DROP IN VALUE FOR OPENED CHOKES

[J. A. EARLY]

Interesting comments on powder burn rates:

http://www.chuckhawks.com/powder_burn_rate.htm

Why Powder Burn Rate Is Meaningless By Randy Wakeman

Perhaps you have looked at various "Burn Rate Charts" and wondered what good they are. Well, you have good reason to wonder. Burn rate charts seldom agree. There is no specific meaning for "burn rate," so it shouldn't surprise us that the numbers don't agree. They mean nothing by themselves.

What amateurs call burn rate is not used by professional ballisticians to develop loads. The actual term closest to burn rate used in interior ballistics is "Relative Quickness."

Relative quickness is defined by "closed bomb tests," which quantify pressure rise in a sealed container. However, professional ballisticians do not use relative quickness for load development, either. A closed bomb relative quickness value does not translate into any type of value outside of that 'closed bomb' test. Powder performance varies widely by actual application. Relative quickness is one of several preliminary considerations when assessing a powder's suitability for a particular application by ballistics, but nothing more than that.

Relative quickness does not tell use the physical shape of a powder, its composition, or the types of coatings. It cannot tell us whether a powder is single-based, double based, or triple based. It does not tell us the heat of explosion, the progressive / degressive gas creation values, the ignition characteristics, and so forth. There is no way to translate a double-based powder performance into a single-based powder performance level with any accuracy. Even further, relative quickness does not define the erosiveness of a powder, the residue left by a powder, its ability to meter properly; and on it goes.

Energy content of nitrocellulose varies by manufacturer. It varies by the amount of nitrogen in the nitrocellulose. The more nitrogen, the more gas a powder can make. Once you have a specific type of nitrocellulose the energy content is further controlled by the addition of nitroglycerin, which is basically what constitutes a double-based powder. Now you have further considerations, as nitrocellulose and nitroglycerin do not behave the same way as temperature changes. The amount of nitro percentage varies by powder to powder, and with it its performance in a specific application.

All this combines to make burn rate charts something to ignore, or to view with very little importance placed on them. Professional ballisticians do not use them at all, simply because they have no particular meaning. Ping-Pong balls are nitrocellulose, but not many of us would bother cutting them up and attempting to use them in a firearm.

[stumpstalker]

The "go ahead and open the chokes, it's your gun", versus the "keep it original" argument is surely a never-ending debate. But, I enjoy following it wherever it leads. The battle lines may be irreconcilable, but that does not prevent me from learning something new each time the topic is brought up.

This may stir things further: Spreader loads can compensate for all the older, tightly-choked Parker guns, but, admittedly only minimally -- given that the shot charge of a modified-equivalent may not be open enough for the grouse woods. But, once you open the chokes, is there any going back? Do you shift to "constrictor" loads, after opening up your factory-choked gun, if later in life you get a chance to hunt the broad expanses of the American West for upland game where longer shots are the norm?

REC

[mobirdhunter]

Originally Posted by Russell E. Cleary

if later in life you get a chance to hunt the broad expanses of the American West for upland game where longer shots are the norm?

REC

This is an easy one...get another gun!! (And now you have another good excuse).