Muzzle breaks

[THEONE]

I made a few 4inch shells for the new year. I fired 7 4inch shells and from two of them got a muzzle break. Actually the second one opened at the top of the gun breaking the top part of the mortal. What actually causes the MUzzle break and how i can actually avoid it. All shells was top fused.

 

Thanks and happy year.

Edited January 2, 2023 by THEONE

[cmjlab]

Do you have any photos or videos of your shells?

 

Cylinder or Ball? Spiking / pasting? Etc.

 

I had a a muzzle break on a shell this year (3" single break / color), but mine was due to a crappy spiking / paste job - the shell was a little soft / squishy, and the lift forces must have crumpled it enough to break the seal and ignite the contents.

[THEONE]

They are cylinder shells, pasted. The spiking and pasting was good. Mostly i am considering the spot where is the spollette. I usually use a bit of wood glue to seal it but i am thinking to use hot glue or a paper with glue to seal it better. If fire would pass through the shell most likely it would be at this spot.

 

I guess during the lifting of the shell inside the mortal, the pressure is high enough and if there would be any spot opened, it would pass inside the shell and cause the break.

[cmjlab]

If it really was your Spolette, you could try wrapping string around where it will sit against the end disk, then pulling the Spolette/string tight against the disk and glue the string to create a better seal (or used string that has glue on it already). The glue will have to be done again after you're done spiking obviously, as pulling on the string could break the glue seal around where the Spolette enters the disk.

 

Just a suggestion. I don't like hot glue around the Spolette because pasted paper doesn't stick to it, and it doesn't lay flat like white glue (so you have bumps and areas where the paper may not lay flat and seal well if there are lumps of got glue there. I do it that way too.

 

Charles

[MadMat]

Were your Spolettes pressed hard enough? If not, the gases from the lift charge can blow right through the spolette, igniting the break charge inside the shell. The tubes for the spolettes must also be strong enough as well. I always start my spiking by applying a fillet of glue around the spolette and wrapping one turn of the spiking string around it. This gives my spolettes all the reinforcement they need and Iv'e never had any flower pots or muzzle breaks. Also the dimensions of the spolette are important. For a 4" shell the I.D. should be between 5/16"-3/8" (8-9mm) and the O.D should be around 11/16" (17-18mm)

Edited January 2, 2023 by MadMat

[THEONE]

The spollette tube is very strong and the powder too. I am using granulated BP for the spollette and it is really rock hard after i press it

[MadMat]

One more thing, when pressing a spolette, the same techniques as pressing a rocket should be followed. One important thing: the end of the spolette that is inside the shell should not have the powder level with the end of the tube. When pressing, a small spacer should go a few mm into the tube on that end AND it can't be a tight fit in the tube. That way when you press the powder, it will expand the tube slightly, but the end of the tube with the spacer will actually collapse slightly. This locks the powder into place.

Edited January 2, 2023 by MadMat

[Richtee]

This is why I just wrap a few cm glued paper around visco. Seat it with glue, glue fillet after.

[MadMat]

Once I tried spolettes, I never used anything else! I hate working with time fuse! Cutting it and cross matching is a royal PIA! I have never needed to cross match my spolettes and they have worked perfectly over hundreds of shells, so far. One thing I like to do is add a couple % of titanium to my spolly powder. Only a couple % is needed to make a nice sparkly tail rising effect. I never granulate my spolly powder and simply use mill dust. Another thing, after making a batch of powder, I always run some time tests to make sure I don't need to adjust my lengths. It usually comes out pretty consistent from batch to batch, but I have had one or two times where the burn rate was considerably different. Never figured out why, just made the length adjustment and went from there.

Edited January 3, 2023 by MadMat

[THEONE]

For this reason, make a big batch of BP and use it only for spollettes. It will take you years to make another batch of BP only for spollettes. With this way you wont have to test again and again your BP. Edited January 5, 2023 by THEONE

[MadMat]

For this reason, make a big batch of BP and use it only for spollettes. It will take you years to make another batch of BP only for spollettes. With this way you wont have to test again and again your BP.

I never mind running a couple baseball shots to check my BP... I actually think it's fun!

[Richtee]

I never mind running a couple baseball shots to check my BP... I actually think it's fun!

Heck..it IS fun! Ever tried to “shell” something? Neighbor’s pool, that annoying barking dog’s pen? I think a good mortar guy will nail something in like 3 shots.

 

On Edit: Well, the bases/mounts are a little more precise... as well as the “lift” and everything damned else about a mortar. But it is amusing.

Edited January 9, 2023 by Richtee

[Carbon796]

They are cylinder shells, pasted. The spiking and pasting was good. Mostly i am considering the spot where is the spollette. I usually use a bit of wood glue to seal it but i am thinking to use hot glue or a paper with glue to seal it better. If fire would pass through the shell most likely it would be at this spot.

 

I guess during the lifting of the shell inside the mortal, the pressure is high enough and if there would be any spot opened, it would pass inside the shell and cause the break.

 

If the shell was spiked and pasted correctly ( Which would automatically include. Saturating the spolette and twine joint, with hide glue. Once properly spiked. ) The joint between the spolette and endisks would be a least likely culprit. More likely would be a failed spolette core. Or the shell casing failing on lift.

 

A spolette core failing. Could be due to using inadequate spolette tubes, improper ramming, ruff handling during building, or using BP mill dust.

 

A casing failing. Could be due to improper filling / consolidation of the shell contents. Pryor to spiking. Improper spiking, not applying enough consistent force, while spiking. The ends of the outer most end disks. Should be driven into the folds of pleated Virgin kraft. ( if you get a lot of folding/creasing, on the sides of the shell. This is an indication. That it was not consolidated well enough. ) Assuming it was spiked with a adequate amount of force.

Edited January 10, 2023 by Carbon796