Maybe some of you QB experts can give me some insight.

My Qb has the typical mods

Bolt Probe Drilled to #16 Drill Bit
Barrel Port Drilled to #16
1/4" Poly tube breech seal
Lighter valve spring
2 holes drilled into face of valve housing to improve co2 flow
Washer inside valve has got the 4 notches, so it kind of looks like an Iron Cross.

So far with these mods the rifle is shooting 700-705fps with a 14.3grain Pellet.. It is still being used with powerlets, I don't like the look of a tank hanging off the front of a rifle so I havent gone to a big bottle..

What else can I do to increase the velocity even more? It's used only for hunting so shot count isn't too high on the priority list.

Thanks in Advance

A bulk Fill doesn't mean a tank hanging off the front of a rifle...

I know the difference between a tank hanging off the front and the extended tube for bulk filling. Maybe I should have been more clear, my apologies.

What do you mean with extended tube? is it the Bulk Fill Cap?

I have seen extended bulk tubes that thread onto the existing QB tube so you end up with 2 tubes which reach the same length as the barrel.. Your fill nipple is at the end on the cap.

I was just wondering what else could I do for a power increase without doing the bulk setup?

I still haven't removed the 90 degree edge in the exhaust port, I still don't have a bolt probe and I haven't shimmed the hammer yet. Would it be worth doing these 3 extra mods? what would I expect from these 3 mods?

thanks

From what I know with the Bulk fill cap you don't need the extra tube. You just need a CO2 bottle with a valve.

And the bulk fill don't increase the power. Just the number of shots...

Bulk Filling will increase velocity by a small amount, there's no puncture pin being pushed into the powerlet so the stem can open a bit more allowing more gas through.

Shimming he hammer spring is worth it but effects cocking ease and trigger weight.
You could taper, round and polish the valve stem head, match up the piercing pins diameter to it also.
Polish the hammer and spring and lube lightly with a moly/oil mix, polish the inside of the main tube where the hammer travels.
Don't take too much metal off those surfaces you don't want room for the hammer to cant and bind.

while running cartridges,and looks almost stock(no tube extension)

Put in a delrin head valve,shaped to the minimum OD at the valve seat ,larger at the spring end.I don't shim the spring,and get well into the 800's on co2 with .22 crosman premiers with this setup.A .047" wire probe,as long as will work, is part of the high output setup,as is careful work in the port bend,and an oval or dual port in the barrel.With the ultralight striker you'll get 30-40 shots on a fill even at this high an output(if you get the valve head to valve body clearance just right)
I've got an even more radical striker and valve body I haven't tested yet,but you get the idea from the pics.

Could you please explain a bit more in depth about the wire bolt probe? I think i'm going to attempt this but I'm not 100% sure on what to do.. Do you any pics?

Also I already have a teflon valve stem from mountainairguns, should I turn down the diameter on this as well?

thanks

Here is a guide that I used for the wire probe and it works great.
http://www.network54.com/Forum/113813/thread/1211599355/How+to+mod+probe

it's quite small and it's on a pedestal,all intended to get it out of the airflow.The spring pressure is similar to factory,maybe a bit lighter.
Teflon works fine in co2 guns,but it distorted (didn't leak,just flowed,and
I think lost me a little power) when I ran it in the pcp gun,so I went to delrin on this one.
The radical striker is 1.3 ounces(factory is 2 ounces)the one in the pic is 1.5 ounces

What I do know...clearance to the valve wall is pretty critical for good efficiency,less so for maximum power(so leave at least part of the valve head full diameter)Too small at the seat will give you problems,but you can go pretty close to the mark left by the seat.
The way I do the wire probe is to straighten the bolt(they are all bent)then put it in the lathe and cut it off at the o-ring groove,then drill it for a press fit to the piano wire I use for the probe(about 3/8" depth)Then I push a section of port seal tube over the probe,cut it off,and test fit to the breach.Some reshaping of the tip of the tube is needed to get a good seal. No more blown bolt o-rings.

I can hardly wait!

Can you elude to it's weight? How low can we go?

by cutting it or did you replace it with a new spring. If you changed it what spring did you use. I lightened the striker to 1.6 oz but I lost 100 fps so I am looking for answers.

Jeff Schock
WB9ZPO
QB78 carbine tuned by CO2une,
QB78 Thumb hole stock
AR2078 mild tune by MM

NT

Jeff Schock
WB9ZPO
QB78 carbine tuned by CO2une,
QB78 Thumb hole stock
AR2078 mild tune by MM

premiers.

If you are getting 700pfs+ with the rifle as is, I say you are doing pretty good. I also use a QB-78 tuned to this level, and I would only change a couple of things that I think would help. First take note of the lightened striker that Classicalgas posted, do that. That will make your rifle much more efficent, while the thing is apart shim the striker spring with a couple of washers, strighten and polish the bolt and striker, and tube. That should let you pick up a few more fps, and not use more gas. You will also notice the rifle is not as loud as before. I changed to a Probe and did not pick up much fps. I did notice the rifle was not grouping as well as it did with the drilled bolt, so I went back to that. Now rifle is shooting one hole groups again. My rifle likes 14.5 grain Superdome Pellets. If you need more power consider building yourself a PCP conversion, That will let you get all the power you need.
Bill...

Can't increase the pressure, can only increase how much co2 get to the back of the pellet. CO2 that gets there "late" doesn't do much but make extra noise; past a certain point, squirting more co2 out isn't going to gain vel. Getting the co2 to the pellet smoother/faster will increase speed.

In .22, past 725fps or so, it's a matter of the little details. Smoother gas passages, better valving will earn more gains that dumping more co2 per shot. That's one of the reasons lighter hammers seem to work better...a sharp "jab" at the valve seems to do more good (with less gas wasted) than a big slow round-house punch.

------
To get the most power (but less speed) converting to .25 can get you into the 22-25 foot pound area. Basically, co2 LOVES a bigger bore (which is why .177's don't get the energy of .22's)....more bore volume, so more of that gas gets to the pellet base "right now" rather than being late to the party.