by Tom Gaylord
Writing as B.B. Pelletier

Today we have something special. This is Part 10 of an ongoing guest blog from reader Hiveseeker, but his report today is so big that I had to break it onto two parts. The second part of this report will run tomorrow as Part 11. He continues to research this subject that fascinates both him and many other readers.

This is about the Crosman air rifle he really enjoys. If you’d like to write a guest post for this blog, please email me. Now, over to you, Hiveseeker.

Crosman 2400KT CO2 Air Rifle – Part 10
The great Crosman 2400KT barrel shootout
By Hiveseeker

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9

This report covers:

  • Barrel variable
  • Barrel challenge
  • Why only .22?
  • The great 2400KT barrel shootout
  • 24-inch barrel — 13 foot pounds!
  • 7.5-inch barrel
  • 10.1-inch barrel
  • 14.6-inch barrel
  • 18-inch barrel
  • That’s it for today

Crosman 2400KT
Meet the Chimera! It is a Crosman Custom Shop 2400KT CO2 Air Rifle with 24” Crosman .22 barrel and shoulder stock. Cost as shown was $108 plus $24 shipping. This gun was named after a mythical Greek monster that was a motley assembly of different animal parts. That’s exactly what I plan to do with this gun and an assortment of barrels!

In this blog we will take a detailed look at how barrel length affects velocity in the Crosman 2400KT CO2 Air Rifle . However, this information should apply equally to modding a Crosman 2240, 2250, Sheridan 2260 MB rifle, or 2300KT. From my research, all these barrels should be interchangeable. Note that all these velocities were obtained using the Crosman Custom Shop power valve, which adds about 90 f.p.s., compared to the standard Crosman valve.

Barrel variable

When you purchase a 2400KT from the Crosman Custom Shop, the single most important choice you make is the barrel. While you can choose from a wide selection of grips, muzzle brakes, trigger shoes, and sights, the barrel is the only option that affects how the gun actually performs. And, as we uncovered in Part 9, it also influences which valve the Crosman Custom Shop installs in your custom gun.

I was surprised when my original two 2400KTs — a .177 and a .22 — had identical velocities. A .22 pellet is twice as heavy and shouldn’t be traveling the same speed! Several blog comments attributed the high .22 velocity to that gun’s 18-inch barrel. That’s certainly part of the equation, but all my research indicated it was more than that, and in Part 9 we found that an extra powerful Custom Shop valve in that gun was adding 90 fps. This extra boost appears to be enough to make one 2400KT shoot a .22 pellet just as fast as another 2400KT shoots a .177 pellet . But the comments were also correct: In a CO2 gun a longer barrel adds velocity. The question was, how much?

Barrel challenge

I spent weeks scouring numerous Crosman fan and modding sites for barrel length and velocity data on the 2400KT . I quickly found that few modders are interested in posting stock velocities. What little stock data I could find usually compared only two barrel lengths, or was for .177. And, as other forum browsers also noted, data from different sources was sometimes inconsistent or even contradictory. I did find some thorough test data on the stock Crosman 2240 in a GTA (the old Gateway to Airguns ) forum post on 6 different barrel lengths for the 2240. However, I still needed to know what the power valve could do in the 2400KT.

I finally realized that I would need to get my own answers. I happily relented and ordered a 2400KT with a 24-inch Crosman .22 barrel, the maximum available length. That’s the gun pictured above. A second order of parts added every Custom Shop .22-caliber barrel I didn’t already own. When my boxes arrived and the dust settled, I was ready to start swapping barrels and testing velocities!

Why only .22?

By far the primary reason Crosman owners mod their guns is to increase velocity. Most are trying to increase velocity in order to hunt. All other factors being equal, the same CO2 gun will generate more muzzle energy (hunting power) with a .22 pellet than with a .177 pellet. I therefore limited the focus of my testing to the maximum achievable muzzle energy, and that meant staying with .22.

Here is the Chimera with installed 24 inch barrel, and the 14.6 inch, 10.1 inch, and 7.5 inch barrels I ordered for testing. I was ready to roll!

The great 2400KT barrel shootout

I ordered the Chimera with the 24 inch Crosman .22 barrel, but I also purchased and installed 14.6 inch, 10.1 inch, and 7.5 inch Crosman .22 barrels for testing. I already had data for a Crosman 18 inch .22 barrel on another functionally identical 2400KT.

I ended up doing all my velocity testing with the Benjamin Discovery Hollowpoint. It’s a 14.3-grain middleweight, a Crosman pellet that works well in many Crosman guns, and when I velocity tested five different Crosman pellets in my first 2400KT this one landed right near the middle as a good representative.

Below are the velocity curves from these stock Crosman barrels. All testing was completed at 84 degrees F using the Chimera, except for the 18 inch barrel for which I already had data at 88 degrees F from another 2400KT. (Be aware that CO2 velocities will be slightly lower at cooler temperatures. Detailed testing by Stephen Archer found that for .22 guns velocity can vary 1.8 to 2.0 fps for each degree F.) I waited 90 seconds between shots to allow the CO2 cartridge and gun to warm back up, which yielded slightly higher velocities and also better simulated hunting conditions, where shooting opportunities usually do not occur in rapid succession.

barrel graph

The first thing to notice about this graph is how similar in shape all the velocity curves are (except for the 24 inch barrel — hold that thought). Although the velocities obviously vary, the performance curve was very consistent from one barrel to the next. All the barrels gave about 20 to 25 full power shots before velocity began to drop. The velocity lines stop at 400 fps because I found that, below that velocity, accuracy decreased rapidly and there was no practical reason to test further.

The second thing to notice I’ve already mentioned — the velocity of the 24 inch barrel drops off more steeply than the others. I believe this barrel is long enough that, once the CO2 starts to become depleted, barrel friction begins slowing the pellet down quickly, giving a steep but almost perfectly straight slope. The other barrels are too short to exert a similar effect above 400 fps.

24 inch barrel — 13 foot-pounds!

I’m going to start out of order with the longest barrel, and tell you about my first test on the stock Chimera as it arrived out-of-the-box with the 24 inch Crosman barrel. This gun surpassed all my expectations! The Chimera clearly shipped with what I call the power valve, the more powerful of two different valves that the Custom Shop uses. (See Part 9) From my own purchases, 2400KTs with 18-inch and 24-inch Crosman barrels ship with the power valve, and 2400KTs with Lothar Walther barrels ship with the lower velocity target valve.)

For the first 10 shots I got an average velocity of 617 fps with the 14.3 grain Benjamin Discovery Hollow Point. At this velocity the barrel generated a muzzle energy of 12.09 foot-pounds, which just meets the minimum recommended 12 foot-pounds for hunting (see The advantages of hunting with an airgun).

This velocity actually exceeded B.B.’s Crosman 2240 conversion to air, in which he got 588 fps with the identical-weight 14.3-grain Crosman Premier using a 14.5 inch barrel. But you have to go to ridiculous (barrel) lengths to beat it!

In CO2 guns heavier pellets usually generate higher muzzle energy, and when I tried the 25.39 grain JSB Exact Jumbo Monster I got an average velocity of 485 fps and 13.25 foot-pounds! This appears to be the maximum performance limit on a stock Crosman 2400KT, which does make this gun a hunter. This barrel was too long to be practical for my needs, but I sure was sad when it was time to remove it!

7.5 inch barrel

The 7.5 inch barrel was LOUD — a sure sign that excess CO2 was being wasted. I actually had to wear ear protection when shooting indoors! Average velocity for the first 10 shots was 464 fps, close to the listed spec of 460 fps for the Crosman 2240 which has the same barrel. Considering that the Chimera has the power valve but here gets less than 30 shots over 400 fps, you know that much of the CO2 is only going toward making noise.

7 inch barrel
Well, you can see why the 7.5 inch barrel is not offered in the 2400KT line! This was a 2300KT barrel, but from what I had read all the Crosman CO2 gun barrels are interchangeable.

These numbers also give us the maximum velocity spread on our barrel test right up front: 153 fps over a range of 16.5 inches of barrel length. This was MUCH more than I expected! Crosman Customer Service had told me to expect about a 50 fps spread across all the available Custom Shop barrels. B.B. found an almost identical 52 fps spread in his report, How barrel length affects velocity in a CO2 rifle. However, this range of barrels — 7.5 to 24 inches — is not actually available on any one gun in the Custom Shop. The 2300KT offers 7.5 to 14.6 inch barrels, while the 2400KT offers 10.1 to 24 inch barrels. And B.B.’s test covered 13 to 20 inches of barrel length. It makes sense that testing a wider range of barrel lengths will yield a wider range of velocities. In particular, including the 7.5 inch barrel and the 24 inch barrel at the extreme ends of the scale increased the total velocity spread by a full two thirds (51 fps and 59 fps respectively, as you’ll see shortly). So that’s the reason for such a broad velocity spread. Subtract the two extreme barrels, and the velocity spread drops to 43 fps — pretty darn close to what Crosman told me and to what B.B. found. These numbers are important, and we’ll discuss them in more detail after we cover the rest of the barrels.

10 inch barrel
Although I’m showing you the 10.1 inch barrel now, this actually ended up being the final form of my Chimera: A compact pistol plinker with significantly more power than a 2240. I swapped the shoulder stock for 2240 pistol grips and installed a red dot sight.

10.1 inch barrel

This was actually the barrel that I tested last, and it represents the final phase of my morphing Chimera. This barrel was a little louder than all the others except the 7.5 inch barrel, again an indication that CO2 is being wasted. However, noise was only moderately loud when shooting outdoors and I actually think the ported muzzle brake helped reduce it. With this barrel velocity jumped to 515 fps, a 51 fps increase over the 7.5 inch barrel. Even though I know that I’m still wasting CO2, this barrel gives me about 25 full power shots over 500 fps and a total of almost 35 accurate shots over 400 fps. With a red dot sight dropped on top, using UTG 11mm to Weaver adaptors, this is my fun backyard plinker which has a significant velocity boost over a 2240. Note that the shoulder stock was replaced with 2240 pistol grips.

14.6 inch barrel

This barrel produced a moderately loud report and provided a velocity of 543 fps, a 79 fps increase over the base 7.5 inch barrel. For many shooters, this will be the maximum practical barrel length, especially if you order your 2400KT with pistol grips rather than a shoulder stock.

18 inch barrel

The data shown for the 18 inch barrel is from my original HiveSeeker which you have seen regularly in my previous blogs. The gun is identical to the Chimera except for cosmetic color differences. However, it did behave slightly differently with a slow rise in velocity that you can see on the velocity curve graph above. This actually gave a higher average velocity for the second 10-shot string. I’m reporting the first and slightly lower 10-shot string to remain consistent, and also because it better simulates actual shooting conditions. You’re not going to pop off 10 blanks before you actually start shooting! This gave me an average velocity of 558 fps, a 94 fps gain over the 7.5 inch barrel.

That’s it for today

I had to break Hiveseeker’s report into two parts. The second part will post tomorrow as Part 11, so it will be as seamless as I can make it.

This is a monumental test he has done. Many readers have been asking for this kind of data and have been talking about it. I hope you readers appreciate what he is doing.