Chinese air rifles and Gas spring conversions

[Scotchmo]

I am going to contribute my findings. Anyone else is welcome to do the same. Hopefully, no drama, just facts.

Can any spring airgun be easily converted to a gas spring?

Some airguns lend themselves to easy conversion. Some do not. If the airgun uses a latching rod down the center of the piston, then it is NOT a good candidate. If the piston has a perimeter latching sear, than it can be a simple conversion. So, good news for all the rifles that can use a GRT trigger. They should be fairly easy to convert. Some of the Chinese copies of high end European rifles use a latching rod so they are not good candidates. Sorry B21, B30, B40 owners.

What kind of special tools are needed?

A spring compressor is a good idea, but once you remove the wire spring, you really only need a simple bar clamp. The amount of preload on a gas spring is small so you do not need a long throw spring compressor to reassemble the rifle. A metal lathe is helpful for making the necessary spacers, top hats and bushings. But some clever use of flat washers, spacers, drill, and a hacksaw can also work. There have been a couple of instances where I was lucky and the gas spring fit with no spacers or bushings.

The gas spring can be installed in either direction. The combined weight of the piston and tophat can affect performance. When you install the spring "backwards" (spring body inside piston), you may be increasing the weight of the piston more so than if you install it "front facing" (spring shaft projecting into piston). I prefer to install the spring "front facing" but a "backwards" installation is often simpler and the spring body will not scrape the piston wall when you cock or fire. If you install it "front facing" you need to use bushings/washers to keep the spring centered. A "front facing" gas spring gives you more control over the combined piston weight.

What kind of gas spring should I use?

The gas springs that will work best are NOT automotive gas springs. Lift struts probably will NOT do the job. Some people have adapted Crosman gas springs. I am not familiar with the specifications of the Crosman gas springs and I have not been able to find any published information on them. But obviously they work. Industrial gas die springs will work. They are high quality so they should last. Detailed specifications are available which makes selection of the appropriate spring easier.

There are a number of manufacturers of gas die springs:

N-Forcer (USA)
Dadco (USA)
Kaller (Sweden)
ASRaymond (Kaller rebadge?)
etc.

http://www.n-forcer.com/content/pdf/Mini.pdf
http://www.dadco.net/Catalog%20PDF/micro_catalog_revC.pdf
http://www.asraymond.com/documents/Counterbalance%20Solutions%202012%20Web.pdf

Some of the manufacturers may not deal directly with end users so you might have to find a distributor. McMaster has a few, though limited to shorter stroke spring guns.

http://www.mcmaster.com/#6643k561/=eo9zhf

Which model springs should I use?

That will depend on the rifle. Most of the rifles that we are considering here use a 1inch (25mm-26mm) piston. The 19mm diameter gas springs fit nicely in these pistons. There are probably three different strokes of the 19mm diameter springs to consider. Low power, short stroke rifles will use the 80mm stroke gas springs. Medium power rifles will use the 100mm stroke gas springs. High power rifles will use the 125mm stroke gas springs.

19mm-080mm = QB36-1, QB57, QB58, TF58, TF67, TF97, etc.
19mm-100mm = QB36-2, TF99, medium power Gamos, etc.
19mm-125mm = AR3000, TF87, etc.

Besides the size of the gas spring, you have to specify a force. They are rated by PSI, BAR, Lbf., Newtons, etc. The lbf. is what I use to calculate which spring might work best in a given instance. So you can do the math and choose it that way. Or - they also include a simple color coding system. Springs can come from different manufacturers, but if they have the same color code, they are generally interchangeable as far as approximate force. Color is usually indicated by a colored shaft seal or a colored label.

Green label - very low force, too low for most airguns, but still usable. - not recommended
Blue label  - good for airguns that need to be smooth.
Red label -  good for airguns that need to be powerful
Yellow label - very high force, too high for most airguns, but still usable. - not recommended

I have found the Blue and Red label gas springs to be good choices for airguns. You can get the most power from the Yellow label spring but there will be consequences from the excess force. Most manufacturers also have a Black label spring. That merely indicates a custom force that can be anywhere between the Green and Yellow ratings. Some gas springs are even adjustable but you will need to buy the charging equipment.

What does a gas spring cost?

Probably $40-$100 depending on the source.

There are some companies that will install gas springs in your airgun for you. Pyramyd air does a few models but they give no details on the type of gas spring that they use. It looks like Mike Melick is now converting some of the Chinese airguns. The dealer/tuner installed springs seem to run $100+.

Gas springs have some advantages over wire springs. I like them a lot so far. But they are not a cure all. Sometimes wire springs are more appropriate.

-Scott Hull

[Addictedtoair]

Thank you for sharing your information in a well written and understandable manner.

Brett

[Onebaddj]

Awesome info. Thanks for sharing it.

[gene_sc]

Fantastic compilation of information Scott. May I place this information in the GTA Library?

Thanks so much for a valuable contribution.

Gene

[amb5500c]

Very well done sir. Easy to understand and well written.
Richard

[z28rod]

Man I really learned alot from that post, excellent.

[stilkikin]

Great post. You make things easy for people like me!

[bradyman1]

Thanks for the info. Very well written and VERY informative.

[Smackey54]

Thank you Scott! Nice job! Do you write for a living? Technical writing for dummies like me? If not, you should!
Thanks again!

[supertech77]

great post ,very informative,very organized and factual 'thank you.

[gamo2hammerli]

That's an excellent and informative post...great for do-it-yourselfers who want to convert to nitro piston power.

[rsterne]

GREAT POST !!!

Bob

[Scotchmo]

Fantastic copulation of information Scott. May I place this information in the GTA Library?

Thanks so much for a valuable contribution.

Gene

Please do so. It is my pleasure to be able to contribute to the GTA library.

[redone1992]

excellent and informative post

[Kailua]

Always wondered where to get gas pistons.  Thanks for taking the time and effort to bring this to our attention.  Have this bookmarked.

[z28rod]

Scotchmo , do you think you could post some of your info. on what manuf. springs fit what rifles that worked safely ?

[Scotchmo]

Scotchmo , do you think you could post some of your info. on what manuf. springs fit what rifles that worked safely ?

Die springs are standardized parts in the tooling industry. A 19x080 spring from one manufacturer is interchangeable with a 19x080 spring from another manufacturer. Kind of like ball bearings or nuts and bolts. Any spacers or adapters that you make for one spring should fit the other regardless of the source. There can be very small differences in external dimensions but usually inconsequential. I have tried N-Forcer, Dadco, and Kaller/ASRaymond/McMaster. All interchangeable.

So far I'm preferring to use the N-Forcer products. It seems to be a smaller company that is willing to deal directly with end users. Just deal with them in a professional manner and it should go fine. They cost about $45+/- for the airgun sizes and they give a small discount for ordering 10+ of any one item.

I have not been doing this long enough to have any kind of definitive list of airguns that can be converted. Just that 19mm OD springs seem to work in most of the Shanghai rifles.

I have worked a lot with the QB57 and TF58. The 19x080 size spring works well in these particular short stroke rifles. They use separate spring guides so no cutting is involved. I am going to use a 19x100 spring to convert my TF99 next but I think it has an integral plastic spring guide that will have to be cut off. You mentioned "safely". The only safety consideration I had was when trying to cock a rifle with the yellow label spring installed. The QB57 with the yellow spring actually performed well. Fairly smooth shot cycle and gave 780fps with medium weight .177 pellets. That was a 130fps increase. Still, it was a bear to cock. Too high to be acceptable. Maybe a long stroke underlever would be easier to cock. But you would still be stressing the other components way beyond what the original designers intended. I think if you stick with the red or blue label springs, you should be "safe".

[z28rod]

"I am going to use a 19x100 spring to convert my TF99 next"
Can you post how it works out with that tf99, i have a tf99 also, would be nice to see how it works.

[lurch420gam]

Thanks for the excellent information. Great post! Joel

[gene_sc]

All this is great informtion and I do respect your research but, I would have to say that messing with using these rams or springs you mention in a QB-57 -58 is treading dangerous ground. As it is now, the trigger system is almost to weak for the stock spring they use now. I would recommend staying away from any power mods on the QB's. One could lose a finger very easily on these models.