Barrel profiles, stiffness, and 'harmonics'

[BAC]

I was thinking (no, really!) more today about having a barrel turned down forward of the gas block, and it got me thinking into the overall performance of barrels based on their profiles. Tac-Ops and others have shown that shorter barrels can actually increase accuracy because they're stiffer. I assume this is also why heavy-barrel profiles, as well as barrels made from superior materials, are also known for accuracy. Along these lines, a barrel that heats up faster is probably also likely to 'wobble' more, meaning be less stiff, resulting in degraded accuracy while the barrel gets hotter.

Does this mean that a barrel with a tapered profile might actually result in less accuracy, as the stiffer rear and 'flimsier' front might induce wobble? If one is getting a barrel turned down, should it be throughout the whole length of the barrel, or can just part of the barrel be slimmed without compromising the barrel's performance?

Or am I just overthinking it all? :o


-B

[KYPD]

The calculations can get complicated with barrels of variable cross-section. Dan Lilja has a couple of short articles on his webpage that explain the basics.

http://www.riflebarrels.com/articles/barrel_making/rigidity_benchrest_rifles.htm

http://www.riflebarrels.com/articles/barrel_making/rifle_barrel_accurate.htm

The study of barrels and accuracy has consumed the lifetimes of many scholars, and the treasure of many kingdoms for centuries. A fascinating subject. But it requires serious study to understand beyond straightforward results.

[BAC]

Both educational and interesting, thanks for the links. Once I fix my computer and convince it to stop randomly deleting MS office applications, I'll take a look at their Excel program that lets you plug in numbers to figure out barrel weight relative to contour, since I don't envision having a 5 lb barrel on an AR to be a good thing and I'll probably wanna put in my own numbers. :D


-B

[Sry0fcr]

The articles are excellent and the excel programs are extremely useful.

[bkb0000]

Or am I just overthinking it all? :o


-B

overthinking can be a hobby, for some.

based on what i know about barrel harmonics (which isnt much), barrels of consistent thickness are preferable with regard to accuracy. as it was explained to me by a great old gunsmith/armorer that taught me a LOT of what i know about the platform, differences in thickness cause vibration bottlenecks and releases that tweak the barrel out as the round/shockwave move down the length.. WHAT exactly happens, or why its important, i can't say. my understanding is that this really only effects accuracy at the extreme level... 1000m+ shooting, and such.

i gather this is why the "medium" profile is desireable in a recce-style carbine... fairly consistent thickness of ~.750 all the way down the length- as thin/light as you can get and still maintain some degree of harmonic stabilization.

its all voodoo to me, though. and hearsay to you.

[BAC]

overthinking can be a hobby, for some.

Don't I know it. :D


based on what i know about barrel harmonics (which isnt much), barrels of consistent thickness are preferable with regard to accuracy. as it was explained to me by a great old gunsmith/armorer that taught me a LOT of what i know about the platform, differences in thickness cause vibration bottlenecks and releases that tweak the barrel out as the round/shockwave move down the length.. WHAT exactly happens, or why its important, i can't say. my understanding is that this really only effects accuracy at the extreme level... 1000m+ shooting, and such.

That's exactly what I was wondering for tapering barrel profiles, which seems to be why there are only very brief tapers in target shooting barrels (reading some of Lilja's articles seems to support this).

Interestingly, plugging the measurements of my RRA 16" middy barrel into Lilja's Excel program, and comparing it to a 16" barrel like what you described (.750 for all but the first 2.5"), it looks like you shave off half a pound. Granted, that's in 416 stainless steel and not whatever the steel is my RRA barrel is made of, but I can't imagine there'd be too big a difference. I wonder if anyone has the weights available for Noveske N4 and SS barrels...?


-B

[Molon]

I wonder if anyone has the weights available for Noveske N4 and SS barrels...?


-B



16” Noveske N4 barrel: 1 pound, 12 ounces

http://www.box.net/shared/static/5bn75v76zv.jpg




16” Noveske stainless steel Recon barrel: 2 pounds, 1.6 ounces (without the gas block)


http://img56.imageshack.us/img56/9426/noveskebarreloutoftheboxframedcc8.jpg

[BAC]

Interesting, thank you for posting that Molon. Based on the profiles, it looks like there isn't going to be much difference between two barrels of identical lengths and profiles, with one 4150 CMV and the other 416 stainless steel. That should make Lilja's spreadsheet even handier.


-B