Wednesday, March 2, 2022

Breech Honing the Tech Force TF79 / AR2078

Got three or four airgun projects in process right now.  Thought I'd get a quick post up with one of the happenings.  I've been shooting my old Tech Force TF79 target rifle, and while I've reworked the stock, the mechanical parts have been left almost untouched.   I did try to smooth out the bolt loading mechanism a few years ago.  Trued up the bolt body.  It's been straightened, polished and deburred.  When cocking, the bolt mechanism feels like it's full of sand and gravel.  It originally felt like it was full of rocks--so at the time this was an improvement!

Thought I'd give it another go and smooth out the inside of the breech this time around.


Removed the breech and took it into the shop.


Yep. Tech Force.  Is that brand name still around?   Pretty much identical to the AR2078A CO2 rifle--or QB78, or QB79, or Crosman 160...




























Found a few 1/2" diameter silicon carbide Flex Hones from Brush Research.   These are also sometimes referred to as "Ball Hones" or "Cylinder Hones"















This particular flex hone is pretty worn.  I'll start with it and see how it does.  I really only want to knock off the high spots.  If this doesn't work, I can always hone the ID on a Sunnen horizontal machine and really get the gouges out.







Simple.  Chuck it in a drill, flood the tube with oil and hone away.  Keep the hone moving.


I cheated and got some honing oil from one of the Sunnen machines.  The used oil works great with flex hones because it's charged with very tiny particulates (micro pieces of grinding stones and ultra fine metal dust) from the honing process.

Still see some rough machining marks.  As long as the high spots and sharp edges are gone, this should be OK. 

Didn't bother with the very front of the breech where the barrel fits.

Fixed?  Dunno yet.  It occurred to me that while the gun was apart, this is a fine time to re-cut and crown the muzzle. 

Are the remaining scratches in the tube a problem?  Doubtful.  If it was a mirror polish, I'd have honed the tube to intentionally put some scratches in there.  The scratches retain lubricating oil.  

Anybody got a favorite grease/oil for the QB bolt mechanism?

More in a couple days.