Mortar Shot Consistency

[Parrott-Cannon]

No matter how I clean my GB mortar about every 5th shoot is an outlyer - longer shot distance.
 
Cleaning:

Clean vent with damp pipe cleaner.

Clean power chamber with damp sponge.

Clean barrel with damp sponge.

Dry vent, powder chamber, and barrel with dry sponges.

I allow 10 minutes between cleaning and next shot.

I shoot 45 grains ffg or fg with a golf ball.  All charges are weighted to the nearest grain.

Any sugestions.

[Double D]

What range are you shooting?

Can you feel any reisdual heat in the barrel before loading?

[Parrott-Cannon]

What range are you shooting?

Can you feel any reisdual heat in the barrel before loading?

There is no reisdual heat in the barrel by touch.
I am using a 50 degree angle on the barrel.
Typical range is 100 yards with a standard deviation of 5 yards.  The hot shots go 120-125 yards.  I also weigh the balls - standard deviation 1% and measure the diameter differences are in the thousands place.

[Artilleryman]

Wind?

[cannonmn]

When I shoot very light projectiles from a mortar, I get very inconsistent ranges, maybe it comes with the territory.  I think a light projectile moves out so fast it doesn't lead to consistent powder burn.  I don't have that much experience with mortar shooting and have never shot golfball size, so my ideas could be all wrong.  I guess the only way to test this in the same scale would be to try heavier golfball-sized projectiles, but if the mortar is relatively thin-walled and was only made for golfball-weight projo in first place, I would not advise it, need a thick-walled mortar to ensure safety.

Have you checked to see if all your golfballs are same diameter and same weight?  Shag balls could have picked up moisture and be heavier-only a guess.

[Max Caliber]

Sounds like you're following proper loading procedures to get consistent shot to shot accuracy and range which is of the utmost importance when shooting most any muzzle loading gun. If you are using loose powder, you might try using aluminum foil cartridges. Make the cartridges as close as possible to the chamber size and seat them firmly with the same pressure each time ( don't ram them, just seat them with firm hand pressure). A cartridge should fit the chamber snugly and not break open when being seated, a broken cartridge is the same as no cartridge at all. You should  get better performance with cartridges, especially in range.

[RocklockI]

how do you reset your mortar after each shot ? is the ground level ? thats important as they go in a funny sideways arc if not . .....

my little sbr 2.25" wont really do any better w /poolballs .

i think getting the powder into the gun correctly every time is the issue for me . loose powder put into or shaken into the chamber .

need to make on of those copper pipe thingggs that go into the chamber

i've tried foil packets in it .......it can be a b%$+*( getting the foil into the chamber ....!

Mont. was the first place i've ever shot it at a target . if i'd have stuck with it longer i think i could have walked them in .....?

b4 that just plopping them outthere they end up faily close to each other .......


in mont. in the open spaces 100yds looks like 30 .........and the 30 yd stake was easy to spit on from the line !!!     just kidding ........!!!!

with the wind in casper 30 yds is nothing .....once we hit nebraska .........just kidding /....

[GGaskill]

I think consistency of diameter is important, especially if you have only a little windage.  Even a few thousandths difference will cause greater or lesser pressure and result in range variations.

Measure the golf balls and stick with a narrow diameter range.

[MikeR C]

Parrott-Cannon,
I don't have any suggestions, but I do have some observations. First of all my mortar's barrel length is aprox 2 times the bore diameter with fairly thick walls, a 30 degree taper down to a .5" by 1.25" chamber. The barrel is fixed at 45 degrees (see pict below) It was was built along these lines:

http://www.go2gbo.com/forums//index.php/topic,70859.0.html

But turned from solid. The chamber holds about 50 grains of FFFG powder. I fired it with a full chamber at the Montana shoot with an old golfball and DD said he found the ball just over 400yds from the line (I put my name on my balls before I shot them). I fired a dozen balls or so at the thirty yd stake and determined that 2 - .22 long rifle cases of FFFFG, yes 4f, got me pretty close to the stake. Courser powder gave me erratic ignition until I got about 15-20 grains of it in there, then I shot way over the stake. Balls fired with the barrel close to horizontal and a full to half load seemed to hook and slice and generally go in everywhichaway.
If I was going to do another mortar/shoot, assuming the standard 30 yd stake for golfball mortars, I would do the following: I would put a smaller chamber in the mortar, or an arrangement whereby I could insert a smaller chamber and hold it in with a threaded vent so I would end up with a full chamber to prevent erratic ignition. (Maybe 1/4" X 1/2") I would definately screw sabots to the balls to keep them from spinning, once the ball is spinning the dimples do their job, they make the ball fly and if you can't get the spin in exactly the same place each time the balls will not go straight.
I started a test mortar with an offset chamber to try to spin the ball on purpose, in a pridictable way, but never finished it. Sabots would probably work as well and for the pressures involved a disk of plywood sheetrock screwed to the ball would be sufficient.

Since you are getting a 100 yds from 45 grs or so I suspect you have a pretty good sized chamber which would cause erratic ignition, this was covered in the posts on the golfball mortar contest, DD seemed to have the smallest chamber and as the chambers got larger there were more complaints about erratic ignition.

[Rickk]

Is there a powder sub-chamber, or is it straight bored for a golf ball all the way?

[MikeR C]

I went out and measured the chamber. It was 1 1/2" before I turned the angle at the bottom of the bore. The actual chamber is 1/2" by 1" long.

[artillerybuff]

No matter how I clean my GB mortar about every 5th shoot is an outlyer - longer shot distance.
 
Cleaning:

Clean vent with damp pipe cleaner.

Clean power chamber with damp sponge.

Clean barrel with damp sponge.

Dry vent, powder chamber, and barrel with dry sponges.

I allow 10 minutes between cleaning and next shot.

I shoot 45 grains ffg or fg with a golf ball.  All charges are weighted to the nearest grain.

Any sugestions.

A lot of good tips have been offered.  Ball weight & diameter, charge weight, leveling piece before each shot etc. are all musts.  In any kind of match grade type shooting all factors have to be exact and the same from shot-to-shot.

Also, in your particular piece I would recommend a slightly lighter charge of high quality 3Fg powder, should give a more consistent burn.  4Fg has no place in the bore of any cannon, no matter how small.

Anthony Variz