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Topics - rsterne

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1
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

2
Airgun Ammo / Hybrid Bullet / Pellet Poll
« on: September 19, 2017, 08:23:43 PM »
This poll is to find out what weight you would like to see for a bullet such as is being discussed in this thread.... Only 1 choice in the poll to force you to choose your most preferred weight....  :P

http://airgunguild.com/ask-bob/hybrid-pelletbullets-possible/

Here is a preliminary concept drawing.... These would have to be cast, it is the molds that would be available, although if we got a successful design we could look into having them produced, of course.... right, Travis?....



There are a lot more people with .25 cal airguns, so it seems logical to start there.... The concept, if successful, could be scaled up (or down) for other calibers, of course.... Shorter, lighter bullets would require a redesign of the nose.... it would need to be "blunter" to keep a long enough bearing area.... either a larger Meplat, or a smaller Ogive Radius, or both....

Bob


3
Heavier pellets will generally produce slightly higher efficiency, particularly if you don't change the hammer spring preload.... They end up going slower, but the valve dwell is still the same, so the valve closes before the pellet has moved as far down the barrel.... That leaves more length for the air to expand, so more of the energy in it gets extracted, and the residual muzzle pressure is lower, resulting in less report.... In addition, slightly less air is released from the valve, because the length of barrel filled while the valve is open is less.... Since the heavier pellet often has higher FPE as well, from that extra energy extracted from slightly less air, the efficiency increases.... This makes the gun quieter, with more FPE, with the heavier pellets.... and often gains you a shot or two as well....

Bob

4
Airgun Ammo / 64 gr. and 74 gr. 6mm Moulds at NOE
« on: September 18, 2017, 01:46:49 PM »
The mould for the 74 gr. FN, available as GC or PB, and also with a Lyman HP Pin, are now in the store at NOE.... along with the shortened version I requested....

http://noebulletmolds.com/NV/index.php?cPath=25

Bob

5
Airgun Ammo / New Arsenal Molds for .224 and 6mm
« on: September 01, 2017, 03:12:57 PM »
I just received my Arsenal Molds, after they went to Erik at Hollowpoint Mold Services to have 2 cavities converted to a HP.... They are beautiful, both the molds and the conversions....



The bullets are a scaled down Lyman 257420, which is the standby bullet for .257 PCPs.... I expect them to shoot every bit as well as the original....

Bob

6
I just purchased one of these from AliExpress.... https://www.aliexpress.com/item/BSA-TMD-4-14X44-FFP-Hunting-Riflescope-First-Focal-Plane-Glass-Mil-Dot-Reticle-Tactical-Optics/32821284918.html

They are on sale for the next few days for $104 US including shipping.... and come compete with sunshade, covers, and your choice of dovetail or weaver rings.... There is a nearly identical model with a different reticle, which you can find on Ali by using the "Find Similar" feature, available from several suppliers, at slightly higher cost....

Bob

7
Ask Bob / What is a Reasonable FPE Goal for PCPs ?
« on: August 26, 2017, 05:12:20 PM »
To be able to figure out what your new "Whiz-Bang" PCP can do, first of all you need to understand what the MAXIMUM POSSIBLE FPE could possibly be, with no losses.... That can be calculated relatively simply, as the "Energy Input", based on the available force, acting through the available distance.... The force is the bore area times the pressure... and the distance is the barrel length.... As always, we must watch the units....

Energy (ft.lb) = Force (lb.) x Distance (ft.)

The Force (lbs.) is the bore area (sq.in.) times the pressure (psi).... and the Distance (ft.) is the barrel length (in.) divided by 12 (in/ft)....

For example, let's use a .25 cal running on 3000 psi, with a 24" barrel....

Bore area = (0.25)^2 x PI/4 = 0.0491 sq.in. times 3000 psi = 147 lbs. force.... 24" barrel is 24 / 12 = 2.00 ft.... The maximum possible FPE this combination can produce is therefore 147 x 2.00 = 294 FPE....

Now before you jump all over me, remember that this would be the MAXIMUM POSSIBLE.... To achieve this, the pressure would have to stay at 3000 psi throughout the shot, which means the reservoir volume must be infinite.... In addition, there could be NO frictional losses, or any other form of loss.... That 294 FPE total would be divided into the energy in the bullet, and the energy in the air exiting the barrel.... and you would be shocked how much air weighs at 3000 psi, it is significant.... and any energy in the air is not available to accelerate the bullet.... To summarize, the maximum theoretical energy is calculated from....

Maximum FPE = Bore area (sq.in) x Pressure (psi) x Barrel length (in) / 12 (in/ft)

Pressure is pressure, regardless of the gas used.... This maximum applies for air, Nitrogen, or Helium....

Bob

8
Big Bore Airguns / Texan .308 FPE ?
« on: July 20, 2017, 07:08:46 PM »
Could any Texan owners out there confirm the following information?.....

Quote
154 gr. bullet at 986 fps ( 332 FPE).... was done with a stock Texan the only thing added was hammer spring stock and limbsaver on barrel

What kind of power are you getting with a stock Texan with just a hammer spring change?.... Note there is no mention of a tank change, so we must assume a stock, or at least safe, fill pressure, and a stock valve....

Bob

9
Airgun Ammo / Bullet Database
« on: July 19, 2017, 08:53:55 PM »
I ran across this tonight, and it appears to be a fabulous resource.... http://www.accurateshooter.com/ballistics/bullet-database-with-2900-projectiles/

It has over 3900 bullets, including many cast bullets.... You can access the data by caliber, and sort by manufacturer, weight, length, or other factors.... It gives the Sectional Density (SD), and the Ballistics Coefficient (I assume G1) at different velocities (if known).... As an example, here are the results for the popular Lyman 257420....

SD = 0.148
BC above 2200 fps = 0.129
BC above 1800 fps = 0.152
BC above 1300 fps = 0.18
BC above 800 fps = 0.20
BC below 800 fps = 0.15

I have only just begun to explore this database, but wanted to share it with all of you....

Bob

10
Airgun Ammo / New .224 cal from Arsenal
« on: July 18, 2017, 09:55:52 PM »
After discussions with Jared at Arsenal Molds, he has agreed to tool up for a .224 cal version of the venerable Lyman 257420.... We decided to name the bullet after John Bowman of Scandalous Airguns fame, because he has several other bullets based on the 257420 available through Arsenal, scaled up or down to 6mm, 7mm, and .338 cal.... Here is the new design, which will actually be made in .225 diameter to allow for sizing....



This bullet is intended to work in a 14" twist, such as the .224" groove x 0.219" land CF barrel available from TJ's.... In fact, it is about the longest, heaviest bullet that will work in that barrel.... You can order the molds for this new bullet from Arsenal Molds at.... http://arsenalmolds.com/products?limit=99999999999

My thanks to Jared for adding this design to his catalogue.... Based on the extremely successful 257420 I can't see how it won't be a winner in .224 cal....

Bob




11
Airgun Ammo / 77-85 gr. Cast in .30 cal
« on: July 10, 2017, 09:09:27 PM »
Discussion for a .30 cal "plinker" at NOE, no reason it could not be designed to cover our slightly undersized bores....

http://noebulletmolds.com/smf/index.php/topic,2175.0.html

Post in the thread if you are interested in it....

Bob

12
Airgun Tanks, Compressors and Filling / Helium Regulator
« on: June 27, 2017, 07:36:35 PM »
I am slowly collecting the stuff I need to allow me to compress Helium to 4500 psi and store it.... I have a used 88 CF SCBA tank coming for storage, and I already have a Freedom 8 to allow me to compress the Helium to 4500 psi.... but I needed a way to feed Helium to the ShoeBox.... Here is what I just put together....



The regulator is from China, by way of eBay for $30, and can be fed from a tank up to 3500 psi, with a regulated output that can be easily adjusted to 125 psi to feed my Freedom 8.... The only change I had to make was to the nut on the input nipple of the Reg.... It had something I didn't recognize, but the nipple is the standard size and only needed the proper CGA 580 nut to allow me to attach it to a Helium Tank.... Three feet of flex hose good for shop air pressures, and a hose adapter, a Street "L" 90* fitting and a standard shop air QD fitting complete the setup.... The QD attaches to the ShoeBox in exactly the same manner as my normal 125 psi regulated feed from my shop compressor.... but without the dryers between, since bottled Helium will be completely dry....

Helium is commonly supplied in 53, 73, 108, 214, or 292 CF tanks for welding, which are normally filled to 2200 psi (the big one is filled to 2640).... That pressure is too low to use directly to fill most PCPs, so I have to boost it.... By using a regulator, I can run the tank down to 125 psi, using 95% of the Helium in the tank.... You can purchase Helium in a 6000 psi, 513 CF tank, but they are a heavy beast, and unless you want to return the tank 3/4 full of expensive Helium, you still need a setup like this to use most of the gas in it.... I'm looking forward to getting my SCBA tank and trying this setup out....

Bob

13
Airgun Ammo / Inventory Run 245-75-FN at NOE
« on: June 26, 2017, 08:24:27 AM »
This 75 gr. 6mm / .243 cal. bullet is now in Inventory Run at NOE.... Once 5 are signed up, they will be run again....

http://noebulletmolds.com/smf/index.php/topic,2146.0.html



Lyman HP pin is available in one cavity, and you can get GC or PB versions.... Most airgunners prefer the GC version (shown)....

Bob

14
Airgun Ammo / Inventory Run 245-46-FN at NOE
« on: June 26, 2017, 08:19:30 AM »
The 6mm / .243 version of the venerable 225107 is now in Inventory Run at NOE.... Once 5 are signed up, they will be run again....

http://noebulletmolds.com/smf/index.php/topic,2147.0.html



Lyman HP pin is available in one cavity, and you can get GC or PB versions.... Most airgunners prefer the GC version (shown)....

Bob

15
Airgun Tanks, Compressors and Filling / Three 500 cc Tanks
« on: June 23, 2017, 04:23:31 PM »
I just received my 300 bar, 500 cc tank from AliExpress today.... I'm very impressed, with both the tank, and the service.... I already had two other 500 cc tanks, so I thought you would be interested in how they compare....



On the bottom is a 3000 psi tank, which weighs 1 lb. 10 oz.... In the middle is the new CF 300 bar (4350 psi), which weighs 1 lb. 5 oz.... On the top is a tank from England, rated at 250 bar (3625 psi), which weighs 1 lb. 13 oz.... The tanks are all sitting level at the bottom, so you can see the difference in length on the left side of the photo.... The 3000 psi tank has 5/8"-18 NF threads, while the other two use 18mm x 1.5mm threads.... They are all 60mm diameter....

Bob


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