.177 test numbers

[mikeiniowa]

Had a little time to do some testing on a .177 QB-78, reached into the case and pulled this rifle out at random. Serial number X701265. Decided to start at the top and work down into the guts to see what changes would come as I worked, first thing was pull the barrel and clean, looked like a snake had bored it, crooked and shot way off so I straightened it first thing before even testing.
1st string with two cylinders
Beeman Laser pellets (light, very light. used for all strings) 62 degrees F
stock barrel only cleaned 620 ave.
cleaned and polished all internal moving parts except for valve
631
installed new transfer port seal, ID.170
651
opened bolt probe inlet to same size as the probe exhaust
687
opened the inlet and exhaust port in the bolt probe to the same size as the port in the barrel
704
opened barrel,bolt inlet to .155 or approx. 4mm
723
now had about 40 shots from the charge and it had 15 more good shots left before it started to drop off so recharged the rifle with two new cylinders
installed a 1/16 inch wire probe to the bolt instead of the tube type that comes with the rifle
724 ?normally the velocity jumps quite abit when the wire probe is installed
time to take the valve apart, the seal on the valve was swelled up and blocking the exhaust of the gas when the valve was opened so replaced the seal with an aftermarket
753 did a quick test with Gamo hunter pellets 705
opened the area in the brass end of the valve assembly around the head of the valve itself to 1/2 inch
759
tapered the piercing pin and reduced the head to match the tapered head of the valve and made the outside of the washer in the valve triangle shaped
773 at 65 degrees F, 650 at 33 degrees
opened the inlet end of the valve to help the flow
769 at 63 degrees, 655 at 21 degrees
These numbers are with all stock parts, no preload on the hammer spring or lighter valve spring, a lighter spring installed in the valve and with a slight preload on the hammer spring of one or two washers will push the velocity over 800 at about 70 degrees.

Nice numbers BUT what does it do with a normal weight pellet? I have never been able to get those real light pellets to group after 15 yards.

CPL's at 7.9 gr pellets would be a more usefull test since this is what most peolpe use in them because thay are always easy to get.

I know that with my QB78 with a 15 inch .20 barrel it will shoot 9.88 grain Silver Bears at 665 fps, but if I up the weight to the normal pellet I shoot a FTS at 11.2 grains it drops to 602 fps.

So the 11.2 beemans have 9 FPE at 602 fps and the silver bears  at 665 fps have 9.7 FPE but the Silver Bears are not accurate and the FTS's are, I chose to go slower.

[mikeiniowa]

For cpl's knock 20fps off, thats about what the change is. the only reason iI used them is it was the only pellet I had with enough in the tin to complete the test, time to place an order.

[jonny1o1]

after all the mods how many shots per 2 cart charge?

[mikeiniowa]

really don't know, some place in the 40's would be a good guess, the .22's get 30 to 35 and the .177's use a little less per shot, another some day when I have the time things to do..................

[jonny1o1]

thats pretty low  :0   in 22 i dont think i could afford that many shots per charge