Air tubes best to be free floated or not?

[Oldblades]

Been really busy with a new Challenger CH2009 that I got from Norm at DiscosRUS. I now have the receiver locked solidly into the stock inletting. Had to go a tape bedding route given the engineered foam stock vs. wood, and am now turning to the forend section.

The barrel itself free floats above the tube, but was wondering if the airtube itself should be fixed to the forend, or floated as well?
I would love to be able to use the tube to add rigidity to the forend by tieing it into it, but not sure if I would be going backwards on this.

[rsterne]

It shouldn't matter, I would prefer to have the reservoir fairly solid in the tube.... Having the barrel restrained by (ie mounted to) the air reservoir is problematic, and sometimes causes POI shifts as the reservoir pressure changes....

Bob

[Oldblades]

Thanks. I was getting mixed opinions in my research on this. With the foam stock I thought that it might not be as much of an issue, as it may be with wood.
The way that Crosman integrated the accessory rail into the forend (vs. screws), it seems that they were also attempting to use that to stiffen the forend.

 

[Ribbonstone]

Give a choice, would want the air tube to be well fitted to the stock from the valve on back. Figure that’s the non-pressurized section, so changes in tube pressure wouldn’t make any difference.  Fore end can be floated or soft pressure bedded (basically a pad of softer material). With the free floated barrel, the front end of the air tube’s bedding didn’t seem to help or hurt accuracy (but if the gun “pings” having a free floating air tube lets it resonate…so it’s more like “pingggggggg"

[Oldblades]

  With the free floated barrel, the front end of the air tube’s bedding didn’t seem to help or hurt accuracy (but if the gun “pings” having a free floating air tube lets it resonate…so it’s more like “pingggggggg"

Ahhhh, you just hit on a 'biggie' there Ribbonstone. The gun does ping a bit and was just getting educated on that aspect of air rifles.
The way I understand it is that it is actually a sound wave ringing the tube? Would a rubber damper in the forend at the corect harmonic be able to 'kill' the wave, or is going inside the tube with a depinger the only way?
I'm going to follow your lead on the exploring the soft bedding. (Really have no choice on that anyway since epoxy aint going to work.)
The rear barrel band also looks like it might make a excellent anchor in the valve area by tapping it and adding a screw from underneath.
 

[HillGSA]

I don't have the huming sound in my right ear anymore, when I go to sleep at night. No more ping is good!! Hill de-pinger

Shooting my action targets (tennis ball) at 100 yards with consistency ( I need to change out the tennis ball ) (scope set on 8 - using 3rd mil-dot - JSB 18.13 at around 910 FPS) . Barrel band has a O-ring that is a tight fit.

[QVTom]

The Crosman platform with its full length mono tube design should be the least affected of all  by pressure variations within.  Funny, they have the most stable tube on which to mount a barrel band then they use the sloppiest floating barrel and shroud system. 

Tom

BTW, nice barrel band.  Looks a lot like this one

[Ribbonstone]

Not really sure why, but changing the geometery of the tune can at lessen it (or make it worse, but at least you’d know what direction to take).  Given the variables of spring tension/fill pressure/stroke there is more than one way to get to 12 foot pounds (and a lot more if you add in transfer ports and striker weight).  Am guessing that that air pressure induced impuse that powers “ping” would be loudest at some resonate frequency that matches the tube’s length.

Who know? maybe it’s still there but outside our hearing range (let me know if the dogs in the neighborhood start barking).

Other people have used external wraps/pressure points/deadening material acting on the ouside of the tube to deaden the noise.  Can always do a quick experiment and grab the tube with your hand to see if it dampens the noise.

Most just make or buy a depinger and put it inside of the tube to break up that pressure pulse, taking away what powers the ping.

[Sfttailrdr46]

I slid 2 orings between the barrel band and shroud on both my Marauders

[HillGSA]

Tom

BTW, nice barrel band.  Looks a lot like this one


That's cute, I like the smiley face 




BTW  -   Anyone who has been on the forums for a while knows that Tim Hill invented the barrel band with picatinny/weaver style mount - sorry 

[QVTom]

Not sure I go as far as calling it an invention   Some folks will stick a picatinny on anything 

[Oldblades]

Not really sure why, but changing the geometery of the tune can at lessen it (or make it worse, but at least you’d know what direction to take).   

I spend a lot of time with blue painters tape, business cards, and rubber binders and blocks, doing temporary stuff to see if it will work.
I'm still in my comfort zone with exploring bedding and blocking of the action, and action harmonics.
That all goes away real quick right now when it comes to following you guys' leads on the internals of a pcp. So I need to keep the back door open. 

ie: Heres my 'receiver bedding' to this point. Turned out to be extremely stable and will likely stay as is. 

[HillGSA]

Not sure I go as far as calling it an invention   Some folks will stick a picatinny on anything 

Said the copy cat….        

[HillGSA]

Just funning with you   

[Oldblades]

Wow, any of you guys that are having issues with horizontal/diagonal stringing, you should really take a look at tape bedding the trigger group to the inletting. (if you only have a single forward action screw and if your TG would be conducive to this).
Its really the only flat spots on the action in this case for the opportunity to try this.

I had some pretty extreme horizontal and found .050 'slop' between the TG and the inletted walls.
Realized the torque applied from cocking had to be doing something to the action in the stock with that kind of free play.

It took 5 layers of tape to snug it up and the difference was amazing. Went from about a 10/1 horizontal (no exaggeration there) to vertical dispersion ratio, to actually a fuzz more vertical now.

[michaelthomas]

FWIW.....I float my air tubes.  The only place my action contacts the stock is a 4 inch section where the single 10-32 bolt fastens it to the stock.  It is relieved both ahead and behind this.  This is on an aluminum stock.  This is where the barrel block and scope mount, also.  Prior to doing this, POI changes could be seen at 25y indoors after barrel cleaning and refilling the tube between cards. 

Mike

[QVTom]

Just funning with you   

As was I   More importantly, I  noticed your band is installed backwards

[Oldblades]

FWIW.....I float my air tubes.  The only place my action contacts the stock is a 4 inch section where the single 10-32 bolt fastens it to the stock.  It is relieved both ahead and behind this.  This is on an aluminum stock.  This is where the barrel block and scope mount, also.  Prior to doing this, POI changes could be seen at 25y indoors after barrel cleaning and refilling the tube between cards. 

Mike

FWIW Mike, with the results that you get, I'm all eyeballs on anything that you have to offer. Thanks

[Ribbonstone]

Got me wondering.  Do like to find things out for myself.

Short test, so its at least indicative if not  proof-positive.


Bedded the Challenger PCP as shown.  Black Epoxy bedding doesn’t show up worth a hoot on a black stock, so for the photo cut out some construction paper just to show where the bedding is.



BTW: they do sell release agents for epoxy bedding. But you can use good old Johnson’s Past Floor Wax.  Has a “carp load” of uses around the shop, and as long as you keep the tin sealed, last for years.



Which set the rear section of the barreled action solidly in the stock without any wiggle/rotation, or see-saw movement.

Also left room for a dollar bill to easily slide between the stock and the air tube.

Thicker target paper took a bit more effort to slide between the tube and the stock.



So I tried 15 shots ( 3 5-shot groups) at 20 yards with 3 settings:

Free floating (top 3 groups)

 Middle set of 3 used 2 target papers, which required me to loosen the stock screw in order to get two layers of target paper in place. GUESSTIMATING by the effort needed to lift the air tube until the paper slides out, would say something like 5-8 pounds of “up” force to the air tube.

Bottom set of 3 targets used one 1 target paper thickness could be slid in without loosening the stock screw.  Probably something like 1-2 pounds of “up” force.



Don’t reallyneed to measure the groups. The quick test indicates this rifle wants to have the air tube free floated.

Will have to test over a few days to see if the POI stays stable to the  POA.  So long as it does, am going to stick with free floating the tube.

[Oldblades]

Teriffic info and nice shooting to boot!

 I was also suspecting the tube should be floated now after today. I had used the blue painters tape test last night on the tube and shot it this morning before work. Dead calm and getting some shifting. Then came home this afternoon, pulled the tape and opened up the barrel channel and give that a try per Mikes post.
Pretty windy by then, but the 4 (5) shot groups were non-directional and all in the low .300's ctc at 30 yds. using flags.
So I suspected that to be in the right direction.
That was just confirmation Ribbonstone. Thanks.

Did you have any issues with the epoxy sticking? I have some Devon epoxy that I use on wood stocks, but wasnt quite sure if it would work or not on the foam. Didnt want to start carving up the inletting for the bedding relief, and then discover the answer was 'Not'.