So, has anybody ever measured how much deflection there is at the end of barrel supported only by the receiver? No particular contour, length or caliber in mind, just wondering ('cause it's cold outside and I'm bored).
Gunsmithing Anybody ever measure barrel droop?
- Thread starter kl3309
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Well to be honest, I would have thought it would be very negligible, or around .001" but its cold outside here too, and I was a bit bored, so...
I modeled a typical Rem Varmint Contour at 26" and just added an additional 1" to the breech end of the barrel to use for "fixturing". I also bored out a 30 caliber hole through the barrel.
Then I fired up a quick simulation where I applied fixed geometry to the 1" extension at the breech, and applied gravity to the part. Didn't have 416 in my materials library so I just used 316 for reference.
Here's the resulting deflection due solely to gravity. I was actually pretty surprised to see a deflection of .006" at the muzzle end. This is a very basic simulation, given the fixed geometry constraint, and just using 316 as a material, but it is pretty interesting. Also, I ran another configuration with a 22 cal bore instead, and the deflection actually increased to approximately .0065" due to the increased mass of the barrel.
I modeled a typical Rem Varmint Contour at 26" and just added an additional 1" to the breech end of the barrel to use for "fixturing". I also bored out a 30 caliber hole through the barrel.
Then I fired up a quick simulation where I applied fixed geometry to the 1" extension at the breech, and applied gravity to the part. Didn't have 416 in my materials library so I just used 316 for reference.
Here's the resulting deflection due solely to gravity. I was actually pretty surprised to see a deflection of .006" at the muzzle end. This is a very basic simulation, given the fixed geometry constraint, and just using 316 as a material, but it is pretty interesting. Also, I ran another configuration with a 22 cal bore instead, and the deflection actually increased to approximately .0065" due to the increased mass of the barrel.
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Out of curiosity, I ran the exact same simulation with a straight 1.25" profile barrel, with a 30 cal bore. Resulting deflection was ~.0058" at the muzzle. So despite the much heavier profile barrel, the increased rigidity (or moment of inertia about the "drooping axis") allows the barrel to have only a marginally greater droop at the muzzle.
Generally speaking, for BR grade accuracy, barrel deflection at the muzzle needs to be kept to 0.0018-0.0020" or less.
The LENGTH of the barrel is the limiting factor for the deflection of the average 1.35" action's tubes. The relative stiffness of a shortening barrel also does not increase in a linear fashion, so 18's figures are WAY stiffer than a 22", where the difference between a 24 and a 26 is not as much.
The longer barrels like 28-30" are HELPED by heavier straight tapers, but they never really catch up. They will still almost always have narrower load windows and be more finicky about things than if they'd been cut at 21.75".
But short is only "okay" if you don't need speed.
-Nate
The LENGTH of the barrel is the limiting factor for the deflection of the average 1.35" action's tubes. The relative stiffness of a shortening barrel also does not increase in a linear fashion, so 18's figures are WAY stiffer than a 22", where the difference between a 24 and a 26 is not as much.
The longer barrels like 28-30" are HELPED by heavier straight tapers, but they never really catch up. They will still almost always have narrower load windows and be more finicky about things than if they'd been cut at 21.75".
But short is only "okay" if you don't need speed.
-Nate
If that's true then the 316 I am using in my simulations must be alot less rigid than the typical 416 used in barrels. I just ran another sim with a straight 1.35" barrel at 26", with a 1" section being "fixed" at the breech, and the resulting deflection at the muzzle was just a hair over .005". Obviously what I am doing is not a perfect replication of the actual scenario, but I would expect the results to be more in line?
Going from memory I think 316 ss has a Yield strength in the 40 KSI and I think, repeat think 416 is in the 80 KSI or higher range.
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