by B.B. Pelletier

Update on Tom/B.B.: Things are really popping at the hospital, as they make their final moves to send Tom home. We still don’t have a discharge date, but it appears to be imminent!

Today, we have a guest blog. Airgunner Paul has written for us before, and I think you’ll enjoy his foray into the world of bulk-fill CO2 with the Benjamin Katana. Summer’s here, and that’s the perfect time for using this gas.

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Take it away, Paul!

The Benjamin Katana: Most people will run it on high-pressure air. After reading Paul’s blog, you might want to try your gun on CO2.

The Benjamin Katana is the fourth PCP rifle released by Crosman. It follows the Discovery, Challenger and Marauder. Of the three high-power rifles, the Katana happens to be my favorite: it’s more compact than the Marauder, it’s a single-shot, and it has a nicer trigger and stock than the Discovery.

B.B. has already gone into detail about the development and performance of the Katana in a previous posts. One nice feature of all the Crosman PCPs is that they’re dual-fuel — capable of using CO2 as the power source. There’s a distinct lack of information on how the rifles perform using CO2; most of what you can find is “many more shots using CO2.” Since it’s getting warmer, I thought this would be a good time for some testing.

I was primarily interested in determining three things:

  1. How many shots per fill does CO2 provide?
  2. What’s the performance loss with CO2?
  3. Is there any accuracy difference between using high pressure air and CO2?

Questions one and two are easy to answer. Question three is a mixed bag.

Why use CO2?
The Katana requires only 2,000 psi fill pressure and is easy to fill with a hand pump. Since it operates at a lower fill pressure than most PCP guns, you’ll get more fills from a 3,000 psi scuba tank than many other PCPs. So, why would someone shoot with CO2? Lots of reasons! Not everyone is physically able to use a hand pump. Pumping when the weather is hot and humid isn’t fun, either. Dive shops aren’t readily available in lots of areas, plus scuba tanks can be quite expensive. You could easily pay 2x the price of the Katana to buy a scuba tank along with all the fittings.

On the other hand a 20-oz. CO2 tank is very reasonably priced and can be refilled for five or six dollars. An adapter is required to connect the source tank to the Katana. The equipment to shoot the rifle with CO2 is much cheaper than the most inexpensive scuba tank, and you’ll have money left over for pellets and CO2 refills. For us incurable experimenters, it’s something new to test.

Filling the Katana
Before filling the Katana with CO2, all remaining air pressure must be exhausted. This can quickly be done through dry firing. When the tank is empty, cock the rifle to relieve any tension on the exhaust valve, put the safety on, connect the tank using the adapter and charge the rifle. As the CO2 will generate around 900 psi, you’ll use a different area of the pressure valve.

Since CO2 operates at a lower pressure than air, the Katana’s manometer includes a separate CO2-calibrated area. Here, the gun is full.

Shooting with CO2
With a good fill, the Katana will deliver around 60 shots at a very consistent velocity. A 20-oz. CO2 cylinder should be good for about 600 shots; this gives a nice, low per-shot cost. When the liquid CO2 has been consumed, the pressure gauge will fall to about halfway through the green CO2 area; and the velocity will drop 5-10 fps per shot for several shots and then really start to deteriorate. The Katana is also noticeably quieter using CO2 vs. compressed air. After refilling with a hand pump after every 25 shots, it’s nice to take 50 shots and have the pressure gauge not move at all!

Depending on the pellet, the velocity is anywhere from 18 to 27 percent lower using CO2. This still produces about 14 to 15 ft-lbs of muzzle energy, which is plenty for hunting within the appropriate limits. Heavier pellets tended to produce better muzzle energy than lighter ones.

The following table lists the velocities and extreme spreads (ES) with pellets that were tested with both compressed air and CO2. It’s interesting that the velocity spread for each pellet was very close between air and CO2. Pellets that have a low ES on air generally have a low ES on CO2.

Pellet Weight Air FPS Air FtLbs Air ES CO2 FPS CO2 FtLbs CO2 ES
Beeman Crow Magnum 18.2 781 24.7 11 625 15.8 8
Beeman FTS 14.6 848 23.3 12 645 13.5 10
Beeman Kodiak 21.1 720 24.3 8 594 16.5 8
Beeman Silver Arrow 17.1 776 22.9 11 646 15.9 4
Crosman Premier 14.3 854 23.2 11 666 14.1 9
Crosman Premier HP 14.3 855 23.2 14 665 14.0 13
Eun Jin Domed 28.4 613 23.7 6 491 15.2 5
Gamo Hunter 15.3 840 24.0 10 660 14.8 11
Gamo Match 13.9 865 23.1 9 638 12.6 10
Gamo Round Ball 15.4 810 22.4 16 602 12.4 10
H&N Match 13.6 870 22.9 10 642 12.5 10
JSB Exact RS 13.4 878 23.0 7 690 14.2 8
JSB Exact 15.9 815 23.5 8 659 15.3 5
JSB Exact Heavy 18.1 767 23.7 5 630 16.0 5
JSB Monster 25.4 655 24.2 6 539 16.4 15
JSB Predator 16.0 808 23.2 4 661 15.5 6
JSB Straton 15.8 821 23.7 17 671 15.8 4
RWS Hobby 11.9 900 21.4 14 680 12.2 17
RWS Meisterkugeln 14.0 878 24.0 16 665 13.8 6
RWS Super Dome 14.5 848 23.2 5 671 14.5 5
RWS Super-H-Point 14.2 845 22.5 2 674 14.3 7
RWS Super Point 14.5 842 22.8 17 670 14.5 12
Skenco Big Boy 26.2 656 25.0 5 539 16.9 6

With the right pellet, the Katana can be very accurate. A number of people have reported groups around a half-inch at 50 yards. I’ve been able to shoot several 5-shot, 0.60-inch groups at 50 yards with the Beeman Kodiak, Beeman FTS and JSB Monster pellets. In general, accuracy with an individual pellet was nearly identical for air and CO2. A few pellets were noticeably more accurate using CO2, and one was worse.

The 11.9-grain RWS Hobby is the only wadcutter that showed improved accuracy using CO2. The group size dropped from 2.19 inches on air (left) to 1.23 inches on the CO2 (right).

The 14.2-grain RWS Super-H-Point improved from 1.10 inches (air) to .75 inches (CO2). In both cases, this pellet tended to string horizontally.

The 15.8-grain JSB Straton pointed pellet produced a 2.00 inch group on the left using air and improved to 1.32 inches on the right using CO2.

The 18.2-grain Crow Magnum is the one pellet that performed markedly worse using CO2. Most of the holes in the CO2 target on the right showed evidence of the pellet tipping (keyholing); this is probably due to the reduced velocity.

Using CO2, the 25.4-grain JSB Monster pellet produces groups like this nice .45 inch sample.

The 21.1-grain Beeman Kodiak (H&N Barracuda) pellets repeated their winning behavior using CO2 and gave nice groups, like this .34 inch group (as long as I did my part).

Final comments on accuracy
At 25 yards, the following pellets all grouped in less than an inch: Beeman FTS, Beeman Kodiak, Eun Jin, Gamo Hunter, JSB Exact, JSB RS, JSB Exact Heavy, JSB Predator, JSB Monster and Skenco Big Boy. All gave nearly identical group sizes on both air and CO2.

At 50 yards, I couldn’t do better than about 1.25 inches with the Kodiaks. I assume this is due to the reduced velocity resulting in a longer flight time and reduced spin stabalization. It looks like CO2 will limit your effective range on small targets. On the other hand, hitting soft drink cans at 50 yards is still easy with the Kodiaks. A couple of other pellets were tried at this range, but all gave groups of 2 inches or more.