doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Muzzleloader vs cartridge pressure.

I wonder if any testing has actually been performed?

Theoretically, a cap lock with a mainspring strength igniting a properly sized cap on a cone with the proper sized hole bored through it should have minimal is any pressure lost back through the cap as the hammer fall after ignition holds the cap in place in effect sealing it. In reality as springs, hammers and cones wear and passages foul things do change. I spent years competing with ML rifle muskets and know full well the effects weak main springs, worn hammers and flame cut cones and filthy ignition channels have on accuracy.

Additionally I wonder about the pressure difference between a ML and a breech loaded crimped cartridge with equal powder loads, wadding and payloads. Theoretically the crimp will cause a minor and temporary increase in chamber pressure as the crimp unfolds but wonder if this is enough of a reality to make any difference in pressure, velocity or pattern.

Dave Myrick

I recall seeing some "Old Info" where they measured the pull necessary to open a crimp. There needed to be enough that the crimp would not open on firing the other barrel, but not so much as to raise pressure unduly. I have never seen a comparative measurement between crimp strength & a tight fitting overshot wad in a ML'er. The tight wad was necessary in the ML'er to prevent the charge from moving forward when firing the other barrel. I seriously doubt there is that much differences in the tight wad & opening a proper crimp in a paper shell though.

True, the difference may be slight, but there would be a difference. A more significant difference would be related to over bore sized wads pressing through a forcing cone. Something that is entirely unrelated when comparing to a muzzleloader.

Many early breech loading shotguns took thin walled brass hulls which were designed to be loaded with larger than bore sized wads in them. i.e. 11 gauge wads in a 12 gauge gun or 9 gauge wads in a 10 gauge gun. There would certainly be a difference in pressures, with everything else being equal, between a muzzleloader and breechloader with those loads.

Having said all that, I am not saying those difference are dangerous or even significant. Just pointing out there would certainly be differences between the two guns relating to pressure.

As of now I have not pitched my tent in either camp. There are factors in both systems which could cause changes in the pressure. Keep in mind what is normally measured is Max chamber pressure, while in reality we have a pressure curve extending the length of the barrels. Max pressure will normally occur just as the charge starts to move. There is no doubt the forcing cone can have an influence on the pressure curve, but it may not actually raise the max pressure as the charge is moving & pressure is falling prior to hitting the cone.

This is a pressure-time curve, possibly Hodgdon Clays from http://www.arizonaammunition.net/

Note the small primer spike then the powder combustion



Courtesy of Neil Winston and similar www.claytargettesting.com



Pressure - distance curve from "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe; E.I. du Pont de Nemours & Co., 1933 promoting DuPont MX (which sorta became PB)



Pressure - distance curve from the Alliant site



I don't see any evidence of a pressure rise, or interruption of the fall in pressure, when the ejecta "slams" into the forcing cone

Pictures are nice, but number would be better however

Drew;
I may not have worded my post well. I was not saying there would be a rise in pressure when the forcing cone was hit. As mentioned the pressure is falling upon hitting the cone. There "May" be a slight lag in the rate of fall. These results were so far as I am aware of were all taken with breech loaders so doubtful we have similar ML'er curves for comparison.

You don't?!?! Since the ejecta will be entering the forcing cone before it's entirety has completely exited the hull, it's impact on pressure would be measured in the first 1-2 inches of the barrel, right where the highest pressure spike occurs.

It's not as if it is exiting the hull in it's entirety and traveling unrestricted through open air, and then "slamming" into a forcing cone as you put it.

While this discourse is interesting. The only way to prove this one way or the other would be to come up with an actual pressure test. One would have to come up with, as much as possible, two identical loads for both a muzzleloader and a breechloader and pressure test the guns. While it would extremely interesting, it doesn't really serve any purpose other than satisfying curiosity. Alas, I don't foresee Sherman Bell doing one of his fantastic test runs on this topic.

If I were a betting man, I would put my money on pressures being higher in the breechloader. As to what degree however, I could not say.

Apparently I don't understand internal barrel ballistics

A pressure - time curve with those same loads



A distance of the ejecta - time curve



Peak pressure with e3 is about .0003 sec. at which point the ejecta has just started to move and has not yet "slammed" (did you miss the ?) into the forcing cone - at .0005 sec. - when the pressure is now falling??

I clearly need the help of a ballistic engineer to understand the contribution of the ejecta entering the forcing cone to peak pressure. I'll look around Neil's site
www.claytargettesting.com

toward the bottom here are some links about "chamberless shotguns"
http://www.trapshooters.com/threads/model-12-forcing-cone.286074/

I have been studying your charts, thank you for providing them. According to them at .0003 to .0005 seconds the ejecta, has not only started to move, it has traveled about an inch. At that point it has overcome the crimp, and has ENTERED THE FORCING CONE. There is no gap in time or space for that process to complete itself.

I have read through the links you have kindly provided, frankly they are not relevant. While they discuss patterning, felt recoil, barrel safety, etc. While interesting, they do not discuss pressure changes do to the modifications.

So to summarize your position if I might. Crimps and forcing cones have zero affect on the pressure of a fired load. And the peak pressure in a muzzleloader will be identical to that of the breechloader when they fire a similar load. Do I have that correct?

Thank you for looking into the other sites.
I blew up the distance - time curve (with of course loss of resolution). How much of the ejecta (length of shot and wad) has entered the cone at .0003? How long does it take for the "legs" of many wads to collapse? Why is the pressure falling at .0005 with ejecta still in the cone? What does overcoming inertia vs. friction vs. some degree of constriction on the ejecta upon entering the cone have to do with the pressure curve? How much constriction IS there from case mouth to cone with modern shotcup loads?



I said nothing about crimps, or wad seating pressure, or plastic vs. fibre wads, the wad design, or internal ballistics of the shotshell.

Neither one of us KNOW the effect of the ejecta entering the forcing cone, nor can we answer (with numbers) the OP's question. Do I have that correct?