Point of no return. .308 cal barrel length?

RIFLEF

RIFLEF

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I see more prominent shooters using longer barrels. 30" in TR was the norm because of sight radius, and true sight adjustment.
In F-Class, this does not apply because of the scope.
So what is the IDEAL barrel length, to get full powder burn, and maximum velocity?
Manufacturers produce quite an array of lengths, from 20" to 26" in their hunting rifles, and barrel makers give us a choice of up to 34" or maybe even longer if the $$ are there.
I am thinking as an F-Class shooter who shoots the regular distances, to 900m or 1000y depending on the location.
Thanks in advance for your input.
 
Guys shooting .308 are using the long barrel for velocity gain as much as sight radius. You can always use a bloop to get a better sight radius.
 
SouthPaw700 said:
Guys shooting .308 are using the long barrel for velocity gain as much as sight radius. You can always use a bloop to get a better sight radius.
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There is no sight radius in F-Class.
I realize that, but the question is IDEAL length for F-Class? Or beyond what length do you stop gaining velocity?
To take it to the absurd could we see 50" barrels on the firing line?
 
That's sort of irrelevant because of the weight restriction. Once you get a solid bipod (assuming F/TR) and good scope on there, you are lucky to be able to use a heavy palma contour, let alone a heavy varmint or some super long custom contour.
 
There is no magic length for all combination of bullets and powders. It depends on the weight of the bullet, the size of the powder charge and the burn rate of the powders. Example: my 190 SMK w/ 42.6 gr. of Varget load only loses ~20 fps. going from one of my 26" barrels down to my 22" Broughton. It gets a complete burn in the 22" barrel. However, my 110 VMAX w/ 48.3 gf. Varget loses over 200 fps. between the two barrels. The powder is probably not fully burned in either barrel. The heavier the bullet, the smaller the powder charge, or the faster burning the powder, the less barrel length you need for a complete burn (all other things being equal).

Keep in mind that nobody loads to max, they load to accurate nodes, and the velocity those fall on can be virtually the same for a given powder/bullet combination over a wide variety of barrel lengths.
 
Seems to be part of the mystery, I'm planning something a bit unusual for my f-tr build, time will tell if it works or not.
Will post results when the time comes.
 
I wish I could quote the source, but it was likely on 6mmbr or some other reputable site that had test results stating that the diminishing returns on barrel length start to kick in at 26". After that you are trading ever increasing barrel harmonics for ever smaller increases in velocity.
 
curseyou said:
I wish I could quote the source, but it was likely on 6mmbr or some other reputable site that had test results stating that the diminishing returns on barrel length start to kick in at 26". After that you are trading ever increasing barrel harmonics for ever smaller increases in velocity.
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With a standard chamber and "typical or traditional" 308 powders and bullet weight, that is pretty accurate. The gains are relatively small. However, it you take a really long barrel, load the 308 with a big heavy bullet (200+ gr.), have a throat long enough to handle that big bullet without losing any case volume, and load the case with a slow burning powder, then you have a different animal entirely when compared to a rifle shooting a 175 SMK or 155 Scenar over Varget.

Additional barrel length is only worthwhile if you're running a load that is actually going to take advantage of it. Otherwise you're just adding weight at the expense of rigidity.
 
kombayotch said:
However, my 110 VMAX w/ 48.3 gf. Varget loses over 200 fps. between the two barrels.
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Wow that's a lot of Varget in a .308 case! Must be a sizzler!

I have heard of guys using 20" barrels to shoot medium long range, enjoying the stiffness of the short barrel. I have been told and wonder if the increased load needed to get the velocity up shortens the life of the barrel due to throat erosion. Not that .308 is a barrel burner but my job isn't exactly mentally taxing so I sit and wonder... ;)
 
The only way to really know is to put various barrels on a pressure trace and see what is happening during the firing process. At some point, there isn't enough energy to keep accelerating the bullet.

For FTR, I stay with 30" finished. It is a balance of velocity, balance, rigidity and overall weight. I run a #7HV Shilen or #17HV Krieger - same contour. Tuning is relatively simple and the weight is ok.

The issues with long barrels being more fussy to tune is very real and there is now growing interest for barrel tuners. Essentially, hanging an adjustable mass at the muzzle. Concept has been around for decades but starting to find favor in F class. More compromises and necessity is up for debate but it is out there. I will be doing some experimenting this year.

Overly long barrels are a mixed blessing and can be more trouble then it is worth. One big issue is the internal length of your rifle case?

The biggest effect on all this will be powders. With what we have now, we have pretty much reached the useable fuel load and thus velocities and pressures. We are always teased by new styles of unobtanium powders that promise all sorts of gains. IF these actually pan out, that can change what we consider the right layout.

But for now, saying X" is better then Y" is really a fools game. There can be more variations in that bore to make any theory real or false. AND the potential difference in velocity of say 50fps isn't going to amount to much on the target.

Availability is more important and overly long barrels can take a very long time to get. They are also far more difficult to make well so will accuracy also be at risk?

For those who ask me, I suggest sticking with parts we can actually source, that work and are sustainable. Load to velocities and pressures that don't wander all over the map with changes in ambient conditions nor run so close to Kaboom that you fear pulling that trigger.

The most accurate shooters will use the most consistent gear and learn how to drive it over the widest range of conditions.

They will also put aside resources to change out that barrel often. At 1000yds, peak accuracy is a fleeting thing.

Jerry
 
AdrianM said:
Wow that's a lot of Varget in a .308 case! Must be a sizzler!

I have heard of guys using 20" barrels to shoot medium long range, enjoying the stiffness of the short barrel. I have been told and wonder if the increased load needed to get the velocity up shortens the life of the barrel due to throat erosion. Not that .308 is a barrel burner but my job isn't exactly mentally taxing so I sit and wonder... ;)
Click to expand...

There are FTR shooters cooking 308 barrels in UNDER 1500rds. I have chatted with one shooter that toasted a barrel around 1200rds. To say loads were spicy, is an understatement.

One of the big issues with some new gen powders is that they burn REALLY hot... as in flame temp. That puts more energy behind that bullet and elevated speeds are possible but that bore is being eaten fast.

So yet, another compromise.

I would love to test all the theories floating around my head but time and money is limited. What we know is that a long barrel is NOT mandatory for 1000yds shooting. As long as the bullet gets there super sonic, it really boils down to how well you can peddle.

Based on 25 fps gain per inch of barrel (not always the case), there is 100fps gain from 26" to 30". That is not a huge gain in external ballistics so a shooter shouldn't feel compromised about coming out to try shooting if they have a varmint rifle in the closet.

Bullets like the Berger 185gr BT are tolerant of slower speeds and would have no issue running ONLY 2650fps at the muzzle vs 2750fps from a longer pipe.

Maybe those 26" heavy barrels will stay more accurate as they get hot?

Always a compromise....

Jerry
 
AdrianM said:
Wow that's a lot of Varget in a .308 case! Must be a sizzler!
Click to expand...

Not really. Varget is very slow for that bullet weight, so velocities and pressure are low. You can get a lot in the case because the 110 VMAX has a flat base, and you only need 1/8" of neck to hold it in.
 
last year, i've decided to give a try to a loooong skinny 34in Bartlein barrel to push the 200 like never seen before. As i had a backup rifle, if this one dont work, at least i'm not screwed up. The contour of that barrel was a heavy palma that weight in at 34 finish a clean 6.5 pounds. The first shot throught the barrel i could feel a "brrrrrr" and then start wonder....that thing never gonna shoot ! And to be accurate, it was. Of course, its not for beginner at reloading and a stiff stock and bipod are absolutely required to handle vibrations and torque of the heavys.

Quickload is of course suggesting that the powder is completely burned at around 22-24 inches in the barrel but so what, if there is still a gain in FPS, i need to take it. I think, and Komby will correct me, that a bullet is slowing down at around 5000psi in the pipe ??!!

My last year barrel was pushing the 200 at 2770fps in a 1/4moa precision...This year is also a 34in fulted barrel that the contour is bringing to 7 pounds. Bartlein took 2 months last year to produce my barrel and this year took 4 months....not bad. I had a couple discussions with a top F-Open shooter in the US, using a Shadetree tuner, and it was the last time a tuner was on one of is barrel....tooo tricky.....but still need to be tested to my opinion.
 
to cook a 308 win barrel in 1500 rounds, you need a smack load, read stupid dangerous, of either N550 or N540 as they are really warm burning powders. Those shooters are UK guys and throw their brass to garbage after 1 firing. If a brass is cooked by then, mean they are runing dangerous pressure for sure. As for the load i stated above, my barrel life was estimated at 2900 rounds...and was done just before that.
 
WG300 said:
Quickload is of course suggesting that the powder is completely burned at around 22-24 inches in the barrel but so what, if there is still a gain in FPS, i need to take it. I think, and Komby will correct me, that a bullet is slowing down at around 5000psi in the pipe ??!!
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Internal velocity is not measured by my equipment. It will tell you when the bullet exits, and you can get MV velocity using a chrony.
 
I'm kind of glad this thread was started , the one going on my f-class gun is going to finish @ 30" rather than 28 which was my original thought.

There is certainly a point where longer is no better but without a whole lot of testing of different barrel lengths it's hard to say for sure.

We know the benchrest guys are using about 20" for there short range guns but f-class is a lot about ballistics so the longer you can go without having to much trouble tuning is the way to go imo.
A lot of the guys I shoot with seem to use between 28" and 32" and it seems to work good so my guess is this :) .
 
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The mechanical tuners have been around a long time in small bore where you can't fine tune with your load.
When you can tweak your load to give you 1/4 MOA, playing with yet another variable, read tuner, might not be beneficial.
Murphy's law: "If it can go wrong it will".
 
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