load test

Justjump

I was a little bored this morning and tried an experiment and got some interesting results.
Loading very soft loads in .44mag. Two guns 5 1/2 redhawk and a Win High Wall 21" barrel.

CCI primer, R-P brass 8 grains of unique. 3 cast bullets weights 240, 200, 180
Now the interesting part. 6 shot avg per string
240 g redhawk 865 ---- Highwall 1169
200 g redhawk 820 ---- Highwall 1210
180 g redhawk 780 ---- Highwall 1235

I don't think I would have guessed that velocity would have gone both directions. Just an interesting observation. I did the test twice and got same results.... Hmmmm

rhope

Just my guess.

The heavier bullets take more pressure to start moving, leave the muzzle later and therefore the powder is burned more completely.

Justjump

I thought of that. but based on that then the lighter bullets should be a lower velocity, all other components being equal. I don't think its an effeciency issue. I suspect that the load just barely makes the threshold showing gap loss in the revolver. Then allowing full use of the small amount of expanding gases in the High Wall.

Rocky Raab

For what seems like the 947th time I've written this, the idea that powder burns all the way down the barrel makes perfect intuitive sense - and is absolutely dead wrong.

What we may have is a pressure threshold issue. All powders burn best in a given "window" of pressures. Too much pressure and the powder can produce erratic pressure spikes. Too little pressure and the powder burns poorly. Some of it may not burn at all and some of it can actually go out after partly igniting. The latter is what I think we see here.

The heavier bullets provide enough inertia and drag that pressure can build to a respectable level before crossing the cylinder gap in the revolver, where some of the pressure is dumped. The lighter bullets offer less inertial resistance and the powder never really gets going - and then much of even that pressure is lost at the gap. Whatever powder hasn't burned or ignited yet never will because the pressure peak has passed.

In the closed breech rifle, the bullet mass is the controlling factor, allowing more acceleration even though the powder burn is less efficient with the lighter bullets.

If you increased the charge a bit, you'd likely see the revolver velocity progression reverse itself, simply because more powder produces more gas which in turn creates more pressure. That in turn again allows more OF the powder to burn faster and more completely.

Justjump

Hey Rocky, Your last sentence pretty much describes my finding. I just thought it interesting that I could actually display the phenomenon. Granted a lot of luck was involved, just nice to see an actual as opposed to a hypothesis or opinion. When I mention effiencey, I'm referring to gas expansion. Honestly, some of us do understand a small bit of thermodynamics. I was just sharing a safe experiment for the purpose of stimulating thought. For a practical load it just doesn't really cut it.

All in all I'd say that we are both on the same page[;)]

Rocky Raab

And a damned good experiment it was, too. (Just between us chickens, if you even mention thermodynamics, most people's eyes glaze over. Even though I'm a math *, I understand the underlying ideas - but I have to explain them in JoeSixPackian, LOL!)