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Power limits, the magic number
15 May 2018, 19:34,
#1
Power limits, the magic number
Been doing a lot of research for the past couple f weeks due to the new need for education in matters that have changed over the past 55 years.

One of those discoveries has been the world of information and data base materials on power and trajectory of airguns.

Both Pyramyd Air and the Hawk Optics company offer several on line resources. Hawk even offers a set of ballistic tables where you punch in your pellet weight, pellet speed and shape and the computer will generate a drop table at all ranges from the muzzle out to whatever you want. Zero the scope, tape the chart to the butt-stock and you do not even have to remember all those tiny little numbers and where to use them.

One of the things I have discovered while searching the sites and playing with the computer options is that when using air guns there is a magic number for velocity.

That number is 671 FPS.

At 671 fps the weight of the projectile is equal to the energy it produces.

12 grain pellet at 671 gives 12 ft/lb energy
10 grain pellet at 671 gives 10 ft/lb energy and so on....

That might not sound too important to the .177 shooter using an 8 grain pellet at 800 fps but it is pretty important to the shooter of a .22 that is smack onto that number or wanting to approach it closely without going over.

Since TPTB pretty muck control the power, all the shooter can do is monkey with the numbers to find the pellet that gives the most energy at the speed it can obtain. Without the proper reference materials and data to input one is like a blind man at the shooting gallery.

I have also discovered a great world of electronic devices available to the air gunner that were not available back in the 1960s! Imagine that!

One item is a chronograph that hangs from the muzzle of the gun and gives an instant read of pellet speed. It will fit in the pocket and is cheaper than a stand alone bench mounted chronograph.

https://www.ebay.co.uk/itm/Combro-CB-625...2463773323

With the current price of air guns being what it is the investment in this small and handy device should be a part of the purchase considered. After the initial purchase it can be used on any air gun one purchases or has floating around in the family.

While most manufacturers offer some velocity number as a sales ploy, they never tell the buyer what pellet was used, or what the velocity will be with any array of pellets available at the local shop. All you can be sure of is that the newly bought rifle is under 12 pounds limit with anything you put into it. That is not much information, and not comforting in any respect.

A little device like this, along with a free piece of computer software will remove all doubt that goes beyond "good enough". Sometimes it is not "good enough", or not nearly as "good enough" as one thinks it is.
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22 May 2018, 15:41,
#2
RE: Power limits, the magic number
That magic number 671 fps works very well for specialized low-noise small game cartridges we sometimes call "cat sneeze", for their mild report when fired in a rifle.

Over the weekend I fired some antique rook rifles which were rescued from the UK before they were butchered into shotguns, and many surviving specimens have been, being converted to .410 bore so that they could remain legal.

One was a Cogswell & Harrison in .380 Rook, which was rechambered to use .38 Special target wadcutter ammunition. The other was an Army & Navy in .450 revolver, which shoots .455 OK.


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73 de KE4SKY
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"Almost Heaven" West Virginia
USA
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