QB78 bulk fill efficiency.. How do I improve it..??

[Tgomez82]

I have 2 QB78 one has a tube extensions and is obviously bulk fill only, the second I have the bulk fill cap for it but it is still capable of using 12g's. I am considering buying the extension and going to bulk fill only with this one as well. But I have read that the shot count is not so great with a QB being bulk fill. They will both be staying co2 only no HPA conversion on these 2. My question is what kind of mods can I do to improve my efficiency with these..??

[nervoustrigger]

In stock form, there is far too much hammer strike which wastes CO2.  The simplest modification you can do to improve efficiency is to shorten the hammer spring, one coil at a time, until the velocity just begins to fall.

To take it further, see about making or buying an SSG which is a device that limits the spring travel so as to prevent the hammer from rebounding with sufficient energy to re-open the valve (which wastes gas). 

There are certainly other techniques that can be used, like lightening the hammer and installing a bstaley O-ring buffer but the two above are the ones I would recommend.

[Tgomez82]

Thank you Jason I will try these recomendations and see what I come up with. Unfortunately I don't have a chrono so it kinda limits the modding I can do, what are th benefits of a delrin valve stem such as the ones available through mountain air..??

[nervoustrigger]

There's really no meaningful benefit to a using a Delrin poppet with CO2, and in fact it may be detrimental because it can be difficult to get a good seal at CO2 pressures (800 - 900psi) and because the material is so hard, it is more apt to bounce and waste gas in my experience.

[Tgomez82]

Thank you again Jason I appreciate all of your help and input I will see what can come up with to get some decent efficiency from these QB's seeing as I won the Chinese barrel lottery with both of them. They are absolute tack drivers. I've inly shot them to 30 yards so far, but they are impressive.

[nervoustrigger]

That's good to hear you got good shooters.  I haven't come across one yet that won't shoot ragged holes at 25 yards or more with some flavor of JSB.  So I guess at some point we should declare the barrel lottery a thing of the past.

[skorec]

And what about to  check  1500 PSI pressured air too ?
I have done universal CO2-800PSI/PCP-1500PSI plug on  my QB78/177 deluxe.

http://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=113196.0;attach=169996;image

Chinese barrel need to be recrowned for encreasing accuracy.
http://forum.gunshop.cz/download/file.php?id=34486&mode=view

CO2 need stable temperature for accuracy
http://forum.gunshop.cz/download/file.php?id=34812&mode=view

You need to clean barrel after 20-30 shoots too

[Doug Wall]

And what about to  check  1500 PSI pressured air too ?
I have done universal CO2-800PSI/PCP-1500PSI plug on  my QB78/177 deluxe.

http://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=113196.0;attach=169996;image

Chinese barrel need to be recrowned for encreasing accuracy.
http://forum.gunshop.cz/download/file.php?id=34486&mode=view

CO2 need stable temperature for accuracy
http://forum.gunshop.cz/download/file.php?id=34812&mode=view

You need to clean barrel after 20-30 shoots too

1) The OP wants to stick with CO2
2) The barrel doesn't NEED to be recrowned if you already have a tack driver.
3) Constant temperature is without question.
4) If you're talking about cleaning the barrel every 20-30 shots, why? Nobody does that, and I doubt that people will buy that. It often takes a barrel several shots to stabilize after cleaning or a pellet change.

[Hobbyman2007]

You can add a couple o rings between the valve and hammer #16 I believe . This should help with the efficiency by  eliminating  some of the hammer bounce . Search for the Bstaley mod it will go into more detail.

[Tgomez82]

I agree with you Doug, I have cleaned the barrel on my first QB once that was when I first got it and I have had no accuracy issues in the 1,500 or so pellets I have run through it, well not counting my ldc pellet clipping which I just can't get figured out.

Hobbyman thanks for the info I will search this mod and see about applying it to my QB

Thanks to all who have taken the time to reply

[skorec]

OK

I had reached sub MOA accuracy only after barrel recrowing and frequent CO2 dirt clearing out.

What is you accuracy ?

[Tgomez82]

Here are various pellets at 25yrds

[Tgomez82]

We'll the other pics won't load but they are all pretty similar to that one

[Ribbonstone]

Have co2 bulk filled, and the only way to really keep track of how well they use gco2 is to figure out the gas use per shot.

I'll metion this up-front: co2 is cheap, and to doesn't matter all that much how much co2 you use per shot if it gets the perfromance you want.  You just bulk fill more often and spend a few more cents along the way.

Co2 is figured by weight, so if you have a handle on the amount of co2 bulk loaded into the rifle,  can figure out the gas used. As much as I am NOT a "metric-head", grams works out better for this kind of figuring.

Co2 gets to be a real "pig" when you puch for higher speeds/energy.  Has a lot of things going against it for a hot-rod.  "Thick" gas, lower pressures, a self-cooling natuure, and heavy enough to actually count as ejecta.

With a good scale, you might notice is how little co2 you manage to get into a bulk fill under "field" conditions (where both the rifle and the fill tank were are the same temperture). Could figure a max as 1oz of co2 per 43cc's of volume as the same ratio of paintball tanks.

[Tgomez82]

Ribbonstone, thanks for the reply I guess I am asking for a lot wanting my QB's to be gas sipping hotrods. The only reason I want as much effieciency as possible is because sometimes where I go it's a long hike to get to good shooting and I didn't want to carry a extra air with me if not necessary but I guess I will have to change plans with that. Either way I will try and get as good as I can with both power and efficiency

[fivestar45]

I have 2 QB78 one has a tube extensions and is obviously bulk fill only, the second I have the bulk fill cap for it but it is still capable of using 12g's. I am considering buying the extension and going to bulk fill only with this one as well. But I have read that the shot count is not so great with a QB being bulk fill. They will both be staying co2 only no HPA conversion on these 2. My question is what kind of mods can I do to improve my efficiency with these..??

You might want to try a Teflon valve stem in your QB. It will seat easier than Delrin @ co2 pressures, and probably be more reliable than the oem stem. I've found that one of the better ways to improve shot count in a QB78 is to reduce striker weight. Several of the folks have done this in different ways ranging from simply grinding the sides, boring the center, or fabricating a new one from a lighter material.

[Tgomez82]

Well now that my local paintball shop has CO2 up and running and I was able to get a couple of fills I am going to get a shot count on both rifles with a full fill. Once I've done this I will lighten the hammer and chop the spring and see where I am at. The we shal go from there thank you all who took the time to share your recommendations with me!

[Back_Roads]

And I am too tired from hand pumping pcp's next years bonus goes to tanks or a compressor, we will see after i meet  with local scuba guy next to fleet farm store

[Ribbonstone]

Just not a lot of volume in a standard 12gr. co2 tube.  Inside it's about 3.5" long and about .75" in diameter.  So that works out to something close to 2.9-3 cubic inches...which we'll call 50-55cc's (have to include the inside of the valve for bulk fill).

Tyopical paintball tank will safely accept about 1oz (28grams) for each 43cc's of volume.  So lets say a safe fill for a QB tube would be something like 1.2oz. (about 35grams) of co2.  Two 12gr. would be 24grams. 
But every time I've measured bulk fill vs 12gr. us, bulk fill shoot a bit faster and used a bit more co2 per shot.  So you may not get any more shots from bulk filling a QB, may just get faster shots.
And you'd not even get the same number of shots unless you got a full safe fill.

So the solution might be to gain volume.  A longer gas tube (or extension) would do that.  But I have to say, if you could stand the extra weight, a tanker QB would cure it even easier. Swapping pre-filled tanks is a lot easier.

Getting a full fill:
Get a full safe fill when bulk filling would likely help, but you can't really get a full fill out in the field.  Co2 is not like air in this repsect: there's little pressue difference between the co2 in the fill tank and left over co2 in the rifle when they're both at the same temperture.
Basically have to create a temperture difference between the rifle and the fill tank.  In the summer, will put the tank on the back porch and the rifle in the house near an AC vent.  In the cool months, will reverse that and have the tank near a heater vent and the rifle out on the cool back porch.  In no case will I let the fill tank get too hot (not more than 90F).

(In the cold of winter, I just don't usually use co2).

When the fill tank is connected to the rifle, the fill tank is warmner...higher pressure...and the rifle is cooler...lower pressure...and more liquid co2 will flow into the rifle before they equalize in pressure.

As the gas flows, the fill tank decompresses a bit and cools down...the cooler rifle  compresses the gas and warms up.  IF you start with a temperture difference between the two, more liquid co2 eneters the rifle before they equalize.

Which is why, when the fill tank and the rifle are at the same temperture, they equalize pressure  quickly, with less gas flowing into the rifle.

It's  hard to over fill a bulk fill rifle.  Guess you could do it with the help of a freezer and a really warm fill tank, but I've not had the urge to try.

[Tgomez82]

Thank you ribbonstone for sharing your knowledge with me now I know that my expectations where a bit high, but I haw also found the direction I want to go. One of my QB's does have an extension and the other does not I believe an extension is in th near future for it and maybe also a bulk fill hpa setup for my QB's