Building a 2400kt for grandson What fps can I expect with mods?

[Gibsonvair]

I have a pile of parts and I am waffling between a 14.6" and a 18" barrel in .22 caliber. Will opening up the barrel port and transfer ports give me a little extra FPS? I could also port and/or enlarge the valve if that would help increase the speed and power. I used the old 2400kt to build a pcp and it makes 25 ft/lbs with a 14.6" barrel as a PCP. The extra power really helps with the trajectory and knockdown power on squirrels. I did kill some squirrels with the co2 version making 8.5 FPE at 520 FPS with 14.3 grain pellets also the 14.6" barrel. I think 10-12 FPE would put the gun in a good place. I just don't know what is possible. I like to tinker!

[mxl]

I think it would benefit you to go to pyramydair.com and read the multipart blog on the 2400kt. I have one with the 14.6 inch Walther barrel and another with the 24 inch Crosman. The Walther barrel is much more accurate...like 1/10 inch at 10 meters for the Walther and 1/2 inch for the Crosman. Apparently the Crosman factory uses a more powerful valve on the 18 inch and above barrels and a lower power on the shorter barrels. I put a more powerful valve in the one with the Walther and think it is still more accurate than the Crosman barrel, but gets a few less shots per cartridge. It's been a while, but I think the Walther went from something like 510 fps to around 550. Plenty much for squirrel head shots at 20-30 yards with a good hold and good scope. In theory you would also gain a little by enlarging the transfer port. Of course I have no idea if your grandson is good enough to benefit from the Walther's accuracy.

[anti-squirrel]

I'm a huge fan of the 18" barrel for the 2400KT.  Mine came from CCS but it uses a boring Crosman barrel and it shoots as accurately at 30 yards on CO2 as my wife's Lelya- which is capable of MOA shooting at 100 yards in the right hands (not mine).

Expectations for power should be a distant second behind accuracy, but I'd say with some minor effort you can draw out a good 12-13 FPE shot string for as much as 50+ shots.  My stock 2400KT can throw 40 to 50 shots (depending on outdoor temperatures) at 13-ish FPE.

An additional note: my experiences with a number of Crosman barrels in pumpers, CO2, and PCP airguns has me shooting RWS Meisterkugeln wadcutters out past 30 yards with superlative accuracy.  JSBs come in close 2nd if using wadcutters or the UltraShocks.  Polymags also shoot very well.  the key is keeping velocity down to 600 FPS or so, which ain't a problem with a 2400.

Enjoy building your Lego-Gun!

[Gibsonvair]

I ended up putting an 18" barrel on the gun. It barely engages the rifling on a pellet. I may need oversized pellets. The first shot was 590 FPS with 14.3 grain. FPS steadily went downhill from there. My best idea is to rest between shots and use a stiffer shorter hammer spring. the transfer port and barrel are drilled to about .150". The front sight is a cobbled globe and blade. I do like that part. The gun seems reasonably accurate, about 3/4" with open sights and elbows on the bench at 10 yards. I was hitting small cans offhand at 20 yards. I had the hammer spring cranked in to spring bind, but have since backed it off and just plinked and worked on the sights. I may port the valve later after I get some new baseline shot strings chronographed.

[Gibsonvair]

Sight alignment

[CraigH]

Should be about 425 with 7.5", and 525 with 18"  some may get another 25 fps  ---  stock unmodified.

[avator]

Steven, I hope your grandson has as much fun shooting it as you have had building it.
"Lego" guns for me are like the old erector sets we had as kids. I build something and play with it then take it apart and build something else.

[Gibsonvair]

The rifle is small and light. A few Co2 cartridges and a tin of pellets gets you out into the woods. Shouldering and shooting offhand propped up against a tree seems natural. The peep sights take me back to my "Black Beauty" M-16 A1 from the Marine Corps. I put a smaller aperture, .050" and moved the peep back as far as I could get it. Testing and tuning gave me 21 shots above 10 ft./lbs., from 574 FPS to 560.7 FPS. Oh, I really want to play more with this one. I am thinking of a 2260 tube, pressurized with two co2 cartridges and a ported valve and a 21" barrel.

[avator]

The rifle is small and light. A few Co2 cartridges and a tin of pellets gets you out into the woods. Shouldering and shooting offhand propped up against a tree seems natural. The peep sights take me back to my "Black Beauty" M-16 A1 from the Marine Corps. I put a smaller aperture, .050" and moved the peep back as far as I could get it. Testing and tuning gave me 21 shots above 10 ft./lbs., from 574 FPS to 560.7 FPS. Oh, I really want to play more with this one. I am thinking of a 2260 tube, pressurized with two co2 cartridges and a ported valve and a 21" barrel.

Careful, the rim of that rabbit hole is mighty slippery. 

[Airnut]

The rifle is small and light. A few Co2 cartridges and a tin of pellets gets you out into the woods. Shouldering and shooting offhand propped up against a tree seems natural. The peep sights take me back to my "Black Beauty" M-16 A1 from the Marine Corps. I put a smaller aperture, .050" and moved the peep back as far as I could get it. Testing and tuning gave me 21 shots above 10 ft./lbs., from 574 FPS to 560.7 FPS. Oh, I really want to play more with this one. I am thinking of a 2260 tube, pressurized with two co2 cartridges and a ported valve and a 21" barrel.

Careful, the rim of that rabbit hole is mighty slippery. 

Ain't that the dam truth!

[Rick67]

The rifle is small and light. A few Co2 cartridges and a tin of pellets gets you out into the woods. Shouldering and shooting offhand propped up against a tree seems natural. The peep sights take me back to my "Black Beauty" M-16 A1 from the Marine Corps. I put a smaller aperture, .050" and moved the peep back as far as I could get it. Testing and tuning gave me 21 shots above 10 ft./lbs., from 574 FPS to 560.7 FPS. Oh, I really want to play more with this one. I am thinking of a 2260 tube, pressurized with two co2 cartridges and a ported valve and a 21" barrel.

Is he gonna hunt with it?

[Gibsonvair]

That is the plan, to hunt small critters and  plink. I just wanted something that had a little more capability than as it comes as a standard 2250 style.

[anti-squirrel]

It might be worth giving a try using different pellets.  My Crosman barrels prefer RWS pellets most, followed by JSBs.  And by Crosman barrels, I mean the following (stock barrel unless otherwise indicated:

Maximus (stock barrels in .177 and .22, sold the gun a couple years ago)
Fortitude GenII in .22
392PA
over a dozen 760 pumpers converted to use the Crosman MK4-177 rifled barrel
Crosman 2100
1322 Medalist
2400KT with 18" barrel
1377 with 14" barrel
1322 with 10" barrel
1377 with 24" barrel
Mark 1 CO2

To put it bluntly, when I sight in a new (or newly built) Crosman, the first pellet I try is an RWS Meisterkugeln wadcutter at 15 yards.  I'll then move to the RWS Superdomes, JSB Exacts and wadcutters, and Polymags.  Crosman domes usually shoot very well but I can never avoid fliers.


For giggles, I recently tried the 17.5 grain .2165 and .217 NSA slugs in my 1322s, 392PA, Fortitude, and the 2400KT.  Color me surprised when they all shot excellent in these lower power airguns.  Not as accurate as the RWS wadcutters, but on par with .22 CP domes.

[Gibsonvair]

The barrel seems loose on this one. I bought 5.54mm and 5.55mm H&N FTT. (have the 5.53mm) The accuracy is actually good. but I haven't done extensive testing yet. I will try Superdomes and I have been meaning to get some JSB's to test.

[Gibsonvair]

Shot a few test rounds at the gallery style target offhand from 18 yards. This is challenging.

[Gibsonvair]

I like to do my accuracy testing at 25 yards scoped and rested. This really brings out the groups. 1/2" is nice, but I will take less for plinking. I wish this was the new gun! this was a 14.6" Lothar Walther barrel.