2.5 inch mortars

[johnybmb]

Hi everyone!

I have an issue with 2.5 inch mortars. So far I have used paper 2.5 inch mortars, that came out of a 2.5 inch cake. They worked great so far, although they were actually 61 mm ID, as opposed to the 63 mm standard mortars; the shells needed a bit of forcing down the tube, but not so much as to require a dowel to push them, just a little jiggling of the tube made the shells reach the bottom. However, these mortars have begun showing signs of wear: the walls of the tubes are getting burned and they started disintegrating.
So I bought some HDPE tube that is close to 2.5 inch ID. The problem is that this HDPE pipe is actually 67 mm id, and that concerns me a lot about the height that the shell will reach when fired from this dimension of a tube. I haven't fired one yet from these mortars so far, because I have to find a remote location to do a little bit of testing.
My question is: Have any of you ever fired a 2.5 in shell out of a 67 mm mortar? If so, has it lowered the height of the shell so as to pose a threat to the audience?
I'm thinking of adding a layer of corrugated cardboard to each shell prior to firing it, so as to compensate for the size difference. Do you think that would work? Or will the lift charge pressure destroy the cardboard sabot so as to turn it to shreds which might jam the shell and cause a possible flowerpot or even a mortar disintegration?
Thanks in advance!

[PyroManiacs]

I would tend to think the cardboard would be destroyed instantly, unless you use "Daves Magic Tape" all the way around.... I also know that if you fire a shell out of a tube a little bit wider then standard, it WILL NOT go as high as it should. I do not think that little bit of space would cause a drastic change in the altitude, enough to cause harm to the audience.

Unless anyone else has had another experience with this..... these are my thoughts. Correct me if Im wrong though.

[johnybmb]

Well, the paper mortars come from a used 2.5 inch cake. Apart from the initial firing from the original shells that were in the cake, I have so far shot about 10 shells out of each tube. The cake was not consumer cake, which are known to have thinner walls, but it was a display 36 shots cake, and fired regular display 2.5 in shells, which have substantially more lift charge than consumer cakes (it is known that consumer 2.5 in shells that are found in consumer cakes are actually 1.75 in shells which are contained in a 2.5 in shell case - and here (http://www.youtube.com/watch?v=oMX5AitwIvc) is the evidence). The paper tubes have so far performed quite OK, but they have started to show signs of wear, and I don't want to take any more chances with them.
However, 4 mm difference between the shell and the mortar at 63 mm ID is quite different from 4 mm difference at a 100 mm ID mortar.
All in all, there's only one way to find out the result, and that is by checking the altitude difference between firing a shell straight as it is from the 67 mm tube that I have, and firing it with a cardboard sabot around the shell that will make up for the diameter difference. I will have to find a remote location to perform the test and I will surely post the results.

[PyroManiacs]

When you do your test, you should video it.

I would not take any chances as well with those burnt up tubes. Time to move on, lol.

We also have a whole thread dedicated to the consumer 1.75" issue. Ill post the link shortly.

[johnybmb]

Hello, everyone!
I have fired a few shells out of the 67 mm mortars, exactly 3 shells so far, and the result was quite acceptable. As expected, the shells did not reach as high an altitude as when fired from 63 mm mortars, but that is not quite a bad thing, because the burst appeared bigger than it does at a standard altitude, comparable to a 3 inch shell burst at normal height. So, all in all, this is not as bad as it appeared at first. Therefore, I will continue to use this diameter mortars, since it is very cheap, and readily available for me.