Increasing FPS Without Decreasing Shoots Per Fill

I was just wondering what mods you could make to the QB78 to increase FPS without decreasing the shoots per fill too much.

Thanks Bill

[DanoInTx]

if you drive your car at say 55mph, and you aim your QB78 out the window and shoot it, you will see an increase in FPS without using anymore gas....unfortunately, as is with most things, the faster you go the more gas you burn.  I would have to say aligning the ports, and extending the bolt probe with be the most mileage for gas consumption you could do.  Making everything smooth as silk without increasing any valve volume, or changing spring tension would be the best way to go to increase fps without losing much more gas.  CO2 and any other gas/liguid sees any sharp turns as a restriction, minimizing those restrictions will definately improve performance.  But as I said, more speed usually equals more gas...not a hard and fast rule, but always seems to do that for me.

just my $0.02

Dan

Forgive my ignorance but aligning what ports and the owner's manual I have with the parts brake down doesn't show a part called "bolt prob".

Thanks Bill

[DanoInTx]

If you take the reciever off of the air tube there will be a little hole with a seal between the two of them.  This is where air travels from the valve into the barrel.  If when assembled these two holes (the one in the barrel and the one in the valve"ports" or "air ports" or "transfer port") are not aligned you will be choking off your air supply from the valve to the to the barrel.  I actually oversized my ports as per Chharlie's tune up guide and replaced the old seal with a very short length(1/8" - 3-16") of poly icemaker tubing, this will alleviate the constriction in this area and give you better gas flow.

The bolt probe is the part at the tip of the bolt, the part that you slide in the action to push the pellet in and cock the gun.  At the very tip of that is a tube area with a hole drilled in the side of it...this is the bolt probe.  For a .22 it is recommended in Charlie's tune guide to cut this area off, drill a small hole in the center, and replace that missing are with a thin piece of drill stock or piano wire(Mike says the wire from those little surveying flags they stick in peoples lawns is the perfect size).  You can also just oversize the hole in the existing probe, and make sure that when the bolt is closed that hole is aligned with the transfer port in the barrel and valve and so on.  I don't know off the top of my head exactly how big you can go here, but the icemaker tubing I think has an OD of 1/4" and an ID of about 3/16"...so going any larger than that on any of these areas to me would seem like a waste and maybe even give you problems with sealing if you go too big.  If doing a .177 you might just want to oversize the hole in the original bolt probe, but if doing a .22 you'll want to do the wire replacement bolt probe route.  All of this is in Charlie's tune up guide along with some pictures and drawings.  Good luck!

Dan

Dan, thanks for explaining all that to me. The gun I have is in .22 cal. and yesterday I took it apart and cleaned and lubed it, no mods, according to Charlie's website. The mods you suggested just makes for better air flow and doesn't increase the amount of c02 you are using, is that correct ?

I don't think I have ever heard of the "poly icemaker tubing", where can I find that ?

Thanks Bill

[DanoInTx]

Uhm poly tubing, you can buy it at Home Depot, Lowes, Ace Hardware, etc...  Mine says on the outside Poly tubing 1/4" x .170"...ask at Ace Hardware for icemaker tubing and you should be right on the money.  You can buy it by the foot, for like $0.10 or something nominal, and a foot will give you enough tubing to last maybe 30 guns.  You only need about 1/8" to maybe 3/16" off it between the breach and the air tube, so not much is used.  Use a very sharp razor to cut it nice and square so it seals properly.  As far as the mods I mentioned, I can't say for sure that they wont use more air, but as the valve volume isn't being increased, and the springs aren't being lightenned to increase the dwell time of the valve, I don't see why it would eat all that much more gas, just gets rid of turbulance, but I'm not really sure here.  With 3 kids, 2 dogs, a working wife, and a full time job, plus a house to take care of I rarely sit down and shoot long enough to use up a set of powerlets with any of my guns, with the exception of one really hotrodded Cr 2240 that eats a caplet about every 15 shots.  So I've never really spent much of my day worrying about shot count.  I would say though that these mods would give you the most bang for your buck without eating too much if any extra gas.  Just my opinion, no lab results to prove it:)

Just got some email from Mike Melick tonight, he seems to be feeling a little better after a few days with a high fever, maybe he'll bounce by the forum in a day or two and give you the skinny on which mods do what, he's THE MAN when it comes to QB's.

Good luck and be safe,

Dan

[ribbonstone]

Good advice and directions.

Won't use more CO2...valve will dump what it did before as the springs haven't changed and the release should be about the same (maybe a little bit more gas as back-pressure is a bit less).

What we're trying to do is get rid of any sharp edge, aligne the holes for a non restricted path, and perhaps enlarge the entrance to the barrel by converting to a probe rahter than the issue bolt tip.  Basically, giving the gas a smooth unrestricted path rahter than letting it lose energy through turbulance.

Personally, once you'e gotten the sharp edges off and aligned the holes (changing the breech tube to the cut bit of tubing...the issue seal squeshes down in the middle under compression and restricts flow), the conversion to bolt probe isn't all that important.

But it's cold now (at least in the Northen hemisphere) and CO2 isn't my favored play thing in cold weather.

[mikeiniowa]

Increasing fps and gas consumption do go hand in hand, aligning the ports in the barrel and reciver is a good place to start, gives 10 to 20 fps, drilling the bolt probe at the same time to the same diameter is also a help. to do this using a .170 or just under drill bit, assemble the receiver/barrel/bolt, just snug up the set screw for the barrel and flip the whole thing on it's back so you can see the port, make sure the bolt is closed and held in place ( use a small block of wood) chuck the bit up in a hand drill or a drill press and slowly drill down until you go through the bottom of the probe. Take it all apart and check the probe first to see that it's open on the bottom, you can drill out the exit post in the front of the probe but do this very carefully, just ake a few thou. at a time(wire size bits work good), at the loading port in the barrel look into the area where the bit came throughand remove any rough edges in the port, a Dremel tool with a chain saw sharpening stone works good here, the small grey colored one for a .177 and the tan larer size for the .22. Now find a drill bit that is smaller in diameter than the bore of the barrel and wrap some 220 grit paper around it and slide it back and forth in the loading channel and into the port area of the barrel(don't go in to far or you will mess up the rifleing, change to progressively finer grits until you get down to 400 or 600, should be nice and shiney and have no sharp edges in the channel r around the opening in the barrel, keeps from cutting probe o-rings. Polish the inside of the receiver with a split stick and a piece of 220 paper making sure to remove the sharp edge from the front of the receiver, take the sharp edges off the set screw hole on the inside and the transfer port hole also. This should give you about a 150fps gain and a shot count of about 50 per charge in .22

Mike , thanks for the information. After you drill the ports and prob as you described what do you do to the port in the tube, just leave it as is and do you use the same seal that you were using before between the tube and receiver or something different ?

Thanks Bill

[mikeiniowa]

The opening in the gas tube/exhaust port for valve doesn't need any work unless you are going for a .25 conversion then open the port in the valve to .20. For a seal you can try reusing the OE one but don't expect to much, might leak. The poly tube for the ice maker is the best, at 9 cents a foot you can buy a life time supply and get change back from your dime. I can send you some, I'll cut a few and send a chunk uncut, just send me the ole mailing addy........