Alternate barrel band theory

[ribbonstone]

Those of you worried about the barrel bands  used on QB’s, this might be an alternative.  Had an old spare QB 78D metal barrel band and an old QB78 standard barrel to try it on.

Cut two o-ring seats just ahead and just behind the cross slot for the barrel band screw.  Want the band to completely hide the cuts.



Slightly widen the cross cut for the barrel band screw if it binds  Want it to have a slight bit of in and out play.

Will have to control the depth.  There is plenty of beef in the barrel, but want the 0-rings to end up a snug fit.  Used a pair of spare barrel breech o-rings (just stretched a bit more to fit over the barrel).  



A slight bevel on the inside edge of the metal barrel band  and a touch of silicon grease helps  to get the band to snugly slide over the o-rings.  A bit of polish on the inside of the barrel band’s upper loop helps.



If I try, can get the barrel to slide front to rear with no side to side or up and down play when the barrel breech lock screw is removed.  With the screw tight, there’s no motion.  Seems to be no band to barrel contact at all, the band holds onto the o-rings which hold the barrel centered in the barrel band.




Perhaps this will let the gas tube expand and contract a little bit without binding on that barrel band.

[DanoInTx]

Nice fix, I like it!

[Gene_SC]

But Rib, are'nt the barrel bands suppose to be a non tight fit? I have seen many pros and cons on barrel bands. Can you give us your opinion on this?

[DanoInTx]

I think the idea with the o-ring is to make the barrel semi-floating.  There's a number of other guns that are using this approach already.  Basically tight enough so that you aren't knocking it all over the place, and loose enough that it'll still slide freely.  Rib also mentioned that he lubed the o-rings a bit during assembly, which would promote this sliding action.  Most of the other guns have the o-ring captive in the barrel band itself, but Rib's approach makes it possible to do the same mod with a normal lathe and a grooving tool.  I actually added a second barrel band to my Discovery, then removed the set screw at that holds the barrel down tight, but I may try this instead, seems a little more accurate....in my mind at least:)

[Gene_SC]

Ok I missed the part about lubing it. Makes sense now. Thanks Dano

[ribbonstone]

...how many (if any) bands hasn't made any real difference in accuracy.  I've tried no bands, single bands of plastic, al. and steel, and two bands. Tried locking the bottom of the band to the gas tube by way of set screws, epoxy, or both.  Fixing the bottom to the gas tube hasn't made much differnece one way or the other.  IF the barrel is set up tight to the breech and the breech tight to the gas tube, they all shoot well.  IF you've a rifle that won't shoot well without a band,  suggest that the real cause is back at the receiver.

Been happiest when I can slide the barrel off the rifle when the rear set screw is removed.  Don't want any side to side or play, just a straight forward slide.  The o-ring solution works, but so does shimming.  If you do shim, then shim with something more likely to allow that slide.  If in a rush, can just wrap teflon tape around the barrel under the  band...band covers it so you can't see it, can get a nice fit, but the barrel is still free to slide.

But the band can help with day to day point of impact shifts.  With the band set up right, the point of impact has been stable.  Nothing is going to save it from a massive hit (like dropping it from a tree), but day-to-day shifts from small knocks are well controled.

[Gene_SC]

Thanks Rib

[Rixtrix]

Nice work, but I have a question or two. Rather than weaken the barrel by grooving 2 places and possibly inducing unwanted barrel harmonics during the firing cycle, wouldn't it work better to groove the inside of the barrel band to install the o-rings? This would still support the barrel from slight impacts, but may help to dampen any harmonics that may already be occuring. My thinking is the most important thing that would happen was that the barrel would be much less resistant to bending from impact if it didn't have 2 grooves cut near the middle of it's length.

When I replaced the barrel in my AR-15 with one that didn't have a "bayonet" groove, the acuracy improved by almost 40%. Admittedly, it has much higher pressure in the barrel during the firing cycle, but airgun barrels are not made with as good a quality of steel, or thickness by comparison to the pressures involved in each.

Just a thought ot two.

Ric G