Longer barrel did not produce velocity increases suggested

wahoowad · October 12, 2013, 11:59:42 PM

In another thread I received advice about increasing power and I went with installing a longer barrel. Today I swapped out my 10" barrel and installed a 14.5" barrel in my 2300kt (.22). I just shot my first 30 shot string and can tell I didn't get anywhere the +/- 15 fps per inch folks thought I would get.

My 10" barrel averaged 500 fps for the first 10 shots (max = 508 fps)

My 14.5" barrel averaged 515 fps (max = 520 fps)

So what gives? I was expecting 4 * 15 = 60 fps increase. The temperature was only 2 degrees warmer the day I shot the 10" barrel string. The gun reassembly was very easy and everything looked and felt good.

arkmaker † · October 13, 2013, 01:23:19 AM

Well, I always figured about 10 fps per inch, but that is with .177 barrels. I've found that it can vary even more with a .22

Still, you sure as heck did not gain 45 fps either. Did you change from a .177 to a .22? If so, then that would be why. Like comparing apples to oranges. .22's shoot slower but have more umphh

Rich

wahoowad · October 13, 2013, 01:27:20 AM

I started with a .22 and ended with a .22. I'm feeling really dissapointed

arkmaker † · October 13, 2013, 01:33:34 AM

Same pellets as the first test?

wahoowad · October 13, 2013, 01:45:06 AM

Yup, same H&N Sport wadcutters.

bgmcgee · October 13, 2013, 02:20:23 AM

Bummer. Did you check for leaks. Could just be a small leak causing you to not see the gains you thought you should.

1377x · October 13, 2013, 02:58:57 AM

make sure your ports are lined up
any gaps under the breech?
4.5" of barrel isnt a substantial increase either
my 2250b with slight port mods netted 535fps so if you dont have any valve mods your numbers about right imo

K.O. · October 13, 2013, 03:02:50 AM

Just suggesting the temps might have been enough different. That's why pumpers are better in the cold.

http://www.archerairguns.info/2010/07/now-we-can-really-understand.html

RetatCDude · October 13, 2013, 03:31:31 AM

The barrel lengths chosen by the air gun engineers are not arbitrary. Just as the 18" barrel on the Ruger 10/22 was chosen as the perfect length for standard .22lr loadings. The barrel (sic) on my Beeman R1 is 19" long but in fact it is only 15" (rifled portion). The remaining length is for aesthetics only and for ease of cocking the gun. In fact you will see a lot of shooters remove the extra length to make the gun handle better. A few years ago one of the gun magazines had a rifle barrel made 30" long in which they intended to fine the best length for a particular loading. They shot a few rounds and cut off an inch. They shot a few more and shot off an inch. So forth and so forth. The feeling is when the propelling force exhausts itself (no longer a thrust), the pellet/bullet/shot load, has reached the muzzle. Otherwise, the load will start to slow down from friction.

wahoowad · October 13, 2013, 03:42:32 AM

I don't hear any leaks. How do I check for leaks?

There is no gap under the breech. Breech and tube went together smoothly. I was very careful with the transfer port and seal....small shoulder of the transfer port is down in the seal, the tall shoulder into the barrel.

Trophyhunter49 · October 13, 2013, 03:52:08 AM

I know on my 2240 build , it went from a round 425 to 535.7 fps with 18 in. barrel vs. the stock barrel that came on it. You should have gained at leat 25 to 35 fps with the 14.5 barrel.

eric · October 13, 2013, 04:18:18 AM

the tissue test --- hold the gun side ways and place a single piece of tp or a tissue over the gun directly over the tp area ,cock and fire the gun .try both sides .baby powder or the likes can be used as well --- that is better fir more subtle leaks .down side is it's a little messier

Quote from: wahoowad on October 13, 2013, 03:42:32 AM
I don't hear any leaks. How do I check for leaks?

There is no gap under the breech. Breech and tube went together smoothly. I was very careful with the transfer port and seal....small shoulder of the transfer port is down in the seal, the tall shoulder into the barrel.

quickster47 † · October 13, 2013, 02:24:13 PM

Maybe your expectations were too high. There are no guarantees in AG building.

Carl

Quote from: wahoowad on October 12, 2013, 11:59:42 PM
In another thread I received advice about increasing power and I went with installing a longer barrel. Today I swapped out my 10" barrel and installed a 14.5" barrel in my 2300kt (.22). I just shot my first 30 shot string and can tell I didn't get anywhere the +/- 15 fps per inch folks thought I would get.

My 10" barrel averaged 500 fps for the first 10 shots (max = 508 fps)

My 14.5" barrel averaged 515 fps (max = 520 fps)

So what gives? I was expecting 4 * 15 = 60 fps increase. The temperature was only 2 degrees warmer the day I shot the 10" barrel string. The gun reassembly was very easy and everything looked and felt good.

1377x · October 13, 2013, 02:32:48 PM

thats true too
i have built a couple guns that had the same parts and got two different results

arkmaker † · October 13, 2013, 04:02:17 PM

Actually, your numbers sound about right. Most 2240's start off around 425 to 450 out of the box. So if you are averaging 520' that makes 10 fps x 7" =70 fps putting you in the right ballpark.

1377x is right, I thought I had numbers for my Transformer build, but can not find them. At one point I was running a 14.5" barrel, but bulk filled. Also, the Transformer 2 build was 14.5". I know I have some number from that. Let me figure out where they are and I will post them for you.