Barrel length and FPS?s

[igolfat8]

I was under the assumption that a longer barrel yielded more FPS. I swapped out my .22 standard Vet barrel for a Vet long barrel which is 3.5” longer. I crono’d the standard barrel at 870 FPS with a 22 grain pellet. Then replaced the standard with a long barrel and shot the same pellet, at the same tune and it averaged 873 FPS. I figured that I would see the FPS increase more than 3 FPS. What am I missing here?

 

[JaceSpace1369]

I was under the assumption that a longer barrel yielded more FPS. I swapped out my .22 standard Vet barrel for a Vet long barrel which is 3.5” longer. I crono’d the standard barrel at 870 FPS with a 22 grain pellet. Then replaced the standard with a long barrel and shot the same pellet, at the same tune and it averaged 873 FPS. I figured that I would see the FPS increase more than 3 FPS. What am I missing here?

Compare transfer ports, see if they are the same size, or if the barrel may be misaligned. Usually jumping from say a 500mm to a 600mm nets 10% velocity increase

 

[Ranchibi]

Tim, the longer barrel may also have a tighter choke in tandem with what JaceSpace said above resulting in the minor fps increase.

 

[Struckat]

Wouldn’t the longer barrel allow for a more aggressive tune? Hence more power?

 

[igolfat8]

There is no port in the barrel to align. It just threads into the block

Yes, I could tune it up for more power but I was expecting to see an increase in FPS by just swapping the barrel.

 

[igolfat8]

Tim, the longer barrel may also have a tighter choke in tandem with what JaceSpace said above resulting in the minor fps increase.

I have no way to measure the choke Randal but just pulling the same patch through both barrels, it feels the same.

 

[6gun]

I was under the assumption that a longer barrel yielded more FPS. I swapped out my .22 standard Vet barrel for a Vet long barrel which is 3.5” longer. I crono’d the standard barrel at 870 FPS with a 22 grain pellet. Then replaced the standard with a long barrel and shot the same pellet, at the same tune and it averaged 873 FPS. I figured that I would see the FPS increase more than 3 FPS. What am I missing here?

Yes they do, but it's a different barrel and will require a different tune more than likely. Maybe your previous tune was spot on for the shorter barrel?

 

[Ta-Ta Toothie]

I have no way to measure the choke Randal but just pulling the same patch through both barrels, it feels the same.

Push some pellets through. Could be a slightly tighter bore, or different twist rate.

 

[Ranchibi]

There is no port in the barrel to align. It just threads into the block

Yes, I could tune it up for more power but I was expecting to see an increase in FPS by just swapping the barrel.

You are correct in my humble opinion! Head scratcher for sure.... I have also found non choked poly barrels to be quite a bit more efficient than a standard rifled non choked barrel, seeing this with my RAW's poly and my Taipans CZ, both non choked. The poly doesn't slow slugs or heavier pellets down as much as standard rifling thru both of mine.

 

[igolfat8]

I’ll try to push pellets down it tomorrow and take some measurements.
thanks all for your input

 

[subscriber]

The new barrel may have higher bore friction. Shoot it some more and see if it improves.

If your tune is mild the last few inches of barrel may not add much anyway. Especially if your reg pressure is high and the valve dwell very short. Then the average air pressure driving the pellet is composed mainly of an early spike; with last so many inches of barrel contributing little to velocity. In other words an air efficient tune.

As others have suggested, the choke may be tighter in the new barrel also.

 

[GerryR]

I would guess that somehow the gas "pulse" (new to airguns, so don't know the proper terms) would have to be increased to effect a velocity change of any significance. If you increase the volume (longer barrel) with the same amount of gas, the pressure goes down. You need to provide more gas to keep the pressure the same for the added length, I would think.

 

[EPG]

Perhaps plenum size is restricting the velocity benefit of the longer barrel?

The 700 Vet2s from the factory come with an additional plenum…

Just a guess. I agree that I would have expected 25-50fps increase going from 550mm to 700mm.

-Ed

 

[igolfat8]

I went from the standard 460mm to the long 550mm, not to the 700mm barrel. It is an increase of ~3.5"

 

[beerthief]

There is no port in the barrel to align. It just threads into the block

Yes, I could tune it up for more power but I was expecting to see an increase in FPS by just swapping the barrel.

I once ask LW barrel company "at what length would a barrel decrees the velocity given the same powder charge /same platform " I was thinking of Kentucky long gun 58 inch barrel on say a .22 standard . Never got an answer . i assume i did not give enough parameters /info ?

 

[subscriber]

I went from the standard 460mm to the long 550mm, not to the 700mm barrel. It is an increase of ~3.5"

I would expect more of a velocity increase, if the starting length was "short". Unless the plenum were very small, and the valve duration very short.

Could be a ,mispositioned O-ring at the breech thimble, leaking air. Put the original short barrel back in to see if you got the original velocity back. Check all o-ring disturbed for any sign of not being evenly seated. Fix that or replace any suspect o-ring, Reassemble with silicone grease on all sides of all o-rings replaced or disturbed..

 

[Peashooter]

I am thinking longer barrel = longer runway and so longer time to either get things up to higher speeds with same or more pressure, or like i do in my 700 mm rifles shoot more normal speeds with very low pressures.

In my Two i shoot 10.43 gr pellets with 40-45 BAR for a about 900 fps speed depending on pellet CUZ some like 880 or so and other like 910 - 940 fps

Mind you on my Maverick i could shoot 13 gr slugs at 970 fps with just 70 BAR, but they did shoot better with 90 BAR on the regulator ( same speed of course )
In my Two i shoot 13 gr slugs with 80 BAR for a 980 fps speed which seem to be the favourite for the unchoked CZ barrel i have.

So the way i see it, if you want a bigger shot count you have 2 choices, put on a bigger bottle, or have a longer rifle and shoot with a lower pressure.

 

[Struckat]

I would guess that somehow the gas "pulse" (new to airguns, so don't know the proper terms) would have to be increased to effect a velocity change of any significance. If you increase the volume (longer barrel) with the same amount of gas, the pressure goes down. You need to provide more gas to keep the pressure the same for the added length, I would think.

That is what I was trying to say. The longer barrel allows for a more aggressive tune. Where the shorter barrel would end up wasting air.

 

[GerryR]

That is what I was trying to say. The longer barrel allows for a more aggressive tune. Where the shorter barrel would end up wasting air.

So, if the gun was tuned for the shorter barrel, there would not necessarily be "enough" air for the longer barrel to increase velocity; makes sense. By the way, how do you "tune" an air gun?

 

[Struckat]

Depends what it is. Adjust may be a better term. To me it means being able to to make it shoot the desired projectile at the desired speed for the best accuracy and shot count.

I think the longer barrel allows more pressure behind the projectile before it leaves the barrel. But I am newb begging to be slapped down LOL.