requesting info from an OLDER gun rag article

[uglygun]

One of the gun mags a couple years back did an experiment to find out just how much barrel length was needed before a cartridge no longer exhibited positive increases in exit velocity.

The cartridge used? 25ACP if I remember correctly. They decided upon that cartridge because to try to do something similar with anything longer would require a huge amount of barrel length. As it was they had like 20+ feet of barrel for the 25ACP experiment if I remember correctly.


Anyone remember the specifics of this experiment? Length of barrel before the velocity was no longer gaining? Length of the barrel before the bullet would get stuck?

Or any of you guys happen to actually know where I can get the article specifics? SOME PLACE I bet I still have this article as it was an interesting one, it will take a LONG time though for me to dig through like 4 piles of old magazines stacks that are each almost 2 feet tall.(i'm a pack rat).

 

[Moparmike]

You could probably do an exercise in theory with some really ugly math. You would need the weight of the projectile, the air resistance inside the barrel, the friction exerted on the projectile by the barrel, the burn speed of the powder and joules of energy produced per grain, along with other stuff you dont want to imagine how it would be obtained.

 

[uglygun]

I figure there is a mathmatical explanation as well, such as how say 20grains of powder behind a 100 grain 45caliber bullet would develop velocity over a 20 inch barrel as compared to how the same amount of powder would develop velocity behind a 100grain 9mm bullet over the same 20 inches. Having a larger bore diameter would mean more volume within the bore to allow gasses to expand for each additional inch of barrel length traveled, that would allow pressures to drop more rapidly and velocity gained from each additional inch would probably be lower.

But then, the diameter of a 45cal bullet allows for more surface area for those gasses to "push" against compared to a 9mm bullet of same weight.


The article just put did it in a way that wasn't quite so math intensive, just was interesting to see that such a small little cartridge yielded such surprising results.

 

[Gordon]

I CAN tell you this: in a .22lr HV load the optimum barrel length for velocity is 19+_ inches. Remington tested this very carefully 35 years ago when they developed the Nylon 66. That is why long 24-26" .22 barrels develop much less report (with sub sonic loads); they are dragging bullet a little slower and lowering gas pressure . A .308 win chester is still accerlerating at a very low rate to 36 " or so acoording to a test I read long ago. A .50 browning is still accerating out of 48" barrel. Those 5foot long 12 gauge barrels they are selling now drag down sub sonic loads to the point of cooling off gases to cut report alot.

 

[Brian Dale]

I saw something like that a few years ago. I'm a pack rat, too, but I think I threw that set out (see? when I clear out clutter, I WILL need it later!). The article I read had a guy using a chrono and different-length barrels, but I don't remember the details.

Mike: I agree emphatically. For instance, just to model

the burn speed of the powder

gets ugly far beyond this humble scribe's talents. The burning of the remaining powder at any given moment, the production of gases and the pressure in the space behind the moving bullet will all be described by nonlinear functions, and the math involved in calculating the resultant bullet speed will have already crossed the "boggle" threshold.

Ammunition manufacturers have both the engineers and the test data to figure these things out (including ballpark mathematical models built up from empirical data) without going to pure mathematical models. It's just easier to do the experiments and write down the results.

Cool beans, Gordon. Thanks.

 

[sm]

Outdoor Life used to have a hard cover book each year one could buy. Seems like back in mid 80's one of the authors took a number of calibers and kept sawing off the bbl on inch at a time. I recall the 44 mag blackhawk with a 1" bbl was a sight to behold.

.22lr , through a variety of cartridges including 30-30 from a contender.
Showed chrono results , I forget what else.

Don't have it, but I bet a used book store , or www.Abebooks.com would.

HTH

 

[Keith]

I saw that article. They used some obsolete .32 - maybe a .32 S&W? Somebody had a large amount of .32 barrel liners and they used a low pressure cartridge that wouldn't blow it out.

It was an interesting read, but sort of inconclusive IIRC.

Keith

 

[JCM298]

Finding articles

I found this site at the Kim Kommando show. I haven't tried it but she says its good:


http://www.findarticles.com/PI/index.jhtml


Let us know if it works for you,

John

 

[B27]

A test using .22 rimfire ammo was just done by this shooter-

http://www.glocktalk.com/showthread.php?s=&threadid=172761