"Unburnt" powder = Underpressure ?

[chriske]

Last winter I developed some new loads in .45 (Long) Colt for 225 gr. Hollow-based truncated cone plated bullets and VihtaVuori N-340 powder;.
Some excellent pointers by RidgwayCo (Hi, RidgwayCo, check the personal message!)
got me started at 7.9 gr and gradually I found two other very promising loads : 8.5 gr and 9.7 gr.
All three loads were checked out in my Ruger Blackhawk . (Haven't settled for one yet)
Last week I decided to give the lightest load (7.9gr) a try in my Cimarron/Uberti
They were wonderfully accurate (6-shot "one-ragged-hole" groups at 15 meters)
STRANGE : although the Ruger is about 9 ounces heavier, it kicks MORE than the Uberti with this load.
Moreover : the Ruger seems to burn up all the powder whereas the Uberti sheds large amounts of "unburnt" powder .
(Actually, I doubt it's really unbunrt: instead of gray-black it looks beige-brown, instead of hard the kernels are friable, so I guess they did get heated up some).
What I DO know is that the Uberti's cylinder chambers are pretty large, certainly larger than the Ruger's (back when I loaded cast bullets I could use .451 or .452 ones for the Ruger but had to find .455 ones for the Uberti.)
SO :that unburned powder/low recoil/ large chambers put together made me wonder if maybe the pressure my loads generate in the Uberti could be too low ?
Can low pressure cause unburned powder ?
Is there any way to avoid it (shame to waste powder !) short of going to a heavier load ?
But.... on the other hand... is it harmful ? Does it HAVE to be avoided ???

 

[Deus Machina]

(back when I loaded cast bullets I could use .451 or .452 ones for the Ruger but had to find .455 ones for the Uberti.)

I'm not the most knowledgeable here, but before they get around I'll chip in that that is probably part of the reason for everything.

Less constriction around the bullet means lower pressure, which means possibly lower velocity, possibly unburnt powders, and--all things equal--less recoil. It's also possible that the weight distribution on the Uberti affects it, or the grips just work better for you.

IIRC, .45 LC used a .455 or .458 way back when, but now often uses the .452 that .45ACP sort of standardized for everything. So your Ruger could be made for modern loads (or just have deeper rifling) and the Uberti is built for the old loads. Considering they're often centered for cowboy shooting, I'd bet on it.

 

[chriske]

Grips and balance certainly do influence felt recoil, I agree.
But I weighed both guns and the Ruger is about 250 grams heavier (isn't that 9 or 10 ounces, trhereabaouts ?) Plus : it was rubber-stocked and the Uberti wasn't.

 

[Alabama2010]

I'm glad you brought this up. I've had certain loads where the powder wasn't all burnt up, and they were light loads. Also, I've read that light loads sometimes lead to unburnt powder. I've thought that it was paradoxical since I would have expected the opposite- more powder in heavy loads leading to unburnt powder. Would be glad if someone could explain that.

 

[Deus Machina]

It's a pressure thing. Higher pressure forces more powder to burn, more quickly. That's also one reason the pressure curve as the powder charge rises isn't perfectly linear.

Think about it like gasoline. Have some in a bowl and drop a match in, and it sets it to a slow, sooty burn. Compress it in the pistons of your car, and--bang!

Slug the bore of the Uberti, if you can. I'll bet it wants .454 instead of .452, and if you try that size it will probably burn a little cleaner.

Try running it over a chrono, too. With less recoil, I'll bet the velocity's also lower than the Ruger right now.

 

[dagger dog]

Is the barrel length the same on both revolvers ? I'm not fimilar with Vit N340, but in Hogdons relative burn rate chart it is 6 steps slower than Unique which a lot of reloaders use to replicate the 900 fps blackpowder charge of the original .45 Colt loading. The bullet weight for the Unique replica charge is usually 255 grs, your 225 gr bullet coupled with the slightly slower powder , plus the over size cylinder throats of the Uberti could be the culprits.

 

[ranger335v]

" cast bullets I could use .451 or .452 ones for the Ruger but had to find .455 ones for the Uberti...
Less constriction around the bullet means lower pressure, which means possibly lower velocity, possibly unburnt powders, and--all things equal--less recoil."

Wellll, maybe, that sounds right anyway. Actually, all bullets swell up some when fired (obturate) and lead bullets often to do to a significant degree. Meaning even undersized bullets will often fill the bore quite tightly by the time they clear the case. On the other hand, if the burn rate is too slow...low peak pressures WILL lead to unburned powder. That's part of why reduced loads work better with faster powders, they can attain proper burning pressures even with light charges while slow powders can't.

 

[chriske]

dagger dog, :
Ruger Blackhawk : 4 5/8 " barrel (or is it 4 3/4 " ?)
Uberti Cattleman : 5 1/2 " barrel

 

[chriske]

Deus Machina:

That's about what I thought as well : makes sense, physics-wise :
As pressure rises inside the cartridge, the remaining powder burns up faster , raising pressure even more, resulting in even faster burning, etc.. until it's all burnt up.

So, in order to use (burn up) more powder, should I use (load) more powder ?
Weird, no ?

But is all that "unburned" powder really wasted ?

 

[Walkalong]

No, not weird at all. Yes, it is mostly wasted. Some of it burned. You can go to a faster power, or more (assuming you are not at max) of what you are using. In some situations you are simply using too slow of a powder and won't be able to fix it without switching powder.

 

[RidgwayCO]

Hi chriske, it's good to read of your success with your .45 Long Colt load.

I agree with Walkalong, what you're seeing isn't weird at all. I suspect what is happening is your minimum load is not expanding the brass enough to fully seal the (slightly oversize?) chambers in your Uberti, and thus not developing the pressure required to more fully burn the powder. The lower pressure would develop lower velocity, and the lower felt recoil would be a natural result of this lower velocity (a chronograph would be necessary to test this hypothesis).

To reduce the problem in your Uberti, you might want to shoot the more energetic loads in it and save the 7.9gr minimum loads for your Ruger.

And yes, when powder isn't burned it's "wasted". I use QuickLOAD software to try and develop loads that not only attain the performance I'm looking for, but to be efficient as well with at least 90% of the powder charge being burned before the bullet exits the barrel (this 90% figure is purely arbitrary on my part).

Enjoy those .45 Long Colts! Sounds like they're real shooters.

 

[chriske]

Many thanks to all for your valued input !

RidgwayCo, good to hear from you again. You expressed my vague thoughts far more eloquently than I ever could.

ranger335v : It's exactly to obtain optimum obturation that I've chosen those hollow-based bullets

Walkalong ; 7.9 gr VV N-340 is not at max by far for this bullets : theoretically I could (but won't) go up to 10.0 gr. And yes, if all else fails, I'll HAVE to try faster powder, I guess (that will probably mean VV N-320).

Thanks again to all, you're great guys !

 

[Walkalong]

My target/plinking load for .45 Colt uses AA #2. N320 is pretty close to AA #2 in how it behaves in numerous pistol calibers, except that AA #2, is less position sensitive. N320 still does well though. N330 might be worth a try, but it is a bit finicky as to what it likes. 7.2 Grs of N330 with a 225 Gr plated bullet gave me an average 638 FPS with a tiny bit of unburned powder from a 6" S&W 25-5. I started playing with AA #2 after that and did not pursue any more N330 loads. It will take more N330 than AA #2 or N320 to get the same velocity.

 

[Eagle103]

It's a pressure thing. Higher pressure forces more powder to burn, more quickly. That's also one reason the pressure curve as the powder charge rises isn't perfectly linear.

Think about it like gasoline. Have some in a bowl and drop a match in, and it sets it to a slow, sooty burn. Compress it in the pistons of your car, and--bang!

That's a very good way of putting it and it tells you why 50 grains for a particular load may be just fine pressure wise but going to 51 can be WAY too much.

 

[Clark]

I have the Uberti 45 Colt and the Ruger Blackhawk 45 Colt.
I shoot the Uberti at 1215 fps 250 gr, and it kicks.
I fired one shot from the Blackhawk with that load, and it cut my hand.
I have not fired the Ruger since.
I has been ~5 years, and I meant to break the edges on the poorly finished Ruger, but I have never got around to it.

The Uberti hit high, so I TIG welded some more material on the front sight.

 

[lwknight]

Just lay out a light colored tarp in front of your firing line. It will be amazing how much unburned powder lands on it. Very few powder/loads are really clean.
I know that some fired speer brass looks new with their secret powder recipe.

 

[Clark]

Don't shoot 800X over the hood of a car.
The big powder flakes will burn into the paint.