Gunsmithing barrel length and accuracy???

[stradibarrius]

I would like to better undersrtand how barrel length effects accuracy? many tactical rifles have 20" barrels but both of my "long range" guns have 26" barrels.
I understand that longer barrels help get the bullet spinning for more stability downrange, but what is the deciding factor when a manufacture designs a gun with a given barrel length?
I am looking at a new gun that seems to easy to find in a 20" barrel but bit more difficult to find in longer lengths.
Example question: Would a 6.5 cr with a 20" barrel shot accurately at a 1000yds?

 

[jg6.5]

Barrel length doesn't have so much to do with accuracy as it does velocity. In your example, a 6.5CM with a 20" barrel would theoretically be just as accurate as one with a 26", albeit slower.

Edited to add: What "new gun" are you looking at? A 20" barrel length may be all you really need unless you're wanting to handload and experiment with slower burning powders to gain velocity.

 

[Gunfighter14e2]

Barrel length is also about usage. Short barrels are faster pointing, an most prefer the balance point more towards the rear than the muzzle. Also with the ability to order the bore you want over what std mfgs sell, helps to keep the speed up. Ie instead of a 300 bore on a 30cal you can get a .299 or .298 which seals better. I have a 18" 10 twist .298 barrel that throws 165s, 8 fps faster (same load) than a 10 twist 22" 300 bore I have. The more compact to me while still reaching the target supersonic, is to my liking over anything longer.

 

[jg6.5]

Barrel length is also about usage. Short barrels are faster pointing, an most prefer the balance point more towards the rear than the muzzle. Also with the ability to order the bore you want over what std mfgs sell, helps to keep the speed up. Ie instead of a 300 bore on a 30cal you can get a .299 or .298 which seals better. I have a 18" 10 twist .298 barrel that throws 165s, 8 fps faster (same load) than a 10 twist 22" 300 bore I have. The more compact to me while still reaching the target supersonic, is to my liking over anything longer.

It's true that shorter rifles are more (some may say subjectively) "handy" than longer rifles, and you may have luck with the bore diameter as you described, but the OP's question is purely about barrel length and accuracy.

Theoretically, if you had two identical barrels in identical calibers built on identical actions by the same gunsmith back-to-back, and the only difference being barrel length, there should be no quantifiable accuracy difference between the two. The only thing that should be different is that the longer barrel should shoot faster than the shorter barrel. Points of impact in reference to point of aim will more than likely be different, but accuracy (or "precision" to be exact) should be more or less the same.

 

[Gunfighter14e2]

It's true that shorter rifles are more (some may say subjectively) "handy" than longer rifles, and you may have luck with the bore diameter as you described, but the OP's question is purely about barrel length and accuracy.

Theoretically, if you had two identical barrels in identical calibers built on identical actions by the same gunsmith back-to-back, and the only difference being barrel length, there should be no quantifiable accuracy difference between the two. The only thing that should be different is that the longer barrel should shoot faster than the shorter barrel. Points of impact in reference to point of aim will more than likely be different, but accuracy (or "precision" to be exact) should be more or less the same.

Had a GAP built 700 with a 5.5 rem taper 26" mike Rock, 35.7 moa to a grand. A 22" PacNor 5.5 taper, shooting the same load got to a grand at 35.7 moa an held a much tighter group. The GAP never won the match, the PacNor did more than once.

 

[ptm121]

In theory, shorter barrels are more accurate. Tolerances are more difficult to hold over longer distances. Shorter barrels also are relatively stiffer for the same profile, and so the harmonics are easier to work with.

Once you get past 100yd benchrest, barrel lengths start creeping up. Longer tubes mean more velocity, and that means less drop and drift. This is why F-class guns have a lot of 30" barrels.

For the purposes of most people on this site, you can forget about the pure accuracy advantages of short barrels. For positional shooting, it's purely a tradeoff in handling vs. velocity. Look at what velocities people are getting in various lengths (and what powders help them get those velocities), and then balance that against weight and handling. Profile obviously comes into play as well - heavier tapers are more forgiving to tune, and take rapid strings much better.

 

[natdscott]

Barrel length doesn't have so much to do with accuracy as it does velocity. In your example, a 6.5CM with a 20" barrel would theoretically be just as accurate as one with a 26", albeit slower.

That's not really true.

Keeping all else about the materials and diametrical contour equal, a short barrel shows lower muzzle deflection than a longer one. In other words, it's stiffer.

Stiffer barrels result in much wider loading nodes; another way of saying that is that they will put slightly less consistent ammunition into small holes on target MUCH better than a longer barrel.

 

[demolitionman]

video seemed fitting for this thread.


Not my video but seems fitting for this thread.

 

[jg6.5]

Had a GAP built 700 with a 5.5 rem taper 26" mike Rock, 35.7 moa to a grand. A 22" PacNor 5.5 taper, shooting the same load got to a grand at 35.7 moa an held a much tighter group. The GAP never won the match, the PacNor did more than once.

2 different manufacturers, so you're introducing more variables. I'm not saying you're wrong, I'm just saying that you can't attribute that to length alone. Also, what caliber are we talking? Assuming 308WIN given that drop. The 308 is a cartridge that is not known for really "needing" a longer barrel unless you want to burn slower powders and push bullets faster.

That's not really true.

Keeping all else about the materials and diametrical contour equal, a short barrel shows lower muzzle deflection than a longer one. In other words, it's stiffer.

Stiffer barrels result in much wider loading nodes; another way of saying that is that they will put slightly less consistent ammunition into small holes on target MUCH better than a longer barrel.

Yeah yeah, I get the stiffness thing. For what it's worth, I personally like to run my barrels as short as possible without cutting my nose off to spite my face in the velocity department. To borrow from @ptm121 above, if I was going to make a rifle that was only going to be used on a 100-200 yard benchrest range, it would have a short barrel about has big around as a truck axle...but given that most guys/gals on this site aren't plugging away from a concrete bench all day, a balance needs to be struck. Contour for weight - heavy as you can stand it hauling around from stage to stage or possibly shooting off-hand; length as short as the desired cartridge/powder combination can stand it without sacrificing too much velocity, and makes navigating it around obstacles or barricades a touch easier.

 

[natdscott]

I get that. My 6.5 is a 30" barrel because I will need the speed, but the fact is that I am ACCEPTING the possibly finicky loads and narrow load windows because I know it is a specialty purpose.

Going into that sort of decision blindly is a good way to make a poor decision for your needs.

Hence: my post.

-Nate

 

[jg6.5]

I get that. My 6.5 is a 30" barrel because I will need the speed, but the fact is that I am ACCEPTING the possibly finicky loads and narrow load windows because I know it is a specialty purpose.

Going into that sort of decision blindly is a good way to make a poor decision for your needs.

Hence: my post.

-Nate

Absolutely. So going back to the OP, it looks like we should be asking them "what are you using the rifle for and what are your expectations?".

 

[CharlieNC]

A lot of the top gunsmiths have been trying to figure this out for a long time. The clencher is harmonics that provide positive compensation; that is as the muzzle oscillates up/down, the higher velocity bullets exit the muzzle when it is pointing lower in the cycle than the slower ones. Therefore, minimizing the effect of variable velocity on the target. When you run a load ladder vs charge weight, this is where a node occurs; and the node varies in width and "flatness". This is the principle by which tuners work. Numerous theories and debates abound on the topic, which is yet to be settled to the general agreement.

 

[SparkyHD1]

It's always been my understanding that if your using a shorter barrel you should use a faster burning powder otherwise a lot of the charge just goes up in smoke after it leaves the barrel. years ago i was working loads up for a 308 with a 20 inch barrel. i would check the loads by shooting after dark to see how much muzzle flash i would get from the unburnt powder leaving the barrel. i know short barrels are very accurate and have a purpose, but i think it's important to match the powder and charge to the barrel length. unless you like watching big fire plumes of fire leaving your barrel...lol

 

[sifer0425]

that is the question i have now adays. i used to have a rpr with a 24 inch barrel and was shooting at 400yards at about 6.5moa up on my dial.
now i find with my new barrel that is 26inches, that i have to go to almost 7.25moa up at 400 yards any reason for that