Check out Hard Air Magazine!

11 July, 2012

Outstanding Test Report and Review of QB78 Deluxe Air Rifle

This post was written by Vance Purdy, an Archer Airguns customer. Vance read the QB78 test report that I published on our site some years ago and was inspired to conduct his own tests of a QB78 Deluxe air rifle. In my opinion, Vance's testing is the most comprehensive that I have ever seen and his scientific methodology is clearly outstanding. It's a great test report.

Among the highlights is his proof that his QB78 Deluxe has the inherent accuracy to place 120 shots inside the area of a Dime at 10 metres! If only we could all shoot that well!!!

The following are Vance's own words, data, photograph and charts...

This test is similar to the one entitled "QB78 Airgun Technical Data and Info" except that it uses a new QB78 Deluxe air rifle in 0.177 caliber. The air rifle is serial number 10600788, with no modifications except an Archer Airguns-installed Hammer Debounce Device ("HDD"). The testing and writeup was done by a customer (& retired engineer) who enjoys doing this sort of thing.

The bottom line is that this recent (May 2012) air rifle performs very much like the older 2002 model. The differences can be attributed to the different aiming method, different caliber, installed HDD, and higher test temperature.
The test was undertaken as follows:

1. The gun was loaded with two fresh "powerlets" and fired for 70 shots using RWS Meisterkugeln 8.24 grain wadcutter pellets.
2. Pellets were used as-is from the tin. No sorting or lubrication.
3. The muzzle velocity was measured for every shot (Shooting Chrony, Alpha model)
4. The Point of Impact (POI) was measured for every shot**
5. The standard deviation of the velocity, muzzle energy and accuracy were averaged every 10 shots.
6. The test was repeated the next day using a second set of Powerlets.
7. All the data was recorded in a computer spreadsheet and graphed to provide the results you see here.

** shots were aimed using a laser, telescope, and rifle clamping mechanism that allows very fine control over the aiming point. One shot per bullseye was fired, and the POI measured using a computer scanner and OnTarget software. Range is "10 meters", 368 inches from muzzle to target. Indoor / no wind conditions, temperature ~73F. 100% of the shots taken were counted (no "fliers").

The first graph shows the muzzle velocities of every shot.

General behavior is very similar to the 0.22 caliber results. Typical value with this ammo and CO2 temperature is ~650 fps.
CO2 rifles will suffer more shot to shot inconsistency as the CO2 runs out. If we take the shots in groups of ten and compute the velocity standard deviations, we can plot the results as shown below.

Again, the results are very similar to those from the 0.22. Consistency is excellent through shot number 50, then begins to fall off as the CO2 depletes.

The next graph shows the calculated average muzzle energy for groups of 10 pellets.

Muzzle energy is quite consistent through shot 50, then begins to fall off. Note that the energy of this 0.177 QB78 is higher than the 0.22 version: 8 vs. 6.5 ft-lbs. Much of this difference can be attributed to the installed Hammer Debounce Device (HDD), which significantly increases muzzle energy. Also, some of the difference is due to the higher test temperature used for the 0.177 rifle here.

The graph below measures accuracy in the same manner as the 0.22. The value is the center-to-center group size for each group of 10 shots, expressed by adding together the vertical c-t-c span and horizontal c-t-c span measurements.

Once again, the result is very similar to the 0.22, in that each ten shot group stays tight through shot number 60, and then degrades.

The typical value for this 0.177 rifle is about 0.4 inches, and for the 0.22 rifle the typical value was about 1.5 inches. However, this large difference is NOT what it looks like. The testing on the 0.22 rifle was done using open sights, and shows the results a typical marksman might expect. The testing on the 0.177 rifle used a laser, telescope, and clamping platform so that each shot was extraordinarily well aimed when released. The 0.177 accuracy measurement is more like the ultimate capability of the rifle itself. Few real world shooters would get this result under normal shooting conditions.

The graph below shows the virtual group -- 120 shots, all shown as if fired at the same target. (Note that this chart should be circular, it became squashed in rendering for the web - Stephen Archer).

It is interesting to see how the muzzle velocity changes the vertical point of impact. The graph below shows where the pellets hit, in the vertical direction, plotted against the muzzle velocity. The "tail" on the left side is from shots taken as the CO2 pressure runs out. The dashed line is theory, assuming the pellet drops due to gravity only, with no aero effects.

The pellet will hit about one pellet diameter lower when the velocity drops from the initial 650 fps down to ~550 fps. This happens around shot number 60. If we get even more precise, and demand only half a pellet diameter drop, we would use 600 fps as the cutoff. This happens around shot number 55.

Vance, thank you. All I can say is "WOW" for the efforts you have taken and your generosity in sharing these results with the airgunning community. Your testing clearly shows the excellent accuracy of which the QB78 Deluxe is capable!


About This Blog

This blog shares information, ideas and knowledge about air rifles. It compliments the information Stephen publishes on the Archer Airguns website, on YouTube and the Chinese Airgun Forum.

  © Blogger templates The Professional Template by 2008

Back to TOP