by Tom Gaylord
Writing as B.B. Pelletier

This is Part 13 of the Hiveseeker guest blog on the Crosman 2400KT. Today is titled Modding the Crosman 2400 family — Primer 2.

This is the most popular guest blog series we have ever published. The marketing folks over at the Crosman Corporation have got to be dancing in the streets!

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 13
Modding the Crosman 2400 family — Primer 2
By Hiveseeker

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9
Part 10
Part 11
Part 12

2400KT Part 12 cover photo
The 2400KT CO2 Air Rifle that I modded for this report is only available directly from the Crosman Custom Shop. It is shown here disassembled with a mix of stock and modded parts. For scale, the background grid on all photos is one inch square.

WARNING: These modifications can change the operation of a gun in ways it was not designed for. Non-factory or modified parts can fail, especially if subjected to higher pressures than originally intended. Pyramyd Air advises against making such modifications or conversions. This report is for information, only.

This report covers:

  • The mods:(1) Steel breech
  • (2) Power or boss valve
  • (3) Power adjuster and hammer spring
  • (4) Max flow transfer port

In Part 12 we provided an introduction to modding the Crosman 2240 family of CO2 guns. We are now ready to actually mod! I’ve ranked the difficulty of these mods from easiest (*) to hardest (*****), based primarily on how much disassembly is required. The gun I modded was the HiveSeeker II from Part 9, a 2400KT with 14.6-inch Lothar Walther .22 barrel. All velocity testing was completed with 14.3 grain Benjamin Discovery Hollowpoints. Temperature was 84 to 88 degrees F for all testing, except for the extended hollow bolt probe which was tested at 76 to 78 degrees F.

2400KT Part 13 steel breech
The Crosman steel breech comes standard on the 2400KT and a number of other Crosman CO2 guns, but can also be purchased separately. You can see here that the breech screw remains hidden under the retracted bolt, a big difference from the 2240.

The mods: (1) Steel breech

Difficulty **
Cost: $40 or included with 2400KT, 2300KT, 2250, 2260MB, 2300S, 2300T
I’m going to start with the Crosman steel breech first because this mod arrives already factory installed on all 2400KTs. It provides a slot for the Crosman LPA MIM Rear Sight, and a dovetail rail for various open sights and scopes. Anyone who has made do with the Crosman 459MT Dovetail Intermounts for years like I did — though they certainly work — will really appreciate the solid steel breech! The 2300KT in the Custom Shop also comes with a steel breech, and offers short and long versions. This is one of the main differences between the Crosman 2240 and the rest of this CO2 family, and is one of the first upgrades to consider on that gun.

2400KT Part 13 valve
Shown here are the Aftermarket High Performance Power Valve from Alliance Hobby (top right), and the Crosman power valve (disassembled at bottom). The arrow in the inset points to the angled exhaust port on the Alliance Hobby power valve, compared with the straight port on the Crosman power valve immediately below it.

(2) Power or boss valve

Difficulty ***
Cost: $60 or included with certain 2400KTs
I completed the power valve mod next, and it gave me the velocity to which I will be comparing all the subsequent mods. We saw in Part 9 that my HiveSeeker II shipped with what I call the Crosman target or standard valve, giving me a velocity of only 434 f.p.s. This was 124 f.p.s. less than my HiveSeeker 2400KT which was ordered identical except for an 18 inch barrel. I had a valve equal to the one in my HiveSeeker installed in the HiveSeeker II, and got 522 f.p.s. — almost 90 f.p.s. faster!

But this velocity came with a price. If you spend more CO2 on f.p.s., you have less left in your wallet for shots per fill. I got more speed, but my shots per fill dropped sharply from 60 to 25. This matched reports I found online that the Custom Shop power valve adds 10-20% in velocity (21% in my specific case) but cuts the shot count in half. Another way of looking at this is that it will now cost me twice as much to shoot this gun. Most modders, however, are quite willing to pay this price. In some extreme examples I read about mods that granted even higher velocities, but got only 10-15 shots per CO2 cartridge! I also noticed that the report of my HiveSeeker II was much louder with the power valve than it was with the target valve.

So as you can see, not all 2400KTs ship with the same valve. Unfortunately the Crosman valve swap I just mentioned is not commercially available. So how do you get a power valve? There are two ways: Based on my own purchases, ordering a 2400KT with an 18-inch or 24-inch Crosman barrel gets you the power valve. However, my 2400KTs with 14.6 inch Lothar Walther and 10.1 inch Lothar Walther barrels shipped with the lower velocity target valve.

But what if you want a Lothar Walther or short barrel? The other way to get a power valve is to buy an after-factory power valve or so-called boss valve. These are readily available on eBay and from various online mod vendors. These valves are often modified with thinner walls and fewer screw threads to create a larger internal reservoir of CO2 for each shot — more CO2, more velocity! Many also incorporate an angled exhaust port so that CO2 flows more directly from the valve into the barrel. (See the arrow marking the angled exhaust port in the aftermarket valve in the photo. In the Crosman valve below it, the CO2 has to come straight up the exhaust port and make a 90-degree turn as it enters the barrel).

I purchased the Aftermarket High Performance Power Valve from Alliance Hobby, a reputable eBay vendor that sells a wide variety of mods. When I tested this valve I got a marginal increase to 525 f.p.s. (3 f.p.s. over the Crosman power valve), but also gained about 5 shots per fill. So to be a little redundant — but this is important! — certain Crosman 2400KTs ship with a legitimate power valve factory installed. Considering that the Crosman power valve does not appear to incorporate the internal alterations that the aftermarket valves do, I’ve developed an even deeper appreciation for Crosman engineers and the velocity they can squeeze from the 2400KT.

Pro tip: Crosman Customer Service informs me that the Lothar Walther barrels are sometimes in short supply and not always available for standalone purchase. If you want a Lothar Walther barrel I recommend that you order it with your Custom Shop gun (and forego the Crosman power valve) rather than trying to buy the barrel separately. Between the barrel and the valve, the valve will be easier to buy aftermarket.

2400KT Part 13 valve graph
The velocity curves (starting from bottom) for the Crosman target valve, Crosman power valve, and Alliance Hobby (commercial) Aftermarket High Performance Power Valve. The Crosman power valve provides a significant velocity increase of 90 f.p.s., but at a cost of half the shots per fill. The Alliance Hobby power valve gave only a 3 f.p.s. increase over the Crosman power valve, but provides about 5 more full power shots per fill.

If you choose to modify a valve yourself, exercise caution when disassembling it. Some force may be required to unscrew the valve body and chamber plug. Most modders use vise grips and pliers, with some padding such as rubber garden hose to protect the parts from the teeth on the tools. Do not over-tighten the vise grips!

Also, be aware that modders have documented that valve springs having the same part number on different Crosman part lists are sometimes actually different. Some of these modders have achieved higher velocities or more shots per fill simply by varying the combination of hammer and valve springs, or by modifying the springs themselves by cutting off coils. It is possible that the Crosman power valve differs from the target valve only in the valve spring and/or hammer spring. When using a power adjuster (see below), an internal valve spacer such as in the 2300S can influence velocity at either the high or low end of the velocity scale. As you can probably tell, of all these different parts the valve is by far the most complex!

A concluding comment on valves: As I researched the 2400KT on various modding sites, I came across diverse and sometimes contradictory information about this gun. Reported velocities varied, and identical mods that worked on one 2400KT would do nothing for another. I think the source of most of this contradiction is the different valves that ship, unmentioned and undocumented, within the 2400KT line. I completely understand the value and role of a target valve and a power valve. But I wish there was more transparency in the Custom Shop as to exactly what valve you’re buying when you place your order, and the opportunity to make an informed choice.

2400KT Part 13 power adjuster
From top to bottom are the stock tube plug, hammer spring, and hammer (first row); the Crosman 2300S Pressure Adjust Assembly which includes spring and spring guide (second row, note that the black spring guide actually goes inside the pressure adjust barrel on the opposite end of the spring from shown); and Benjamin Discovery hammer spring (third row).

(3) Power adjuster and hammer spring

Difficulty *
Cost: $30-$35 for power adjuster, $10 for hammer spring
This is the easiest mod of all and a good start for the beginner. All you need to do is remove two screws and the tube plug. The hammer (or striker) in a CO2 gun strikes the valve stem, causing it to release CO2 to propel the pellet. A tighter or stronger hammer spring makes the hammer hit the valve stem harder, causing it to remain open longer, release more CO2, and push the pellet faster. An extremely popular mod for controlling this is to replace the tube plug with a Crosman 2300S power adjuster that lets you fine-tune the hammer spring tension (Crosman 2300S Pressure Adjust Assembly, part 2300-124). However, when I tried this using the original 2400KT hammer spring, I got velocities that varied between 507 and 520 f.p.s., all below my base velocity of 522 f.p.s. I suspect that some of these power adjuster settings would provide more shots per fill, but I was strictly after more velocity and did not test this. This mod did not work for me.

Another popular mod in this category is a heavier hammer spring, for the same potential velocity increase outlined above. One that is often used is the Benjamin Discovery Air Rifle hammer spring (part 2261-009). When I tried this spring with the Crosman 2300S power adjuster, it seemed to produce too much tension even at the lowest pressure setting. It was very hard to cock! Velocity testing provided only 509 to 517 f.p.s. across the full range of adjustment. When I was finished testing and tried to remove the CO2 cartridge, it would not come out. The heavy hammer spring had forced the valve stem so deep into the CO2 cartridge that it got stuck! I had to fully disassembly my 2400KT to remove it. When I researched this, I found reports of others experiencing the same problem. This was another mod that did not provide a velocity increase.

Pro tip: To reassemble, you will need to pull the trigger in order to slide the hammer, hammer spring, and tube plug or power adjuster in place.

2400KT Part 13 transfer port
Shown in the center of the photo are the Max Flow Transfer Port Bushing (top), stock Crosman transfer port (middle), and breech gasket (bottom). The inset better shows the larger reamed opening of the Max Flow Transfer Port at top.

(4) Max flow transfer port

Difficulty **
Cost: $15
I told you earlier that there is usually no free lunch in modding, but here’s one that does not have any trade-offs! The transfer port (or sleeve, part 1322A026) is the narrow passage through which CO2 flows from the valve exhaust port into the barrel. A modified transfer port is usually a stock Crosman part that has been reamed out to a wider inside diameter, allowing CO2 to flow more freely into the barrel to provide more velocity. I purchased the Max Flow Transfer Port Bushing from Alliance Hobby on eBay. This one sounded like a no-brainer and I was fully expecting at least a modest velocity increase. Nope — this did not provide any improvement, yielding the exact same velocity (525 f.p.s.) as I was already getting with the commercial power valve. I would have bet money this one would work — and would have lost!

2400KT Part 13 transfer port install
Pro tip: When reassembling, the longer and slightly wider end of the transfer port goes up, into the steel breech. The narrower, shorter end seats into the breech gasket resting in the main tube. Tightening the breech screw while maintaining good alignment of the transfer port top and bottom was one of the trickier operations I encountered during my modding efforts.

That wraps up the modding for today. The final installment will cover 6 more mods, and some last words about the Crosman 2400KT CO2 Air Rifle!