7 replies to this topic

[pyrochris]

Given a FIXED shell size and mortar size, and lift charge, is there a way to SAFELY reduce the muzzle report from an HDPE mortar?

For example, would drilling small holes near the top of the mortar do anything?

The reason why I ask is because I just bought some shells and some mortars. They are supposedly compatible with eachother, but the muzzle report is a *BANG*, whereas I know they should be more of a *THUMP*.

I like the performance of these shells, I've set off 20 of them without problems. But it just seems so unnatural for the muzzle report to be so loud!

I thought about taking some of the lift out of the shells, but I don't want to lose any altitude...

[karlfoxman]

its possible that drilling holes will silence it yeah. i have heard lots of shells leaving mortars with more of a bang than thump. correct me if im wrong but it may have something to do with the length of the mortar? plus paper morters soak up the sound to produce a thump and hdpe ones wont.

hope it helps a bit

[pyrochris]

Yeah, I'm sure the length of the mortar also has something to do with the noise. If drilling holes doesn't help, maybe I'll do a "chop-job" on a mortar, and see if that does.

That will probably reduce altitude though, right? I don't mind a slight drop in altitude, but a larger one would be a problem...

[karlfoxman]

i cant remember the site but there is a site to get the correct sizes, what size shell is it?

[pyrochris]

It is a 1-7/8 inch shell, and the mortars I'm using are 15 inches with a 3 inch plug, so that is an effective length of 12 inches. I believe that the typical length of a mortar for these shells is 10 - 12 inches, so I might just try taking a couple inches off of one.

I think the main problem is that there is not enough of a gap between the tube and the shell to release the excess pressure before the shell leaves the tube. Maybe if I take the plastic label wrapping stuff off of the shells they will be slightly smaller in diameter...

[karlfoxman]

yeah sounds good, most small shells will crack or bang on launch. 3" and up tend to thump in my experience. take a couple of inces off and see if it helps.

k

[alany]

Most "festival ball" type shells are lifted *very* hard, with extremely fine BP. I gather it is a marketing thing more than any technical reason, many people like a loud lift, makes them seem powerful and I guess has the effect of making the user believe the shell went up really high. Along with the flash break, it makes the experence more awe-inspiring?

It may also be required to achieve reasonable heights with highly variable mortar IDs. The HDPE tubes many people are using for racks now days are up to 1.85-1.95" in ID, which is a very slack fit for a conventional festival ball.

You can drill holes in the last 2" to allow some of the gas out early and dissipate the shock, but a good silencer needs an expansion volume larger than the mortar volume, ideally many times larger. You could construct a 4" or so diameter tube coaxial with an extended mortar (with lots of holes in the core tube) to vastly reduce the amplitude of the pressure transient released after the shell.

[pyrochris]

I forgot to mention, the shells I'm using are cylinder in shape. They are also pretty heavy for the size. I'm guessing this could have something to do with it?

I don't have any 2" mortors right now, but maybe later I'll buy some of them and see what that does.

Do you think that I could reduce the sound without ruining altitude if I took out the stock lift and replaced it with a more coarsely granulated BP?

Good Idea with the silencer Alany. I was thinking though, that it may be difficult to do. Not sure if this is true, but I have heard that HDPE cannot be glued to anything for some reason. This is also supposedly why wooden plugs are stapled into the bottom of HDPE mortars.

Not to mention that HDPE mortars with silencers would take up alot more space than just an HDPE mortar!

Thanks for the ideas guys!

Edited by pyrochris, 04 July 2005 - 03:38 PM.