Wednesday, June 17, 2009

Fathers Day Gift for the Airgunner with Everything!

Richard Middleton's book, "The Practical Guide to Man-Powered Bullets", may make the perfect gift for the airgunner who has everything.





















While the book deals with catapults, crossbows and other man powered weapons a huge portion is dedicated to theoretical and practical information on both low-pressure and high-pressure airguns.

Many those chapters not directly dedicated to the discussion on airguns layout physics principles and experiments with direct application to the sophisticated airgunner. For instance Middleton's simple analogy's clearly illustrated the difference between muzzle energy and momentum with regards to on-target performance. He helps us understand the science behind why a heavy slow moving projectile that has 10 foot pounds of force versus a light projectile with more velocity and an equal 10 foot pounds of force have a substantially different terminal effect.

"Middleton's narrative is lively, humorous and full of exciting information and experimentation."

"He likes to test things for himself rather than to believe handed-down orthodoxies - an attitude not without its costs, some might add." Which is another way of saying that the furniture in his home has more than the occasional spherical impact mark and his garage has more than one or two holes in it's door.

If you or the person you are buying for is interested in constructing or modifying their own home-made airguns, this book is a must read.

Anyone with a general interest in airguns, blowguns and other man-powered weapons will find this treatise absolutely fascinating, will occasionally chuckle out loud during the read.

Printed by Stackpole Books in England, with a retail price in the US of $39.95, The Practical Guide to Man-Powered Bullets, By Richard Middleton is an absolute must read.

Until Next Time....

Sunday, June 14, 2009

Gamo P-23 Review Velocity PART II Velocity with Gamo Raptor, Match, Rocket, Hunters & other Gamo Pellets


This is a follow up to a post started sometime ago regarding Velocity of Gamo Raptors and other Gamo Pellets (plus Copperhead BB's) from the Gamo P-23 Pistol.

As you may know, the Gamo P-23 is a CO2 operated double action pistol. It is capable of firing .177 caliber round lead pellets and .173 cal. BBs semi-automatically. It also fires any .177 caliber pellet loaded individually into the tip-up barrel.

Part 1 of this P-23 Velocity Post, included testing with the Gamo .177 Match Pellet (7.7gr). This wadcutter pellet served as our control pellet displaying velocities as high as 417 fps, with most shots falling between 394 and 409 fps.

For part 2, we begin testing with another popular pellet as our control. The Crosman 7.9 grain, brown box, Premier, a pellet of known performance it serves as this weeks benchmark. As done previously shots were made 3 and 1/2 feet from the muzzle to the Alpha chronys 1st skys-creen/sensor.We observed the following velocities:

Crosman Premier (Domed) .177 cal, Highest Velocity Measured from Gamo P-23 is 424.3
Shot
Lo: 393.0 5 397.2
Hi: 424.3 4 393.0
Av: 407.2 3 410.8
ES: 31.22 2 410.9
SD: 12.24 1 424.3

Note: Cardboard Box - Premiers used, 7.9 gr.

Gamo Round Ball .177 cal. 8.2gr, Highest Velocity Measured from Gamo P-23 is 400.2 ft/sec.
Shot
Lo: 387.3
Hi: 400.2 4 382.2
Av: 393.4 3 387.3
ES: 12.94 2 397.9
SD: 6.46 1 400.2
Note: Shots were rapid fire from the magazine.

Gamo Hunters (Domed) .177 cal. 7.6gr, Highest Velocity Measured from Gamo P-23 is 448.4 ft/sec.
Shot
Lo: 424.5 5 424.7
Hi: 448.4 4 431.5
Av: 437.9 3 440.0
ES: 23.7 2 445.0
SD: 9.94 1 448.0

Gamo Magnum (Pointed) .177 cal. 7.9gr, Highest Velocity Measured from Gamo P-23 is 437.2 ft/sec.
Shot
Lo: 407.6 6 422.1
Hi: 437.2 5 407.6
Av: 424.4 4 420.9
ES: 29.6 3 422.4
SD: 11.18 2 436.4
1 437.2

Gamo Master Points (Pointed) .177 cal. 7.9gr, Highest Velocity Measured from Gamo P-23 is 433.0 ft/sec.
Shot
Lo: 405.3 5 405.3
Hi: 433.0 4 424.0
Av: 423.9 3 426.0
ES: 27.73 2 431.4
SD: 11.09 1 433.0

At this point I installed new CO2 cylinder lubed with a drop of Crosman Pelgun Oil then discharged a few shots before letting the pistol rest for a few minutes before continuing. Normally I expect at least 40-60 shots per cylinder. This time I put the new cylinder in just to be safe. When I saw the velocity drop in shot 5 above this was done in order to guarantee that reported Raptor Velocity did not drop from a lack of gas.

Gamo Raptor (Specialty) .177 cal. 5.4gr, Highest Velocity Measured from Gamo P-23 is 489.9 ft/sec.
Shot
Lo: 467.5
Hi: 489.9 4 467.5
Av: 475.8 3 489.9
ES: 22.35 2 477.0
SD: 9.94 1 469.0
Note: Light weight domed shaped pellet from non-lead alloy (PBA).

Gamo Rockets (Specialty) .177 cal. 9.6gr, Highest Velocity Measured from Gamo P-23 is 386.0 ft/sec.
Shot
Lo: 368.7 5 368.7
Hi: 386.0 4 384.7
Av: 379.6 3 372.8
ES: 17.34 2 386.0
SD: 8.36 1 385.9
Note: Rockets are a composite pellet with a steel shot pressed into the nose and a lead body.

Crossman Copperhead BBs (Premium) .173 cal. 5.1gr, Highest Velocity Measured from Gamo P-23 is 443.3 . ft/sec.
Shot
Lo: 390.1 5 390.1
Hi: 443.4 4 421.6
Av: 424.5 3 426.1
ES: 53.30 2 441.1
SD: 21.3 1 443.4
Note: Crosman Copper Plated steel bb.


RESULTS OF ALL TESTS:
As we should expect highest velocity was achieved by the Raptor at 489.00 ft/sec. Although it came at the expense of both accuracy and power.

Highest Velocity among the standard weight projectiles was the Gamo Hunter (Domed) at 448.4 ft/sec. The Magnum at 437.2 and the Master Point at 433, came in second and third both of these are 7.9 grain pellets against the Hunters 7.56 grain, so this is not a surprise.

Discussion:
There are two of items that I noticed or would like to discuss. For one , the pistol seems to deliver the first couple of shots at a higher velocity. This happens after a period of resting on it's side for a while (maybe 15-25 min.). And seems to happen for all pellet types.

Second, this kind of pellet velocity out of a barrel measuring less than 4.5 inches is a pleasant surprise. My sense was that this pistol did not shoot that fast out of the box. Unfortunately I didn't have I Chrony to test it then, but I'd swear it shoots harder now. Of course, Gamo had stated a velocity of 410 ft/sec., but I'd always suspected that number was for bbs. I was pleased to see the claim met with pellets as well. Given the velocities produced and the high number of shots produced per cartridge, the valve system seems to be well optimized. Since the pistol is pretty loud and there is often a discharge of vapor from the muzzle I doubt that the pistol could be modified from much higher velocities. Even if the modification were done at the expense of gas per shot/shots per cartridge.

Still it might be fun to try.

Until next time..


Thursday, June 4, 2009

Spring Gun Twang - Where did my grease go?

The is much talk about firing behavior in spring powered airguns. Some guns are described as smooth firing out of the box. Many rifles are described as exhibiting a fair amount of vibration and "twang" upon firing. The conventional wisdom is that the firing characteristics of these twangy rifles may be improved through tuning, by a competent tuner.

I also read a posting on another blog the other day, where an individual had described a great deal of twang in a rifle he just purchased and was told to keep returning it to the retailed until he got on that shot smoothly as it was generally known to be a smooth shooting rifle.

I happened to own one of the rifles in question and had always found mine to be remarkably smooth firing, so I tended to agree with the advice given.

A few days later, I got my own rifle out to shoot after it had been in storage for the winter and I noticed it had developed an incredible twang. The rifle had been stored standing barrel up with the action slightly open. And it had been stored in an area that gets pretty warm.

What happened to my rifle? Well about a year ago I had a similar experience with a springer that was stored in the trunk of a car for several days during the summer. As a result of the two experiences, I've come to develop the following theory.

AJ's Theory:

When some spring piston airguns are stored in certain positions and exposed to heat for a protracted period, the grease which lubricates the spring and piston is migrating away from it's intended area and pooling up somewhere. The result is an under lubricated spring and piston which is producing the increased vibration and twang. To test the theory on this rifle. I moved it to another location (although still very warm) and stood it on it's barrel (action closed, butt in the air) for about 72 hours. What do you know? Now it shoots as smoothly as it did a year ago.

If this theory about the spring lubricant migrating during storage is accurate, the next question becomes how should they be stored.

In an ideal world all airguns would be stored in a cool and dry environment. Unfortunately that does not always happen. Manufacturers, distributors, retailers and frequently the owners are sometimes forced to store them in areas that are warmer than we would like. Also, many of the commercial groups are storing large quantities (sometimes boat loads) and tend to store rifles on one side for months on end. I've truly come to believe that this is part of the explanation for variance in some "stock" rifles.

Without any real knowledge coming from the manufactures, it is my guess, that a springer which is stored horizontally in a shooting orientation (sites on top, trigger on the bottom) will be less likely to be effected by this phenomena (if that is really what's going on here.)

Please feel free to post your thoughts on the matter.

Until next time...