Author Topic: Barrel Shortening  (Read 3245 times)

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Barrel Shortening
« on: October 08, 2006, 07:54:59 AM »


Just a quick question, does shortening the barrel of a QB78 have a detrimental effect on power?



Jon


Offline IJL

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RE: Barrel Shortening
« Reply #1 on: October 14, 2006, 11:11:34 PM »
I've seen adverts for QB carbines with 3" off the length but I figure the answer would depend on the "tune" or your rifle. i.e. Does your gun deliver enough CO2 that it is still expanding enough to be still accellerating the pellet when it's 3" short of the muzzle.?
It will also depend on the weight of pellet you use.
My GUESS would be yes, it is still accellerating and therefore shortening the barrel would be detramental to the velocity.

Don't ask me how to find out for certain without a hacksaw!  Hopefully someone else on here can advise further.

Ian

Offline Gene_SC

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Re: Barrel Shortening
« Reply #2 on: October 15, 2006, 12:47:13 AM »
Maybe Mike will chime in on this one..:) Or one of our other experienced QB guys..

Gene
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Offline mikeiniowa

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Re: Barrel Shortening
« Reply #3 on: October 15, 2006, 02:49:04 AM »
It's going to slow it down some but not alot at 3 inches, call it at the most 50 to 70 fps. The big thing is what is the barrel like at the point you wish to cut it? If it is the smallest bit loose on the pellet you won't hit the broad side of a barn, try to find a spot that the pellet is snug in the bore at and shorten to there, kind of like a buildt in choke.

Offline CharlieDaTuna

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Re: Barrel Shortening
« Reply #4 on: October 15, 2006, 05:52:17 AM »
Yep...Mike is right. Shortening it will almost certainly cost you velocity and a waste of power. If when you shoot your gun you see there is a lot of vapor loss, then that usually means inefficiency. In fact, most Co2's (both rifles as well as pistols) benefit from a bit longer barrel especially when mods have been made to the valve and/or ports. Getting more gas out with more efficiency has no value unless it is harnessed or utilized and not wasted...... or just goes out the muzzle in a nice white cloud.
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Offline ribbonstone

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RE: Barrel Shortening
« Reply #5 on: October 15, 2006, 06:24:51 AM »
CO2 needs heat to give power...barrels are a heat sourse..so shortening the barrel will deprive the CO2 of that much heat for liquid-to-gas conversion, and end up losing  bit of power. Wish I could tell you a magic number...can't, too many other vriables...but a guess would be about 30-60FPS for that 3" of barrel.

So far as I can tell, those barrels aren't choked (slightly smaller at the muzzle), so if it doesn't happen to be enlarged at the point you choose to cut, shouldn't do a lot to harm accuracy (of course, that depends on how well you crown that barrel stump too).

OF course, you could do a tune and get that velocity back (and ignore that it would have been even faster with the "extra" 3' of barrel that got chopped off).

Will certainly make it a bit louder...maybe not objectionably louder.  Noise comes mostly from the exit presure of the gas/air that dirves the pellet, short barrels generally have the gas exiting behind the pellet at higher vel. than longer barrels, so they are usually a bit louder.

(that last is hard to judge by yourself.  A lot of the noise is conducted to your ear through the stock you have your face pressed against. Same reason your vocie sounds "different" on a recording...recording doen't get the sound of bone conductivity that your ear does.)
Robert