Shorten Hatsan barrel.

[Gut2Fish]

http://www.gatewaytoairguns.org/GTA/index.php?topic=26322.0

The above link has good data on a lot of common break barrel guns. You'll note the piston volume increases with power of each rifle. Volume speaks volumes. I've read the 6" barrel length and heard anything after 10" of barrel is only for leverage to cock the gun. Well, that's all well and good and would imply all guns are the same. The fact is they are not. For a given power there is indeed a related volume of piston. As the volume of piston increases so too must the volume of barrel or that added energy is wasted. Now 10 year old magazines stating 6 inches of barrel do not keep up with the times. A 10 foot pound gun certainly does not need a long barrel but one can not say the length of barrel needed for this pea shooter is all you need when you get to 33 foot pounds monster. It's not a one size fits all application. Not only will optimal barrel length change for a given piston sweep volume it will change to each caliber. It's a volume to volume ratio. What that ratio exactly is I could not tell you. All I did was crunch #'s to find a 10:1 ratio and compare to different guns to find there is a correlation in different manufactures and a 10:1 volume ratio- it holds true. Optimal barrel lengths are longer for .177. If assuming the barrel on a given gun is optimum in .177 then I crunched #'s to show how short it could be (in 125 and 135) if a .25 caliber gun. All that # crunching was to show there are variables and drastic differences by caliber.

There is more to lengths than leverage and sighting distance. Length is also a function of volume in barrel. There is another part to this story as it's not all volume to volume. There is also the factor of piston/spring force. But that is merely another variable that is not needed. There are enough variables by piston volumes and barrel calibers changing volumes in a given length.

In the 1995 book "The Airgun; from trigger to target" there was a lot of excellent experimentation. What many are citing to this day is it's data that the full velocity of pellet is realized in first 6 inches of barrel. What is not stated is that this was a .177 caliber with 649 fps. Pellet weight is not mentioned but if we assume 8 grains that's a 7.48 foot-pounds gun. Hardly a Webley Patriot or Hatsan 125, 135, 155. What is good to see in that publication is friction and force loss due to pushing air did not start to show effect on that caliber for another 25 inches of barrel travel. So friction loss seems a non issue in small caliber. It won't be that long a distance of no consequence coasting down the barrel with a much larger circumference .25 that's displacing/pushing more air out the barrel.

[rsterne]

I was asked to give my opinion, and it hasn't changed since the post I made long ago that was linked to earlier.... 10"-16" depending on the gun.... However, the statement Scott (Scotchmo) made in the post linked above, that a .177 cal Hatsan 135 could probably use a barrel up to 30" long to take full advantage of it's very large air chamber, and a .25 cal about 15", should not be dismissed.... Scott knows a LOT about Springers, and in fact I would ask his advice above all others on the subject of shortening barrels, particularly on a Magnum Springer....

Most of Cardew's work was done on guns so low powered you would be hard pressed to even find one like that still in production today.... I am not surprised by their conclusion RE barrel length.... and I am well aware of all the opinions about barrels in the 9-10" range.... I have no doubt they work just fine in medium powered guns.... but the more power, and the larger the compression chamber volume, the more barrel length you will need to extract the energy completely....

Accuracy is another matter.... You have the conflicting ideas of muzzle flip increasing with a shorter barrel, to the fact that the pellet will spend less time in that shorter barrel, so you are less likely to pull the shot, or have the guns recoil send it off target.... Just like each Springer likes to be held differently, I suspect that is also true of the effect of barrel length on accuracy.... some will improve, some get worse....

As far as cocking the beast, if you shorten the barrel, the effort will go up in direct proportion.... Yes, you can put on an extension, but that defeats the idea of increasing portability and handling.... My gut feel is, that if you need an extension to aid in cocking, you shouldn't even consider shortening the barrel in the first place, because you probably need that length to extract the maximum velocity from the air....

Bob

[Back_Roads]

 Here's a short barrel example , the Crosman MTR .177 has an 11" barrel shoots 10.5 gr about 940 fps, good accuracy out to 20 yards in most cases , hold it like a PB real tight and accuracy increases.

[SpiralGroove]

Thanks Bob,
Here is a Marketing Irony from Hatsan:

1) Hatsan 135 (.177 springer - barrel length 17.7") advertised max velocity = 1250fps.

2) Hatsan 135 (.177 Vortex - barrel length 17.7") advertised max velocity = 1250fps.

3) Hatsan 135 QE (.177 Vortex - barrel length 10.6")  advertised max velocity = 1250fps.

Maybe the extension tube/baffles on the end of the QE barrel act as if it was actually 17.7"?

[rsterne]

or maybe they didn't bother changing the advertisement?....

Bob

[SpiralGroove]

Probably your thought, + Vortex users already know it can't quite match the velocity of the original spring.
So the vortex should show 1230/1240fps.

 

[SpiralGroove]

Hey Bob,
Now that I roped you into commenting on this thread , it would be great if you have your thoughts on potential (margin) increase/decrease in power which could be lost or gained by cutting 2", 4" or  5" off a Springer barrel ; compared to the losses/gains to be had with a PCP?

Do you think we should see a significant increase/decrease in velocity with in the above changes to a Magnum Springer - aka Hatsan 135?

Thanks .................

[rsterne]

I'm not really a Springer guy.... Scott (Scotchmo) would be much better to ask.... Assuming his number of 100 fps is correct, beyond which you won't get much velocity decrease, that would occur on a Hatsan 135 at about a 16" barrel.... The swept volume is 85 cc.... The compression chamber left with the piston at the front will be VERY small, so virtually all the volume left will be barrel volume.... The bore area is .25^2 x PI/4 = 0.049 sq.in., so each inch of barrel is 0.8 cc.... ten inches would be 8 cc, etc.etc.... Air at 100 psi is 6.8 atmospheres, so each inch of barrel at 100 psi would equal a chamber volume of 6.8 x 0.8 = 5.44 cc.... That 85 cc chamber could fill a barrel to 100 psi that is 85 / 5.44 = 15.6" long.... That is where Scott got his 15" barrel minimum to get the maximum performance out of a .25 cal Hatsan 135.... He also said that the pellet doesn't really start slowing down for another few inches after that, so you could assume that anything between 15-18", maybe even out to 20", would have virtually the same velocity.... but if you cut the barrel shorter than 15" you would start to lose velocity.... and the shorter you made it, the more you would lose, and not in a linear fashion.... When you consider cocking the beast, going shorter than 15" would seem to me, to be pointless.... Smaller calibers would benefit from longer barrels.... The minimum length for maximum velocity would be about 20" in .22 cal, and 30" in .177 cal....

Bob

[Yogi]

Yogi,could you show the link to that info please. I've got 2 shortened barrel rifles that I can see no drop in fps.

http://www.diana-airguns.de/index.php?id=605&L=0&width=1440&height=900

Is what I found.  I swear that there used to be a 20meter/s difference, not the 5 mps listed now.

-Y

[SpiralGroove]

Hey Yogi,
I'll buy that: 15 fps drop in .22 caliber, upon losing 4" of barrel.  I think that falls in the marginal zone  
In .177, it shows no difference, but there is likely a 4 to 5 fps loss

So if you've got a medium(+) powered powered break barrel, don't fret about losing velocity with a 4" reduction in barrel length.  In magnums, you should see more, but I doubt there will be any more than a modest difference.

I wish we had a chart for a reference when modifying barrel length

 

[Bryan Heimann]

Thanks Bob,
Here is a Marketing Irony from Hatsan:

1) Hatsan 135 (.177 springer - barrel length 17.7") advertised max velocity = 1250fps.

2) Hatsan 135 (.177 Vortex - barrel length 17.7") advertised max velocity = 1250fps.

3) Hatsan 135 QE (.177 Vortex - barrel length 10.6")  advertised max velocity = 1250fps.

Maybe the extension tube/baffles on the end of the QE barrel act as if it was actually 17.7"?

Hatsan markets all of their big magnums at the same fps.  The 125, 135, qnd the 155 underlelvers all have different swept volume and different power, but they are all in the ballpark of 30 fpe and fairly close. 

[SpiralGroove]

Hey Guys,
Update:
Just received my .22 caliber Hatsan 95 from buyer who returned it due to inaccuracy.
I was thinking "Barrel Flip" could be real on this gun since the barrel was cut to 10" and it's a magnum springer.  Went down to my 13 yard range and adjusted (lightened) trigger, then proceeded to shoot 3/8" dots regularly using CPUM from a tin.
Now this was from the bench (bag) with a very gentle hold, left hand underneath and just touching trigger guard.

So I believe worrying about barrel flip in this case was unjustified; but the gun is a finicky shooter ........ just read Tom Gayord's review of the Hatsan 95 in 2012.  Accurate gun, but you gotta be hold perfect and having a light trigger helps.

My two cents .............................. Kirk