fps lost per inch of barrel reduction?
- Thread starter Peep
- Start date
Yes, cutting and crowning on a lathe by a very skilled machinist.
18.13 - Thanks for the info.
18.13 - Thanks for the info.
Upvote 0
i dont know the exact formula but ive screwed around with a couple of barrels ... given no changes to the tune youll likely lose two three hundred anyway cutting it down to 12 ... id be sure its not a choked barrel either or accuracy will be in the shtcan ..
Upvote 0
12fps per inch is a huge reduction in velocity, but still may do it. Looks so cool and handles so well.
Upvote 0
Cut the barrels on a few springers, not a 12" reduction but a few inches here and there. In most cases little to no loss in velocity, however on my .22 barrels (R1) I actually increased velocity and accuracy!! Cut off two different barrels and had same results with both. On the 3rd rifle I used a factory carbine barrel rather than cutting but lost 20 fps and accuracy was not as good.
Upvote 0
I will chrono before and after the chop. Now really curious about the outcome. Will try a shot or two next to a sound meter also. My compressor is down or I would baseline the gun, as it is I'm glad to have a few shots left.
Upvote 0
Springer (wouldn't think your 24" is one but) down to 10-12" no change or slight increase.
PCP tuned in a normal range 10-15fps per inch however unless tuned low & slow somewhere around 14" you may see a greater lose per inch.
John
PCP tuned in a normal range 10-15fps per inch however unless tuned low & slow somewhere around 14" you may see a greater lose per inch.
John
Upvote 0
It depends if you are talking Pneumatic, or Springer. If a springer, there will be very little change. Sometimes even improving in velocity if coming down from 18 inches to 12 inches. The minimum to go is 11 inches as a reduction in power starts around 10 inches.
With Pneumatics you will get a big reduction. Most barrel mods (lengthening) on Crosman pistols. or single stroke, usually see 25fps per inch increase (very roughly gun dependent) On PCP rifles, short carbine versions see a big reduction in shot count for the gun to make the same power, meaning they must dump more high pressure air per shot to make the same power in short barrel versions.
The only time i have seen springer guns improve for having longer barrels is in the case of air pistols with decent size power plants, where their barrels are not quite long enough to make the most from that power plant. A good example being the old BSA Scorpion pistol, where the 18 inch barrel version for the Buccaneer air rifle (shared power plant) would make a bit more over the shorter barrellled pistol. ….Trimming it back to 11 inches long made even more ….suggesting an optimum of 11 to 12 inches for this gun. The HW45/P1 will also gain a bit up to a point…approx 9 inches before nothing else is gained.
With Pneumatics you will get a big reduction. Most barrel mods (lengthening) on Crosman pistols. or single stroke, usually see 25fps per inch increase (very roughly gun dependent) On PCP rifles, short carbine versions see a big reduction in shot count for the gun to make the same power, meaning they must dump more high pressure air per shot to make the same power in short barrel versions.
The only time i have seen springer guns improve for having longer barrels is in the case of air pistols with decent size power plants, where their barrels are not quite long enough to make the most from that power plant. A good example being the old BSA Scorpion pistol, where the 18 inch barrel version for the Buccaneer air rifle (shared power plant) would make a bit more over the shorter barrellled pistol. ….Trimming it back to 11 inches long made even more ….suggesting an optimum of 11 to 12 inches for this gun. The HW45/P1 will also gain a bit up to a point…approx 9 inches before nothing else is gained.
Upvote 0
Depending on the gun, projectile, and tune it's possible to gain velocity going shorter. You didn't say what gun, or really any other factors.
https://www.airgunnation.com/topic/looking-for-info-regarding-pistol-barrel-length-and-velocity-correlation/?referrer=1
I chopped a FX Crown barrel to short pistol lengths and logged results here. The gun (pcp 1322) I was doing the testing for wound up with a 7.6" barrel that hit 872fps with 16gr .22 pellets
https://www.airgunnation.com/topic/looking-for-info-regarding-pistol-barrel-length-and-velocity-correlation/?referrer=1
I chopped a FX Crown barrel to short pistol lengths and logged results here. The gun (pcp 1322) I was doing the testing for wound up with a 7.6" barrel that hit 872fps with 16gr .22 pellets
Upvote 0
At 12 inch or 300mm your sweet spot max speed should be between 720-760 FPS depending on how high your reg can go regardless of projectile weight, so go as heavy as you can if you want to retain power.
Upvote 0
Great idea, also a safety factor for not going to far. Once you see a significant drop, you may not want to go any more!!!!
Upvote 0
This is for a .177 using 850psi hpa.
21" barrel 814fps
20" 813
19" 804
18" 801
17" 781
16" 766
15" 747
14" 738
John
21" barrel 814fps
20" 813
19" 804
18" 801
17" 781
16" 766
15" 747
14" 738
John
Upvote 0
Interesting question to me because I would think that shortening a barrel would increase the velocity due to decreased friction. With a firearm the power is continuing to burn and gasses are expanding as the powder burns so a longer barrel gives more velocity. But with an airgun you have a fixed amount of air and constant pressure vs. building pressure as the pellet goes down the bore....right? I guess I must be wrong, but I am curious to hear the reason and why it would be different by type of air gun.
thanks
Matt
thanks
Matt
Upvote 0
can there be a universal answer? i don't think so.
it must depend on how long the pressure behind the pellet is still accelerating it.
if you get higher velocities from cutting the barrel, obviously that gun/tune had stopped pushing before the pellet left the barrel, and the pellet was already slowing down. this sort of thing probably provides a very quiet gun compared to excess pressure where there is more air being used than needed to achieve a given velocity - because the pellet already exited the barrel.
it must depend on how long the pressure behind the pellet is still accelerating it.
if you get higher velocities from cutting the barrel, obviously that gun/tune had stopped pushing before the pellet left the barrel, and the pellet was already slowing down. this sort of thing probably provides a very quiet gun compared to excess pressure where there is more air being used than needed to achieve a given velocity - because the pellet already exited the barrel.
Upvote 0
True. I would be curious to better understand the physics behind this topic. I assume there are many variables, but essentially you have a pulse of air that starts at a fixed pressure. As the pellet moves down the bore, the space expands and therefore the pressure is decreasing the entire time. The biggest variable would be the volume of the pulse of air I would think and how much volume of air is behind the pellet. I guess another variable would be the timing between the release of the full volume of air vs. when the pellet starts to move.
I have read that with a springer the piston is fully forward before the pellet even begins to move. With a higher powered PCP it may be possible that the pellet is moving before all of the air pulse has been discharged.
At some point there has to be a sweet spot that i guess would be different for every gun.
However, if that sweet spot does not correspond with the barrel length on the gun, then what good is the extra length doing you? All it would do is slow the pellet and increase barrel time and reduce accuracy as a result....I would think.
With firearms the pressure curve is dynamic. You have a very high pressure upon ignition of the propellant in the chamber. Then as the volume expands the pressure reduces. But as the power continues to burn going down the barrel the pressure starts to built again. That's from memory so I could be wrong, but that's what I recall---and that the highest pressures occur at the chamber and then later at the muzzle (although lower here than the chamber). I probably need to research this again, but this is called internal ballistics. I would be intererested to learn more about air gun internal ballistics.
Matt
I have read that with a springer the piston is fully forward before the pellet even begins to move. With a higher powered PCP it may be possible that the pellet is moving before all of the air pulse has been discharged.
At some point there has to be a sweet spot that i guess would be different for every gun.
However, if that sweet spot does not correspond with the barrel length on the gun, then what good is the extra length doing you? All it would do is slow the pellet and increase barrel time and reduce accuracy as a result....I would think.
With firearms the pressure curve is dynamic. You have a very high pressure upon ignition of the propellant in the chamber. Then as the volume expands the pressure reduces. But as the power continues to burn going down the barrel the pressure starts to built again. That's from memory so I could be wrong, but that's what I recall---and that the highest pressures occur at the chamber and then later at the muzzle (although lower here than the chamber). I probably need to research this again, but this is called internal ballistics. I would be intererested to learn more about air gun internal ballistics.
Matt
Upvote 0
Upvote 0
Matt, Look around for , Cardew "The Airgun From Trigger To Target" for the low down on springers.
John
Upvote 0