Optimal Barrel Length?

I mostly hunt in the mountains of Northern Colorado and it occurs to me that Miles = Elk and pounds kill miles. If I was carrying my rifle 200 yds to my stand it would make no difference if I was to carry a 15 lb rifle, but in the hills I want as light a rifle as I can get within my budget, that will humanely take my quarry at distances I am competent to shoot. As the Barrel is usually the easiest place to cut weight that is a good place to start.

But when you cut a barrel there are consequences. The longer a barrel is, the more time you give the powder to ignite and more ignited powder propels the bullet faster, is less loud and less muzzle flash. so any discussion about barrel length is a discussion about trade offs.  

There seems to be a lot of speculation as to what the proper barrel length is and what you are giving up for a shorter, lighter rifle. I have heard a few rules of thumb which state that there is a XX foot per second (fps) loss for every inch of barrel removed. But where is the actual data? In comes  Ballistics By The Inch. The guys at BBTI  took 25 different calibers (mostly pistol) and measured  exactly what the per inch velocity loss is and I am here to tell you that it is not a linear loss of velocity. This data makes it possible for us to quantify what that extra inch of barrel we are lugging around is getting us.

For this article I will take a look at the .22lr to see if there is any merit to lugging around an 18" barreled rifle. I hope to find good data that will allow me to determine the optimal length for 6.5 Grendel. 6.5 Creedmore, 300 BO and 308 Win for future articles.

In my other life I have found that looking at a chart can sometimes be illuminating and can tell me things that I can't readily see in a spreadsheet. This is very true in the case of barrel inches vs velocity I copied and pasted the data assembled by the BBTI experiment into a Google Sheets spreadsheet. I then used a line chart to plot the different cartridges and see if I could identify the optimal barrel length by finding the point at which another inch of barrel was not gaining me much additional velocity.

 

I believe that this chart illustrates the fallacy in stating that there is a known linear loss of velocity per inch of barrel. In .22 lr alone the velocity delta (difference) from inch to inch varies from 8 fps (from 18" to 17") to over 155 fps (from 2" to 3"). 

From this chart I can see that after 6" I stop getting big increases in fps and by the time I get to 10" there is a very minimal gain per inch.

  • From 2" - 10" I gain around 478 fps or ~60 fps per inch of barrel
  • From 11" - 18" where the gain is a paltry 47 fps or 5.9 fps gain per inch

From this data I conclude that past 10"  I am not really getting much velocity for any additional inch of barrel. And in a perfect world (with the NFA abolished) 10" would be the barrel length for all of my hunting .22s.

Can't wait to dig into more calibers and see what the data says!