Almost finished the QB79

[ribbonstone]

Did say I'd not fool with the insides once I got to 600fps...and I haven't....but I've been fooling with the outside.  Cut  4 1/2" from the barrel, recrowned, remounted the brake, and got a surprise.

Might be becasue the only internal work has been to the transfer port, could be the rifle breaking in and smoothing out, but chronographing the 17" barrel showed a slight gain over the issue 21 1/2" barrel.  Nothing major...like an average of 8fps...but still a surprise.

Rifle isn't short....but it's a bit more proportional to the stumpy stock.  Swaped scopes, putting the short one on the short rifle, and resighed in...accuracy isn't harmed, so the recrown is OK. Next step is to strip the finish and see if I can get it to match the QB 78.

[ribbonstone]

Not quite...shoots just as well (it had a good crown from the factory), so accuracy wasn't harmed...but was surprised that it shot a little faster.

[shadow]

Pretty girl's there. Ed

[Big_Bill]

Hey all,

I read a report about the max. barrel length for a .22 cal. powder burner, years ago.

The projectiles accelerate until the propellant is expended, and then the projectile begins to slow down due to the friction of the barrel. So if a barrel is cut down, one inch at a time, velocity increases. When they went to 16 inches on a .22 cal. rifle, the velocity began to slow down, due to exiting before all the propellant was expended.

Air pressure would have the same affect from an ari rifle, but I think at a shorter barrel length. Sat 12-14 inches.

[ribbonstone]

Considering that I'm using a stock valve and spring, might just be letting out all the gas 17" of barrel can handle.  Let out more CO2, and the longer barrel would shine...let out less, and an even shorter barrel might work just as well.

Kind of like the .22LR anology...letting more CO2 out per shot would be like using more powder....same pressure, just more volume.

[ribbonstone]

Got the stock done, refitted the recoil pad, converted to a 90 degree safety, inletted the stock so the safety can pass on take down, tuned/polished the trigger.

Looking real sharp, still sanding off the old finish on my 79 a couple hours each day on it.  That finish penetrated real deep in some areas and I'm getting a little nervous about going to thin.  

 http://archerairguns.com/airguns.html  has a Carbine 7" shorter barrel (3" overall after brake added) .  His experience is it looses roughly 10% with a 14" so my guess is you found a sweet spot at 4" shorter with stock valving.   I have a Carbine from him in both .177 & .22 and they do shoot lower FPS than my reg barrel length 78d .177 and AR78 .22 by a bit more than 10%.  

I had the brake off the .177 and it looks like it was shortened from the front of a stock barrel as the crown behind the brake is near a straight 90' with a tiny chamfer if any to speak of.  Still is repeatable though I like to shoot it offhand as I have thumbhole stocks on the carbines.

Cheers
Mark
Sure hope Mike M's stuff is going well for him as the 79 he did for me is just awesome and Gene's (AirGunToys) castled end shroud is sweet on it too.

[ribbonstone]

I'll just use chemical stripper.  The nasty chemical-wear-glooves-burn-the-crap-out-of-you stuff works better than the eco-friendly stuff, but you'll need to take care.  Then I'll break out the sand papers (various grades)to smooth the wood.  Will put on a coat of VARNISH and let it dry for two days...then steel wool that back to wood, this tends to fill the pores in the wood and make for a glass smooth surface.  From there, will usually use thin rubbed in coats of TruOil.

Have read of people bleaching their stocks with hydrogen peroxide...haven't tried that myself.

Know 17" is an odd length, but that will let me attach a 9oz. bottle without hitting the muzzle-handle.

I'm down to wood now in all but a few places with deep penetration.  It has a couple of small filler areas but I'm hopeful it will work out with a light stain like Shadow's project.   Last night I did a quick water douse and the fresh exposed grain has risen so I can sand that back off.  If I screw it up to bad plan B involves truck bed liner ;-).

Cheers
Mark

[ribbonstone]

..and it's called on account of rain 1/2 through.

Only had 22 yards to play with, ran 6 different pellets through for one 5-shot group each, just feeling the new rifle out for what it will like and what it will hate.  So far, it's not a real picky eater. Will try the better choices again at longer range (40yards) as I get a chance.

Think the shorten and recrown didn't hurt it any.




(BTW: on a dark day, seems hanging the targets on the windowns helps....but this crappy camera won't focus well at close distances)

[CharlieDaTuna]

Now that's pretty decent....but... isn't just a wee bit hard on the windows tho... :p

[ribbonstone]

...after that, the others don't seem to do much damage.

Just figured back-lighting would be the best way to show the group sizes....the "reject" pixs were worse.