This was taken from this article:
http://www.sniperschool.com/sniper-rifle-barrel-length/" “All Great Truths Start as Blasphemy†-George Bernard Shaw
Appropriate barrel length for sniper rifles has been debated at length in tactical communities and online forums alike. In the spirit of GPS Defense’s teaching principle of deciphering the truth out of the piles of opinions by testing a theory and seeing the results first hand, we decided to put the barrel length issue to rest.
As our previous students can attest, and as you will experience in any of our classes, we often choose to prompt our students to figure out the answer to a question or previously held belief on their own. Chances are, we have encountered their question or opinion many times before and we have learned that the reason they are led to believe a certain point is simply because somebody else told them it was so. If we do the easy thing by simply telling them the correct answer, the truth we tell them will have no more weight in their mind than the possibly incorrect information that has been unquestioned and passed down from person to person.
Simply put, barrel length (within reason) does not affect accuracy within a manner many people believe. My personal rifle, based off of a Remington 700 action, has an 18" .308 barrel. When people see my rifle, they often ask, “How much does that affect the accuracy?â€
Their question, although a valid one, is usually asked in such a way that assumes accuracy must have been compromised in order for the barrel to be so short. The exact opposite is true.
My rifle came from the factory with acceptable sub minute of angle (less than 1" group per 100yds) accuracy out of a 26" barrel. I had my barrel cut down to 18", took it out to the range and was pleasantly surprised to see the accuracy improve to a 1/2 minute of angle. Yes, you just read that right… the shorter barrel was more accurate.
When I dropped off the rifle to have it cut and re-crowned from its factory length, the gunsmith asked how short I wanted the barrel to be, and when I told him 18", he tried his best to talk me out of it. He explained to me that 20" is a “safe†length and about as short as he has seen people go while maintaining accuracy. I decided that since I was cutting the barrel to create a more manageable and compact shooting platform and partly to prove a point, I shouldn’t go to a “safe†length…. I should go shorter.
A common argument I hear from disbelievers revolves around some sort of belief that the twist rate must relate to the barrel length. This fallacy tries to say that since the twist rate of my .308 700 PSS is 1 in 12", the barrel must be cut to a length in multiples of 12 inches in order for the bullet to spin properly. This is absurd. If this was true, Remington would never ship the PSS from the factory with a 26 inch barrel. And for that matter, a 1911 style .45 with a twist rate of 1in 16" would have a 16" barrel in order to be able to hit the target.
So, if a bullet from my barrel is spinning at a 1 in 12" rate regardless of the length, why did cutting it down increase the accuracy? The answer lies in the effect of barrel stiffness. We all understand that a thicker bull barrel will provide better accuracy than a thin sportster style barrel. From this we know that a stiffer barrel helps increase accuracy by negating excessive barrel flex and vibration. The only way to stiffen an already stiff bull barrel from the factory is to shorten it. Let me explain….
Inch per inch, the barrel’s stiffness has not changed. But when taking the entire length into account, the overall effect is a stiffer barrel. Think about a 2 inch stick that is just stiff enough to be unbreakable. Now, take a stick of the same diameter with a length of 12 inches…. it would be much easier to break. Each individual inch of the two sticks share the same rigidity, but the longer stick allows more leverage to be imparted on the stick and therefore nets less overall stiffness and more leverage.
So, by cutting the barrel, the twist rate was not affected and the barrel was relatively stiffer. The only other concern lies in whether or not the powder has enough time to burn before the bullet leaves the barrel. This should not affect accuracy since it should burn consistently whether or not it burns completely. The only problem will in fact lie in the change in velocity of the bullet.
At 100 yards, I found absolutely no change in the point of impact of the bullet from the longer 26" original length to the new shorter 18" length. I did, however find a significant difference at longer distances.
At our 920 yard target on our range, school rifles with standard length barrels are able to hit the target with a 34 minute of angle adjustment above their 100 yard zero. When I first shot my rifle to compare the bullet drop from my rifle with the short barrel to the school rifles, I was using 168 grain Federal Gold Match ammunition and recorded hits at 39 1/2 minutes up from my 100 yard zero. That translates into a little over 50 inches of difference between the barrel lengths at 920 yards!
After realizing that the powders used by Federal (ammo I used) and Black Hills (ammo the students use) may burn at different rates, I decided to re-test my rifle with the 175 grain Black Hills Match ammunition that our students use. When using the same ammo, my rifle only needed 36 minutes of elevation in order to hit the target. Based on changing the ammo, I had a 3 1/2 minute change at 920 yards! Using consistent ammo and consistent environments, my 18 inch barrel only requires two additional minutes of elevation to engage a target 920 yards away!
With a more manageable, compact, lighter, and more accurate rifle only requiring only 2 more minutes of angle at 920 yards, I see no reason to not cut down a barrel on a sniper rifle. Still don’t believe me? Enroll in a class and I will shoot my short barrel rifle next to yours and you can learn what happens in the manner we suggest the most… you can see for yourself.
–Ryan Cleckner"
Comment: Even though airguns are working on a slower muzzle velocity and does not use powders to propel a projectile I think the principle of barrel rigidity still applies. Shortening a barrel does not lessen the metal's stiffness but rather "enhances" it. Working like a "whip" in motion (an exaggerated analogy) a longer barrel will have a bigger vertical deflection than a shorter barrel since the cantilever principle is more defined. With a shorter barrel it would be much harder for the same material to have a greater bending moment at the end of the cantilever because the force (due to weight) has a much shorter moment arm to deflect it. However, everything must be taken in the light of the muzzle velocity. I think PCP's have a better advantage on this one (should you want to further experiment on the idea of barrel length versus accuracy) because on some PCP-based design you can change the pressure of the air and therefore change the muzzle velocity of the pellet being used. With springers it would be very hard since we only deal with one specific type of piston spring to generate that air pressure at the chamber. I guess this is also the reason why every springer are not alike and tend to favor a certain type of pellet to another. Even if you shorten the barrel of a springer it will probably more of a trial and error since there are a lot of variables that has to be factored in and there is no definite formula yet that can give a clear explanation as to how all these things come into play. However, I know some guys who were quite successful in shortening the factory barrels of their airguns and achieve excellent results ( C.A.P. is one of them) after shortening. A big trade-off would just simply be a harder time to cock the rifle since you have a shorter barrel to help you compress the psiton spring during cocking. Just my 2 cents on the matter.
Speedturtle
