Have a qb78, tuned every which way you can, but I seem to have hit a stumbling block...
Put in one of rich from mich's .20 walther barrels, and I knew the power would drop as previously it was a .22 but I now struggle to get 10ftlbs or 630 fps with H&N Field & Target Trophy .20 (11.4gr) when previously I had to be careful to keep it under the uk 12ftlb limit.
Have I limited the power to this by using a 15" barrel or am I missing something else?
In our CAR78a carbine version of the QB78, the barrel is shortened by 7-inches from the standard factory length - down to 14-inches. This reduction in length lowers muzzle velocity by about 10%, according to our tests. This applies to both calibres when tested at the same ambient temperatures.
So, as you have made a similar reduction in length, you would have up to a 10% reduction in muzzle velocity compounding the effect of the calibre reduction.
Interesting,
My QB78D .22 barrel is pretty bad as well. Not straight by over a 1/16" over it's length. I straightened and recrowned and it improved but is still not accurate at relatively low velocities (590 f/s )with any of the pellets I have tried . I get lots of flyers.
I am looking for a new barrel preferably in .22 cal would like a L/W or other quality barrel. Rich doesn't have them, Mac1 is out of stock, anyone else I should try that would stock them ?
There was a bad run of the Deluxe barrels a while back.
Ask Rich or Mike Melick if they might have a good replacement
barrel. Or if you really want a Lothar Walther barrel you can buy a blank direct from them and have it shipped to Rich to have it machined for your QB78,and then blued. The Lothar blanks run $101.00+ shipping. One of the guys could hand pick an OEM standard or Deluxe barrel for less than half the price of the Lothar blank alone.
using RWS super points 14.4g --601-604 fps ,
JSB Stratons 15.9g avg 588,
Cr point 14.3g avg 583,
Benji HP 14.3g? avg 583.
JSB Preditors 15.9g avg 560,
all shots were taken around noon time at about 81 degrees.
My QB seems to like the pointed pellets more than the domed ones, the preditors guess the gun doesnt.
Mods, ice maker tube breech seal and open up the bolt and barrel to allow more air. Accurate out to 30 yards and have taken ratters at 20 - 25 out and 20 -30 feet up in the trees.
Had the Deluxe 15mm barrel, wasnt worth a crap shoot, got a 14mm from archer air, that did the trick.
I'm not into power, just accuracy.
Buster
\\\ X ////
one step closer to the ultimate goal
..two shortened .22's (17" barrels) both earn significantly higher energy heavier pellets. A 5mm 12" Talon SS (on co2) prefers heavier pellets. Might want to give something in the 14 - 14.3 gr. range a try (Cp's would be the long range choice, but the basic Benjamin black box clyndrical is worth a try).
Mr. Archer has the numbers...which seem about right to me. Something like 8-10% less for the short barrel, 5-7% for the reduction in caliber to .20.
The QB I use for starlings is a .20 and it shoots FTS's at 710 fps. I can make them go faster but the shot count really suffers, but 710/720 fps is a sweet spot with the .20 cal. and it has the same barrel as I sent you
All the .20 rifles I have done shoot in this speed range so it sounds like you have a problem some where, seal? valve?
The probe is a 2mm pin type
Valve has been flowed with 4 2.5mm holes and he valve stem has been done (all part of a kit in the uk)
The transfer port is a 5mm od 4mm id brass tube that pushes into the valve and reaches to the barrel port which was set by Rich and all fits together well.
The hammer spring is externally adjustable, and when tensioned fully seems to have little effect on the power.
The barrel seals are new as supplied by Rich
I am using 12g crosman powerlets.
Will try again today and order some heavier pellets.
Wondering if the probe length and/or width could be wrong for the .20?
It has been left the same length as when it was a .22, and I did take the diameter down a little but what should it be optimally?
pull the barrel band screw and the set screw for the barrel, load a pellet then pull the barrel and see if it's past the port in the barrel, if so you are good to go, if not have to make it longer..........I've been using a 1/16th inch diameter probe.........
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