3000 psi tube QB78

[remtom1200]

I too got a new QB78 Deluxe from Scopes and Ammo and I must say I like the looks of this. so, as usual I haven't tried it yet only because It hasn't been completely disassembled and smoothed out. Its been one of my rituals with new air rifles here lately...lol. My plans are being made around the 3000 psi tube and a hand pump rather than Co2 because really I live in one of the freak temperature provinces Nova Scotia. It is nothing to see the temperature be -xx and then +x in 24 hours. Co2 just isnt gonna make me happy i know. I do believe I will be going into this project blind as I haven't read any detailed posts on this conversion, other than shot strings and psi drops, fps and fpe. It will be interesting getting to that part being as picky as I am to detail doing the conversion.

[SeanMP]

A fellow over on another forum has a great expression "QB's are a diamond in the rough, but they are rough as a badgers bum" He loves tuning them and has great success.

When you tear it down you'll find that the barrel Orings are pre shredded so have a seal kit or a supply on hand.

I run my 2078A on HPA with the stock tube at this point. I get just about 2000 shots off the 62oz buddy bottle that Eric sells.

You'll find it handy to make a "screwdriver". the valve has a slot that accepts a blade 3/4" wide by 0.100 thick. I made mine from 1/2sq bar with a piece of 1/8 flatstock tacked and ground to suit. The valve will not come out until the two halves are loosened

[jpsgunworks]

A fellow over on another forum has a great expression "QB's are a diamond in the rough, but they are rough as a badgers bum" He loves tuning them and has great success.

When you tear it down you'll find that the barrel Orings are pre shredded so have a seal kit or a supply on hand.

I run my 2078A on HPA with the stock tube at this point. I get just about 2000 shots off the 62oz buddy bottle that Eric sells.

You'll find it handy to make a "screwdriver". the valve has a slot that accepts a blade 3/4" wide by 0.100 thick. I made mine from 1/2sq bar with a piece of 1/8 flatstock tacked and ground to suit. The valve will not come out until the two halves are loosened

Hi Sean, sounds like an Al Stone "across the pond "comment. I assume you're using a bulk fill cap and paintball line? What is the reg set at to get 2000 shots?

[SeanMP]

Hi Sean, sounds like an Al Stone "across the pond "comment. I assume you're using a bulk fill cap and paintball line? What is the reg set at to get 2000 shots?

Yessir that is a direct AL quote....quite a fellow when it comes to QB's

Yes I'm using the bulk fill cap and connecting it with the Ninja coil hose that Eric sells.

I'm filling to 1500 psi and I reduced the hammer spring weight to get 480avg fps. I use my AR2078 strictly as a 10m trainer so I tuned the velocity to optimize the best pellet. At 1500 fill I get exactly 30 shots off the stock tube. If I shoot ponied to the bottle I set the reg at 800 and blam away. This is the condition for 2000 shots on a bottle. I went through 4 tins in two days at the bench breaking the barrel in.

[Doc Sharptail]

I took the plunge, and ordered a tube, yesterday.
It's going to be done a bit at a time- I still have to get a pump. That will come a bit later.
I'm going to play around a bit with my "D" on co-2- until I have a pump in hand.

In the mean time, the bbl will have to come off the "D" again. I'd like to get the breech end of the bbl cleaned up a little more. The JSB Predators feel like they're binding at loading- as do the heavy exacts. The smaller 14.3 gr daisy and crosman offerings seat in the bbl with no problem now...

Regards,

Doc Sharptail

[remtom1200]

Thank you Eric, and I made the valve POS seal a pos taking it out....he he. PCP for me tomorrow!

[remtom1200]

Well, ...interesting! At 1500 psi it sounds like a 22LR but there is something not right. Following the shot it sounds like i have a load of air traveling through the barrel after the pellet has left. I am guessing the valve is staying open too long? I had modded the valve and made a pedestal for the spring and might not have put enough tension on the spring, as well put a spacer about 3/16 on the hammer side. I am now left with the question do I remove the spacer or crank up the valve spring tension?. I have no numbers to share at this point but it shoots very strong. Shot count is way down as well, around 12 shots from 1500 - 650 psi

[SeanMP]

I pull mine apart all the time and reuse the breach seal and Orings

Did you do some deburring while you had it apart...I'm guessing yes

[AirGunEric]

When you tear it down you'll find that the barrel Orings are pre shredded so have a seal kit or a supply on hand.

Out of roughly a dozen I have had apart now (ones that leaked straight-out-of-the-factory box) I have found two without "pre shredded" barrel o-rings- so it does seem to be a real feature of the factory to jam those things in there to ensure the majority get chewed up...

[remtom1200]

I finally give in and ordered the PCP conversion and the hill pump from Eric...no rum and beer for me for ...ever....lol. Now trying do pick through a million posts about tuning this type of conversion mostly to avoid a locked valve while utilizing more psi. Now I see I have to pin the valve for safety as well. Now this is my type of happiness...MODS!