Shooting the Spanish 7CM rifled mountain gun

[cannonmn]

We tried the trash can projectiles in this gun yesterday.  We didn't mention this in the video since we couldn't get all we wanted into the max 10 min., so here's "the rest of the story." 

These Belieu-system muzzle-loading rifles mostly seem to have an abrupt end to each rifling groove, and behind that is what I'd call a chamber that's the same diameter as the rifling lands.  If we'd taken more care to measure the length of our complete round, and mark it on the rammer staff, we'd probably have avoided what I think happened.  I think the first five rounds were not fully seated, and in fact stopped with the skirt resting on the rear of the rifling grooves. 

We wanted to use projectiles we had made for a larger-bore rifled gun, but those would not fit this one.  I made a resizIng die, not a beautiful one but made one in an hour that worked  I ran all six soft lead projectiles thru it twice using a 20T. motrorized hydraulic press to push them.  Then they'd fit the bore but not with as much windage as you'd normally want (about 0.040 in.)  So they fit down the bore but the skirt was still large enough to hang up on the rifling origin and feel very solid to the rammer, but we diidn't figure that out until after we were done shootiing.  When fired, the powder gas mostly whooshed past the projectile through each of the six deep grooves.  The unbalanced forces here tended to crack the projectile also we think.

I chamfered the last round at its base, with a jack knife before loading it, and it seated an inch or so further down the bore than any of the others.  I think it want far enough in to go into the chamber and past the origin of rifling.  I think that's why it expanded into the rifling grooves very nicely.

Haste makes waste, I shoulda followed the procedures I know all too well, measure and mark the rammer staff for proper ram depth for the particular rounds you are using that day.

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[Double D]

Man that Ed, he's just a babe magnet isn't he.

John why don't you turn some wooden plugs to fit in the base of those slugs like they used on the 577 Snider.  That would keep the gases from blowing the skirt out and force expansion when fired.

[RocklockI]

Very cool ,as always . Could you move the camera to one side a little so we could see the impact ? How far did the "trashcan" class bullet go into the dirt ?

[cannonmn]

Good ideas thanks.

[dan610324]

ed said in the video that it was 18 inch deep into the dirt .

[navygunner]

Nice shooting!!! What is the max service charge on that gun?
NG

[cannonmn]

max charge?

I assume you are asking about the orignal max charge that was specified.  I don't know that since I haven't run across any Spanish documentation on that piece. 

However I do have lots of data on British 7-pounder rifled mountain guns, several different models of which were in use between about 1865 and 1890.  If I pick one of the lighter-weight barrels of that model and check the data, it should be in the ballpark for the Spanish weapon.  The Spanish barrel weighs 69 Kg, or about 154 lbs.??  There should not be a difference due to barrel material, since the "compressed bronze" I think was in use in most of Europe for smaller gun tubes post-1865 had a tensile strength about equal to mild steel.

My data comes from "Treatise on the Construction and Manufacture of Ordnance in the British Service" HMSO, London, 1877.

pp. 431-432 show two different rounds provided for the "7 PR Rifled M.L. Steel Gun, 150 Lbs."

The charge used with "double shell" which I think weighed 12 lbs., was 4 oz. "F.G." powder. 
For common shell, approx. 7 lbs., charge was 6 oz. "F.G." powder.  I have no idea what the granulation equivalent of British 19th C. "F.G." powder is to our current powders.

The double shell would travel to 1700 yards in 17.33 sec. with elevation of 37 deg. 37 sec.
Common shell would travel to 2000 yards in 11.4 seconds with elevation of 16 degrees 0 sec.

My loading of 4.5 oz. "cannon" grade powder behind a 5.5 lb. hollow lead projectile is I think a conservative load.

[cannonmn]

I should mention that in my Spanish bronze rifled gun shown in the video, there is a "chamber" space of about 4 inches to the rear of the origin of the rifling grooves.  The diameter is full bore diameter or about 3 inches.  Since the studs on the shell were not at the very rear of the shell, but I'm guessing at least an inch from the projectile base, the base would have used up an inch of that space behind where the grooves begin.  So the usable chamber length would have been somewhere around 3 inches.

[Artilleryman]

What is "double shell" ? 

[cannonmn]

What is "double shell" ?

I'm assuming it is simply a longer shell that weighs more so it has greater explosive and fragmentation effects than the standard 7-pound shell.  The double weighed 12 lbs.

[Frank46]

Cannonman, really enjoyed your presentation. Still like the one where you hear "hey we're trying to sleep up here" in slow motion. Get a kick out of all your videos. Keep them coming. Frank

[cannonmn]

Thanks Frank, sure that was one of our early efforts where we tested a 7-pounder steel gun against half-inch steel plate.

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[Frank46]

Cannonman, thanks for reposting that video. Like a voice out of nowhere "hey we'er trying to sleep up here"
Still gets me going. Thanks again. Frank

[GGaskill]

Two questions:

1) What happened to the half inch plate?

2) What hour of the day was this fired?

[cannonmn]

We found the severely deformed plate in the woods when we were trying to find one of our cannonballs a few weeks later, I still have it and sometime will get a picture.  It was starting to get dark when we fired that shot, after sunset I'm sure but no idea what the local time was.