Barrel length and velocity extreme spread.

[lroseen]

I remember years ago reading something about the effects of barrel length and its effects on velocity. I’m not looking for the effects on overall velocity increase/ decrease but specific to average velocity and extreme spread.

An example would be your shooting the same load in two different rifles one ‘Short’ and one significantly longer with a factory load. The shorter barrel should have a greater variation in the extreme spread of velocity compared to a longer barrel up to a point.

I’m just trying to find something on the specifics behind it and can’t find anything with a google search. Everything just comes up with short barrel slower, longer barrel faster….

 

[supercorndogs]

What makes a shorter barrel have a higher ES?

 

[alamo5000]

Just off the top of my head, it would obviously depend on the load and other factors. Say for example you have X percentage of powder burn in one barrel and Y percentage in the other. Then on top of that if the conditions are hot and dry one day and humid and cool the other the results can vary daily.

Not even talking about different barrel lengths, in the same barrel you can get various ES on different days. I would hypothetically speaking say it could change things even more with different barrel lengths, however the primary difference is not the actual barrel but the ammo and it's components.

 

[Rob01]

I remember years ago reading something about the effects of barrel length and its effects on velocity. I’m not looking for the effects on overall velocity increase/ decrease but specific to average velocity and extreme spread.

An example would be your shooting the same load in two different rifles one ‘Short’ and one significantly longer with a factory load. The shorter barrel should have a greater variation in the extreme spread of velocity compared to a longer barrel up to a point.

I’m just trying to find something on the specifics behind it and can’t find anything with a google search. Everything just comes up with short barrel slower, longer barrel faster….

Why? They will be two different barrels and you can see differences in ES/SD in two different barrels of the same length. Unless you are cutting down the same barrel it’s a waste of time to try and figure any difference which is itself is a waste of time.

 

[bulletbluesky]

There's variety of reasons for that, and not every case of barrel and load is the same. It certainly has to do with interior ballistics of the powder burning rate , building up of a pressure, and barrel's resistance. In the case of a very short barrel much of the powder will not burn out in the barrel and intermediate ballistics might even come into play (greater velocity spread is expected)

 

[Edsel]

The shorter barrel should have a greater variation in the extreme spread of velocity compared to a longer barrel up to a point.

308 Winchester / 7.62x51mm NATO: Barrel Length versus Velocity (28″ to 16.5″)

308 Winchester / 7.62x51mm NATO: Barrel Length versus Velocity (28″ to 16.5″) Introduction Released by Winchester in 1952 (and adopted by NATO in 1954 as the 7.62x51mm NATO), the 308 Wi…

rifleshooter.com

Intuitively, this would seem to make sense - like using a large capacitor to crudely dampen electrical noise (in our case, a smoother pressure curve and transfer of energy to the projectile (?).

The idea doesn’t necessarily translate as such into real world, however.

The data in the tables suggests a decrease in SD with longer barrels in some of the strings (sorta, kinda) - but I’m not sure if all the information is available to test for degree of fit in somekinda regression curve. I didn’t really read much into the article…. It doesn’t look like the barrel was “processed” as one would for a regular rifle, for one thing (no proper crown after each cut, etc.)… And five shots per cut length really can’t tell you much.

There’s the well - established observation that certain powders perform better with particular barrel lengths and calibers… Does this imply that there’s a different ideal pressure curve for different barrel lengths? Don’t know…

For those being persnickety over details, there’s also the issue of “all else being equal” getting violated… Your barrel twenty shots later isn’t necessarily the same barrel that it was in the beginning.

I have no idea if firearm data actually follows a normal distribution in the first place.

 

[lroseen]

Why? They will be two different barrels and you can see differences in ES/SD in two different barrels of the same length. Unless you are cutting down the same barrel it’s a waste of time to try and figure any difference which is itself is a waste of time.

Because I’m curios more than anything I suppose! It’s just a different area of containing velocity spread.

Ultimately this gets into building the best loads for a specific gun but also selecting the best barrel length for a factory cartridge. Years ago I observed that a 16” 308 had an ES of upwards of 80+ fps with FGMM, and a 24” have ES of right around 40 fps with the same lot of ammo. Obviously, there is a range due to tolerances of each specific barrel etc. A big principle in theory is that the more powder that burns outside the barrel the greater the ES.

I’ve read info on this years ago and just can’t seem to remember where. There was testing data and all sorts of good information. Just wondering if anyone has any info.

 

[Rob01]

Because I’m curios more than anything I suppose! It’s just a different area of containing velocity spread.

Ultimately this gets into building the best loads for a specific gun but also selecting the best barrel length for a factory cartridge. Years ago I observed that a 16” 308 had an ES of upwards of 80+ fps with FGMM, and a 24” have ES of right around 40 fps with the same lot of ammo. Obviously, there is a range due to tolerances of each specific barrel etc. A big principle in theory is that the more powder that burns outside the barrel the greater the ES.

I’ve read info on this years ago and just can’t seem to remember where. There was testing data and all sorts of good information. Just wondering if anyone has any info.

Good luck.

 

[MikeMiller]

ES versus barrel length
Depends on powder type
You run a faster powder and less ES in shorter barrel once is shorter than load requires for complete burn

In short if you run N570 in 20” 338 Lapua barrel it will suck
You run 748 in a 20” 5.56 barrel it will be good

Because of charge size and speed of burn

Basically common sense

This was proven in handguns before most of us were born

 

[supercorndogs]

ES versus barrel length
Depends on powder type
You run a faster powder and less ES in shorter barrel once is shorter than load requires for complete burn

In short if you run N570 in 20” 338 Lapua barrel it will suck
You run 748 in a 20” 5.56 barrel it will be good

Because of charge size and speed of burn

Basically common sense

This was proven in handguns before most of us were born

 

[Gunfighter14e2]

I remember years ago reading something about the effects of barrel length and its effects on velocity. I’m not looking for the effects on overall velocity increase/ decrease but specific to average velocity and extreme spread.

An example would be your shooting the same load in two different rifles one ‘Short’ and one significantly longer with a factory load. The shorter barrel should have a greater variation in the extreme spread of velocity compared to a longer barrel up to a point.

I’m just trying to find something on the specifics behind it and can’t find anything with a google search. Everything just comes up with short barrel slower, longer barrel faster….

Well if you really want to see the difference the simple way is to load the same case over & over the same way with a subsonic recipe. I did this many years ago and found shorter barrels most always have a lower ES/SD than a longer barrel. Why? Not sure but guessing the added friction points could be higher in the longer. This showed up more when I went from using a .309 cast vs a .314 cast sized back to .313 in a 308win. One of the reasons I went to 16.5" tubes as once past 350yds a 10fps change starts making huge changes, depending target size. Past 550 on a small target and a 10fps change is a very quick miss.

 

[lroseen]

Well if you really want to see the difference the simple way is to load the same case over & over the same way with a subsonic recipe. I did this many years ago and found shorter barrels most always have a lower ES/SD than a longer barrel. Why? Not sure but guessing the added friction points could be higher in the longer. This showed up more when I went from using a .309 cast vs a .314 cast sized back to .313 in a 308win. One of the reasons I went to 16.5" tubes as once past 350yds a 10fps change starts making huge changes, depending target size. Past 550 on a small target and a 10fps change is a very quick miss.

Subsonics would not help in measuring this other than showing the effects when using subsonics. So yes a longer barrel in that case may actually increase the ES if you have already burned all your powder by 16”. Again in theory.

 

[Edsel]

Unfortunately, the great many of us in this hobby can only approach your question from the level of an artisan - that is, trying out different limited combinations to see what works. Guided speculations and limited observations at best.

Even if we had the education and training to do the proper math - we’d probably be limited by skill, proper instrumentation, and time.

 

[xpshooter]

What I've encountered when working up loads for 15" barreled XP and a 24" Rem 700 both chambered in 22 Creedmoor with the same reamer is the load for the XP (H4350 and Berger 85.5) shoots equally well in both guns with small e.s.'s. The load I use in the rifle (H1000 and 88 ELDM) shoots very well in the rifle but sucks in the pistol with a wild extreme spread.