Basics of powder and other beginner questions

[badmack]

I'm just getting acquainted with reloading and have a few questions I'm hoping someone can help me out with. (looking to load 9mm and 40 S&W)

After looking at Accurate's reloading data (Hodgdon's also) it appears that higher velocities are obtained with slower burning powder but only up to a point.

Is slower burning powder limited by barrel length?

Does there come a point when you are just spitting unburned powder out the end of your barrel?

Is there a way to check to see if your powder is too slow for your gun? Like maybe shoot through a wet rag to catch unburned powder?

What is the difference between CUP pressure and PSI? And why does Hodgdon arbitrarily list one or the other but not both in their data?

Is there a way to convert CUP pressure to PSI or PSI to CUP?

Thanks for tolerating stupid questions. I'd rather ask stupid questions that do stupid stuff.

[Unclenick]

Welcome to the forum.

After looking at Accurate's reloading data (Hodgdon's also) it appears that higher velocities are obtained with slower burning powder but only up to a point.

That's correct.

Is slower burning powder limited by barrel length?

Not exactly. Not until you get to 2" barrels in handguns and maybe twice that in rifles. The problem is that powder not only has to make gas, it also has to make it fast enough to keep up with the bullet, or pressure drops.

Does there come a point when you are just spitting unburned powder out the end of your barrel?

Or worse, the pressure drops so much the powder actually extinguishes, leaving a bullet stuck in the barrel for the next round to collide with a burst your barrel.

Typically, slower powders need higher pressures to burn efficiently. You may get unburned powder because it too slow for your application, or you may get it just because you loaded the powder charge too low to reach adequate pressure. If the powder is slow enough, you may not be able to fit enough in the case to make gas fast enough to reach or maintain adequate pressure.

Is there a way to check to see if your powder is too slow for your gun? Like maybe shoot through a wet rag to catch unburned powder?

Usually it's too slow if it is slower than the powder that gives the highest velocity. A lot of powders don't burn completely in the barrel. Look at the ground out in front of the firing line at any range and you see lots of unburned grains. Indeed, dust swept up of the floor of an indoor shooting range will usually ignite with a match. The concern isn't whether the powder burns completely in the bore, but whether the portion that does burn in the bore gives maximum velocity. Such loads are often associated with unburned portions of the charge, large fireballs at the muzzle and enough rocket effect to increase perceived recoil

What is the difference between CUP pressure and PSI? And why does Hodgdon arbitrarily list one or the other but not both in their data?

CUP stands for Copper Unit of Pressure. It is pressure measured by a device called a copper crusher. It has a piston driven by gas through a hole made in the chamber. When the gun fires, the pressure drives the piston to crush a calibrated copper slug against an anvil. You measure how far the copper was crushed by firing, then look the pressure number up on it calibration table based on that measurement. This technique was invented about 1860, and its accuracy reflects its age. It was believed to accurately reflect real pressure in psi until sometime in the 1960's, at which point it became clear the inertia of the piston and other technical factors tended to make the dynamics of actually firing cause it to under report psi over about 30,000 psi. By the time it gets to 50,000 CUP actual pressure is more often near 60,000 psi.

Today, due to the inaccuracy, copper crusher results are reported commercially as CUP, while psi is reserved for the more accurate conformal Piezo transducer measuring method and for strain gauge systems. There is confusion about this because the military never adopted the CUP terminology,and continued to refer to copper crusher results as psi until at least the mid 1990's.

The reason both standards exist is manufacturers did not want to simply discard their old test barrels for expensive new ones when the new system first came along. They also didn't want to re-fire everything they'd ever tested, either, so you get a mixture now. Eventually CUP will die out, but until that happens, you have both.

Is there a way to convert CUP pressure to PSI or PSI to CUP?

Denton Bramwell came up with a correlation for rifle cartridges above about 30,000 psi, but its not a very exact convertor and doesn't apply well to pistol rounds. SAAMI and the CIP maintain both standards.

[bobquickshot]

Hello,

I have improved my knowledge by reading some articles from www.chuckhawks.com:-

http://www.chuckhawks.com/powder_cartridge_testing.htm
http://www.chuckhawks.com/powder_relative_burn_rate.htm
http://www.chuckhawks.com/powder_burning_speed.htm

Regards.

BoB

[badmack]

Thanks guys. I appreciate the depth.

[Don P]

It may help if you check the stickies out in this thread

[Jim Watson]

I might add that as a practical matter, recently published loading data will keep you from really gross mismatches, like using a fast pistol powder in a bottleneck rifle cartridge or a slow magnum rifle powder in a handgun. They just don't list them.
Once upon a time they did, see below.

Now, looking at the reasonably suitable powders, would I give up 100 fps for markedly better accuracy?
You bet.
Would I give up 150 fps to be able to make use of a powder I had on hand rather than buying the optimum fuel?
Depends. If for moderate ranges or medium game, yes. If for long range shooting or great big hairy animals, I'd pay for the best available.
Would I give up 400 fps to use an oddball powder on hand?
Yes, for special purposes, like the small statured friend I wanted to be able to shoot a .30-06 without getting beat up.


CUP vs PSI
There is no real need to "convert" data from one unit to the other.
If I am loading a 190 grain .308 Win it does not matter that 42.8 gr of Varget is shown by Lyman to develop 60,200 piezo psi and 42.5 gr of Reloder 15 produces 50,500 CUP in the same table. They are both maximum loads and I should not exceed them.

[Dan44149]

I'm new to reloading myself. I also load the 9mm and .40S&W and have been working up loads on the .40 for best accuracy, which is still an ongoing process. I've been using the Hornady loading manual, and their powder suggestions.

Might I suggest you use the load data available in the loading manuals first? This will give you more experience in the basics of reloading, allow you to get more comfortable, gain a better understanding of the questions you asked, and do it all rather safely.

I'm not sure what load manual you are using, and I understand my Hornady manual is a good beginner manual, but others are better once you decide to move up.