Pressure and minimum powder charge--can someone explain it to me?

[John in WI]

I'm very new to this. And I have been RELIGIOUS about following published reloading data--to the point of weighing each powder charge by hand, weighing each shot charge by hand... Using all the published components...

I can see where one could get into problems very quickly by using MORE powder than the listed maximum. But I'm curious--what's the worst thing that could happen if you use slightly less than the listed minimum?

Specifically, I noticed something for some loads listed for 7/8oz with International.

2" 17.0/1160 7,500psi
2 1/2" 20.0/1250 8,200psi
2 3/4" 27.0/1450 9.600psi

these are using the same primers but different wads and hulls.

Anyway--that's a 10 grain span in powder charge, and a 2100psi range in pressure.

What are the dangers if you use, say, the 17.0 grain charge (for the 2" shell), in a 2 3/4" shell?

I'm not planning on doing it (sticking strictly to the book at this point!!), just curious how the low-end of powder charge can be potentially dangerous?

[UNIQUEDOT]

The worst that can happen is getting the wad stuck in the barrel, but it shouldn't be a problem with that load although it might not burn cleanly. Some manuals do publish reduced loads for shotshells, but there is a working minimum especially with slower burning powders. I use reduced loads quite often, but mostly only with faster powders and i have never had any problems other than having a dirty bore at the end of the day.

[sargenv]

I've loaded ammo where pressure was as low as about 6500 on the scale.. according to data.. Shotshells generally are a bit more forgiving.. and a tenth or two of powder usually doesn't make much of a difference unless you are pushing the max 11,000 psi upper reaches of 12 gauge up to 3" or 14,000 in the 3.5" chambered guns.

In most cases, the bushings for the powder will get you in the ball park but may not be exact.. and for shotshells, it's usually good enough. Personally, I like the adjustable shot/powder bar where you can get the exact charge you want, usually within a tenth of a grain.. it also depends on which powder you are using.. 17 gr of Red Dot is not the same as 17 gr of Unique or Blue dot.. without knowing the powder(s) you are using, I couldn't tell you what I thought was safe and what was folly.

Loading shotshells is not like loading metallic since the wad will not allow any space between the powder and the wad. Unlike metallic where there may be excess air space. Until I know what kind of powder you are using, I can't really make a judgement call. I can tell you that you will likely never see 27 gr of Red dot being used nor will you see using 17 gr of Blue Dot.. Different burn rates in the powders produce different pressures with a given payload. Blue Dot being a magnum shotshell powder (that burns very slow relative to the target powders), and red dot being a target powder that burns very fast.

[35remington]

Take a good, close look at the data you quoted.

Now look at it again.

The shortie 2 inch shell needs 17 grains of International to produce 7,500 psi. Assuming you copied the information correctly, if you used 17 grains of International in the 2 3/4 inch shell, instead of the 27 grains you quoted, two things will likely happen:

1) pressures will be very low, to the point of bloopers and squibs, especially in cold weather. A ten grain reduction, or more than one third of the normal charge weight, is a bit much. Velocity will be low. Almost uselessly so. It's only 7,500 psi in the two inch shell, which is near the bottom end of what is desirable in pressure for shotshells. Reducing it further, a lot further, as you presume to do by placing the same charge in a larger shell will make ballistically inconsistent and unreliable shotshell loads.

2) The crimp may be dished in as the height of the components is not correct when a lot of the powder column is missing.

The short shells generate more pressure with the same amount of powder than the long ones do, as the short shells have less room remaining for combustion space if the shot charge is the same.

Or, said another way, the long shells generate much less pressure with the same amount of powder as the short ones.

Since you're not likely to be running across too many 2 inch shells for reloading, stick to the standard length shotshells, or make sure you use the data as published. Substitutions of this sort are not to be recommended.

The lesson here is that too little pressure is also a bad thing. A reasonable amount is needed to make things go bang correctly, and the pressure with such a substitution is unreasonably low.

[John in WI]

Thanks for the heads up. I'm not going to make any shorties (I thought of it--but to make them work in my Mossy I would have to do some modifications that may or may not be reliable). I was just curious about how it worked. I wouldn't have guessed there would be such a range in powder charges, when the only real variable is the length of the case.

No--I'm sticking strictly to the book, I don't know nearly enough about it to try and make any safe substitutions.