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Messages - rsterne

Pages: [1] 2 3 ... 77
1
Ask Bob / Re: Balanced valves in pcp's
« on: Today at 08:27:13 AM »
Tim, I don't really understand the drawing, or concept.... Is the valve at the left?.... Is the main hammer spring inside the hammer, with the preload adjusted on the right?.... From your description, it seems that this would only be useful in a regulated PCP....

Bob

2
Ask Bob / Re: Hybrid pellet/bullets possible???
« on: September 24, 2017, 02:25:24 PM »
It sounds to me like Nick already has a handle on everything needed to make what Travis suggested.... a slug that shoots like a pellet, and can even be varied in weight.... There is little point in trying to reinvent the wheel, IMO....

Bob

3
Ask Bob / Re: Balanced valves in pcp's
« on: September 24, 2017, 02:14:17 PM »
If your used Bellevilles, or wave springs to counter the force holding the valve closed, you would not be able to fill the gun from empty without finding a way to hold the valve shut.... and if the air pressure dropped below the spring force the valve would dump all remaining air in the reservoir.... Balanced valve change the "counter balancing force" in proportion to the air pressure, your idea of a mechanical spring would have a fixed force (the spring) countering a variable force due to air pressure.... It could be made to work in a regulated gun, subject to the problems mentioned above....

Functionally, your "hollow poppet" works the same as the 4th drawing above, the "Balanced Valve", except that the vent used to pressurize the balance chamber is through the poppet instead of through the valve body.... The Balanced Valve as drawn also has increased closing force while cycling because of the oversize hole around the stem between the balance piston and exhaust port.... There are lots of ways to physically come up with the same result, yours is yet another variation.... You will need an O-ring on the balance piston to prevent the HPA from leaking past it into the exhaust port when the valve is closed....

Bob

4
Ask Bob / Re: Hybrid pellet/bullets possible???
« on: September 23, 2017, 10:11:46 PM »
NOE will make custom moulds, you just have to pay for the tooling, and then purchase however many moulds you need at their regular prices.... If you will allow Al to use the tool for others, I believe the tooling cost is $300, if you want it proprietary, it is higher.... You should ask Al for the details....

You can also ask Jared at Arsenal about a custom mould.... He did the .224 cal "Bowman" 47 gr. at my request, and added it to his catalogue, and I just paid for the mould I purchased, with no surcharge for tooling.... I don't know if that is his normal procedure or not.... Arsenal does not do HP or HB moulds, however....

Bob

5
Ask Bob / Re: Spring weight?
« on: September 23, 2017, 10:04:48 PM »
Sorry, I don't know the spring force on a QB valve, but I would think somewhere around 7-10 lbs. when on the seat....

You can leave the seat in the valve stock, just make the seat on the Delrin poppet flat....

Your question about having a spring "lift" I do not understand....

Bob

6
Ask Bob / Re: Hybrid pellet/bullets possible???
« on: September 22, 2017, 09:55:50 PM »
Nick, I really appreciate your input, your experience is invaluable, IMO.... There is indeed a lot to ponder before trying such a venture....

Bob

7
Ask Bob / Re: Hybrid pellet/bullets possible???
« on: September 21, 2017, 02:46:30 PM »
I have been doing some playing around with this idea at different calibers, and I think it might be an idea to shorten the design slightly as it would then scale better.... If we shorten it to 1.50 cal. long, it reduces the weight about 4 gr. and gives this design in .25 cal.... SD = 0.091 for the 40 gr. version.... BC should be about 0.08....



This bullet can then be scaled up exactly to .30 cal and still fit in the MRod and Flex mags.... SD = 0.111 for the 70 gr. version.... BC should be about 0.10....



I haven't drawn it yet, but if scaled up to .357 cal the weight would be 110-118 gr.... and if scaled down to .22 cal it would be about 25-27 gr.... Half the length of the bullet is supported by the barrel, which would increase the stability in the bore a bit.... and I think the weights are more realistic for high powered PCPs without having to get silly about the required FPE.... To reach 950 fps, this design would require 50-54 FPE in .22 cal.... 75-80 FPE in .25 cal.... 130-140 FPE in .30 cal.... and 220-235 FPE in .357 cal.... I think that is a good balance between the desire for a heavy bullet and the ability of the more powerful PCPs available today.... At 850 fps, the required FPE drops by 20%....

On the other hand, there is an advantage to using longer, more slender designs in the smaller calibers, to take advantage of the reduction in SD they give for the same shape.... This would mean making the .22 cal longer, and the .357 cal shorter to keep the SD constant....

Bob

8
Basically, yes.... and also for pumpers.... Pretty much any "pneumatic" airgun will follow the same trend.... There are a few exceptions, if you tune a gun for low power with a light pellet and then use a heavy one, the velocity may be so low that the power and efficiency may drop.... Springers (inc. Gas Ram) are totally different, because they work on a Adiabtic cycle which heats the air.... and the air used for the shot is the swept volume of the compression chamber.... Most Springers have an optimum weight range where the FPE, and hence the efficiency, will peak....

Bob

9
Except in a cork "pop" gun the cork is at the end of the barrel.... and it is the pressure buildup behind it that launches it at all.... PCPs already have 2000-3000 psi available at the instant the valve opens.... Virtually that entire pressure is present at the base of the pellet/bullet before it has moved even 1 mm.... Any restriction in the barrel just increases friction, IMO.... At 3000 psi in a .22 cal the force available to accelerate the pellet is 114 lbs, and the drag is only a few lbs.... Most of the force goes into acceleration, and how rapidly that occurs depends on the mass (weight) of the pellet....

Bob

10
Airgun Tanks, Compressors and Filling / Re: Compressor Explosion
« on: September 20, 2017, 05:49:38 PM »
Apparently the compressor filled a tank to about 1000 psi, and then the pressure stopped increasing and BOOM!.... First time he used it is the story....

Bob

11
Ask Bob / Re: BSA Scope from China
« on: September 20, 2017, 05:46:24 PM »
I think it's in Customs.... probably 1-2 more weeks....

Bob

12
Tim, why would a choked area at the breech make any difference to velocity/FPE, efficiency, or report?.... You lost me completely, I see no connection.... ???

Bob

13
Airgun Tanks, Compressors and Filling / Re: Compressor Explosion
« on: September 20, 2017, 01:23:03 PM »
My guess was a sudden leak that pressurized the crankcase.... Perhaps the piston cracked, or maybe a ring failure?.... I suppose the vent could have been plugged?.... If you fill the oil through that vent, I suppose it's possible it was leaking and the user found some creative way to plug the vent to stop the leak, causing the pressure buildup....  ::)

Bob

14
Airgun Tanks, Compressors and Filling / Compressor Explosion
« on: September 20, 2017, 12:33:32 PM »
No idea of the make or model, or what caused the failure.... but this HPA compressor failed big time....





Anyone recognize the type?....

Bob

15
Ask Bob / Re: Hybrid pellet/bullets possible???
« on: September 20, 2017, 12:23:29 PM »
Travis, I really have no idea.... The only slugs I have seen shoot sub MOA at 100 yards from a PELLET CALIBER barrel are Nick's swaged designs.... He spends a huge amount of time trying different designs and weights in different guns, and for most PCPs he knows what to recommend.... There are quite a few guys who can get dime sized groups at 50 yards, but very few of them can repeat that at 100 yards.... mind you, the same thing applies to pellets.... There are very few guys who have qualified as "Master" in the NUAH Club, which requires a 5-shot group under 1"....

There are a few "specialists" like Doug Noble and Carl who seem to be able to get MOA groups at 100 yards frequently.... but they are using PB barrels and calibers, and generally FPE levels well beyond what we are....  I have never managed it with any airgun.... Sub MOA groups at 100 yards remain uncommon in airguns, and quite elusive, IMO....

Bob

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