To Chop or not to Chop the Barrel.

[snIPer]

Hi,
here are a few interesting links on the topic.
i've actually chopped off the barrel on my New Lite underlever to 12.5 inches. now recrowning and a test is pending, will try to do that this month and post up results.

http://www.pyramydair.com/blog/2005/04/ ... rtant.html
"Cardew determined optimum spring gun barrel length
A spring gun gets all of its "push" in the first few inches of the barrel. Gerald Cardew pointed out in The Airgun from Trigger to Target that only the first six inches of the barrel is needed for a spring gun to achieve maximum velocity. His experiments were conducted in the mid-1970s. Although technology has advanced since then, today's spring-piston guns probably don't use more than the first 10 inches of barrel for top velocity."

http://airgun-academy.pyramydair.com/bl ... el-length/

http://www.network54.com/Forum/79537/th ... +too+long-

http://www.network54.com/Forum/184474/t ... ke+or+not-

http://hobbiesforum.proboards.com/index ... thread=177

If anyone has tried it please do share the results.

/S/

[hamiclar01]

Reducing the barrel length of a springer has the theoretical benefit of conserving energy, against the potential loss of distal choke that some springers are manufactured with (re Cardew himself). Also, a longer barrel aids cocking better than a shorter (for the break barrel variety).

I have had the barrel of my standard length Hw80 reduced and recrowned. No problems with accuracy, but I had a Mk1 version, which according to my airgunsmith, is suited for barrel shortening as it did not have any choke. If there was a choke present, i would have left it alone.

My cocking problem was alleviated by adding a muzzle brake/silencer at the end

[fantumfan2003]

On a PCP longer is better but on a springer anything above 11 or 12 inches is a necessary evil to reduce cocking effort.
Never tried and never will coz you do not get barrels here off the shelf, even for a premium price.
You might want to read up comparisons on HW80 vs HW80K or 95 vs 95K
An enthusiast on the Dianawerk Collective, chopped off his D34 barrel with great results another was not.

Do let us know what happens in your case....

M.

[gitana]

what happens when instead of focusing on maximum speed, we focus on maximum accuracy, and then determine barrel length?

(not strictly airgun related sources):
http://www.airsoftforum.com/board/Barre ... 52887.html the direction a projectile actually goes when it leaves the barrel is based on the direction it was going last
http://www.sniperschool.com/sniper-rifle-barrel-length barrel length (within reason) does not affect accuracy within a manner many people believe ... a thicker bull barrel will provide better accuracy than a thin sportster style barrel. From this we know that a stiffer barrel helps increase accuracy by negating excessive barrel flex and vibration. The only way to stiffen an already stiff bull barrel from the factory is to shorten it
also, http://bellmtcs.com/store/index.php?cid=580

so it seems shorter barrels = stiffer barrels = less harmonic variance = more accuracy. this agrees with shorter barrel = increased speed. as your experiment is on an underlever, cocking effort isnt a factor.

so if you have a spare barrel lying around that you are willing to junk, go ahead and reduce it to the length by which the maximum pressure would have developed behind the pellet... 10 inches... or even 5, depending on how much you want to believe Mr Cardew. In all probability, you will get a super accurate and super fast airgun. it may even fail the dealwood test (India), or the 12 ft.lb limit (UK) thus requiring you to get a firearms licence / certificate.

since you have already chopped the barrel to 12.5, the following is immaterial, but a better way would have been to cut off 1 inch at a time... compare the results (and post them!!!)... till you reach a self imposed minimum.

[pkjeetesh]

very good post by Gitana...thanks to him....Yes, 10'' seems to be right for our IHPs....during one of my experiments, i decided to chop the barrel of an IHP35 .177cal by 10''s straight....the intention mainly was to reduce the lock time, enough was done on the internals....so this one was to also eliminate as much error caused due to barrel flexion, pellet travel etc.,...you will have a stiffer barrel, and cocking effort would be more...therefore decided in order to reduce cocking effort while minimizing weight on the barrel and also to eliminate any turbulence caused by air inside the MB (?), decided to go with a HDFE muzzle brake with its inside front end almost flush with the muzzle end....to tell you the truth, not much was gained in accuracy or fps (barrel again, you need a better barrel), but the gun got more balanced making shooting more pleasureable...here are some pictures...only very light crowning was done on the chopped barrel....many of these things are trial and error, see what works best for you....you need spare guns, spare barrels and of course TIME ....the first two i have, not the third...







regards

p k jeetesh

[vijaycool]

PKJ nice mod you made on ihp. It would be delightful if ihp provide such crowning in their guns. Old IHP's had that crowning. I have a weird problem in my gun. The breech side is slightly choked compared to the muzzle end. I passes one pellet (MS export quality)from breech end to the muzzle with the help of broom stick. It was so hard to push from the breech end. After passing 2 inches it becomes free but doesnt fall. The pellet movement is rough and come out in the muzzle freely. If I push the pellet from muzzle to breech it gets tighter. I checked in suresh ihp 25 it was ulta tight in the muzzle end. so i hope it will be there for every ihp tighter in the starting point and out of tolerance on the other end of the barrel.
I want to know whether its possible to remove the barrel from the breech block and machine the other to fit to breech.

Regards,
Vijay

[snIPer]

PkJeetesh - looks good mate- did you get a chance to chrono the gun after the chop. also where did you pick up the HDFE muzzle brake from - i would be interested in one.

Mine - after the chop ive recrowned the barrel and tried approx 10 shots with Master shot export round head pellets - the grouping was horrible - a 3 inch spread at just 10 yards - I was just beginning to wonder if the crown job had gone wrong - then i changed to - Master shot round head (the one that comes in the red packaging) grouping immediately improved and i was able to get a very good grouping at 10 yards.
Ive also noticed that these pellets do very well in IHPs.

Well now the grouping problem is solved but a new one has come up - the sound has just increased a lot - its almost like shooting a .22 lr. ive shot around 30 pellets but still its the same - there is also a thwack in the piston so i guess i will have to open it and clean the parts and try again.

Havent had a chance to chrono it yet but will do so soon - pics coming up in a day or two.

Vijay - try the normal Master shot round head - it works wonders. Also use a vernier calliper if you have one - to measure the dia of the muzzle and breech end.
i havent tried switching over the breech and the muzzle but if you do so then please do let us know.

Thanks
/S/

[fantumfan2003]

Sniper,

What was your need to shorten the barrel ? Have you derived any advantage out of it apart from a slightly less weight and improvement in balance ?

M.

PkJeetesh - looks good mate- did you get a chance to chrono the gun after the chop. also where did you pick up the HDFE muzzle brake from - i would be interested in one.

Mine - after the chop ive recrowned the barrel and tried approx 10 shots with Master shot export round head pellets - the grouping was horrible - a 3 inch spread at just 10 yards - I was just beginning to wonder if the crown job had gone wrong - then i changed to - Master shot round head (the one that comes in the red packaging) grouping immediately improved and i was able to get a very good grouping at 10 yards.
Ive also noticed that these pellets do very well in IHPs.

Well now the grouping problem is solved but a new one has come up - the sound has just increased a lot - its almost like shooting a .22 lr. ive shot around 30 pellets but still its the same - there is also a thwack in the piston so i guess i will have to open it and clean the parts and try again.

Havent had a chance to chrono it yet but will do so soon - pics coming up in a day or two.

Vijay - try the normal Master shot round head - it works wonders. Also use a vernier calliper if you have one - to measure the dia of the muzzle and breech end.
i havent tried switching over the breech and the muzzle but if you do so then please do let us know.

Thanks
/S/

[snIPer]

Experiment - Just to see if shortening the barrel still preserves the power. Have read in a few places that springers need a max of 12 - 12.5 inches so.... also yes the weight has decreased, feels more compact, balances fine, power is good (yet to chrono) grouping is good.

Here is the beast.

The grouping in the red circle is from - Master shot Round head the pics are large but the actual size of the red circle is less than an inch high.
all the pellets out of the red circle are from the Master Shot Round head - Export type



The gun had rusted badly and so to prevent further rusting ive painted it green


Stock has been modified to suit a diana mod 23 - so i use the same stock on both guns.


/S/

-- Thu Mar 10, 2011 11:46 --

Good info here Gitana - Thanks

what happens when instead of focusing on maximum speed, we focus on maximum accuracy, and then determine barrel length?

(not strictly airgun related sources):
http://www.airsoftforum.com/board/Barre ... 52887.html the direction a projectile actually goes when it leaves the barrel is based on the direction it was going last
http://www.sniperschool.com/sniper-rifle-barrel-length barrel length (within reason) does not affect accuracy within a manner many people believe ... a thicker bull barrel will provide better accuracy than a thin sportster style barrel. From this we know that a stiffer barrel helps increase accuracy by negating excessive barrel flex and vibration. The only way to stiffen an already stiff bull barrel from the factory is to shorten it
also, http://bellmtcs.com/store/index.php?cid=580

so it seems shorter barrels = stiffer barrels = less harmonic variance = more accuracy. this agrees with shorter barrel = increased speed. as your experiment is on an underlever, cocking effort isnt a factor.

so if you have a spare barrel lying around that you are willing to junk, go ahead and reduce it to the length by which the maximum pressure would have developed behind the pellet... 10 inches... or even 5, depending on how much you want to believe Mr Cardew. In all probability, you will get a super accurate and super fast airgun. it may even fail the dealwood test (India), or the 12 ft.lb limit (UK) thus requiring you to get a firearms licence / certificate.

since you have already chopped the barrel to 12.5, the following is immaterial, but a better way would have been to cut off 1 inch at a time... compare the results (and post them!!!)... till you reach a self imposed minimum.