A couple of points:
- I have 18.5", 20" and 26" the 20" is over 100fps slower using the same action. Believe it or not, there IS a difference in group size at 1000 - 1200y, the shorter thus stiffer barrel, may have a theoretical benefit, but you load to your barrel's harmonics anyway. I can tell zero practical difference other than my 26" is more accurate with less wind deflection past about 600m.
- I guess LR is relative. However, you are talking about subsonic accuracy, so I must assume your talking past 1k with the 308. - When shooting way out there, you might have 1 degree of angle. While your math is impressive, an over stabilized bullet will try to retain is angle of departure. Thus causing a nose up angle of attack on the way down. This can negatively effect the flight thru the transonic zone. The trick is to use the correct twist to maintain gyroscopic stability without grossly over stabilizing (my comment only pertains to extremely high angles 12-20 mils and transonic entry) your round if you are truly looking for predictable flight back into subsonic speeds. If you question the wisdom of this, look into why the 408 Chey Tac "system" (bullet and rifling) is such a precision ELR round and pushing accurately to distances not thought possible.
- I also got say again, since the title was about LR hunting; LR hunting with a .308 isn't the best in my option and I am a .308 fan.
PS edited to include: for long range hunting you have seen a lot of good caliber suggestions..
Jt
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JT, I appreciate your input and your points are well taken. That said, and I don't want to appear argumentative, but your arguments go both ways...
You have experienced a loss of 100fps between these four barrel lengths, while using the same action. OK, my question is, "how well did you control the variables when comparing the muzzle velocity of each barrel length?"
Were you changing out barrels in an effort to compare the muzzle velocity between the different barrel lengths, or are you comparing historical data that you have from different barrels which were mounted on your action? In other words, was this a structured test?
Were all of the rounds fired the same kind of ammunition, and were they from the same lot? If they were hand loaded, did you check the calibration of your scale before loading each lot and were your components identical between lots?
Most importantly, were all rounds fired (between each barrel) under the same environmental conditions?
The fact of the matter is, a variation of 100fps can easily come from any number of variables... most notably a simple change in temperature.
So far as whether or not the IS a difference is group size at range between barrel lengths (all other things remaining equal)... until I see the results of a structured test, where all the variables have been controlled as much as possible, this claim is also theoretical. I do not dispute that a longer barrel will allow you to use more of a slower burning powder, which can increase velocity and result in small groups down range. That said, the .308 Winchester cartridge will only hold so much powder. The bottom line is, I have seen guys hitting 10" targets well in excess of 1000m with 20" barrels and I've seen published accounts as well as video of guys hitting 10" steel at ranges over 1000m with 18" barrels. Heck, Todd Hodnett recounts hitting targets (silhouette width not specified) out to 1 mile with a 14" barrel (1:8 twist), in his article on twist rates. Could there be a difference? ...sure. Is a 20" barrel going to provide excellent long range accuracy? ...yeah, I'm confident that it will.
And, yes, you load to your barrels harmonics. That said, a thicker barrel offers less flex and less variation. Less significant vibration = easier to find and load to the sweet spot and less variation if you come out of the sweet spot (i.e. change in MV due to change in environmental conditions)... in other words, more forgiving. Less variation = better consistency. Consistency = accuracy.
So far as your comment, "I guess LR is relative." Not quite sure where you're going with that... one could easily interpret that as a bit of a venomous remark... but, I'm going to leave it alone. That said, regardless of your definition of long range... I doubt too many (if any) of the folks on this site would condone taking shots an excess of 1000m (or more likely 800m) at game, regardless of the caliber you're shooting. Guys feel free to correct me on that if I'm making a false assumption. For me, shots at 1000m or longer (with this rifle) will not be taken at game and will be for entertainment and bragging rights. I've already got a gun set up for shooting 1000m plus... I'm not trying to build another.
In respect to over-stabilization... While I recognize that this is a commonly held belief, I'm not buying it. Your argument makes sense in theory, but I don't see it in practice. Do some comparisons on a sheetrock target at range with the "accepted" twist rate and with a faster twist rate (using the same ammunition). Look at the holes each of the rounds puts in the sheetrock and see if you can find any more evidence of yaw or a nose up angle of attack in the faster twist than in the slower... I'll bet you don't.
The fact of the matter is: the formula used to determine "optimal" twist rates is antiquated and does not take into account the advances that have been made in bullet technology. Many of the newer bullets on the market will not only handle a faster twist, but some may actually require it to truly see the potential of that projectile. You can throw all the theory you want at me, I'm seeing evidence to the contrary. Tell me how a shooter can fire a 16 round group that measured less than 4", at a 1000m target, shooting a .308 Winchester with a 1:7.8 twist, if the round is "over-stabilized"... and this was a tactical rifle, not a bench rest gun.
To completely blow a hole in your theory, I'm going to quote something from Todd Hodnett's article for you: "While shooting the 1:7.8 .308 rifle in my class, I noticed the drop at 1300 meters was only .3 off the normal supersonic algorithm, and the 1:11 twist barrels have an average of about 1 mil deviation from the supersonic algorithm at range. The standard twist will show more than 3-4 times more loss in gyroscopic stability at these ranges. This is more than 200 meters into subsonic flight, but we are getting better groups up close as well."
Frankly, I'm not seeing the relevance of the Chey Tac argument... we're talking about an entirely different caliber. I'm not looking to build an anti-material rifle. Plus, I've read up on the Chey Tac and it looks impressive... then, I've also read some articles debunking the Chey Tac's superiority. Who's right? I don't know... don't really care either at this point. I'll look more into that when I decide to build a large caliber, ultra-long range rifle.
In the end, YOU ARE ABSOLUTELY RIGHT... the .308 is not the optimal caliber for a long range hunting rifle... and I have never made any claim to the contrary. In fact, I think I acknowledged that fact in a couple of my posts. I chose to go with the .308, despite the fact that (in my opinion and in the opinion of probably everyone here) there are many calibers which will outperform it for this purpose. I simply decided that I don't want to get set up for another caliber, when considering that the .308 is fully capable (though not optimal) of doing everything that I want it to do. In the end, it was a decision of cost vs. benefit... while there is undoubtably a benefit to using a different caliber, FOR ME (at this point in time), it isn't worth the cost.
So, I do want to make the point that I appreciate everyone's advice and input... to be sure, it was a learning experience for me. As I said before, I was not at all familiar with the hunting and wildcat calibers before I started this project.
