The Truth About Barrel Length, Muzzle Velocity and Accuracy

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The Truth About Barrel Length, Muzzle Velocity and Accuracy
BY DAN ZIMMERMAN

The Truth About Barrel Length, Muzzle Velocity and Accuracy
Josh Wayner’s taken it upon himself to challenge what everyone “knows” as far as barrel length, velocity and accuracy are concerned. According to his results, the conventional wisdom ain’t all that wise when it comes to longer-barreled ballistics. The only question then is, if you buy in and go with a short barrel, can you stand the noise?

Abstract: This is an independent scientific study that has been conducted in western Michigan. This study addresses the misunderstanding of the concepts related to barrel length, muzzle velocity, and accuracy in a rifle . . .


Elements of the Study: This study was conducted with a set of standards that do not necessarily correspond to all manner of firearms. The combination of weapon and ammunition used for this study was carefully determined and analyzed for the best results. This study was conducted with what the author and fellow researchers determined to be the most precise materials and methods available gathered from expert input and other existing studies.

The platform used for this is a Shilen match barrel which began at 26 inches in length and ended at 13.5 inches. The chamber is of standard SAAMI specification in .308 Winchester and the barrel features a 1:10 right hand twist. The ammunition used for this test is of several types, all of which are of corresponding lot numbers. At each range, handloads were used to seek out advantages given the barrel length by modifying the bullet and powder. This data is included gratis and represents the abilities of the weapon system when tuned ammunition is available.

For this test, the barrel was attached to a Savage short action target receiver in a Scally Hill Systems MK4 Mod7 folding chassis. This test measured all three variables at the same time in the most similar conditions available. Testing was conducted at Southkent Sportsman’s Club in Dorr, Michigan and Chick-Owa Sportsman’s Club in Zeeland, Michigan. Firing was conducted at a distance minimum of 100 yards and a maximum of 540 yards. Informal ‘field’ shooting was conducted on private land at safe targets out to a distance of 900 yards, accurately measured by satellite using Google Earth.

Ambient conditions were on average 70-75 degrees Fahrenheit with 40-50% humidity at an elevation average of 670 feet. Shooting was conducted with a 16x SWFA SS optic, a piece well noted for its durability and ruggedness. Velocities were obtained using a chronograph and extrapolation of shooting results. Group size was measured with a micrometer. Five shot groups were used to measure accuracy. Firing was conducted on standard IPSC silhouette targets at all ranges.

COMPLETE ARTICLE HERE:

https://www.thetruthaboutguns.com/2013/10/daniel-zimmerman/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/
 
Interesting study but I didn't think anyone still believed that a longer barrel was more accurate? A longer barrel does allow you to get more muzzle velocity for a same load/pressure though. At distance, higher velocity equals less drift from the wind ergo more accuracy (in that your wind call doesn't have to be as precise to still hit your target). When the guy says this: "There is a downside to longer ranges and reduced velocities, that being increased susceptibility to wind as range increases. Increased drift is not the end of the world, though, and if measured properly, can be overcome with ease." it makes me wonder how he could've been shooting long range for a decade and still think that it's a trivial matter to "properly measure" wind... At one point he talks about a 300fps difference as if that was no big deal. I'm too lazy to punch the numbers into JBM but I'm willing to bet that 300fps makes a real sizeable difference to your drop (and ergo your danger space for a mismanaged target) not to mention your wind call...
 
rugbydave said:
Interesting study but I didn't think anyone still believed that a longer barrel was more accurate? A longer barrel does allow you to get more muzzle velocity for a same load/pressure though. At distance, higher velocity equals less drift from the wind ergo more accuracy (in that your wind call doesn't have to be as precise to still hit your target). When the guy says this: "There is a downside to longer ranges and reduced velocities, that being increased susceptibility to wind as range increases. Increased drift is not the end of the world, though, and if measured properly, can be overcome with ease." it makes me wonder how he could've been shooting long range for a decade and still think that it's a trivial matter to "properly measure" wind... At one point he talks about a 300fps difference as if that was no big deal. I'm too lazy to punch the numbers into JBM but I'm willing to bet that 300fps makes a real sizeable difference to your drop (and ergo your danger space for a mismanaged target) not to mention your wind call...
Click to expand...

For the gold standard Federal GM 308 Win 175gr :

Muzzle Velocity Wind drift per 1mph Wind drift per 1mph
sidewind at 1000 yards delta from 2600fps
2600 fps 11.17 " 0.00 " (0.00 MOA per MPH)
2500 fps 11.91 " 0.74 " (0.72 MOA per MPH)
2400 fps 12.65 " 1.48 " (0.14 MOA per MPH)
2300 fps 13.37 " 2.20 " (0.21 MOA per MPH)

So here you have it: with 300 fps lower muzzle velocity, your accuracy is increased by 0.2 MOA per MPH of error on a side wind.
I'm not much a wind reader so it's really going to hurt since a 3-4 MPH error will add an extra 0.6-0.8 MOA to overall accuracy.
(Note overall_accuracy = SQRT ( inherent_accuracy ** 2 + wind_error ** 2) - the square root of the sum of squares)

Also by comparing wind drift of a 2600fps load to a 2300fps load we can see that the 2300fps load at 920yards has as much drift as the 2600fps load at 1000 yards.
This implies that you effectively lose 80 yards in effective range and explains why low drift cartridge/bullet combo are practically unbeatable when shooting for a score not for group size.
When shooting purely for group size, if you can shoot fast enough, wind drift is a much lesser issue.

In any case, all my shooting is from 0-500m, so I prefer the shortest reasonable barrel length.
(This can be 26" for an overbore cartridge since I consider muzzle blast to be a huge issue for me)

Alex
 
Here's another article on "Barrel Length versus Velocity (28″ to 16.5″)" with actual chrony numbers to prove.

h ttps://rifleshooter.com/2014/12/308-winchester-7-62x51mm-nato-barrel-length-versus-velocity-28-to-16-5/
 
Questions I have that don't get answered in the article. Difference of ambient wind conditions when shooting on the private range. Any flags?

I know there is a suggestion that a long barrel can shoot worst at LR vs a shorter barrel. I don't buy that especially when there is no real difference to 540yds regardless of length for pretty much all bullets weights.

He doesn't explain his test sample size... 1 group of 5rds.... 100 groups of 5rds per bullet, per length, per distance, per etc. I suspect more likely the former so 1 missed shot and the data is badly corrupted.

So the only thing he was able to confirm... higher speeds are possible in longer barrels for a given load of powder. Match bullets are typically more accurate then non match bullets. It is easier to shoot small groups at short range then long range. pretty straightforward stuff.

His point about wind drift is relevant if you are able to quantify the winds. You will see this often now in LR F class where 308 shooters can win the relay when shooting against 7mms. The 7mms have a much easier time so over many relays and shots, they have an advantage.

If you can get a good read on the wind, drift is merely a number and that can be compensated for... and the benefit of high speed/higher BC is also reduced by how big that target is.

For example, if 1 combo drifts 0.1mil more per MPH and shooter misses wind call by 2MPH, the impact will be 0.2mils further down wind then expected. But if the target offers a 0.8 to 1 mil diameter and all that is required is to hit anywhere on the target to score the same point, odds are the score will still be the same between the 2 options... all else being equal.

Jerry
 
Pretty much all the long range competition is 30-32" barrels, its what gives the best scores in the end.
Accuracy is about the entire gun, ammo, and the shooter, not any single component. Though it does just take 1 problem to turn the whole thing into a pile of crap real quick.
 
Not a very scientific study.

Some say there are accuracy benefits to a shorter barrel. At the Houston Warehouse, they determined that rifles with 21.75" barrels had the highest degree of precision (all else equal). They shot in a warehouse in which all the environmentals were essentially eliminated.

Tactical Operations, a producer of precision rifles whom have supplied rifles to over 600 alphabet agencies, has also found that shorter barrels (amongst other things) provide for a more precise system. Of course, they are providing rifles for agencies which would see most of their shooting within a few hundred yards.

Of course, shooters like you and me would never be able to shoot the difference. The environmentals, which will never be eliminated in our shooting situations, will have much bigger effect on the precision and accuracy of our rifles. A longer barrel also gives us the advantage of more velocity, which helps mitigate those pesky environmentals.

Some resource material:

https://precisionrifleblog.com/2013...-warehouse-lessons-in-extreme-rifle-accuracy/

https://www.tacticaloperations.com/edgefall2000/index.html

https://www.tacticaloperations.com/swatdec2000/index.html
 
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