Drilling out the air ports and/or more psi In a QB for more velocity ?

[wll2506]

My '79 is behaving badly. I checked the valve and it is OK, but will modify it to a no body front spring valve when parts arrive from McMaster-Carr

The barrel port is now .161.. I could go a little more as Jason has recommended, have poly seal in place and all the standard stuff, bolt stuff are done .... my out going is ~1350+ ish.

All the seals look good .. is this a pure and simple matter of I need more juice in this short Plenum gun ? ------ Do I really need 1450-1500 outgoing to get the speed up to another 50 fps with CPHP pellets . I would like about 850fps at least with CPHP pellets for general use with this gun.

wll

[SpiralGroove]

Hey Wll,
 - What velocity are you trying to get with the 1350 set-point?
- 11/64" or .171875 is the largest I would go in .22 caliber.  The barrel port and the bolt probe should be the restrictions.  You will likely need a lathe for the bolt probe drilling. 

[mackeral5]

Your post prompted me to run my qb79 repeater across the chrony for the first time.  I had a little left over air in one of my tanks and managed to get off a total of 3 835fps shots with 1100psi on the gauge.  14.3gr CHP's.  I have no clue as to efficiency as this was the first time I ever ran this one on hpa.  It is typically attached to a 9oz co2 bottle.  The gun has an RVA and the fuel line over the valve stem bstaley type of hdd mod. 

Most of my valve body is removed and the tank block hollowed out just a bit.  piercing probe is still in place.  Valve head is tapered and diameter reduced to a thin border of brass around the stem seal.  This work is easily done chucking the valve stem in a dremel and using a file to shape and fine sandpaper to smooth the finish.  Brass part of valve body is opened up as much as possible without getting into the threads.  Valve throat is opened up, corner is knocked off of valve transfer port, creating a nice radius to the valve throat.  Barrel transfer port was opened and slightly elongated with a 1/8 ball shaped diamond bit. 

I'm sure there is more in this particular gun performance wise, if I ever get around to tinkering with it.  Again this one is primarily used as a co2 gun for guests to shoot.

[Acapulco]

One of my favorite guns I own...79. Don't know why you want more power? I set mine up to shoot 650ish and I get a lot of shots off a bottle and accurate too.

I own pcp's that cant shoot like this

[wll2506]

Your post prompted me to run my qb79 repeater across the chrony for the first time.  I had a little left over air in one of my tanks and managed to get off a total of 3 835fps shots with 1100psi on the gauge.  14.3gr CHP's.  I have no clue as to efficiency as this was the first time I ever ran this one on hpa.  It is typically attached to a 9oz co2 bottle.  The gun has an RVA and the fuel line over the valve stem bstaley type of hdd mod. 

Most of my valve body is removed and the tank block hollowed out just a bit.  piercing probe is still in place.  Valve head is tapered and diameter reduced to a thin border of brass around the stem seal.  This work is easily done chucking the valve stem in a dremel and using a file to shape and fine sandpaper to smooth the finish.  Brass part of valve body is opened up as much as possible without getting into the threads.  Valve throat is opened up, corner is knocked off of valve transfer port, creating a nice radius to the valve throat.  Barrel transfer port was opened and slightly elongated with a 1/8 ball shaped diamond bit. 

I'm sure there is more in this particular gun performance wise, if I ever get around to tinkering with it.  Again this one is primarily used as a co2 gun for guests to shoot.

Want a good 850+ with CPHP or 800fps with Exact would be great. Everything is opened up, I may have an issue with the valve as it still has most of the aluminum taking up space, I need to make that a mini. I have not smoothed out the port, just made it bigger, I thing taking off the edges and rounding them may make a difference

Just got back from the field and I'm getting 775-782fps with Exacts... would like a bit more, I just have to smooth all air passages I think and that should do it ....hopefully.

wll

[wll2506]

One of my favorite guns I own...79. Don't know why you want more power? I set mine up to shoot 650ish and I get a lot of shots off a bottle and accurate too.

I own pcp's that cant shoot like this

That looks like a good shooter for sure .....

.. but mine is for outside and in a the desert area where many of my shots are 40-60 yds, it will be used for plinking and pest control --- I may get a 17ci tank for it. I tried one of my 22ci tanks and it was just a little to long from my point of view.

 i have two AR2079A's in .177 and they are my target guns ... they are great fun ;- )


wll

[wll2506]

Just got back from shooting, she is fun to shoot, blasted rocks and stuff at 40 to 70 yds, I was surprised .... took her all apart as tomorrow I will polish and taper the barrel air port a bit ..... have the valve out and will work on that too ... can't put that back in till I get stuff from McMaster.-Carr ... don't think I will up out going, I think maybe like your guys said it is a matter of air flow ... I will work on that.

wll

[Austringer]

William. I thought you already built the springless valve? Is this valve different? I finished my valve last week. Need to work on my bolt probe tonight. If we do everything right, I see no reason we should not be able to achieve performance close to what Jason (nervoustrigger) attained with his 1510psi QB79.

Troy

[wll2506]

William. I thought you already built the springless valve? Is this valve different? I finished my valve last week. Need to work on my bolt probe tonight. If we do everything right, I see no reason we should not be able to achieve performance close to what Jason (nervoustrigger) attained with his 1510psi QB79.

Troy

Troy, I did and after playing with it (and it does work) i decided I wanted a bit of pressure on the poppet as when you are first loading, the poppet has to seat, and it seats easier with a bit of spring tension ... don't need much, just a bit.

This whole thing is a learning curve and I'm experimenting as I'm going along. I say one thing, and then something else comes along. If i had the experience I could give a list of what to do, where to get parts, and that is that ...for the most part ;-  )

Once I get the final valve done I will post a pic and tell you where I got the parts and what they are. I did not want to use a spring as it complicates things, but I could not find a way to stop the poppet from falling out.. shrink tubing did not work and glue did not hold ,,, the valve thing is a pain until you do it, and then you go right to it and you know what to do I'm sure. How did you stop your poppet from falling out !

I have my little lathe that has been abused in recent years ... I very well may buy a Grizzly lathe and milling machine combo ... it would make some of this stuff soooooo much easier and exact. Now if my company can pay me back a bit of what they owe me i can get it !

wll

[Austringer]

In my QB78, I retained use of the spring housing, slotted it heavily and used a lighter spring, so there is no problem in that gun. In my QB79 I am currently modifying, I will not use the  spring housing as you are, but plan to use the rear mounted spring and e-clip on the poppet shaft as Jason has done. If I haven't posted it before, I attached a pic of my valve MINUS the spring and eclip which I think as you have found is kind of important. BTW... try filling your gun with the bolt cocked. If your hammer spring has a lot of preload on it like my 78 does, it will hold the valve open preventing easy filling from an empty state.

Troy

[SpiralGroove]

Yeah Troy,
For the QB79, the (Jason) valve mod you show seems to be the "No Brain-er", way to go to maximize plenum space.  I will try that on my last OEM QB78.  I will keep the (long spring) housing "just in case" and use an 1/4" scrap piece from a prior QB conversion.  If the valve stem, mounted spring works, I'll modify the valves on my remaining QB's the next time their broken down.

After that, my last QB mods will likely be making a few SSG's.

[Austringer]

Spiral Grove
Will you use an eclip or thread the poppet shaft?

Also, anyone reading with a HPA bottle mounted QB79, does your bottle touch your barrel? I know it is not supposed to, but mine touches unless I twist the bottle to a certain position. Unfortunately, that position doesn’t put the fill nipple in the best position.

Troy

[rufus80]

Spiral Grove
Will you use an eclip or thread the poppet shaft?

Also, anyone reading with a HPA bottle mounted QB79, does your bottle touch your barrel? I know it is not supposed to, but mine touches unless I twist the bottle to a certain position. Unfortunately, that position doesn’t put the fill nipple in the best position.

Troy

I have 4 of these rifles. Two with reverse bottles and 2 with the front. I am using the Ninja SHP 13ci bottles and both have at least 1/8" clearance.

[wll2506]

In my QB78, I retained use of the spring housing, slotted it heavily and used a lighter spring, so there is no problem in that gun. In my QB79 I am currently modifying, I will not use the  spring housing as you are, but plan to use the rear mounted spring and e-clip on the poppet shaft as Jason has done. If I haven't posted it before, I attached a pic of my valve MINUS the spring and eclip which I think as you have found is kind of important. BTW... try filling your gun with the bolt cocked. If your hammer spring has a lot of preload on it like my 78 does, it will hold the valve open preventing easy filling from an empty state.

Troy

Troy,

That is beautiful work .. my set up is pretty much the same, but i need to open up the inside of the valve body a bit like you did ... nice job ;- )

I'm going to use a very small steel split ring to hold the pen spring, I'll post a pic when it is done. The split ring is only .187 in OD , .093 ID so it should work fine with just a little groove in the poppet to hold it in place.

wll

[SpiralGroove]

Hey Austringer,
Sounds like the QB79 tank block is tipping upward.  The next time the tank is empty, unloosen the stock and air cylinder screws and see if the tank block can be moved downward enough to give reasonable clearance? 
Either that or the barrel is bent downward too?  You may need to inlet the stock a bit for more downward tank block movement and/or bend your barrel at bit upward. 

The simplest thing to do is to rotate the bottle as you have done and live with it .     

- I will likely use a eclip.                                                                                                   

[wll2506]

Hey Austringer,
Sounds like the QB79 tank block is tipping upward.  The next time the tank is empty, unloosen the stock and air cylinder screws and see if the tank block can be moved downward enough to give reasonable clearance? 
Either that or the barrel is bent downward too?  You may need to inlet the stock a bit for more downward tank block movement and/or bend your barrel at bit upward. 

The simplest thing to do is to rotate the bottle as you have done and live with it .     

- I will likely use a eclip.                                                                                                   

My 13ci tanks don't hit and when I put on a 22ci tank, that too cleared. I will buy a 17ci tank tomorrow for my "79 as I want a few more shots. My '79 will not be set up for max power, but it will be sending them, that is for sure.  On this gun I'm looking at in the 22-24fpe area. My ;78 in .22 I'm looking for 27-30 fpe ! My 177 cal QB78 is giving me over 18 fpe with 10.5gr  Kodiaks as we speak !

As it stands now my 177 will hold enough air for a days worth of hunting for sure. My .22 '79 will give me a very good number of shots around 50+ in the 21fpe area .. I'm building the 22 QB78 now !

wll

wll

[Mr. Panther]

All this stuff is really interesting. I am getting my 78 tomorrow from AGD, and March I am getting the 79 with an extra bottle, (CO2). All this terminology  about these mods is confusing for right now. The more I read though the more I learn. Just a quick question, I have seen the term SSG, but have not seen a deffinition for it, what does that mean?

[Austringer]

Nick

SSG stands for Spring Stopping Guide. If you are new to QB mods, I recommend you start by reading rsterne’s “$200 PCP” thread a couple times, then read posts by nervoustrigger regarding 78’s and 79’s. The foundation of these mods lies with those threads.

Got my ball point pen sprung, e-clip retained, rear mounted spring valve installed. Belvilled my bottle to 1475 psi. Installed a rear RVA. My porting is all done as most everyone has done before. I have not yet drilled out the tank block at all. I shot over the chronograph in the garage tonight with crappy lighting and shot 14.3 cphp’s in the 820 range. HOWEVER, my chrony does not work reliably indoors, so I won’t have any definitive results until I’m able to shoot in daylight hours. I’m really hoping to get close to Jason’s figures, but reality is setting in and telling me that’s probably not possible unless I bump up the pressure just under the burst valve threshold (which I don’t want to do) OR add a couple inches op plenum volume using a QB78 tube (which I don't want to do cause I don't want to tear down a brand new gun still in the box!

As far as my tank hitting the barrel, It tended to straighten out a bit when pressure was added. I will make it work out one way or the other.

William, did you drill out your tank block at all? That little bit of extra volume may be our problem.

Troy

[wll2506]

Nick

SSG stands for Spring Stopping Guide. If you are new to QB mods, I recommend you start by reading rsterne’s “$200 PCP” thread a couple times, then read posts by nervoustrigger regarding 78’s and 79’s. The foundation of these mods lies with those threads.

Got my ball point pen sprung, e-clip retained, rear mounted spring valve installed. Belvilled my bottle to 1475 psi. Installed a rear RVA. My porting is all done as most everyone has done before. I have not yet drilled out the tank block at all. I shot over the chronograph in the garage tonight with crappy lighting and shot 14.3 cphp’s in the 820 range. HOWEVER, my chrony does not work reliably indoors, so I won’t have any definitive results until I’m able to shoot in daylight hours. I’m really hoping to get close to Jason’s figures, but reality is setting in and telling me that’s probably not possible unless I bump up the pressure just under the burst valve threshold (which I don’t want to do) OR add a couple inches op plenum volume using a QB78 tube (which I don't want to do cause I don't want to tear down a brand new gun still in the box!

As far as my tank hitting the barrel, It tended to straighten out a bit when pressure was added. I will make it work out one way or the other.

William, did you drill out your tank block at all? That little bit of extra volume may be our problem.

Troy

No, I have not drilled the 79 tank block, but I will be drilling a new hole and tapping for an additional 8x32 allow cap screw, that will give me 3 screws in the block for extra security -- two alloy 4mm x.07 and the 8x32 .... this of course does not count the two stock screws.

I very much want to hear your velocity in good light, because if I went through all that work and got a crappy 820fps, I think I would kill myself .. you using the original hammer spring ?


wll

[mackeral5]

Troy, assuming your porting mods are on par, you are likely not hitting the valve hard enough.  But your gun is probably running pretty efficiently with 1475psi, 14.3's at 820fps.  smack the valve a little harder and you should be able to increase velocity, assuming that is your goal.

BTW, 820fps isn't crappy, actually a pretty good number.  I'm willing to bet if you dropped reg pressure with no other changes you would see an increase in velocity.