Rack Question

[displayfireworks1]

Email Question if someone can help with this?

Hey Dave my names xxxx I?ve recently got my atf permit for the big stuff I?ve been building a few mortars too. What I?ve been doing is lathing down posts of various lengths to get the desired plug dimensions. As far as you can tell from this picture is there anything you would change? I?m just asking a professional opinion on what I?m doing. I?m pretty much copying the ones that xxxxxx is selling. These 6 inch are made out of DR 21 hdpe I yet to shoot these I haven?t had the time. My biggest fear is that what xxxxxx is selling is a DR 26 pipe which is a little thinner walled than the Dr 21 I?m still thinking a six inch will fit what do you think?
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[Rick_In_Tampa]

I don't have a 54 so I don't play in that league, but aren't those big enough to have to be buried in the ground?

[Crush630]

use the thickest pipe you can get, need to add cross members on each side.

[displayfireworks1]

Where he is referencing this DR 26 and/or DR 21 , is that of any inner diameter significance when shooting a 6 inch shell? His frame structure appears to be adequate

[Rick_In_Tampa]

Shouldn't be. 6" is 6" regardless of the thickness of the walls of the tube.

[cptnding]

Shouldn't be. 6" is 6" regardless of the thickness of the walls of the tube.

You would think that would be the case but it isn't. The thicker the wall = smaller ID. Chart in the link below will show you the differences.

http://www.jmeagle.com/sites/default/files/HDPESpecSheet4710%20.pdf

[PyroJoeNEPA]

I hate to be the bearer of bad news--BUT---a 6" mortar tube should be DR26 pipe which has in Inside Diameter of 6.04". Wall thickness is .255". A DR21 pipe is only 5.957" Inside Diameter [wall thickness is .315".
Sooooooooo----it is most likely that a stock commercially made 6" shell will NOT fit in the DR21 pipe. At least this is what the math says.
I will stop at the magazine and measure a 6" shell--I have a couple set aside to shoot at a club event this weekend.
Also, on your rack build--the bottom side boards should only extend to the top of the tube plug [called a "bung"] to vent gas around the tube in the event of a blow out in the tube. Typical plug length in a 6" tube is 4 1/2".
The spacers between the guns are ok--but if you want to make the racks compliant to NFPA standards, the spacers should be half the diameter of the tube--therefore 3".

[PyroJoeNEPA]

I don't have a 54 so I don't play in that league, but aren't those big enough to have to be buried in the ground?
Rick---6" guns can be racked. We also have 8" guns [3 in a rack] that are a bear to move around. When you get into 10" they have to be buried---or in sand filled barrels.
I understand there are some areas that do require 8" guns to be buried--I guess it is up to the AHJ. But you can rack up 6" guns all you want.

[displayfireworks1]

What do you think Joe, he should be using only the DR 26? If I remember correctly the DR 26 is not real thick and I think that someone new may think that is not a good thing.

[PyroJoeNEPA]

What do you think Joe, he should be using only the DR 26? If I remember correctly the DR 26 is not real thick and I think that someone new may think that is not a good thing.

Dave, yes--he should be using the DR26. The .06 difference in wall thickness is not going to be an issue----but if he uses the DR21 the shells may--or may not fit. A 6" shell isn't exactly 6"--it depends on how many layers of tape are laid up on the hemi when they are pasted. A 6" hemi is 5 3/4" diameter--before any layers of tape are applied. There is "wiggle room" in the DR26 pipes--so it is possible he can get away with the DR21. I will try to get some measurements later today. It is a good point to research.

[Crush630]

See my post a couple weeks ago

http://www.pyrotalk.com/bulletin/showthread.php?7535-Broke-a-few-6inch-tubes-this-weekend

[Rick_In_Tampa]

Rick---6" guns can be racked. We also have 8" guns [3 in a rack] that are a bear to move around. When you get into 10" they have to be buried---or in sand filled barrels.
I understand there are some areas that do require 8" guns to be buried--I guess it is up to the AHJ. But you can rack up 6" guns all you want.

Thanks for that clarification Joe. Learned something new. That's why I love coming on here!

[Rick_In_Tampa]

You would think that would be the case but it isn't. The thicker the wall = smaller ID. Chart in the link below will show you the differences.

http://www.jmeagle.com/sites/default/files/HDPESpecSheet4710%20.pdf

Great reference document! Thanks for posting.

[PyroJoeNEPA]

I just tried some 6" shells in three new guns made of DR21---THEY WILL WORK FINE. Not a lot of wiggle room...but I need to back track my previous statement that they might not work.

[cptnding]

Thanks for the follow up Joe