CO2 rifles

[Phil Russell]

A few years ago I bought a QB78 on impulse at auction, mainly because no one else bidded. Since then it has sat at the back of the cupboard but yesterday I decided to give it a try. Now these rifles had never really interested me and I tended to think they were just fun guns. In a way I guess they are but having had a play then delved inside my rifle (.22 by the way) I am beginning to appreciate them more and more.
As a newcomer to them there are a few questions that come to mind. Firstly, from what I have read, the .22 is far easier to tweak for improved performance than the .177. My rifle was running at c. 430fps with Accupel or AA Field plus a few others, which seems about on spec for an unmodified action. Predictions are that it can easily make 10 or so ftlbs. But predictions for a .177 suggest it is far more difficult to tweak and I am wondering why. As I believe it takes more 'puff' to propel a .177 pellet down range maybe the answer is that CO2 simply does not have the gas pressure or volume at the firing valve available to do this efficiently. I am not asking for info on how to mod these rifles by the way as there seems to be enough available on the web. But the difference between .22 and .177 intrigues me ... any physicists out there to help?
Also, the main valve sealing O ring (BS113) raises a question. I see references to it being made of silicon rubber and not to use nitrile 70 shore. Yet I see another list stating the ring is nitrile 70 shore. Now I expected to see messages suggesting not to use nitrile because of the operating conditions ... CO2 and low temperatures ... so who is right?
Maybe for devilment I will now look for a .177 version....

Cheers, Phil

[MartynB]

A few years ago I bought a QB78 on impulse at auction, mainly because no one else bidded. Since then it has sat at the back of the cupboard but yesterday I decided to give it a try. Now these rifles had never really interested me and I tended to think they were just fun guns. In a way I guess they are but having had a play then delved inside my rifle (.22 by the way) I am beginning to appreciate them more and more.
As a newcomer to them there are a few questions that come to mind. Firstly, from what I have read, the .22 is far easier to tweak for improved performance than the .177. My rifle was running at c. 430fps with Accupel or AA Field plus a few others, which seems about on spec for an unmodified action. Predictions are that it can easily make 10 or so ftlbs. But predictions for a .177 suggest it is far more difficult to tweak and I am wondering why. As I believe it takes more 'puff' to propel a .177 pellet down range maybe the answer is that CO2 simply does not have the gas pressure or volume at the firing valve available to do this efficiently. I am not asking for info on how to mod these rifles by the way as there seems to be enough available on the web. But the difference between .22 and .177 intrigues me ... any physicists out there to help?
Also, the main valve sealing O ring (BS113) raises a question. I see references to it being made of silicon rubber and not to use nitrile 70 shore. Yet I see another list stating the ring is nitrile 70 shore. Now I expected to see messages suggesting not to use nitrile because of the operating conditions ... CO2 and low temperatures ... so who is right?
Maybe for devilment I will now look for a .177 version....

Cheers, Phil

Interesting post Phil, will be interested in what comes back from learned members on here

[--ped--]

less surface area for the co2 to act on -smaller barrel volume for the co2 to expand into -smaller port sizes due smaller bore max is 3.4mm on .177 and about 4.2 on .22(you can increase area of bore by oblong porting or radially porting the barrel)
for your seals any can be used on the valve with poly 90 being the most suitable but as the valve oring isn't significantly exposed to atmosphere swelling isn't a massive issue I supply epdm
barrel orings can be nb70 as can probe oring
the co2 cap is the most important one to get right I supply as std a red silicon one which will expand a fraction on being exposed to atmosphere but very quickly returns to normal but silicon is very soft and can be easily damaged
the best choice is poly 90 again as it inert to co2 and verey resilient to abrasion and cuts but can be hard to fit and get the co2 cap on plus is much more expensive to buy

[jirushi]

less surface area for the co2 to act on -smaller barrel volume for the co2 to expand into -smaller port sizes due smaller bore max is 3.4mm on .177 and about 4.2 on .22(you can increase area of bore by oblong porting or radially porting the barrel)
for your seals any can be used on the valve with poly 90 being the most suitable but as the valve oring isn't significantly exposed to atmosphere swelling isn't a massive issue I supply epdm
barrel orings can be nb70 as can probe oring
the co2 cap is the most important one to get right I supply as std a red silicon one which will expand a fraction on being exposed to atmosphere but very quickly returns to normal but silicon is very soft and can be easily damaged
the best choice is poly 90 again as it inert to co2 and verey resilient to abrasion and cuts but can be hard to fit and get the co2 cap on plus is much more expensive to buy

Now that's expert info!
Good to know.
Some other interesting CO2 airgun info, from Tom Gaylord aka BB Pelletier:
https://www.pyramydair.com/article/W...ecember_2003/6
I love my QB78. Didn't think much of it first either, but the tuning options are endless and it is a lot of fun to shoot.

[rovercoupe]

They are a bit rough round the edges but on one of mine all it took was taking out the stupid co2 filter, enlarging the probe and put back together with new rings and it was at 11 ftlbs on bulk fill, I did increase Spring preload and the power went through the roof so took the preload off.
Have another project gun in bits that eventually will be something special but it's a long burner project!

[peddy]

I gave up on .177 78's, they struggled to get over 10fpe without becoming gas hogs. My .22 has just about every mod and polishing done possible. Good therapy while recovering from op. Mine does 11fpe with a weaker hammer Spring, very accurate and fun to shoot. The older qb were better made

[Hsing-ee]

Is it true that the amount of work you need to put in to a QB78 to make it good is the same as the amount of work you would need to do to buy a new BSA Scorpion, working at the national minimum wage?

[peddy]

Is it true that the amount of work you need to put in to a QB78 to make it good is the same as the amount of work you would need to do to buy a new BSA Scorpion, working at the national minimum wage?

If you lived in Greece yes!

[Phil Russell]

Is it true that the amount of work you need to put in to a QB78 to make it good is the same as the amount of work you would need to do to buy a new BSA Scorpion, working at the national minimum wage?

As I am retired and do not work anymore for financial gain then the above is not really relevant. But I guess for anyone 'employed' you could be right.
An interesting thought when contemplating fiddling is that with a CO2 rifle like the QB it is far easier to monitor any changes you make. It will only 'cost' one CO2 bulb per change/monitoring operation compared to a full cylinder of air with a pcp, unless of course you want to use a pump. just thoughts.
Cheers, Phil

[Benelli B76]

Phil, I have resealed dozens of these, and have become more and more impressed with them, especially the .22. Once you have replaced all the seals with quality
polyurethane, you do not get any further problems. They can also be extremely accurate, my Dad's QB78 is phenomenal. I have hundreds of the the main seals for sealing the valve in position and the end cap. PM me and I will send you two.

Baz

[Phil Russell]

That is very good of you Baz. PM inbound.
As an aside, I am wondering why there are not more CO2 rifles used in competitions as in HFT (I excude 6m / 10m here). The advantages seem good: no air bottles to carry / fill / get tested. No sweet spot as the gas pressure is pretty constant until CO2 runs out. easily carried power source. etc I am sure I am missing the disadvantages but do wonder why there are no quality CO2 rifles used in HFT. .. or indeed why there are no quality CO2 rifles.
Cheers, Phil

[jirushi]

That is very good of you Baz. PM inbound.
As an aside, I am wondering why there are not more CO2 rifles used in competitions as in HFT (I excude 6m / 10m here). The advantages seem good: no air bottles to carry / fill / get tested. No sweet spot as the gas pressure is pretty constant until CO2 runs out. easily carried power source. etc I am sure I am missing the disadvantages but do wonder why there are no quality CO2 rifles used in HFT. .. or indeed why there are no quality CO2 rifles.
Cheers, Phil

No quality CO2 rifles? Under PY Hahn and Rudi Merz, Crosman made fantastic CO2 rifles in the fifties and sixties. For instance the 160, which was used in competitions.
The QB78 is a copy of this 160. I have both, and the 160 is certainly a quality gun. Most of them have survived a few decades of good use, and they are still popular in the states.
You probably mean: a quality modern CO2 rifle? I think CO2 is often dismissed because of temperature sensitivity. In an indoor setting, or on a nice day outside, this shouldn't be an issue though.
Pcp's and springers are just more predictable - this gives confidence. I guess this explains it?
Another interesting article, with an example of a modern CO2 target pistol:
https://www.pyramydair.com/blog/2006...k-fill-co2-gun
(Just to be clear: I do not sponsor BB Pelletier )

[MartynB]

Thanks guys, this has been a very interesting read

[Phil Russell]

You probably mean: a quality modern CO2 rifle? I think CO2 is often dismissed because of temperature sensitivity. In an indoor setting, or on a nice day outside, this shouldn't be an issue though.
Pcp's and springers are just more predictable - this gives confidence. I guess this explains it?
)

Yes, I was thinking about 'modern' rifles. I too would not think temperature sensitivity to be a major issue ... you wait long enough between lanes on an HFT course for it to become stabilised anyway ... (). Not sure about predicatbility as I tend to think that a well engineered CO2 rifle could overcome any worries. I admit I had not really thought of bulk fill compared to capsules, or indeed the large capsules (88g?). I guess bulk fill is cheaper in the long run.
Just thoughts ...
Cheers, Phil

[Geoff555]

Hello just a plus 1 for the Crosman 160, bought for £75.00 and with just a general clean and reseal is a steady 11 ft-lbs. and is the most accurate rifle I have got at 30 yds. and quite accurate at 50 yds. Bought just to play with but is so much more.
Cheers.
Geoff.