Accurate #5

[Brick]

Happy Day! (well sort of!) I made it to the range today for another round of load testing.

This time it is Accurate #5 in .45 ACP. I made a couple minor changes. One I moved the Chrony out to 15' as suggested by Accurate Powder's ballistician, and two I changed my postion slightly so there was no bench under the muzzle of my revolver. But my arms from elbow to wrist were fully supported by the bench. The revolver was grasp with two hands, fired single action and allowed to recoil normally.

Again I was firing at a 25" wide by 65" high target carrier with a standard 50' bullseye target tacked to it as an aiming point. Accuracy results were miserable, no groups were produced. Shots scattered in a random manner from side to side and within the top 3 1/2 feet of the target carrier. I can only guess that my revolver doesn't like to be fired from the bench so I'll have to conduct accuracy testing offhand. (This might explain the poor performance I see when firing from the prone position in PPC)

Velocity results were equally as scattered. And it appears that all I proved was that manufacturers data is not to be trusted for velocities.

At the starting load my average velocity was 137 fps below published data. Roughly 15%. Likewise testing at 0.1 intervals is a waste of effort also. Velocity increases varied from 10 fps to 20 fps.

But, it appears that I'll be able to make my required 825 fps at between 8.3 and 8.5 grains of powder.

[Pizza Bob]

Velocity results were equally as scattered. And it appears that all I proved was that manufacturers data is not to be trusted for velocities.

At the starting load my average velocity was 137 fps below published data. Roughly 15%. Likewise testing at 0.1 intervals is a waste of effort also. Velocity increases varied from 10 fps to 20 fps.

Brick:

You stipulate that you are using a revolver (25, 625 or 1917 I assume). Most likely the published data was arrived at through the use of either a pressure barrel or a closed breech semi-auto. Velocities would be expected to be lower with the barrel/cylinder gap of the revolver dissipating some of the "push". Plus, of course, you would need to know not only the type, but the length of the barrel used to arrive at the published data.

I am also not sure that I buy the revolver not shooting well from a rested position - not disparaging your ability, but this has never been my experience - mine have always shot well from a rest. As is usually recommended in these incidences, take a friend along next time and let them shoot also to see if they have the same result. Good luck in your quest.

Adios,

Pizza Bob

[Brick]

You stipulate that you are using a revolver (25, 625 or 1917 I assume). Most likely the published data was arrived at through the use of either a pressure barrel or a closed breech semi-auto. Velocities would be expected to be lower with the barrel/cylinder gap of the revolver dissipating some of the "push". Plus, of course, you would need to know not only the type, but the length of the barrel used to arrive at the published data.
snipped

An interesting assertion and well worth considering. Here's the results of a test to compare the effects in the revolver vs, semi-auto debate.

VELOCITY COMPARISONS: REVOLVER VS. PISTOL

S&W REVOLVER

LENGTH CYL GAP STND
(INCHES) (INCHES) VEL (FPS) DEVIATION

4 .004 808 14
5 .006 823 14
6.5 .007 822 16

1911 PISTOL

LENGTH STND
MAKE INCHES VEL (FPS) DEVIATION

Brown 4.25 766 18
Wilson 4.25 812 22
BarSto-1 5.0 843 16
BarSto-2 5.0 864 15
Kart-1 5.0 869 9.3
Kart-2 5.0 873 6.6
Colt NM 5.0 859 14

All ammunition is CCI Blazer Brass 230-grain TMJ from the same lot.
Velocity is the instrumental average of 10 shots over a PACT
chronograph.

Read the whole article at: http://findarticles.com/p/articles/m...1/ai_n7581216/

Using this data we see the 4" revolver at 808 fps and the 4.5" Wilson Semi-auto at 812 fps. A whole 4 fps difference. Even using the extremes of 873 (Kart-2) and the 4" revolver the difference is still only 65 fps. Or stated differently less than 1/2 the difference between my data and the published starting load velocity.

If we consider that the bullet itself will seal the cylinder gap briefly and that the bullet might well be beyond the muzzle (where the expanding gases no longer have effect) by the time gas starts blowing out the gap, we start seeing that the gap might have a negligible effect.

I recognize the test presented is limited and there are many variables that effect the velocity and the measurements we make with our limited equipment. Is the gun barrel smooth or rough? Is the battery in the chrono at full power? Powder charges are weighed to the nearest 0.1 grains but because of that limit, they are really + or - 0.05 grains.

And just so I don't forget, Accurate Powder says they used a 5" barrel to develop their data and according to their ballistician there is no difference in velocity data from a test barrel or semi-auto.

[Pizza Bob]

My head hurts.

Too much data to crunch with way too many variables. You can't take a 5" revolver and compare it to a 5" semi-auto and say the difference results from XYZ - because of many of the variables you pointed out. Also don't forget the barrel dimension on a semi-auto includes chamber length (muzzle to breech-face), while on a revolver the barrel length does not include chamber length (muzzle to cylinder face, minus cylinder to barrel gap). You can also get variable and/or tolerance stack, which can really skew things.

I know that you are trying to match ballistic data, all I can say is good luck. One test, conducted by one of the gun rags years ago, that eliminated a lot of the variables, was strictly how barrel length affects velocity. They accomplished this task by using a T/C Contender and simply sawing off an inch of barrel (and recrowning) after each series of shots (same ammo throughout the test). IIRC they got pretty consistent results, as you would expect, since they eliminated variables and simply demonstrated the linear relationship of barrel length to velocity. But to take multiple guns and test barrels and try to do some kind of correlation with load / velocity / barrel length et al, is tilting at windmills. Find a load that doesn't exceed max (or show pressure signs) and that makes the power threshold you need and stick with it. Sometimes we tend to overthink things. Good luck.

Adios,

Pizza Bob