Good that thanks for taking the time to write that dunks
Great write up and explanation, I was right back in 1995 in my physics lesson for a minute there
Nicely explained, even for my limited memory of classroom physics.
I have a Theoben Fenman .22 with their High Efficiency gas spring system. Lovely to shoot. Very little kick.
Last edited by EightSides; 28-06-2013 at 14:31 PM. Reason: Pic added.
Well done and nicely done, god I miss my gas ram.
Steevie Dan the Shooting Man
Great thread....would be nice if it was made a sticky
Loved the post, very interestingly it revised my Physics lessons I had over 45 years ago! Keep up the posts :-)
hmm have an issue with the q&a bit questions 3 & 4
3. Q – Will a Gas Strut make my rifle quieter internally?
A – Yes it should, as there is only the strut and the piston without any spring or guides to rattle around inside the rifle when firing
(depends on the ram manufacturer the gamo/bsa rams are some of the worst around and make an ox spring sound like a silencer besides fitting a fitted top hat and spring guide to any spring will reduce the noise level and aid in smooth shooting)
4. Q – Will a Gas Strut improve my air rifle?
A – in many cases YES, however they are like Marmite and not all guns seem to suit a Gas Ram conversion
(will only improve an air rifle to the shooters perception it will not make a air rifle anymore accurate or magically shoot further in fact in some cases can make an air rifle hold sensitive when it wasn't before )
i like some gas ram rifles the cheaper market ones you can keep owned a gamo igt once worst thing i ever shot however had a hw90 and it was beautiful never had a chance to own my own theoben but shot a few also lovely rifles, i think with gasram a rifle needs to be built around the powerplant not a ram placed in a rifle that originally had a spring, however that could be because i think spring is king
The physics is fine as far as it goes but takes no account of the energy required to overcome the inertia of the moving parts of the rifle. Otherwise a gas ram would behave much the same as a PCP. You need more potential (stored) energy in a springer than a gas ram, which needs more than a PCP. The moving parts are heavier for a springer and, according to Newton's 3rd Law (for every action there is an equal and opposite reaction) this will result in more of a kick back. The overall recoil is going to depend on how the potential energy is converted to kinetic (moving) energy. This will depend on the mass and acceleration of the piston, friction, the mass of pellet and resistance to travel up the barrel - and how these change through the firing cycle... all too difficult for me to calculate! But the bottom line, I believe, is there is more wasted energy in a springer and consequently more recoil.
Piston assembly mass certainly makes a difference to recoil (total rifle recoil travel being equal to the piston stroke multiplied by the ratio of the piston to rifle masses), however I'd dispute the assertion that pistons in gas ram guns are lighter than those in springers - at best they're usually comparable, at worst gas ram pistons are horrendously heavy.
For example an HW90 piston weighs nearly 400g, its inertia weight adding another 70g+. By contrast an HW80 piston "only" weighs around 340g, a typical spring weighing around 130g - although only 1/3rd of this contributes to effective piston mass, giving a total effective mass of around 385g.
What kills gas ram efficiency are the very high forces due to the expansion characteristics covered in the Boyle's law part of the first post; meaning the parts are subject to very high accelerations initially, giving higher piston velocity and a faster firing cycle overall. The downside to this is that the duration "window" of meaningful pressure behind the pellet is reduced, meaning more energy goes into piston bounce (and hence is wasted) and less into the pellet.
This is compounded by the fact that, compared to a spring a gas ram rifle has much less forward force acting on the piston at the end of its stoke - meaning the piston is comparatively much easier to force backwards under bounce; further reducing efficiency (this is why many gas ram guns have "inertia weights" in an effort to minimise piston bounce and improve efficiency).
Another area where efficiency is lost in gas ram guns is isothermal compression - when the gas in the ram is compressed during cocking, some of its energy is converted to heat, which is then lost through conduction to the outside world, reducing the pressure in the ram.
Many people state that gas ram rifles have "less" recoil - like for like this simply isn't the case. Due to the relationship between piston and rifle masses discussed earlier, recoil displacement will likely be greater, while accelerations are much higher (as many who've had scopes knackered by gas ram rifles will attest). It's true that the firing cycle is over faster and is sometimes subject to less NVH, however for like rifle and piston masses a decent spring gun will have less recoil, whichever way you spin it.
Welcome to the forum
Last edited by cloverleaf; 21-03-2017 at 16:38 PM.
Please post tech queries to the forum and request my input rather than asking me the question via PM - this way everyone can contribute and benefit