Information overload...QB 2079 HPA conversion...How do I get where I want to be?

[Gipper]

I have been reading all of the QB threads here and there is a mountain of information to sift through, it is mind boggling!!.  I think I know what I need to do to get what I want out of this rifle but I want a sanity check from you all as there seems to be several ways to get there.  Here is what I have and where I am at:

AR2079 with Ninja 3000psi 13ci bottle set to 850 PSI.

I have not done any internal work at all to the rifle.  Since I had to pull the barrel to mount the bottle I did polish up the loading port.  I also polished up the hammer, spring guide and bolt and the rear of the tube.  I also swapped out the stock port seal with a Crosman piece.  This bit of work resulted in a rifle shooting 8.4 JSB's at 720fps for 100 shots before POI shift....not too bad I thought.  The barrel orings were a bit rough and I was feeling a slight puff of air leaking from the breech. 

I ordered up some replacement orings based on recommendations from folks here from the Oring store.  Yesterday they arrived so once again I pulled the barrel and the bolt. I decided to perform Bob's stage 1 mods while I had the rifle apart again.  I do not have a numbered bit set so the plan was to go with the 9/64 bit to stay as close to the 75% of caliber rule of thumb.  Starting with the bolt I started pulling bits to determine what size I need to start with.  Sizing things up I was not comfortable taking the bolt out to 9/64, it just seemed like it would not leave enough wall thickness so I ended up only taking it out to 1/8".  I then opened up the bottom of the bolt a bit with the dremel and smoothed things out...everything looked good so I was moving on to the barrel.  Once again I started pulling bits to determine what I needed to start with to get up to 9/64".  To my surprise the barrel port was already drilled out to that size!!  So I decided to stop there and put the rifle back together, the result was the rifle was now throwing the JSB's at 750fps and no more puff of air...Great!!

So that is what I have done and where I am at.  My initial goal is to get this thing up to 900 fps with the 8.4's.

My question is what is the best path to pick up the additional 150fps I am looking for?  Can/should I go larger on the barrel and breech ports?
Would upping the reg output to 1100psi do it alone?  I am sure some valve work is going to be required but how extensive?  Will just gutting the  unnecessary parts to give me a bit more plenum do it or do I need to go further?

So let me hear what you think.  Once I get the power level where I want it I will tune it for efficiency.

Thanks - Brian

[SpiralGroove]

Hey Gipper,
You have done some good work
I especially like the way you are thinking through things, erring on the side of caution.
Two Basic Mods will get you there, you may need both.
One increases the pressure of the entire system, the other increases the volume of air available for each shot.
1) Increase the set-point of the regulator to 1100/1200 psi. Please see Bob's recommendation on installing an additional sheer pin through the air cylinder & tank block. 
2) Increase the volume of your plenum.  To do this, cut off all but 1/4" of the aluminum Valve shroud so it looks like the one in the picture below.  The remaining piece of aluminum shroud needs to be secured with J-B Weld to hold the valve o-ring. This is the maxi-valve as designed by Bob.  Instead of using the larger spring on the rear of the poppet (see my picture below), turn the spring around to the front per (Jason).  A small spring over the valve stem retained with an e-clip saves work and increases your plenum volume.  There is a picture of this posted recently..... somewhere?


See Bob's comprehensive post here:
http://www.gatewaytoairguns.org/GTA/index.php?topic=49943.20

Increasing the hole of your pellet probe to 9/64" would help, but would be marginal to the above 2 changes.  Plus, you really need a lathe for that.

Good Luck - Be Safe

[wll2506]

I have been reading all of the QB threads here and there is a mountain of information to sift through, it is mind boggling!!.  I think I know what I need to do to get what I want out of this rifle but I want a sanity check from you all as there seems to be several ways to get there.  Here is what I have and where I am at:

AR2079 with Ninja 3000psi 13ci bottle set to 850 PSI.

I have not done any internal work at all to the rifle.  Since I had to pull the barrel to mount the bottle I did polish up the loading port.  I also polished up the hammer, spring guide and bolt and the rear of the tube.  I also swapped out the stock port seal with a Crosman piece.  This bit of work resulted in a rifle shooting 8.4 JSB's at 720fps for 100 shots before POI shift....not too bad I thought.  The barrel orings were a bit rough and I was feeling a slight puff of air leaking from the breech. 

I ordered up some replacement orings based on recommendations from folks here from the Oring store.  Yesterday they arrived so once again I pulled the barrel and the bolt. I decided to perform Bob's stage 1 mods while I had the rifle apart again.  I do not have a numbered bit set so the plan was to go with the 9/64 bit to stay as close to the 75% of caliber rule of thumb.  Starting with the bolt I started pulling bits to determine what size I need to start with.  Sizing things up I was not comfortable taking the bolt out to 9/64, it just seemed like it would not leave enough wall thickness so I ended up only taking it out to 1/8".  I then opened up the bottom of the bolt a bit with the dremel and smoothed things out...everything looked good so I was moving on to the barrel.  Once again I started pulling bits to determine what I needed to start with to get up to 9/64".  To my surprise the barrel port was already drilled out to that size!!  So I decided to stop there and put the rifle back together, the result was the rifle was now throwing the JSB's at 750fps and no more puff of air...Great!!

So that is what I have done and where I am at.  My initial goal is to get this thing up to 900 fps with the 8.4's.

My question is what is the best path to pick up the additional 150fps I am looking for?  Can/should I go larger on the barrel and breech ports?
Would upping the reg output to 1100psi do it alone?  I am sure some valve work is going to be required but how extensive?  Will just gutting the  unnecessary parts to give me a bit more plenum do it or do I need to go further?

So let me hear what you think.  Once I get the power level where I want it I will tune it for efficiency.

Thanks - Brian

Brian,

I have a couple QB2079A's. My outgoing on both is about 1100 and I plan on leaving it like that. I will do valve mods on both but that's about it. Last I remember they both were getting in the very low 700's with Kodiaks. I very much need to work on both these guns and get them in shooting shape. I want both to be in the mid+700's with heavy pellets for target and that will be fine... 55 yds will be the most for these guns, as they will be paper punchers and maybe air rifle silhouette if I should decide.

They have 13ci tanks on them, and those will change to 17ci before long.

I like you don't need a lot of speed with these guns, just good consistent shots and enough of them where I'm not running out of air in the middle of a match ;-  )

Both have 8x32 Mueller target dot scopes for paper target or Silhouette.

After all the stuff I'm doing with my QB field guns and Discos ... I REALLY need to work on these, thanks for reminding me  ;- )

wll

[Gipper]

Thanks for the replies and suggestions they are appreciated.  I have read Bob's $200 pcp thread many times, it is what prompted me to build this baby in the first place. With 16 pages (at the moment) of reading though it is a ton to take in hence the title of this topic and I wanted to make sure I was correctly understanding everything.

I do have a Taig mini lathe though I am by no means a good machinist by any stretch and it is what I used to bore out the bolt.  9/64 to the eye just looks too big to me so I will hold off on that until I have exhausted other possibilities. But what about the barrel and breech ports?  Will I see any gains from doing those if the bolt is only at 1/8"?

I knew valve work was inevitable to get where I was going just was not sure how much.  I was hoping the pedestal style with the bulk of the aluminum body ground away and some tweaking on the poppet would be enough as I am confident I can accomplish that with little to no trouble.  I think I will order a second valve to do the maxi valve work on so I have a backup if I manage to screw the pooch making it!!  Any suggestions on where to order one other than from he who shall not be named?

Instead of an e-clip I think it was wll who used a slip on collar from Mcmaster Carr to secure his front mounted spring that I though was pretty slick...am I correct on that?  If so wll how is it holding up and do you have a part number handy?

As far as the rifle itself goes this thing is incredibly accurate!!  It is the easiest rifle I have to shoot accurately and will do 1 hole groups at 10 meters all day long.  I did work on the trigger a bit swapping the stock spring for one off a Telecaster bridge and did the plunger mod as well.  It is not a Rekord by any means but is very smooth and breaks clean.  If you miss with this baby you CANNOT blame the trigger!! 

Thanks again for the input...(keep it coming) and thanks for sharing the the information with us all.

Brian

P.S. wll I thought I was a maniac when it came to my hobbies!!  I have been reading your threads and have to admit you definitely went head first into this hobby!!

[SpiralGroove]

Hey Brian,
1) The 1/8" probe hole is a limiting (air flow) factor, how much I can't say.
Your Taig mini lathe is much better than my Harbor Freight 12", so I would go to 9/64" on the bolt probe.
Just take your time making sure it's centered in the chuck.  If for whatever reason you blow through the walls, remove the probe completely and insert a 1/16" drill instead.

2) I don't even think you need to do any machining mods to the brass valve as Bob suggests (maybe with the exception of drilling out the throat to 7/16"), to get what you want with 8.4 JSB's.  Just use J-B Weld on the 1/4" aluminum piece and call the maxi valve good except for the retaining spring on the stem/poppet.  I have some extra aluminum shroud I could send you

3) Spend any other time pinning your tank block.

4) Installing an RVA with cock on open are also very helpful 

Arrcher airguns sells the valve alone for about $40.  This is almost 40% of the cost of a new gun.  As you financial planner, I would recommend you buy a whole gun for $105 and use the remainder for parts. 

Kirk

[rsterne]

I believe this conversion is being done on a .177 cal.... The OD of the hollow probe may be too small to drill to 9/64" (0.140").... It would seem reasonable for that to be the case, if the OD of the probe has to fit inside a 0.177" bore.... It could well be that 1/8" is a large as you can go and maintain enough wall thickness in the .177 cal bolt probe, but I don't know that for a fact....

Bob

[SpiralGroove]

Yeah Bob,
I used 9/64" on all my .177 conversions, it's close though. 
I took a solid piece of wood, wedged between the bolt & lathe bed, to carefully straighten the probe in the chuck.  Just make sure the probe is "true" when rotating.  The 9/64" should be doable, but you need to go with your gut.  Otherwise, get the correct numbered bit suggested in Bob's post.

The Valve and barrel ports already meet or exceed air flow requirements for needed velocity/fpe.   

[rsterne]

The numbered bit I suggested is for .22 cal....

Bob

[SpiralGroove]

9/64" = .1406
#29 = .1360
#28 = .1405

Pick your poison

[Gipper]

Bob you are correct it is a .177 rifle.  Would converting the bolt to a probe style be more effective than the 1/8" porting?

Also I am curious as to why the maxi valve collar has to be glued into position.  The stock valve does not use any adhesive to keep it together....why so in this case?

As far as adding additional security to the block I will do so if/when I move my reg point off of 850 PSI.  The gun shoots so well that I am thinking I may just let the power fall where it may with the valve work and call it good.  As it sits the gun is accurate to the point of boredom (if accuracy can be called boring) and since I do not plan to hunt with it what I get may be good enough and staying at 850psi gives me the piece of mind that I am not over stressing the design parameters of the rifle as it sits.  It would also allow me to switch over to Co2 if I wanted with the smallest amount of performance difference possible.

The 900fps goal was so I could shoot as flat as possible out to 50 yards, however 99% of my shooting is at 10 meters so 900 fps is kind of overkill at that distance.  I  am sure I would be better off starting with a .22 cal to get more power and better efficiency. but the problem with that is I live in Illinois and if larger than .177 AND faster than 700fps it is considered a firearm and I do not want to go there.  With .177 the sky is the limit.   I can always build another one and tune it for max power. In that case I would start with a full tubed model and cut it down to allow for more plenum space.

So with that windy response let me ask this.  If I do nothing else but the maxi valve to this baby what kind of speed could I expect with the 8.4 jsb?  As I said the rifle is current;y shooting 750 fps.

Thanks - Brian

Brian

[Gipper]

9/64" = .1406
#29 = .1360
#28 = .1405

Pick your poison

Using the 75% of bore for port size the desired hole would be 0.13275 so all of those choices are larger.....not saying they won't work (obviously the did for you).  Next time I poull it apart to do the valve I will look at the bolt again and see what I think,  it just looked like it would leave very little wall thickness to these old eyes.


Brian

[rsterne]

I glued the valve collar in place so maintain a constant width for the O-ring groove.... In a stock QB valve, you tighten the front of the valve against the rear to expand the O-ring AFTER assembly into the tube and bolting the rear half in place.... With the maxi-valve, the groove is slightly wider than the O-ring, just like a normal valve that you simply slide into place.... The O-ring moves up into the outer, rear corner of the groove to seal.... Without gluing the ring in place, or tightening it against the rear of the valve, it could vibrate lose and fall off, IMO.... If you notice, after gluing in place, I machined much of it away, leaving no room for a slot to tighten or remove it.... 



Bob

[Gipper]

Bob,

That makes sense if you are not tightening the valve after assembly.  I will reread your post to see how tight to make the fit when I glue the collar in place.

Thought I would add a couple of pics as well.

Brian

What she looks like:


What she can do:

[wll2506]

Thanks for the replies and suggestions they are appreciated.  I have read Bob's $200 pcp thread many times, it is what prompted me to build this baby in the first place. With 16 pages (at the moment) of reading though it is a ton to take in hence the title of this topic and I wanted to make sure I was correctly understanding everything.

I do have a Taig mini lathe though I am by no means a good machinist by any stretch and it is what I used to bore out the bolt.  9/64 to the eye just looks too big to me so I will hold off on that until I have exhausted other possibilities. But what about the barrel and breech ports?  Will I see any gains from doing those if the bolt is only at 1/8"?

I knew valve work was inevitable to get where I was going just was not sure how much.  I was hoping the pedestal style with the bulk of the aluminum body ground away and some tweaking on the poppet would be enough as I am confident I can accomplish that with little to no trouble.  I think I will order a second valve to do the maxi valve work on so I have a backup if I manage to screw the pooch making it!!  Any suggestions on where to order one other than from he who shall not be named?

Instead of an e-clip I think it was wll who used a slip on collar from Mcmaster Carr to secure his front mounted spring that I though was pretty slick...am I correct on that?  If so wll how is it holding up and do you have a part number handy?

As far as the rifle itself goes this thing is incredibly accurate!!  It is the easiest rifle I have to shoot accurately and will do 1 hole groups at 10 meters all day long.  I did work on the trigger a bit swapping the stock spring for one off a Telecaster bridge and did the plunger mod as well.  It is not a Rekord by any means but is very smooth and breaks clean.  If you miss with this baby you CANNOT blame the trigger!! 

Thanks again for the input...(keep it coming) and thanks for sharing the the information with us all.

Brian

P.S. wll I thought I was a maniac when it came to my hobbies!!  I have been reading your threads and have to admit you definitely went head first into this hobby!!

Brian,

The little split ring so far has worked out good .... but firing on an empty air chamber can smack it hard enough to move it back.. I may use my lathe and just put a very small etch/grove in the poppet... it doesn't need much as it is very tight and very small and can wedge itself in a very small grove. One of the things I like about the ring is it is about the same OD as a pen spring...so I have nothing hanging out and it makes it look cleaner.. I must give Jason all the credit on this as he really opened my eyes on this modification.

Apparently, the next BIG mod is the weight of the hammer for increasing your shot count., I'll need to study that ... and the other is "cock on opening" ... i don't want to do it, but I'm REAL tired of taking the gun apart to make adjustments ....I can feel the force pulling me in that direction ;- )

wll