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PostPosted: Mon Aug 27, 2018 12:08 pm 
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Joined: Wed Aug 22, 2018 8:31 pm
Posts: 16
Location: Southern Ontario
rsterne wrote:
Easiest way is to double the swept volume and the power of the spring and increase the caliber to .25 -.30 cal.... We did a "how would you do this" thread on the GTA a few years ago to come up with the criteria for a .30 cal.... The conclusion was it would be a 20 lb. gun that nobody would want to cock, let alone carry around....

Bob


Or a ratchet system where one could use multiple strokes to....wait, they already done this. Benjamin pumper...

I have a couple of "medium" 12" springs that i used to counterbalance 1200 pound platen. I'm sure that one of those can put a 22 long to shame......if you compress it 3 inches. It's 185 pound per inch.

If you compress it at 1 inches, it will last millions of cycles......if..if

How about 725 pounds per inch in a 12"? Poor man's 308?

I have a Diana 6 air pistol that is dead. One hand canon coming up! LOL


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PostPosted: Mon Aug 27, 2018 2:21 pm 
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Location: Coalmont BC
Here is a link to the thread on the GTA where we discussed the relationship between swept volume and FPE....

https://www.gatewaytoairguns.org/GTA/in ... opic=94485.

Successful springers produce about 1 FPE for each 3 cc of swept volume.... so to make 40 FPE you need about 120 cc.... The appropriate spring force required is also discussed in that thread....

Using the 125 mm stroke N-forcer gas ram, and allowing some room for installation (120 mm stroke), to get 120 cc you need 1 cc per mm, or a cross sectional area of 10 cm^2.... That is a diameter of 3.57 cm = 1.40" ID for the compression chamber.... The ratio of stroke to bore would be 120 / 35 = 3.4:1, which is just about right for a typical springer....

There are a couple of ways to estimate the spring force required.... The simple way is to use the stroke in feet to divide into twice the desired FPE (so that assumes a 50% loss, which is typical)…. You want 40 FPE, and the stroke is 120mm = 4.72" = 0.394 ft, so you take (40 x 2) / 0.394 = 203 lbs. average force.... A 25mm N-forcer "blue" averages (225 + 305) / 2 = 265 lbs. which is 30% more than required.... so you would want a "black" (adjustable) one with about 1000 psi in it.... Using the other method of average starting psi, that area of a 1.40" piston is 1.54 sq.in.... so to get 171 psi you would need 265 lbs cocked force, and to get 132 psi you would need 203 lbs. uncocked…. The 25mm "blue" gas ram (225-305 lbf.) is about 10-15% greater than that, so might be pretty close.... It shouldn't be drastically overpowered, at least....

So, if you have a compression chamber with a 1.4" ID (~36 mm) and used a blue N-forcer 25 mm gas ram with a 125 mm stroke (using 120), you should be in the ballpark.... It would be about 56% harder to cock than the red ram in my Phantom, which believe me would make you work at it....

Bob

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PostPosted: Mon Aug 27, 2018 5:13 pm 
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Joined: Wed Aug 22, 2018 8:31 pm
Posts: 16
Location: Southern Ontario
rsterne wrote:
Here is a link to the thread on the GTA where we discussed the relationship between swept volume and FPE....

https://www.gatewaytoairguns.org/GTA/in ... opic=94485.

Successful springers produce about 1 FPE for each 3 cc of swept volume.... so to make 40 FPE you need about 120 cc.... The appropriate spring force required is also discussed in that thread....

Using the 125 mm stroke N-forcer gas ram, and allowing some room for installation (120 mm stroke), to get 120 cc you need 1 cc per mm, or a cross sectional area of 10 cm^2.... That is a diameter of 3.57 cm = 1.40" ID for the compression chamber.... The ratio of stroke to bore would be 120 / 35 = 3.4:1, which is just about right for a typical springer....

There are a couple of ways to estimate the spring force required.... The simple way is to use the stroke in feet to divide into twice the desired FPE (so that assumes a 50% loss, which is typical)…. You want 40 FPE, and the stroke is 120mm = 4.72" = 0.394 ft, so you take (40 x 2) / 0.394 = 203 lbs. average force.... A 25mm N-forcer "blue" averages (225 + 305) / 2 = 265 lbs. which is 30% more than required.... so you would want a "black" (adjustable) one with about 1000 psi in it.... Using the other method of average starting psi, that area of a 1.40" piston is 1.54 sq.in.... so to get 171 psi you would need 265 lbs cocked force, and to get 132 psi you would need 203 lbs. uncocked…. The 25mm "blue" gas ram (225-305 lbf.) is about 10-15% greater than that, so might be pretty close.... It shouldn't be drastically overpowered, at least....

So, if you have a compression chamber with a 1.4" ID (~36 mm) and used a blue N-forcer 25 mm gas ram with a 125 mm stroke (using 120), you should be in the ballpark.... It would be about 56% harder to cock than the red ram in my Phantom, which believe me would make you work at it....

Bob


Or........a PCP with 4000-5000 psi reserves and 30 cal bullets. Far easier to go up the scale in PCP then springs.

What I like to see is a dual power air gun. Put in 3 cents primer or 22 blank. Set it off in a high pressure chamber hidden/stored in the stock and then feed the gas to a storage bottle. I don't have a clue how much gas will be generated, but assuming it's good for ten shots, you now have the ability to easily carry enough ammo and charges to start a small war.

Or how about a small propane tank and igniting a small charge into a storage rank. No powdrer fouling.

I bet I'm not the first crazy person to think of this....


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PostPosted: Mon Aug 27, 2018 6:39 pm 
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Location: QC
Spartan wrote:
I bet I'm not the first crazy person to think of this....


You can't really use the gas directly because a lot of the energy comes from the heat generated by the chemical reaction, once this dissipates you're left with much less, it's better to use that force to compress an inert gas mechanically in a separate chamber.

You're right that this is an old idea, the Sims-Dudley Dynamite Gun for example used a smokeless powder charge to compressed the air that fired explosive shells and saw active service well over a century ago.


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PostPosted: Wed Aug 29, 2018 11:46 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1233
Location: United States
If you want to tinker you can get the NP2 full power spring and put it in your gun. If that works for you and you want to go a step further you can get the old NPSS/RNP spring.
The NP2 spring is # NP214-012 and ~$16CA. I'm not sure how much stronger it is than a BT9 since I have no BT9's w/ full psi for comparo.
There's also a couple Vortek springs you might consider, and they don't leak ;)

Imo the BT9 is pushing the edge of too much already. It's at this line where gains in power increase less but negatives via piston impact get worse faster. Spring strength to power output will be ~1-1 up to that point, which is why when I removed my spacer it was half the cocking effort, which is half the spring strength, and as a result the power was half to match. As you know the air in your gun is already compressing as far as mechanically possible bc the piston is impacting the breech. All a stronger spring will do is get the air compressed to that point sooner, which does help bc the pellet starts moving b4 it the piston hits so a faster piston means it can get psi up higher. The volume of air hasn't changed, and the speed won't be all that much faster so the gains will be small.
Another example is if you double the spring but you haven't changed the volume of air to slow the piston and dampen impact, you'll net some small power gain but piston impact will be brutal. It'll prolly destroy any scope quickly, assuming any mount could hold it. It may even break the stock screws.
In short the power gains will be small but reverse coil will get much worse. Imo the BT9 is at that point were piston impact vs power is prolly not worth it to most people but it's how it's sold and they have little option. This is one reason why I like the coil spring, it's not so deep in that "not worth it" zone so I could net 95% of the power but much less reverse recoil, and a good chunk less cocking effort! That example gun I removed the spacer from made 18.5ftlbs but was significantly easier to cock than a BT9. It's spring was oem but a good chunk weaker than a new one due to its low quality and use, yet made power. Adding the much stronger BT9 would no doubt break 19, maybe even 19.5ftlbs, but imo not worth it. Lets say it did add 1ftlb, and the BT9 is an est 25% stronger. Another 25% would add <1ftlb, but maybe tear the gun apart, plus accuracy, noise, cocking effort all go down hill to match.

The NP2 spring is pretty cheap so I say give it a try. If you like it then great, if not it was a worthwhile learning experience and you may be able to sell it to someone, or save it for the day you get an NP2, and I think you should since it's some easy power. The NP2 has more volume, I believe it was just over 40% more, yet it doesn't make 40% more power bc it's not as good of a design. The bore to stroke ratio is off. The Trail XL has a more ideal bore to stroke ratio, same bore as the NP2 but longer stroke. It's ratio is more like the B18, so the % increase in volume is met with = power gains. It also has a stronger spring to match, but the key is match, it matches the increase in volume so it's not too much.

Try to picture what's happening in the gun. The piston compresses the air into the xfer port, and that little compressed pkg of air launches the pellet. In the real world the pellet starts moving b4 that happens so the peak possible psi is never reached, plus the piston hits and rebounds off the breech so whatever air is just a short spike of pressure. This is why springers don't do well with heavier pellets, and the heavier you go the worse it gets bc the piston only pushed on it for a microsecond but it cudda used two or three. A pcp's air pushes until it leaves the barrel. A light pellet moves earlier since it takes less psi to start moving and it moves quicker so it never sees the psi the heavy does, but it does take more advantage of the short pressure spike since it's speed is a closer match to it. It surfs the pressure where the heavy pellet kinda misses it, like how a surfer tries to catch a wave but he's too slow, or heavy, and he ends up over the top and dwn the back side going nowhere.
So there's an ideal pellet wt for every springer based on the guns mechanics and condition, lighter or heavier from there you lose power. Usually it's a range of a few grains that are pretty much close enough in power, then it tapers off and the further you go the worse it gets in non-linear fashion. Light alloy can net some power over = wt lead bc the skirt is harder to force into the breech so movement is delayed like a heavy, then when psi is high it breaks free and moves very quickly which is surfing the pressure spike better.
In a way it's like you throwing a rock, there's a certain wt rock you can throw to max ftlbs, if you throw a rock half the wt or double the wt you won't hit that same energy level. So like your body, the gun has a sweet spot of pellet wt it works best at, and there's a sweet spot for each part in the gun, including the spring... Imo that BT9 is on the outer edge of too much.

I'd focus on increasing the guns stroke, then add more spring. The stroke will net a small amt of power, ~1% per mm. I call it free power, meaning cocking effort is no different. The spring you have is more than enough to make use of that extra stroke so it'll not only give power but reduce piston impact. I don't think you'll notice the latter, but the power will show on the crony. The guide covers stroking but you're limited on what you can get from a B18. The first mm is easy, at ~3mm you're really working for it, and you will likely never hit 5mm.
The stroke in addition to all the other stuff you've been experimenting on to get the peak from what you have. And don't forget the barrel. I can't remember if you sanded it yet or not but there's usually a tight spot ~3" in that'll do you know what to that precious air. And I still have one barrel I saved that mysteriously costs power of whatever gun its on, but that loss varies gun to gun so it's even more of a mystery. So sanding and if possible try other barrels to be sure yours isn't holding you back.
Hope this helps...


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PostPosted: Thu Aug 30, 2018 6:32 am 
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Location: Thunder Bay,On.
Big thanks to you and rsterne......I understand more spring force than what I presently have(NP) is not the answer for more power so today I will concentrate on barrel sanding......since I have NEVER checked any of my gun barrels for tight spots....I'm sure to find SOME that need sanding…. :D

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