Barrel bands - floating, locked, o-ring, or......

[lloyd-ss]

How about some opinions on barrel bands for PCPs?
I am refining my Discovery Double air tube project/kit and am wondering what to do. You'll see that I made the band very wide for more secure alignment.
http://www.gatewaytoairguns.org/GTA/index.php/topic,23613.0.html

PCP air tanks tend to move as the pressure in them goes up and down, and usually the barrel bands are attached to the tank.  There are bands that let the barrel fully float, bands with set screws locking the barrel to the band, and bands with o-rings inside a groove in the band that lightly grips the barrel.  I have recently tried using soft Sorbothane, which damps vibrations instead of acting like a spring as o-rings can do.

I'd appreciate any opinions, thoughts, or experience, particularly if it relates to the Disco. I know a lot of folks have those TKO gizzmos hanging way out front.
Thanks very much,
Lloyd

[rkr]

Is there any reason why you are not considering free floating barrel? One could easily have a free floater inside a shroud if that's the point.

[lloyd-ss]

Good point about the free floating barrel in a full shroud, if the barrel is stiff enough for the length.  With full shrouds, I have seen them totally free floating, and also where the band ties the air tube and shroud together.   In this setup the two tubes would need to be tied together by a band, but it sounds like you are thinking the barrel and/or shroud would be independent.  That does make sense.
Thanks,
Lloyd

[Ribbonstone]

Some times free floating works, some times it doesn't.  A lot depends on how secure the barrel attachment to the breech and the breech attachment to the air tube. Can shoot great, but shoot to a widely different point of impact the next time the gun is picked up.

Have used tight barrel bands right up against the breech as a way to better anchor a less than rock solid breech. Did seem to help.

Normally used bands usually work best when used as "bumper guards".  tight to the bottom tube, slip fit to the barrel. Think of them as limiting devices, allowing a little motion of the barrel.

So...generally, will start with free floating.  IF that shows too wide a POI change from day to day, will add a barrel band used as a "bumper guard".

Got an old post somewhere...let me look.

More than one way to get a Discovery to shoot to the same point of impact day after day...consider this as a possible solution; it worked for me.
After looking over a Challenger PCP, realized what that rear band (just ahead of the action) was doing. The rear band was making the rear end of the barrel  and breech more stable.  Its job seems to be to pull the action down tight to the air tube.

Tried it on both a Discovery and a QB, and point of impact stability greatly increased. Adding a set screw front band seems to have elimated wandering zero.

Due to the Discovery's dimensions, decided to fit this one ahead of the gauge. With the QB, can butt the rear band right up to the breech. Discoveries have a sight base that is too large for a standard band. Unless you use open sights, can abandon the sight base completely.  The other trick is to cut the sight base and fit the band between the two halves. Has a nicer look this way; makes people wonder where you got a band that fits over the sight base.



 Here is a rear band on a QB:


Did try this trick with one QB.  By using a 78D metal band and a 78 standard(skinny) barrel, there is considerable slack between the barrel and the band.  Lathed two races and fitted two o-rings to the barrel (the band fits over them).  Polish the inside the the band, silicon grease the o-rings, and the barrel is tight yet free to slide in and out.



This QB  carbine got both a rear band against the action to help hold evrything tight at the rear, and the above o-ringed 2nd band.



In the front, use a 4-screw band. Besides the top and bottom set screws, add two at an angle from the side.  Seems to work best when they are drilled/tapped through the solid web (its not high grade metal, so the more length for threads the better).

With a QB metal band, can do the same trick, just besure to go though the thick part of the metal.  Crosman band already has two set screw, the QB has none and only needs the 2 set screws to lock it to the gas tube.

These pictures are from a 2260 build, but its the same band and the same process. The key here is to snug the band to the air tube, but NOT hog tie the barrel to the band. Once snug on the tube by 3 screws, will set the top screw to take out most of the slack in the barrel, but still leave it free to slide.  This band serves more as a “bumper guard”.

Set screws before trimming, to give an idea of the angle:

Screws shortened and band installed:

[lloyd-ss]

Ribbonstone,  Wow, thanks for all the detailed information and pictures. You have certainly presented a lot of variables to consider. From what you said, it seems that the common thread in the 2 tube setup will probably be tying the 2 air tubes securely together.  From that fixed base, the security of the barrel can vary from floating to fixed.  Your explanations also beg the question of the spacing between pairs of barrel bands.  Even though the barrel harmonics won't have the amplitude of a springer, they will still be there and it seems like shifting the bands along the barrel would have to cause some sort of change in accuracy.

[Ribbonstone]

Can play with band spacing, hoping to change the barrel vibrations for the better, but generally you'd need a pretty accurate gun and a lot of testing to sort out random error from real results.   

Think bands get a lot more blame...and a lot more credit...than they really deserve.  When they make that drastic a difference, there is usually some other cause they are masking.  In the examp;le Discovery, once I got the breech nailed down with that rear band (it is a "band" but I think of it as a breech clamp) the only think that front band does is act as a bumper guard (it shoots the same with it or without it, but with it small bumps and knocks don't change the POI).