FX Barrel length vs fps
- Thread starter Douglesolocam
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700/600 = 1.166, so about 16% more POTENTIAL energy, this may require a different state of tune and pellet weight to obtain.
-Matt
-Matt
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Sure, the formula is energy % based which you can extrapolate to velocity with a given pellet weight, but you can't calculate the raw fps gain without knowing the pellet weight, if that makes sense.
So if you're shooting 33.9 gr out of a 600mm barrel at 900 fps making 61 fpe, the 700mm barrel may push that same pellet upwards of 970 fps @ 71 fpe, however it would need re-tuned for much longer dwell.
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To complicate this, the higher you get on the Maxwell-Boltzman distribrution bell curve with projectile velocity, the harder it will be to obtain that potential energy without increasing pellet mass. This is because molecules have a WELL known, theorized, confirmed and proven distribution of probable velocity.
Well under Vp is going to be that approximate velocity for dry air (1250 fps) where you'll struggle to obtain your potential energy increase without increasing projectile mass. V max is 1200+ mps, but to obtain such speeds, you'd need an incredible system shooting incredibly light projectiles that take advantage of the small % of incredibly fast moving molecules in air...
Well under Vp is going to be that approximate velocity for dry air (1250 fps) where you'll struggle to obtain your potential energy increase without increasing projectile mass. V max is 1200+ mps, but to obtain such speeds, you'd need an incredible system shooting incredibly light projectiles that take advantage of the small % of incredibly fast moving molecules in air...
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This graph is nice asf and good to know about. But do you have any idea or info what can be the "chamber" what is actually transferport air temperature?
Just for example i have pushed with my .22 impact 800mm barrel pellets at 370+ m/s and looking to this graph for me its hard to believe that impact is so efficient that its able even on the bottom of the graph reach such a speed.
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Barrel length alone will effect dry fire, why? Because of the mass of air present in the barrel... just like removing a barrel entirely will have the most inefficient dry fire of them all...and of course loudest, however marginal, this effect is still going to be present if you test...use hearing protection if you do...
Temperature right behind the pellet before the adiabatic dump into the barrel can reach upwards of 580-600F given the right conditions. I've dieseled pellets and gotten smoke from the barrel in .177 fairly easily and frequently. (Transfer port can reach up to 1.4x that of reservoir discharge in Kelvin, and barrel can reach upwards of 1.4x that of transfer port in K.)
370 m/s is well under the average air molecule speed so with the right pellet weight nearly any pcp with enough barrel and pressure can reach those velocities, to go higher you simply need to go lighter on projectile, there is less and less air molecules traveling at higher and higher speeds the higher you go, and those molecules energy are first to decay and get soaked up by your projectile, hence why lighter projectiles can move the fastest, certainly up at the extreme speed, the need to go lighter becomes exponentially greater the faster you intend to go, till you reach the absolute limit...it boils down to simple probability
-Matt
This graph is nice asf and good to know about. But do you have any idea or info what can be the "chamber" what is actually transferport air temperature?
Just for example i have pushed with my .22 impact 800mm barrel pellets at 370+ m/s and looking to this graph for me its hard to believe that impact is so efficient that its able even on the bottom of the graph reach such a speed.
Temperature right behind the pellet before the adiabatic dump into the barrel can reach upwards of 580-600F given the right conditions. I've dieseled pellets and gotten smoke from the barrel in .177 fairly easily and frequently. (Transfer port can reach up to 1.4x that of reservoir discharge in Kelvin, and barrel can reach upwards of 1.4x that of transfer port in K.)
370 m/s is well under the average air molecule speed so with the right pellet weight nearly any pcp with enough barrel and pressure can reach those velocities, to go higher you simply need to go lighter on projectile, there is less and less air molecules traveling at higher and higher speeds the higher you go, and those molecules energy are first to decay and get soaked up by your projectile, hence why lighter projectiles can move the fastest, certainly up at the extreme speed, the need to go lighter becomes exponentially greater the faster you intend to go, till you reach the absolute limit...it boils down to simple probability
-Matt
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Matt, I currently have the .25 M3 in 700mm but I am looking to go up to 800mm. I like to shoot heavy slugs (typically 36 to 40gr, sometimes I shoot 46gr and sometimes as low as 30gr, but for the most part around 40gr) and I shoot them around 960-980fps
Would you recommned going to the 800mm liner? My thought process was the M3 needs to work harder than the Panthera to reach the same velocities so having a longer barrel would relief some of that work from the rifle.
I guess you also have to consider the longer barrel would introduce more harmonics (I have the barrel tensioned) not sure if that would be a factor as well
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Definitely going to have a bit of adjustment to make switching to that length barrel due to the added dwell and harmonics as you mentioned.
14% difference between those two bore volumes which suggests you'd be able to either make 14% more power if you push it, or save 14% of air, so if you're making enough power or hitting the velocities you desire without requiring much over-dwell, it's probably not too necessary, but if you feel you're maxed out on reg, and want more out of it, say 990-1020~ fps, the 800mm is not a bad choice. Slugs do very well in this fps range.
-Matt
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Thanks Matt, appreciate it. I already have the 700cc bottle on there but an extra 14% of air (or power) is always attractive. =)
When you say dwell you are talking about the amount of time the projectile is in the barrel, or takes to leave the muzzle, correct?
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An excellent example of this in the PB world is the .17HMR 17 grain at 2650fps. The thing is a laser out to 125 yards or so. I can only wish that we could beat the laws of physics with pellets/slugs like that little round.
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I believe he's referring to the dwell on the valve. My understanding is that it's a very delicate balance, get it right and you are rewarded with efficiency get it wrong and you either suck up air and / or get erratic shots.
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You are correct, the pellet dwell. Our pcp's have a few different 'dwells', from hammer dwell (time from release of sear to striking valve), to valve dwell (time from open to close), to pellet dwell (time pellet spends in barrel once valves opened).
Longer barrels suffer a tad more from pellet dwell which as you noted would have a play on harmonics through the barrel and possibly shooter.
-Matt
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