Which build? QB78 or QB79

[BigTinBoat]

I am looking to build a bottled QB in .177 to get max shot count at about 13-14FPE. (Wanting to shoot around the 900FPS mark)

I'm trying to decide between just putting a bottle on a QB79 or doing a QB78 by drilling the end cap and tapping it 1/8NPT to put a reverse bottle on. Thinking any internal work will be the same for each.

I know the QB79 would be less work, but I'm liking the idea of the QB78 being more "carbine like" with the bottle reversed. The overall length is probably the same, but I like the weight more towards the rear of gun like my 1720T is. I'm thinking cost will be just about the same.
I've got both a 13 and 17CI bottle. One set at 1100 and the other at 1400 right now though easily changed.

Thoughts? Pics of reverse bottle builds anyone has done?

Also I see the 78 Deluxe advertised as having a barrel that is thicker then the Standard, which is the 79 barrel like?

Thanks

[HappyHunter]

I chose the "reverse bottle" method for my AR2078 that I used to shoot FT with...mostly for aesthetic reasons (just a personal choice), although you also get a longer plenum for air by going this route. True, like you said, it's a little more work with the reverse bottle, but worth it IMO.

I didn't own a lathe back when I built this, so seeing as I had no way of making a reverse tank block from a block of aluminum, I just used an ASA on/off adapter, a 90* elbow and 1.5" long pipe nipple from Swagelok ( both thick-walled, heavy duty units). Cutting/shaping the stock to fit the bottle was a little time consuming (more to do with me not know what I was doing!) as I wanted to keep some of the forestock rather than cutting it completely off (again, just a personal choice for aesthetics).



With the power adjuster installed that SeanMP made for me, I can run it anywhere from 500 shots @ 3fpe for when my nephew comes over to shoot for the weekend, or 210 shots @ just under 12fpe for FT. Still using the stock valve poppet too...said I would make a delrin one when this one crapped out, but it's still going strong after roughly 4500 shots!

RVA settings/velocities:

                                AR2078 /  13ci Bottle Reg’d @1375 psi / 10.34 gr JSB  / Clipped H-Spring
                                                                 

RVA (turns in              0          1           2          3          4            5            6             7            8            9             9.5
from min preload)

Velocity                     N/A      N/A       N/A       N/A       N/A       179.2     357.1      587.9      731.4     853.5      870.7

FPE                           N/A      N/A       N/A       N/A       N/A        .74         2.93        7.94        12.29     16.73      17.41
   
# Shots                    N/A      N/A        N/A      N/A       N/A         780        510         276         180       108           66

PSI used/shot          N/A       N/A        N/A      N/A       N/A        1.9           3             5              8          14            23

Shot Count              N/A      N/A         N/A      N/A       N/A        780        510         276          180        108          66

Efficiency                 N/A       N/A        N/A      N/A       N/A        0.42       1.11        1.62         1.65       1.34        0.85

[BigTinBoat]

With the power adjuster installed that SeanMP made for me, I can run it anywhere from 500 shots @ 3fpe for when my nephew comes over to shoot for the weekend, or 210 shots @ just under 12fpe for FT. Still using the stock valve poppet too...said I would make a delrin one when this one crapped out, but it's still going strong after roughly 4500 shots!

Todd - love the "adjust-ability" of your gun. Is this just with a spring tension RVA? Can go from plinking to small game hunting with just a screw turn and scope re-sight?   Any pics? from the pics you posted I can't see any adjuster.
Any other performance mods done?

Also - is that a standard end cap that you drilled and tapped? I already and ASA on/off and some 1/8" fittings rated at 4500 so I should be good there.

Would love to have something real similar except with the regular deluxe stock or maybe even a thumbhole stock.

[HappyHunter]

Also I see the 78 Deluxe advertised as having a barrel that is thicker then the Standard, which is the 79 barrel like?

If I'm not mistaken (?), I believe the QB "Deluxe" models (both '78 and '79) have 15mm barrels (same as the AR series) while the "regular" QB's have 14mm barrels.

[Ribbonstone]

Usually get a higher shot count with a heavier pellet so am not so much into lite pellets @ 900 as I am in heavy pellets at 725fps.  Am also into long shot counts (+150 shots per fill) so usually stay around the 12-13 foot pound mark and only run 850psi air.

But if given a choice, would rather have a long tubed 78 tanker conversion than short tubed 79 conversions.  Having that large volume of pre-regulated air on tap gives wider range of options than the short tubed 79.

Have kept 3 “tanker QB’s” in service (threw once was 5). Left to right would be a 5mm QB78 conversion, a .22 QB79 conversion, and a .177 AR2078 conversion.  All running on 850psi tanks, all in the 12-13 foot pound range.



Doesn’t seem to matter if it’s take forward, tank down, tank on a coiled remote, or tank to the rear.  Long tubed 78 conversions leave enough wood fore end for a grip, so you won’t be grabbing cold metal in the dead of winter, which is a plus.   That’s the only real irritation with the QB79 (or rear hanging tank conversions). I just don’t like holding a tank with my off hand.

 The front tube conversions do make for a forward balance, but that’s not a bad thing for most shooting (bag rest or off hand).

Will say that the record holder for shots per fill is the .22 QB79, but even after taking it apart, I’m not really sure why that one will manage +200 (starts to let down somewhere at shot #204=#206) shots per tank (12 foot pound shots). 

Either I got the balance just right, of something freaky is going on.  Whatever it is, I can’t duplicate it and the .177 and 5mm tankers are in the 150 to 175 shots per fill area

Not quite stock, but the majority of the “work” has been in getting  (1) the weight of the striker (2) the size of the transfer port, and (3) the strength of the striker spring in agreement.

Lets give you a visual of +200 shots per fill in terms of 41 5-shot groups. Fill it up once (to 300psi) and shoot it down to 800PSI, and it comes out like this (5-shots per target @ 20 yards):



Other people will go for power, but think the best use of a regulated 13ci tanker is in shot count at moderate (12-13 foot pound) speeds.  Yes, they can produce power.  So can every other PCP. BUT regulated tanker QB’s can produce super long uniform shot strings that the PCP’s cannot, so I go with their strong suit.


So while I’ve done both, if I wanted the most versatile QB HAP conversion, I’d start with a QB78 tube, convert to a tank block, and leave it long.

[HappyHunter]

Todd - love the "adjust-ability" of your gun. Is this just with a spring tension RVA? Can go from plinking to small game hunting with just a screw turn and scope re-sight?   Any pics? from the pics you posted I can't see any adjuster.
Any other performance mods done?

Also - is that a standard end cap that you drilled and tapped? I already and ASA on/off and some 1/8" fittings rated at 4500 so I should be good there.

Yep, just a spring tension RVA... . Lol...you can't see it because there is nothing externally to see other than a tiny access hole in the end cap to insert an allen wrench... . Rather than re-type the project (I'm painfully slow at typing!), here is a link describing the process: http://www.airgunforum.ca/forums/topic52794.html

Other than the RVA and bottle conversion, the only "mods" done was to get rid of piercing pin, filter, etc from valve and open up the sides of valve front for improved air flow. Also had to chop about 3/8" off muzzle and re-crown as there was a tooling mark from the factory that was causing me some accuracy issues.

The end cap is an after market one that I picked up from ScopesAndAmmo. He hasn't had anymore for a loooong time now (over a year) so I'm not sure if he's getting more in or not.....have no idea where he was getting them either. Pretty sure you could modify/use the stock end cap easily enough as long as you kept the pressure under 1500psi.

Would love to have something real similar except with the regular deluxe stock or maybe even a thumbhole stock.

You mean like this?... (AR2078 thumbhole stock on my 2260)

[BigTinBoat]

Other people will go for power, but think the best use of a regulated 13ci tanker is in shot count at moderate (12-13 foot pound) speeds.  Yes, they can produce power.  So can every other PCP. BUT regulated tanker QB’s can produce super long uniform shot strings that the PCP’s cannot, so I go with their strong suit.

This is my thought for this gun. I also like that you can pump to just 2K if you want and not get as many shots, but they will all be the same.

I usually shoot for the 900FPS for trajectory reasons. Flat is what I like.

You mean like this?... (AR2078 thumbhole stock on my 2260)

YES - like that look.

What pressure are you running on your bottle? I was thinking about taking the 17 back to 800-900 but most of the stuff I've read seems the efficiency is better at like 1300-1400.

[HappyHunter]

What pressure are you running on your bottle?

I'm running the AR (.177) @ 1375psi. I admit that I haven't played around with output pressures too much, but FWIW it seems to work well for me....efficiency peaks out right at 12 fpe - 1.65 fpe/ci. 

I very rarely (if ever) hunt with .177 so although I have no desire for more fps/fpe in this gun, if the urge hits me I can still get just over 100 shots at 16.7 fpe at a somewhat respectable efficiency of 1.34 fpe/ci with just one more turn in on the RVA. BUT...if I go just a 1/2 turn more, the gun maxes out at only .5 fpe more (17.4), my shot count drops to 65-66 and efficiency plummets to 0.85 fpe/ci.

I've never tried it @ 850psi before, but seeing as I have another bottle here set at that pressure, I may try it out after reading several posts by Ribbonstone on the subject. I'm sure he has done waaayyyyy more testing than I ever have and he seems to get great results too. If nothing else, it'll be interesting to see the differences (if any) in shot count/fpe/efficiency between the two pressure settings (not to mention another excuse to shoot! )

[BigTinBoat]

I'm running the AR (.177) @ 1375psi. I admit that I haven't played around with output pressures too much, but FWIW it seems to work well for me....efficiency peaks out right at 12 fpe - 1.65 fpe/ci. 

Well I guess I'll keep each bottle they way they are and test before changing anything. I think this is another plus for the reverse build - I can change the bottle w/o removing the barrel.

Now all I need to do is find a QB78 in .177. They have not been on the FD website in quite a while and the other guy (who can't be mentioned) does not have them in stock either.

[BigTinBoat]

Got a 78 on the way.

Even though his website had the 78's as "not available" I decided to email Mike at FlyingDragon and sure enough he replied that he in fact did have a 78Deluxe in .177.

Sent the Paypal minutes ago.

Thanks for help deciding

[Ribbonstone]

Many times,when I expect to only need 40-50 shots, will just fill the tank up to 1500psi and shoot it down to 1000psi (950 output bottle).  Neat thing about regulated HPA tanks is that the power is proportional.  If I get 180 shots from 1000 to 3000psi, then I'll get 45 shots from 1000 to 1500 psi.


Once set up right, they've been quite trouble free over the years.  May be that running mine at such low pressure actually stresses the system LESS than, but suspect most of the problem free life span is due to the use of cleaner/filtered air rather than co2. Blowing grit though a valve system at 10X the pressure usually used in a sand blaster just isn't conductive to long valve seal life.

If Bob does get those reverse tank blocks made, have one more QB78 that will be converted, there is a 1200psi 13ci bottle at hand, and a couple of old stocks that could be chewed up to fit.   May have to go .30 as I already have a 177, 5mm, and .22.  IF i do that project, will most likely take advantage of the reverse bottle and build a short barreled little blaster.

[HappyHunter]

Got a 78 on the way.

 Congrats!.......let the games begin!

Looking forward to some pics and eventual range report...

May have to go .30 as I already have a 177, 5mm, and .22.  IF i do that project, will most likely take advantage of the reverse bottle and build a short barreled little blaster.

Oh, I like the sounds of that....looking forward to that one too!

[BigTinBoat]

If Bob does get those reverse tank blocks made,

I've too been watching whenever he posts......waiting......

[BigTinBoat]

light striker
[smg id=1288]

John

John,

Since you "boosted" the power up from stock, what does lightening the striker do? I would think it would need more at 1100 then at the CO2 pressures....what did you do with spring tension?