Smaller Shells

[Arthur]

Tried to master 65mm shells. Using Pro GRP mortars. They seemed to break too low with 1.5 seconds lift delay, Pyroguide suggests 3 secs for a 75mm shell. What timng does anyone else think reasonable? 2sec? 2.5sec? for a 65mm (2 1/2") shell. I like my shells reasonably high so that sparks don't touch the ground. Would you lift them with 2Fa or 4 or 7Fa.

[Shizznt]

I made my 2 1/2" shells with a 2 to a 2 1/2 sec delay but I don't know about the 2fa or 4fa.

At the time, I used geox 2fg and they worked fine.

They went at a good height.

 

-Ryan

[LambentPyro]

You can solve a proportion if you like Math. 3 seconds is to 75mm as x is to 65mm. Cross multiply and divide and you get 2.6 seconds for a 65mm shell.

[Mumbles]

Delay time isn't linear with shell size unfortunately, so that isn't very applicable.

[SideGlance]

i would do some testing.. shoot some dummy shells and time the peak of the lift... everyones black powder, pasting, tubes are different. Make the dummy shell the same weight and size as the real shell.. you want your shell to break at the peak of the lift. Recording the dummy shells with a video camera then playing it back is helpful for more exact measurments

Edited December 17, 2013 by SideGlance

[LambentPyro]

Delay time isn't linear with shell size unfortunately, so that isn't very applicable.

 

Always worked for me. For small shells, it is somewhat linear. For large shells though, I would agree with you, but that's not the case.

[dan999ification]

I lift 3" shells with 3 second fuse and 10% cheese grater bp, porous grains, 2mm holes in the grater. Worms and fines.

They go a bit high for my liking ( but safe ) on 10% of 3hr milled willow bp.

Fit, weight, bp, grain size, method, all play a part as you know.

Without testing I have lifted plenty of 100g shells with 20g, never had a problem with them hitting the moon. They are over 400ft

Bengalflair lifts 3"s with an ounce of 2fa iirc.

The 40mm cans get 2.5secs but I do tend to overlift with amount and grain size range.

 

Dan.

Edited December 17, 2013 by dan999ification

[SideGlance]

yes i have had great success with finer grains Dan...for my new lift powder i am trying something new for my own amusement... ball milled bp mix into hot water... mix real good and let dry, break up chunks...then ball mill some more and mix less water then push through screen. lets see if it makes a difference

Edited December 17, 2013 by SideGlance

[psyco_1322]

I'd say that using 4fa would be good. For the smaller shells, a bit more fine powder is acceptable, you can use a bit less than if using 2fa.

 

Timing, I'd go around 2secs, adjust it to your needs after a few shells. I use 2secs on my 3s and it seems to be ok.