Air Gun Home :: View topic

Robw · Veteran Member

I am going to put a 16 inch barrel on a 1377 and was wondering how much
of a velocity increase can be expected. Is there a general rule as to how
much of a gain in fps can be expected per added inch?

Any thoughts would be appreciated.

Rob.

ZipSnipe · Veteran Member

Not sure of the velocity increase, you should see some. I recently added a 16" barrel to my 2240 but have not had a chance to shoot it yet. I read somewhere that after 14" you don't see anymore increase in velocity and that any longer barrels will just add to accuracy.

Robw · Veteran Member

Actually, barrel length has little to do with accuracy. The crown and last bit of
rifling the projectile passes are the major players in accuracy.

I have heard of people experiencing increased velocity with this model by
increasing barrel length (up to 24 inches) before, but can not remember the
formula of how much of a velocity increase per inch can be expected.

AirGunEric · Site Admin

It is not as straightforward as barrel length=x, velocity increase=y as it is dependent on whether anything else has been done to the gun.

Typically, a .177 has done better with LESS air volume (i.e. smaller transfer port) getting through the barrel at HIGH pressure. The actual volume as compared to the barrel length (i.e. how long the pressure can remain high based on volume filling the barrel behind the pellet) dictates the ultimate 'power' of the pellet coming out the muzzle. If I recall correctly, one of our mad nut scientists here- Bob- had experimented with this a few years ago and found something like 22" (I may be a bit off here) worked quite well with a 13xx gun using a stock valve, slightly smaller transfer port (i.e. than a .22 of the same platform) and a flat-top piston kit (build up pressure more quickly in valve to make the whole thing less labor intensive).

I have seen this 16" barrel thing a couple times recently- where has this come from? Is 16" the new "fashion" of the month, or why is this length being chosen?

rsterne · Moderator

The higher the performance of the gun, the more it will benefit from a longer barrel.... I have never had such a mildly tuned gun that it produced more velocity with a shorter barrel, even on CO2, let alone with HPA or with a pumper.... The exception would be on 1-2 pumps....

Bob

Robw · Veteran Member

I have heard that the increase in length will also reduce the report.

Robw · Veteran Member

I decided to start at a barrel length of 18.5". It looks a little cumbersome
and it is very easy to bump the business end into things. It is putting out in
the mid 700s fps.

Replacing the BB peened faint rifling sure increased the accuracy. Part of
that may be due to the increased sight span. It is now 21 inches.

I am just waiting on a projected reticle sight and it will be done.

Robw · Veteran Member

Now I need to find a new pistol rug.