Barrel shortening... take a guess.

[Ribbonstone]

A little guessing game.

How much is losing 10” of barrel (from 24” to 14” going to cost in velocity/energy?

Well-tuned little rifle about 15 foot-pounds for 11-12 shots (inside 4%).



Wanting to fit it into a gym bag, needed to be 10” shorter.



Not wanting to take a chance on some other variable entering into the numbers, didn’t disassemble the gun to cut the barrel.  Was cut from the front with the gun completely together (just plugged the bore to keep any steel chips from dribbling down into the back end).

Will take the barrel off and do a “real” recrown later this week, but the hand recrown it has now is working  just fine and todays velocity numbers won't care.

So it’s all ready for a couple of shot strings with the new length, just going out the door to find out what the numbers are. figure I'll make a late lunch and watch a little TV after, so will be back early this evening to post results.

So come on guys, make a guess on velocity loss.

Simple little tiny volume PCP running from 2000 to 1000psi losing 10” of barrel.  Can look at it as losing  42% of its barrel length if that helps. 

[rsterne]

Give us a hint on the caliber, reservoir volume and pellet weight?.... I'm guessing .22 cal and 14.3 gr. and I'll work on that, but if I'm wrong it could make a big difference.... Anyway, my estimate is 47 fps....

Bob

[wilsonj1018]

im gonna say somewhere around 40 fps. if the gun was higher powered I would be willing to bet on more.
Josh

[PakProtector]

15 FPE is not much considering a long barrel...and so I am betting less than 40 fps drop. Now if it was shooting 40 FPE...that guess would change.
cheers,
Douglas

[Oldblades]

My guess is that it may actually gain speed, in addition to being much louder.

[sixshootertexan]

I'd said you will lose 45fps.

[Ribbonstone]

Lost 5% (34fps) velocity which equates to about 10% in energy (1.5 foot pound less).

Volume is about 1/2 that of a P-rod (about 33cc's)
15.9gr. JSB's



Doesn’t need to be any more powerful, there is enough power and range there to do what the Benjamins or Sheridans I grew up  with could do (except I only have to  pump it 16 times for every 12 shots).

[rsterne]

KEWL !!!.... I would have still guessed too high, even if I used 15.9 gr. and 33 cc.... *LOL*.... It's interesting how much the total energy in the 4% string dropped, though.... from 179 FPE to 147 FPE....

Bob

[Ribbonstone]

No doubt about it, so far, shorter has always equaled “less” than longer barrels.  Have to decide if it is worth the trade.

In this case, it is.  Found I was not shooting iron sight pistols very well.  Scoping them helped, but realized I was shooting them as if they had a “pretend” butt stock (sand bag rests, taco hold, etc).

Figured I’d just make the pretend butt stock a real one.

BBQing steaks, figure I’ll scatter a few tit bits and (just after dark) see if any of the local rat population can’t resist.

[kenhiraihnl]

Lost 5% (34fps) velocity which equates to about 10% in energy (1.5 foot pound less).

Volume is about 1/2 that of a P-rod (about 33cc's)
15.9gr. JSB's



Doesn’t need to be any more powerful, there is enough power and range there to do what the Benjamins or Sheridans I grew up  with could do (except I only have to  pump it 16 times for every 12 shots).

Your numbers accurately extrapolate data I got with my stock 12" barreled P-rod shooting 16gn PPMs between 1700 and 2700psi, measured with my ProChrono.  Dang, these PCPs are reliably consistent.

[bnowlin]

Sorry but I would say it would be better and cheaper to buy a longer gym bag.
Bob

[Ribbonstone]

Thats what the old golf bag is for.  Load the long rifle in the bag butt first, put a golf club sock over the barrel, and no one looks twice.

Got + two dozen airguns about the place,  so it certainly makes sense to me that they are not tuned to be good for the same thing.