The_Shadow]

sqlbullet explained the short barrel/derringer accuracy that I think of when in a defensive situation and putting the firearm in to action quickly.
Yes they can be very accurate with well aimed shots.  I can't tell you how many snakes lost their heads along the bayous with a S&W model 10 2" 38 spl. 

My reason for suggesting faster powder is to yield a more complete burn before the bullet exits the cartridge and also the barrel.  Having shot over a chronograph I can tell you powder particles can out run the bullet for some distances.  They can trip the sensors if the distance is not great enough...

[Forrest]

So if I had to go 180 grain the verdict is more in favor of #7 than #9?
That's a long barreled .44. My introduction to that caliber was in a 3" Lew Horton with pacmayr grips. It was fun.
I'm currently playing accuracy quest with the NAA Mini in .22 Short. When the bullets don't keyhole it's quite nice. You gain a lot from a trigger job and action tuning. You gain even more figuring out how to do both.

[The_Shadow]

I would opt for the AA#7 from the shorter barrel, save the AA#9 for the longer barrels...