Barrel Contour and Accuracy

Actions aside, when does barrel contour become a point of diminishing returns? Is a light barrel accurate out to 200 yards, with a medium out to 600 yards, and heavy out to 1000+ yards?



Granted, handloading ammunition and free floating the barrel will help accuracy.


Looking to rebarrel a bolt action rifle, and debating between medium and heavy contours.


Q

Qbeam said:

Actions aside, when does barrel contour become a point of diminishing returns? Is a light barrel accurate out to 200 yards, with a medium out to 600 yards, and heavy out to 1000+ yards?



Granted, handloading ammunition and free floating the barrel will help accuracy.


Looking to rebarrel a bolt action rifle, and debating between medium and heavy contours.


Q

Click to expand...

It depends, what is the rifle going to be used for and what caliber?

308, 400-600 yds.

As the barrel heats up your groups open up. Heavier barrels heat up slower. Range isnt really the issue, volume of fire is.

Barrel length will be a bigger factor for you for longer ranges.

Barrel harmonics play a part as well. If the harmonics are bad the barrel contour or thickness doesn't much matter. One reason earlier Mini-14 rifles weren't known for accuracy was due at least partly to harmonics.

Qbeam said:

308, 400-600 yds.

Click to expand...

I don't know all the variables you are considering but based on limited information I would say If it's going to be a bench gun then I would go heavy barrel, if weight is an issue then go medium profile. The medium profile should be fine at those ranges as long as you buy a quality barrel, have a good trigger and use good ammo.

TheOriginalMexicanBob said:

Barrel harmonics play a part as well. If the harmonics are bad the barrel contour or thickness doesn't much matter. One reason earlier Mini-14 rifles weren't known for accuracy was due at least partly to harmonics.

Click to expand...

A shooting buddy of mine (Sgt.Preston ) had a Mini-14 with a harmonic damper chambered in .223. As I recall, we had a heck of a time getting 1 MOA groups.
We did a lot of damper adjusting but just could not get it dialed in.

The Mini-14 is a very reliable weapon due mostly to the gas system which does not vent back to the bolt area.

I believe barrel length is more important vs. contour for long range accuracy. Also the barrel manufacturer plays an important part. I have a Browning X-Bolt with a pencil thin, 24 inch Miroku barrel that shoots the nads off of nats!!!
As previously mentioned, barrel heat will affect accuracy. Usually for hunting, you are not firing at a high volume.

ezracer said:

A shooting buddy of mine (Sgt.Preston ) had a Mini-14 with a harmonic damper chambered in .223. As I recall, we had a heck of a time getting 1 MOA groups.
We did a lot of damper adjusting but just could not get it dialed in.

The Mini-14 is a very reliable weapon due mostly to the gas system which does not vent back to the bolt area.

I believe barrel length is more important vs. contour for long range accuracy. Also the barrel manufacturer plays an important part. I have a Browning X-Bolt with a pencil thin, 24 inch Miroku barrel that shoots the nads off of nats!!!

Click to expand...

Length gives you velocity, which can reduce drop and wind drift a bit, but it in itself doesn't make a barrel more repeatable. Given a barrel profile, a longer barrel will have more flex than a shorter barrel. Less rigidity can make harmonic issues play out more significantly.

Accuracy stacks up from a multitude of factors being controlled. Barrel profile doesn't mean as much as the manufacturing details of one barrel make compared to another. It also doesn't really take into consideration what that barrel is mounted on and how....what ammo is being fed through it, optics...etc.

It's almost similar to making a blanket statement on which knife steel is best without taking into consideration factors like the heat treat of different manufacturers, blade geometry, and ergonomics.

One thing I did see that was interesting is how fluting is misrepresented. A guy took barrels, mounted them to a fixture, hung weights from the end, and measured deflection to gauge rigidity. He had heavy, lightweight, medium, and a heavy profile that had been heavily fluted. It turned out that the fluted barrel deflected the same amount as a standard profile barrel of similar weight. In other words, the I beam theory of fluted barrels didnt hold up under testing. They do seem to have some advantages with shedding heat and offering weight savings if you're stuck with a heavy profile(thanks md) though.

So a medium contour from Criterion may be better than a heavy contour from XYZ company based on manufacturing method and materials? This would be something to look at.


Q

Qbeam said:

So a medium contour from Criterion may be better than a heavy contour from XYZ company based on manufacturing method and materials? This would be something to look at.


Q

Click to expand...

Bolt gun? There are a few major contours with half dozen or so variations within them. Best bet is call one of the big match barrel makers and ask.

Answer #1 - It doesn't matter . It's about bore straightness, concentricity, smoothness, etc

Answer #2 - Everything else equal , heavier is more forgiving of bbl heat , stiffer is more forgiving of minor variations of bedding or harmonics, and likely to be more consistent between different loads .

TheOriginalMexicanBob said:

Barrel harmonics play a part as well. If the harmonics are bad the barrel contour or thickness doesn't much matter. One reason earlier Mini-14 rifles weren't known for accuracy was due at least partly to harmonics.

Click to expand...

this.... also how much time between shots, rapid / timed / etc.
Heavy barrel (stiff) Contours all play a very important part.
http://riflebarrels.com/the-details-of-accuracy/
http://riflebarrels.com/what-makes-a-rifle-barrel-accurate/
https://gundigest.com/more/how-to/ballistics-understanding-barrel-harmonics-and-accuracy
https://www.shootingsoftware.com/barrel.htm
https://www.varmintal.com/alite.htm

Bryan Litz has some very good books and the Berger manual at
800+ pages is full of info

I'm not no expert, hopefully E. Shell will chime in.

Anyway got one 700 action .308 medium tapered, another
700 action Heavy contoured barrel both built by the same
Gunsmith, same barrel maker, twist etc.the heavy gives me
better group sizes, don't have the details at a quick grasp.
but....rifles built the same may-not shoot the same... can
see a lot of range time in my future.


-Rock

Form should follow function. If you are going to hunt this rifle up and down hills, you will need to start with a weight limit and an overall length maximum.

As others have said, barrel heat due to rate of fire is more of an issue with thinner profiles. Harmonics CAN be tuned with loadwork but keep in mind that benchresters tune this out by CHANGING their load constantly. Given that you have limited your engagement to 600 yards, I would offer the following opinions: At 600 yards, I would willingly trade some velocity in the 308 for less trouble tuning out harmonics and consistent predictability. I have shot 18 and 20 inch 308s to over a grand (I will qualify that statement by saying that I would NOT take that shot at an animal). My current 308 wears a "truck axle" 24" Krieger max varmint contour and it was a dream to work loads up for. My short/fat barrels were easy too. I have only had real trouble working up loads for very thin barrels (unless I did something stupid like picking the wrong powder).

Some rounds, the more overbore they are, can really be the next thing to a waste in short barrels. Fortunately, the 308 is not one of them. I just did up a load for a guy's shorty 308 using 175s and ARComp. It is warm but it is very consistent. In testing I got the ES down to around 15 average. Achieving a very low extreme spread is critical to longer range shooting and having a barrel that is less harmonically sensitive will make it more likely that such a "tight" velocity node will coincide with a "tight" harmonic node.

When you have your barrel cut, be sure that you specify a reamer that will maximize the projectile you intend to shoot AND allow it to be magazine loaded if your intended use requires it. Far too many 308 reamers (even non-factory ones) have excessive freebore and will not let you get the projectile to or into the lands while retaining magazine feeding ability. Some people do jump their bullets very long distances (using a pill with a very long bearing surface makes this more likely to work) with good results. I am in the opposite camp. I jam most of my varmint or paper match loads and barely jump everything else. This plays in not only to precision but also achieving velocity goals in short barrels. For example, the famous weatherby magnums have huge freebores to enable enormous doses of very slow burning powder to be used while avoiding startup pressure spikes. These rifles also tend to have long barrels. In a shorter tube, with a smaller boiler room, higher velocity can be achieved by using a higher startup pressure and a shorter pressure curve (faster burning powder). Balancing the burn rate with barrel length and startup pressure is the art thus created.

EDIT: Darn, rockzilla beat me to the punch!

Accuracy = the ability to place the round where you want it to go.
Precision = the ability to repeat that over and over and have each round go to the same place.

Barrel weight has little to do with accuracy. It does help with precision however for reasons described above.

I'm a big proponent of looking at a firearm as a tool, and then picking the right tool for the job. If your job is to hike in the woods and up and down mountainsides for hunting and you're only going to shoot one round (maybe two), then a heavy barrel 24" Palma target rifle is a poor tool for the job. If you're trying to compete on the 1000 yd line, then a light barreled hunting rifle is a poor choice.

smokey0118 said:

Length gives you velocity, which can reduce drop and wind drift a bit, but it in itself doesn't make a barrel more repeatable. Given a barrel profile, a longer barrel will have more flex than a shorter barrel. Less rigidity can make harmonic issues play out more significantly.

Accuracy stacks up from a multitude of factors being controlled. Barrel profile doesn't mean as much as the manufacturing details of one barrel make compared to another. It also doesn't really take into consideration what that barrel is mounted on and how....what ammo is being fed through it, optics...etc.

It's almost similar to making a blanket statement on which knife steel is best without taking into consideration factors like the heat treat of different manufacturers, blade geometry, and ergonomics.

One thing I did see that was interesting is how fluting is misrepresented. A guy took barrels, mounted them to a fixture, hung weights from the end, and measured deflection to gauge rigidity. He had heavy, lightweight, medium, and a heavy profile that had been heavily fluted. It turned out that the fluted barrel deflected the same amount as a standard profile barrel of similar weight. In other words, the I beam theory of fluted barrels didnt hold up under testing. They do seem to have some advantages with shedding heat and offering weight savings if you're stuck with a heavy profile(thanks md) though.

Click to expand...

Yes to all of this. Except maybe the last. Plenty of calcs on the rigidity of a cylinder, both whole and fluted. Having taken engineering classes and done lots of work with bars and rods, I’ll believe my own experience. A fluted barrel of similar weight will be more rigid than than a non-fluted barrel of the same weight. It isn’t going to be a dramatic difference, but that fluted heavy barrel that weighs the same as a medium contour barrel will be slightly more rigid.

Also as you said, dissipate heat faster due to the higher surface area. It will be a fair amount less rigid than a heavy barrel of the same outer diameter and also less heat capacity because of the lower weight.

Plenty of pencil barrels out there more accurate than heavy barrels. That said all else being equal, a heavier barrel may be more accurate and will be more accurate in sustained fire. For a hunting gun I’d go medium contour on a bolt gun. My personal limit is 8lbs. Heavier than that and starts to wear on me a bunch as I tend to move around a fair amount hunting. My 6.5 Grendel AR with a fluted 18” heavy barrel tips the scales at 7lbs 13oz with scope and sling. A bit over 8lbs with a loaded mag hunting. I just covered a bunch of Greenridge up and down the ridges. Probably covered 2.5-3 miles each day, but probably 1000ft of vertical change (at least). Rifle didn’t bother me.

A ten and a quarter pound Garand hiking maybe 5-6 miles around the Eastern Shore and no vertical change and my back and arms are aching by the end of the day. My 9lb 20” HBAR .223 AR and the same, I know I’ve been carrying it at the end of the day.

So my personal goal in a hunting rifle is 8lbs or less. Maybe if I was hunting mountain goats or hiking the Rockies or something for Elk. Then I’d probably try to find any way to shave as many grams as I could. Otherwise a little weight is nice in controlling recoil. It still means faster reset if I need a follow-up shot and for a higher energy cartridge, makes it more comfortable to practice on the bench.