The makers of the Theoben air rifles incorporate a gas spring in some models instead of a mechanical spring. Pressurized air or nitrogen is held in a special chamber built into the piston, and this air is further pressurized when the gun is cocked. It is, in effect, a gas spring commonly referred to as a "gas ram" or "gas strut". Gas spring units require higher precision to build, since they require a low friction sliding seal that can withstand the high pressures when cocked. Gas spring units the advantages of the gas spring include the facility to keep the rifle cocked and ready to fire for long periods of time without harming the mechanism. Also, since there is no spring (and therefore a reduction in moving mass during firing) there is less recoil. There is also an elimination of the associated problems of long-term spring fatigue and a faster "lock time" (the time between pulling the trigger and the pellet being discharged). The improvement in lock time makes for better accuracy since there is less time for the gun to move off target. Finally, gas springs are practically maintenance free and last longer than conventional metal springs.
The advantages of the Theoben H.E. System
1. The main benefit must be the consistency of power, because the system is sealed, then each time the rifle is cocked the same air pressure is used over and over again.
2. This means that precisely 12 ft/lbs in .177 cal, .20 cal, .22 cal or .25 cal can be set and maintained for thousands of rounds with no maintenance.
3. The gun can be left cocked whilst hunting, something not recommended with a spring rifle, due to spring fatigue.
4. The rifle has a very low cocking effort.
5. The action is quicker than a spring rifle.
6. Very low recoil and very quiet action.
7. It still has a one stroke cocking, not like a pump-up rifle.
8. Theoben break action rifles are self-contained. They do not rely on external power for their operation.
9. Individually hand finished for supreme accuracy.
10. Theoben break action rifles are about one pound lighter than comparable rifles.
11. The system is totally reliable. Theoben break action rifles are used world wide.
12. The scope mount ramp built onto the rifle permanently, so scope shift is a thing of the past.
13. All Theoben rifles are made from traditional gun makers materials externally, housing our unique system of power that incorporates many features of technology.