Compression chamber and TP

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ReeceMTunes

ReeceMTunes

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Jan 12, 2025
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Just out of sheer curiosity, I've been toying with the idea. Now stay with me. I will make it as concise as possible.

Assuming there was no legal limits to the power a spring piston rifle could produce AKA the American market, what differences to the internals of the gun are altered to restrict for the UK market. I'm under no illusion that, ofcouse, the main spring will be weaker, but what about the piston stroke? Or the cylinder diameter/air volume or TP? If you disassembled hw95k, one bought in UK and the other bought in USA what differences would you find internally. One produces 17ft lb(usa) and the other sub 12(uk).

Do sub 12 guns even have the capacity from a piston stroke, TP, cylinder volume stand point, to ever achieve that of an identical American verson in principle? It's certainly not the case to just put a larger spring in or wack half an inch of spacers in as the gun just goes coil bound and you are unable to cock the rifle. So there must be other powers at play.
 
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Okay, lets explore that for a moment then. Spring being the only difference, are we talking a larger diameter spring in a larger compression chamber, or the same diameter spring but with larger coil count?

And is it fair to say that, the stroke length is a huge denominator in the amount of compressed behind the pellet. Increase stroke length = increase power, right? Well if we just add a spring with greater coil count, we then shorten the stroke length, all else being equal, we speed up the short cycle, but the power is essentially a stalemate. Not to mention, the larger spring compressed into the same size piston, you're likely to go coil bound and be unable to cock the rifle. Maybe I'm wrong here, but to me it doesn't seem as straightforward as just wacking a bigger spring in with the same components
 
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Most UK EXPORT guns come from their distributor with sub 12 ft lb springs. usually smaller wire bigger OD AND LESS PRE LOAD ..Our FAC springs are different. polar opposite. They do not tune them to 12 ft lbs either. It’s harsh over there. If your gun goes over 12 ft lb with ANY PELLET they can seize the weapon. Most shoot for 11 to be safe.

As for stroke ,port, spring set up. It’s a balancing game of cards. Stroking a gun don’t alway make more power as well as bigger spring. You can blow the pellet out before the piston hits TDC. If you have ever shot a over sprung gun you will know it. Same as under sprung. Weight to port to stroke to spring size and coil count has to be factored to get the best balance. Most people will over spring a gun without knowing and can get better shot cycle with lighter spring and same or better power if they know the port size and piston weight.
 
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Will an FAC spring necessarily have a greater coil count than a UK spring?

So that part about a balancing act, I totally agree. But what are the American versions doing that the brits aren't, to achieve a well shooting 24joule spring powered air rifle.

If we have UK and US identical rifles and strip them apart, what differences are we finding? If as you say, a longer stroke and bigger spring doesn't always equal better performance, does that imply that, our British 'watered down' sub 12 air rifles perform better than the full powered US counterparts?
 
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Take a Hw 80. Same everything. Except ones 12 ft lbs and ones 17 ft lbs. The 12 ft lb gun will have a thinner Wire with less pre load. , the shot cycle will be slow and sluggish. As compared to a thicker spring with more pre load and a faster shot cycle. Same gun but, THE more powerful one feels better. Some power plants are better off FAC.

Now take a HW 99 /50 and it’s a different story. No matter what you do your not getting much more than 12 ft lbs and the gun that’s leaned on will shoot poorly if over sprung Or added weight. It’s a 12 ft lb platform. It’s exactly why many will sleeve a 30 mm tube to 25 and shorten the stroke .. Now that big heavy Hw 80 gun behaves like a Hw 99 with little recoil
 
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A.G.R said:
Take a Hw 80. Same everything. Except ones 12 ft lbs and ones 17 ft lbs. The 12 ft lb gun will have a thinner Wire with less pre load. , the shot cycle will be slow and sluggish. As compared to a thicker spring with more pre load and a faster shot cycle. Same gun but, THE more powerful one feels better. Some power plants are better off FAC.

Now take a HW 99 /50 and it’s a different story. No matter what you do your not getting much more than 12 ft lbs and the gun that’s leaned on will shoot poorly if over sprung Or added weight. It’s a 12 ft lb platform. It’s exactly why many will sleeve a 30 mm tube to 25 and shorten the stroke .. Now that big heavy Hw 80 gun behaves like a Hw 99 with little recoil
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Great breakdown. I appreciate you taking the time. And good point with the hw99s. Completely explains what I was asking. One rifle is made to be full power, and the other is manufactured to be limited to 12ft lb. So wacking a 34 coil titan spring in a hw99s wont do it any favours. Do the same in the hw80 and because of its greater capacity, will run far better than at sub 12. Thanks again for the comparison.
 
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A.G.R said:
Most UK EXPORT guns come from their distributor with sub 12 ft lb springs. usually smaller wire bigger OD AND LESS PRE LOAD ..Our FAC springs are different. polar opposite. They do not tune them to 12 ft lbs either. It’s harsh over there. If your gun goes over 12 ft lb with ANY PELLET they can seize the weapon. Most shoot for 11 to be safe.

As for stroke ,port, spring set up. It’s a balancing game of cards. Stroking a gun don’t alway make more power as well as bigger spring. You can blow the pellet out before the piston hits TDC. If you have ever shot a over sprung gun you will know it. Same as under sprung. Weight to port to stroke to spring size and coil count has to be factored to get the best balance. Most people will over spring a gun without knowing and can get better shot cycle with lighter spring and same or better power if they know the port size and piston weight.
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You mean some manufacturers?
 
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DesertSilver said:
Hatsan uses a threaded TP along with a weaker spring to adjust the power. The TP can be changed in the H135 I have.
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I bought a hatson dominator recently. I'll never again buy a hatson. It got returned a week later. The firing cycle was fine, but the gun was just really cheaply built and the squeek it made when cocking was awful. Not something you'd expect from a new rifle, even at that price point. Ever looking to spend under 400quid/bucks I'd go for a gamo. I have the gen 2. Its a cracking bit of kit
 
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