Those are some interesting pictures, Paul Hoskins. I really like the 'eyebrows' at the far end of the tubes. That is a great idea. I might employ something along those lines here.

Paul

Random thinking out loud.

1. Yes, baffles "create" more sound absorption, but

2. adding insulation may be more a PITA than it's worth (?) I'm wondering if muzzle blast may "blow" it out even with the use of chicken wire to hold it in and it can get soggy if it gets rained on (?)

3. 3/4" sheetrock screws through the sidewall(s) may be an easier way to "tie" the tires together (?) If they rust, so what, just put more in and you can always take them apart pretty easily. A #8 flat washer will keep them from pulling through and make them more visible for removal if desired (that's how I fastened the belting to my target board)

4. Looks like you "save" boards like I do. I hate to throw out boards, especially 2X's. Heavy is good, keeps them from blowing away I may not have notched the 2X6's a. because I'm lazy and b. becuz it's stronger (maybe)

I like the concept(s) of portable and easy.

RJ

Was just clowning around about the unwanted advice, Paul. As for the insulation, I "did" misunderstand. Can't see to read much any more but reading is a passion with me. Can't hear much either so I prefer reading instead. That way I don't have to ask someone to repeat what they say seven times. :grin:......They have changed the "eyebrows" on the shooting tubes. Used to be just a flat piece of 5/8 th inch thick plate of steel welded on that covered about 1/3 of the top of the tubes & angled down around 45 degrees. You wouldn't believe how many people shot the plate. There is still a trench under the end of the tubes in the ground caused by deflected bullets. There was a sign along the road going back in the wildlife refuge saying the range is closed for maintenance. Too many yahoos & other vermin going back there destroying & messing things up for the rest of us. Only bowhunters allowed to deer hunt. Don't mean to hijack your thread. .......Paul H

New info as of this morning.

I decided to do some preliminary testing to get some "groundtruth" before I finished the system, so I shot one of my AR-15s through the tube.

1) Nothing in the tires.
2) Tires not 'stuck' together, but positioned exactly as they would be if they were.
3) Sound pressure meter 2 meters from the muzzle and perpendicular from the muzzle.

First shot was outside the tube: 81 dB
Second shot was with muzzle about 3" into the tube: 78 dB. So the tires took the sound down about 3dB. That's more than I expected, actually.

Also, there was no "blast plate" on my end. I was curious how that would 'feel'. I didn't like it. It wasn't "bad", but it wasn't "wind in my face". It was a 'slap' in the face. VERY sharp and very short duration. Nothing that I couldn't stand if it was necessary, but I didn't 'like' it either. There WILL be a blast plate on my end of the tube.

Now I have a 'baseline' from which I can quantitatively evaluate the effectiveness of the fiberglass insulation.

RJ - The act of adding the fiberglass insulation won't be a pain. Maintaining it, MIGHT be. We'll have to see. (I have it in hand, and will be adding it this PM.) I'm not TOO worried about 'soggy', but I intend to mitigate that possibility with a tarp.

I thought about sheetrock screws through the sidewalls, too, but the more I think about it, the more I think I'll just screw a couple of 2x4s or 1x4s to the outside of the tires. This of course requires SOME similarity in OD of the tires. I don't think the variation in the ones I have in hand will preclude using an 'outside' stringer.

Thanks for the input!
More later.

Paul[/SIZE]

Here are some pictures of the insulation, chicken wire, and the first tire 'filled'. (I have to put on my insulation installation uniform before I do any more!)

Here is the insulation and chicken wire. If you drew a line down the middle of the insulation from left to right, and folded it along that line with the insulation "out" (this is paper-backed insulation), you would have the "unit" that I put in the tire. Each piece of insulation is about 8 feet long and I use right at 6 feet per tire.



"Installed", without chicken wire. Truth is, I'm not certain chicken wire is absolutely necessary as the insulation fits the tire pretty well. However, with the 'banging' from the firing, it might be necessary to secure it more firmly than "pressure fit".


Paul

Ive worked with fiberglass insulation like that in the building trade, & I seriously dont like breathing in all those fibers that float about when you disturb the stuff, & I think there will be plenty blown into the air shooting that close to it.

I just think it would be an idea to "encapsulate" the stuff some how, rather than just use Chicken wire to hold it in.

You could wear a dust mask I guess, & goggles to keep the fibers out of you're eyes, but it wont do much for you're shooting "comfort" !.

Your points are well-taken, Jaeger88. I THINK the 'blast-baffle' that will close the gun-end opening to as small as reasonably possible, will mitigate the blow-back of fibergalss. If not, then 'something' will have to be done to reduce that hazard/annoyance. Using any sort of hard surface (even paper) to contain the fiberglass will reduce it's effectiveness for sound absorption to some unknown degree. I suppose a muslin barrier would be both effective and not too difficult to put in place.

Paul

Thinking about it, Ive seen sound attenuators with woven fiberglass mat ( Woven Roving ? ), over the soft inner core to keep it in place.


Roving wouldnt be water proof.


Maybe the exiting combustion gases would carry a lot of the loose fibers out with them anyway ?.

Any time you have an explosion & the pressure drops back to normal, it creates a vacuum. Shooting a gun creates an explosive effect. When the pressure column collapses it creates a vacuum sucking anything loose & light back toward the source of the explosion. I highly suspect a collapsing muzzle blast will suck up loose fiber particles & deliver them to your face. Also when I shoot thru the tubes at the local F&W shooting range, the muzzle blast seems much worse than shooting out in the open. I highly suspect it's because the pressure collapse also sucks the confined sound directly back into your face & ears. Hearing protectors are a must. .......Paul H

I'm sure 'ears' will still be required.

Lot's of 'dynamics' going on when you pull the trigger on a firearm! Time will tell which of them are important.

I was thinking of purchasing some muslin and wrapping the insulation in that, loosely, before installing in the tires. It might not stop 100% of the 'particulate', but it would help a lot.

I'm not overly concerned about 'wet'. It rained yesterday, and I intentionally left the one tire with insulation - vertically oriented - exposed. No 'wetness' in the insulation. Of course, it wasn't a gully-washer and the wind wasn't blowing the rain sideways. I intend to cover the whole with a tarp when not in use. That will also help A LITTLE with critter issues.

Paul

We have "Critter" issues at the gun shop, namely The Brown Rat.


They are quite happy to nest in the roof in the fiber glass & Rock wool insulation.

We tried putting down bags of Rat poison, but the bags vanished & no dead Rats. Turns out they weren't eating the poison, they were stealing the bags to line their nests.

Rats are smarter that people (that haven't dealt with them) think!

Paul

A little water in the insulation may not be a bad thing Paul.


1) It should (may?) keep the glass dust down and the glass fibers from separating.


 2) "Wet" sound suppressors are actually very effective. So much so that they almost universally work better than dry suppressors.


http://www.youtube.com/watch?v=pG_ADkNy3E0

Yeah, Jamie.270, I thought about "wet" suppressors. I just think with regular insulation, "wet" will be more problem than benefit.

Paul