She said: no such thing.
But in all seriousness, what is the point of diminishing returns on velocity and energy for barrel length?
But in all seriousness, what is the point of diminishing returns on velocity and energy for barrel length?
How long is too long?
- Thread starter caliusoptimus
- Start date
Depends on multiple factors. With metallic cartridges powder burn rate and the amount of powder used influences how long of a barrel gains velocity before starting to get parasitic drag. In an airgun replace powder with air and the PSI the air is being released at and I would imagine volume of air and that would be the determining factor. So no two rifles will have the same perfect length barrel unless the valving, PSI and volume of released air is the same.
Upvote 0
For me, 500-650mm is the sweet spot for most things. Beyond 650 (for a traditional rifle at least) the thing gets VERY cumbersome and finding a case that you can fly with for such a long rifle is difficult.
My Impact .22 is wearing an 800mm tensioned barrel and the thing just seems way fussier than the same rig with a shorter liner.
With Airguns, lock time is a factor. If you’re shooting a center fire, the round is leaving the barrel at approximately 3x the speed and is therefore (assuming the same barrel length) in the barrel for 1/3 the time as our pellets. As your barrel gets longer your follow through and fundamentals have to get better as well.
Just my .02
My Impact .22 is wearing an 800mm tensioned barrel and the thing just seems way fussier than the same rig with a shorter liner.
With Airguns, lock time is a factor. If you’re shooting a center fire, the round is leaving the barrel at approximately 3x the speed and is therefore (assuming the same barrel length) in the barrel for 1/3 the time as our pellets. As your barrel gets longer your follow through and fundamentals have to get better as well.
Just my .02
Upvote 0
There is a custom rifle built by Scott Hull that has a 48" long barrell.
there is a picture of it in the Benchrest section under "Match Report for the 2024 AirGun Oregon & AOA Extreme Air Gun Challenge"
there is a picture of it in the Benchrest section under "Match Report for the 2024 AirGun Oregon & AOA Extreme Air Gun Challenge"
Upvote 0
It depends on the volume of air and its pressure, dumped into the barrel by the valve. It depends on the expansion volume of the barrel. Thus, the smaller the caliber, the longer a barrel can be and still gain velocity - if you can dump enough air into it, fast enough. As a small barrel bore diameter is in itself a flow restriction, you need higher reg pressure to make "full power".
So, there is no single answer to that question. It depends on the other factors.
If you are shooting sub 12 FPE, then more than 12" is "too much" already in .177; and doubly long in .22. There is a point to shooting a barrel that seems "too long". It reduces the muzzle report and is more air efficient than a shorter barrel, producing the same power. So, handling qualities that stem from overall length; and barrel harmonics must be considered. When the barrel bangs into everything you walk past, and oscillates wildly during the shot, it is probably too long...
So, there is no single answer to that question. It depends on the other factors.
If you are shooting sub 12 FPE, then more than 12" is "too much" already in .177; and doubly long in .22. There is a point to shooting a barrel that seems "too long". It reduces the muzzle report and is more air efficient than a shorter barrel, producing the same power. So, handling qualities that stem from overall length; and barrel harmonics must be considered. When the barrel bangs into everything you walk past, and oscillates wildly during the shot, it is probably too long...
Upvote 0
Maximum FPE is limited by pressure and barrel volume. Assuming you have full control over the valve dwell, and sufficient plenum to maintain adequate pressure, longer will always perform better and/or be more efficient. It becomes a trade off for cost, ergonomics, and necessary follow through. A longer barrel is more expensive. A very long barrel becomes overly cumbersome at some point. A steady hold during the entire long duration shot cycle might also be an issue, Though the weight of a long, heavy barrel can mitigate that.
With airguns, there is rarely any benefit to going above sonic velocity. So for a given relatively light weight projectile, even a short barrel can get you there easy enough. As the sectional density of the projectile is increased, a longer barrel becomes a viable and/or necessary trade off.
With airguns, there is rarely any benefit to going above sonic velocity. So for a given relatively light weight projectile, even a short barrel can get you there easy enough. As the sectional density of the projectile is increased, a longer barrel becomes a viable and/or necessary trade off.
Upvote 0
When it’s only for benchrest or prone shooting what’s too long? 61”? This airgun is intended to shoot 150gr to 180gr .308 slugs at near sonic velocity.
Upvote 0
Upvote 0
There is a point of diminishing returns for barrel length relative to pressure, friction, etc. I've seen tests done on PBs where they plotted the results at different lengths and there is a clear plateau and then a drop off eventually. For those PBs it wasn't crazy lengths, either. Pressure dependent, but they were seeing the plateaus at fairly reasonable lengths of 24-28" if I recall. Even less for some setups. So there is a reason the manufacturers choose their barrel lengths for full length rifles. Some of their testing was on YT, so you could probably find it with a search. It would be interesting to see similar tests done on the airgun side.
Upvote 0
Spartan,
The image grab below may be from the video you mentioned. It is on the MDT Sporting Goods channel. They started with a 6 foot long .308 Win barrel, and shot 175 grain factory loads to capture the velocity as they cut the barrel shorter incrementally. The results may be different from what you remember:
They also did a similar test for .22 LR:
I am not posting active video links because I do not want to violate the firearm discussion forum rule. If you are interested in watching the videos, copy and paste these partial links into YT, or do a google search on them:
watch?v=XCqa2umL8ME
watch?v=xB6izQ8bkq8
.
The image grab below may be from the video you mentioned. It is on the MDT Sporting Goods channel. They started with a 6 foot long .308 Win barrel, and shot 175 grain factory loads to capture the velocity as they cut the barrel shorter incrementally. The results may be different from what you remember:
They also did a similar test for .22 LR:
I am not posting active video links because I do not want to violate the firearm discussion forum rule. If you are interested in watching the videos, copy and paste these partial links into YT, or do a google search on them:
watch?v=XCqa2umL8ME
watch?v=xB6izQ8bkq8
.
Last edited:
Upvote 0
I personally see no reason for me to go longer than a 32" gun. I have 2 at 32" one a bullpup with 21.5" barrel, the other a carbine with 10" barrel. I shoot 18gr pellets out of both Long at 915fps short at 860fps. Longer barrel is obviously more efficient and I'd say easier to shoot consistently. Shorter is just as good when I can hold my own as it is alittle more jumpy. I think anything above 600mm is excessive. I'd never buy a rifle style gun longer than 500mm or bullpup over 600mm. Just personal preference. But I just pest. Like things compact and I'm not shooting high power or anything either.
Upvote 0
For offhand shooting I seem to like rifles around 40" long, with barrels either side of 20" long. Being greedy with barrel length might optimize velocity, but may compromise the rest of the system.
I like rifles that weight either side of 7 lb for the same reasons: Weight, balance and the resultant handling qualities. But then, I am not a "bench shooter".
I like rifles that weight either side of 7 lb for the same reasons: Weight, balance and the resultant handling qualities. But then, I am not a "bench shooter".
Upvote 0
With airgun s different than powder burners..40/inch barrel on pcp still.gaining speed.....22lr loses speed.after 26 inches..
Upvote 0
Comparing PB's to AG's in regards to barrel length is silly.
That is like drawing comparisons between sling shots, and their bands elasticity versus the elasticity of a mans arm muscles when launching/throwing rocks.
The equations that factor into barrel length are complex, and highly dependent on molecular velocity from the propellant in use, where atm air's peak velocity at 1,500-3,000 (average pcp shot pressure) is far less than a firearm's average velocity at 40,000-60,000 psi. There is a velocity curve for all the molecules present in the shot cycle be it air or powder, and as the molecules enter the barrel, the lightest, fastest ones present in the velocity curve push the projectile down the barrel, those super light, and fast air molecules have their energy transferred long before the heavier, slower molecules present in the velocity curve. Consider this a 'race against time', rabbit vs the hare if you will. Just take the Skout PCP for example, its a long barrel PCP, why is that, because it uses much lower pressure than the typical pcp. If you were to go to a more extreme and shoot down to 200-400 psi, you could still reach incredible velocities, but man will you need a lot of barrel to do so...So as to the race against time, the complex calculus involved with barrel lengths is shot duration (time) and pressure/average molecular velocity.
Also note, the way pcp's discharge is via valve dwell, which is not present in firearms/powder burners, which use ignition. Meaning you can discharge for a longer duration of propellant during the shot cycle than a firearm, which lends air guns to be more favorable in obtaining notable gains as barrel length is increased, a pcp shooting at 1,000 psi, making 50 FPE needs far more valve dwell (and barrel length) than a pcp shooting 3,000 psi making 50 fpe.
To answer the question how long is too long?
Really that is subjective, depends on your projectile weight, shooting distance, caliber, target/use case, available pressure, energy desired, noise reduction requirements.
It's really not a one size fits all, and to reiterate, comparing barrel length between airguns and firearms is...silly
-Matt
That is like drawing comparisons between sling shots, and their bands elasticity versus the elasticity of a mans arm muscles when launching/throwing rocks.
The equations that factor into barrel length are complex, and highly dependent on molecular velocity from the propellant in use, where atm air's peak velocity at 1,500-3,000 (average pcp shot pressure) is far less than a firearm's average velocity at 40,000-60,000 psi. There is a velocity curve for all the molecules present in the shot cycle be it air or powder, and as the molecules enter the barrel, the lightest, fastest ones present in the velocity curve push the projectile down the barrel, those super light, and fast air molecules have their energy transferred long before the heavier, slower molecules present in the velocity curve. Consider this a 'race against time', rabbit vs the hare if you will. Just take the Skout PCP for example, its a long barrel PCP, why is that, because it uses much lower pressure than the typical pcp. If you were to go to a more extreme and shoot down to 200-400 psi, you could still reach incredible velocities, but man will you need a lot of barrel to do so...So as to the race against time, the complex calculus involved with barrel lengths is shot duration (time) and pressure/average molecular velocity.
Also note, the way pcp's discharge is via valve dwell, which is not present in firearms/powder burners, which use ignition. Meaning you can discharge for a longer duration of propellant during the shot cycle than a firearm, which lends air guns to be more favorable in obtaining notable gains as barrel length is increased, a pcp shooting at 1,000 psi, making 50 FPE needs far more valve dwell (and barrel length) than a pcp shooting 3,000 psi making 50 fpe.
To answer the question how long is too long?
Really that is subjective, depends on your projectile weight, shooting distance, caliber, target/use case, available pressure, energy desired, noise reduction requirements.
It's really not a one size fits all, and to reiterate, comparing barrel length between airguns and firearms is...silly
-Matt
Upvote 0
The barrel length limit for my latest build was set by the length of the gun case that I already had. I left enough room for 1” of padding on each end of the rifle.
Long black case for .308 with 61” barrel:
Long black case for .308 with 61” barrel:
Last edited:
Upvote 0
I saw a chart on another site just the other day showing results of a couple real world tests using decreasing length barrels with a couple different guns. If I remember right, 600 was about the sweet spot.
Upvote 0
It is all about expansion volume as a ratio to case volume (powder capacity). So, shorter for larger calibers using a given case capacity; and longer for smaller calibers with a given case capacity. For PCPs, "case capacity" translates to plenum capacity, reg pressure, and valve area, lift and dwell. Also flow efficiency through the TP. So, there is no one barrel length that is best for all PCPs. "Best" in this context may be for obtaining 90% or less of the potential energy, as trying to obtain 100% is likely to make the airgun unwieldy.
Unwieldy is in the eye of the beholder, and depends on the main purpose for that airgun. Scotchmo's .308 shown above is not unwieldy as a long range bench rifle. It would probably be unwieldy to shoot offhand or walking around a hunting field. There a 600 mm barrel sounds much better.
Last edited:
Upvote 0
It’s certainly possible that 600mm was the “sweet spot” for that particular tune. While a different tune might use an 800mm barrel for the “sweet spot”.
Upvote 0