Don't be afraid to try...barrel contact

[Ribbonstone]

Barrel contact on a QB79.


Return of the "pig" (it's short/thick/heavy....it's a pig).

DSCN2050 by Robert Dean, on Flickr

Idea of the "pig" was to let one rifle collect as much abuse, scraths, scars, dings as possible....it's already ugly, beating it up a bit won't change that.  Back yard duty (great rat-rifle) so .22 and about 12-13 foot pounds (depending on pellet weight).

With some adjusting, manages 200-205 shots per charge (3000 to 850psi)....which isn't great efficiency, but a reasonable amount (basically it gets 2400 foot pounds per fill up...just in 12 foot pound bites).


Making the barrel stable/shooting well.


THIS IS NOT something most rifles need....but this one did resond well to CONTACT between the barrel and the tank.

Normally we'd not think that could help....but then I thought on it and experimented with soft and hard contact points.

THOUGHTS:

The regulated HPA tank is not going to expand it's thick base as pressure changes.
The pressure beteen the tank and rifle is the same (so long as the regulator works as a regulator),so the "stiffness" of the tank-tube joint should remain the same.
Tank is  slung below center from the tube,so I'd expect some "up"pressure with the tank filled.  just from o-ring compression.


Some experiments with semi-soft materials as a contact point showed a lot of promise, just didn't live as long as I'd like (the rifle has been going in this cionfiguration for years).
Problem with soft stuff jammed beteen the barrle and tank is that is's compressable and kind of "sticky"...the barrel may not self center as well on a pad of boot-heel rubber if it can't naturally find self-center.

Made an  aluminium "ring".

Idea was that a radius cut on the bottom of the ring would pretty well self-center the barrel to the tank. Knock it, nudge it,and it's going to want to go back to the matching radius of the tank.

DSCN2047 by Robert Dean, on Flickr
  Implimetation was simple...put the ring on the barrel, shoot the rifle a few times for it to find it's natrual  set point, marke it, glue it to JUST THE BARREL.

The radius cut seems to self center. It'snot attached to the tank,so the barrelcan slide in and out for expansion/contraction issues, and it provides a bit of "Up" tension when  the tank is pressurized to the rifle.

I did "jack leg" test it for up tension by putting a dollar bill between the two, and judging the effort to pull it free.
With the tank as "zero", the tension was in ounces.

With the tank filled and the tube pressurized, the effort to pull the bill free was about 2-2 1/2 pounds.

What that means in actual "up"force, I really don't know as it is in "dollar bill slide force" numbers....but it feels the same from a 3K fill down to 850psi (the running pressure of the regulated HPA tank)   

Likely helps that the barrel is a shortened QB barrel; there just isn't a whole lot of barrel (about 1 1/3") sticking out past the end of the HPA tank(mostly covered by that fat LDC).

TEST:

The "pig" without  it's ring,,,,wasn't touching...so will call that: Free-float + Band.



THe same "pig" with the shown "ring"...we'll call that: "ring" and band.
DSCN1281 by Robert Dean, on Flickr


The difference (although I need some "left" windage):

DSCN2049 by Robert Dean, on Flickr


I actually ran 3 tests,but there was no differnce beteen  no barrel band and no ring and +barrel band  and no ring, although I don't think that the fully free foated barrel (no band and no ring) would  keep it's zero with even a moderate "knock".


So there you have it....one old gun's revival.  It's not the most accurate, I think of the "pig"as "steampunk-ugly",  but it will chug along year after year.l

[grand-galop]

Robert!!
I would think 3 orings could replace this white bit if ever it fail you... It has made it more accurate for sure...
The level of power the rifle provide isn't enough to rip through this bit for awhile …..