optimum barrel length for 308 Win?

[Bullshop]

I searched the forums three times to find the right place to post this so hope this is it.
This project has to do with choosing the best or optimum barrel length for a 308 rifle that will be used for long range coyote hunting.
I don't want to give up much by way of velocity potential but I want the barrel as short as possible. I want it short because it will be varmint taper and I will be packing it.
I built one two years ago in 221 FB with a 17" heavy barrel and it worked out great. Plenty of barrel for the cartridge since the cartridge was designed for a 10" barrel, very accurate and legal length.
I would like the 308 to be about the same but don't want to limit velocity too much. I don't want screamer loads I just want to at least be able to achieve mil match performance of about a 168gn bullet at about 2400 fps.
I also shoot a lot of cast in the 308 but because I use powders in the 2400 burn rate area and shoot for about 2000 or slightly + fps velocity with 200gn ish boolits I doubt I will loose anything from this type load by shortening from 24" to ? and possibly may gain velocity.
Going way back to some articles from Precision Shooting I remember reading about the Houston warehouse testing. In the windless environment of the warehouse and plenty of time to shoot they found that for the BR type guns they were shooting there was indeed an optimal length for best accuracy. I think they determined that 20 3/4" was optimum for accuracy. With that in mind I am wondering if there is an optimum length for the 308 Win cartridge.
I understand that for a given case volume as bore diameter increases so does expansion ratio. As expansion ratio increases optimum powder burn rate must also increase, or get faster to produce gas fast enough to compensate for the increased per inch bore volume.
A good example with the 308 case would be to look at the 243 win, 260 rem. 7mm/08 rem. and 308 win. If the 243 is at optimum length at 24" all things considered then a 260 can/will be slightly shorter, a 7mm/08 shorter still, and the 308 shortest for optimum length. This because the optimum powder burn rate for the 243 will be much slower than for the 308 and so on.
Sooooooo with that in mind I would like to know what would be the best compromise in barrel length for the 308 for best accuracy and minimal velocity potential loss.
If 17" turns out to be best for both that will be just wonderful.

[izzyjoe]

I think 20" would serve you well, and a good brake would be nice too!

[Ernest]

My guess, and it is just a guess not science, would be decide what is most important to you
#portability to carry and set up for shots
#ease of getting in and out of truck or how quickly you want to be able set up and shoot from your vehicle
# Muzzle blast
etc. put those things in order of importance and then make the decision about barrel length on that.

if it is an option my choice would be a 16.5 inch with suppressor. More that anything because I want to keep the little bit of hearing I still have;-)

[kir_kenix]

For what its worth, Federal Gold Match 168gr is supposed to do 2500+ in an 18" barrel. I could look at my notes, but I'm 99.9% certain I come up with about the same velocity out of my 18" AR10 with 168gr handloads.
I also have an 18" Rem 700 (Benchmark Barrel) set up as a tactical rifle, and Black Hills 150's (Blue Box) does somewhere around 2750 out of it.

[Bullshop]

Adding a suppressor will defeat the purpose of shortening so that is not an option. Pick up portability is not a concern only shoulder portability.
I have a rifle that is a dedicated "shoot off the truck" gun but this 308 project rifle/carbine is strictly a walkabout gun.
Kir Kenix
So it sounds like at 18" you aren't giving up anything for velocity. With that in mind dropping another 1.5" should not have too great an effect on velocity. If the drop from 18" to 16.5" lost 100 fps velocity it would still be acceptable at 2400 fps from the match load.
I wouldn't go less than 16.5 as I want no question as to it being legal.

[Doc Highwall]

Dan, don't forget that the muzzle blast will get greater as the barrel gets shorter. I would try a 20" plus barrel length.

[tomme boy]

I would go with the 20" cut as the balance will be better. And I would do a Remington varmint taper. A 20" OAL barrel with a muzzle brake included in the OAL would be about perfect for a walk about vaminter.

[John Taylor]

Dan, don't forget that the muzzle blast will get greater as the barrel gets shorter. I would try a 20" plus barrel length.

When I was testing muzzle brakes on a 308 I used a 22" barrel. Gas pressure on a 308 is still quit high at 22" and is the cause of half the recoil. Gas pressure = muzzle blast . The brake I came up with will reduce recoil 50% on a 22" 308. Best to wear hearing protection with any short barreled rifle.

[725]

All guns may be different, 21 1/2 inches seems best. No, really. Try and google "texas warehouse" for some interesting info on extreme accuracy testing. Been a long time since I read the article, but it was impressive. Wish I still had the link.

[David2011]

Secrets of the Houston Warehouse: http://www.angelfire.com/ma3/max357/houston.html

Awesome reading.

David

[Doc Highwall]

The 21 1/2" barrel is for a 22 PPC and 6mm PPC case capacity.

[Bullshop]

The 21 1/2" barrel is for a 22 PPC and 6mm PPC case capacity.

Exactly! and is the point I wanted to make with the OP. So if 21 1/2 ( I think it was actually 21 3/4 or 1/4 but not 1/2) is the optimum length for accuracy with the PPC case what is optimal for the 308 case at 30 caliber? If I could determine that I would make my compromise from there.
It seems to me that there are two points that at least partially cancel each other out.
First since the 308 has far greater case volume than the PPC case that would seem to dictate a longer barrel would be optimum. Secondly the larger bore with greater expansion ratio over 22 and 24 cal would dictate a shorter barrel. For instance with a 30/06 case and given boolit/bullet weight what it takes a 22" barrel to do in 30 cal can be done with a 20" barrel in 35 cal.
I doubt anything solid will come of this thread unless it prompts someone to shoot a 308 in the warehouse starting with a long barrel and chopping 1" at a time and testing each length just as they did in the Houston test.

[Love Life]

How far are you shooting Bullshop? I would say an 18 or 20 inch would work fine. Steel is hit constantly out to 800 yds with a 20 inch barrel where I am. I can put the guy who shoots it in touch with you if you like. He did a bunch of testing with a 24 inch, 20 inch, and 18 inch last year, and decided to stick with the 20 inch.

That is what I have seen in person. Now patrolling the interweb, and snipershide forums specifically, it seems with the performance envelope of the 308 winchester you are good with 18 inches and longer. The real loss comes below 18 inches, from what I have read, not tested. If you like I can PM you the links.

[TexasBubba]

I like a 20" barrel for 308 Win. I have a 19.5" barrel on my 308 Mauser and it had more muzzle blast than I expected. An 18" barrel will have lots more muzzle blast than a 20".
Have you ever shot an M-38 or an M-44? Check out those fireballs on YouTube!

[Artful]

Military Weapons have between 21 1/2 inch (FAL) to 17.7 (G3) but they are not so worried about velocity.

20 inch is a very good compromise barrel length for what you want.

Test from Guns and Ammo magazine
From G&A 7/89
Load......22".....21".....20"......19"....18.5"
150FL...2674...2636..2617....2595...2598

From G&A 9/87, handload with IMR4320
Load......24"......22".....20".....18".....16"
180HL..2700...2660...2620...2550...2480

http://www.6mmbr.com/308win.html
QuickLOAD Projected Velocities in FPS with Increasing Barrel Length
Powder__________________20" 21" 22" 23" 24" 25" 26" 27" 28" 29" 30" 31" 32"
44.5gr Varget (ADI 2208)___2592 2620 2646 2671 2694 2716 2736 2756 2775 2792 2809 2825 2841
44.5gr IMR 4064__________2628 2656 2681 2705 2728 2749 2770 2789 2807 2824 2841 2857 2872
http://www.riflebarrels.com/articles/longrange_shooting/ideal_barrel_308_tactical_rifle.htm

72127

there is a lot of links about this topic...
http://www.tacticaloperations.com/SWATbarrel/
http://thefiringline.com/forums/showthread.php?t=382935
http://thefiringline.com/forums/showthread.php?t=479272


It's not a myth. Velocity does change with barrel length. How much depends on the ammunition, caliber and gun.

Here is an example. My granddaughter did a science project showing something else but she needed to know what changes to velocity occurred.

She started out with a 26 inch 308 barrel, and Remington factory 180 grn corlok bullets.

The first column is barrel length the second is velocity (at 10 ft from muzzle.)

Quote:
26 2826
24 2722
22 2713
20 2677
18 2654
16 2552
__________________
Kraig Stuart
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071


Standard Formula is
MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.

Ball park for the .308 is 2600-2800 fps MV.
So if you were to go with a 20" over the 24" I'd be giving up about 80 fps +/- at the muzzle.

And I will say I prefer shooting my FAL over G3 as far as muzzle blast goes.

[Bullshop]

I was also thinking in terms of optimum for accuracy but since its for field use I doubt any advantage would be realized.
What I have now is 24" heavy. Maybe I should be not only looking at shortening but also tapering. Perhaps something like a 21" with heavy sporter taper.

Love Life
No more links needed thank you!
Artful
I think that's about everything I need right there. I like the graph! It makes 20" or so look like a good place to be.

[Artful]

Instead of tapering you could also loose weight by fluting it - makes a stiffer barrel with same weight as tapered

[Bullshop]

I can cut and crown and taper but not flute. My ability is limited.

[Hickory]

This is an excerpt from: Secrets of the Houston Warehouse.

But no bit of information was, Virgil believes, more valuable than a little advice Jim Gilmore passed along. Jim said a barrel MUST be 21 3/4” long for optimum accuracy. That precise length, he stated, sets up a vibration pattern that duplicates well from shot to shot. Virgil faithfully followed that advice on his guns.
Anyone who strictly observes the 21 3/4" doctrine will screw off a failing barrel of that length and run a new one under it. Rechambering and rethreading, in order to achieve more pristine lands just forward of the throat, shortens the barrel. Shorten the barrel, spoil the magic length.
Through the years, the Houston Warehouse shooters were able to rate the relative accuracy of the various benchrest calibers — .22, 6mm and .30. In the perfect conditions of the warehouse, the .22’s outshot them all, followed closely by the 6mm’s. The .308 calibers were a not-too-distant third. The most accurate .30 caliber ever to find its way into the warehouse also belonged to Virgil. The rifle, built around a Shilen DGA action with McMillan barrel, shot consistently within a few thousandths of .100". The barrel length? You guessed it: 21 3/4".

[felix]

Hickory's statements above are 100 percent accurate about what happened in the warehouse. Also, Artful's statement above about fluting is incorrect. Fluting takes off weight AND stiffness together. Tapering a barrel into sections might or might not help accuracy, but sure lightens the gun for snap shooting purposes. This was once popular with German smithies making guns for running boar shoots? I have a European Browning made up this way, and really like it for beer can snap shooting. The gun is 22 inches, but will be cut back to 21.75 when re-crowned in the future. ... felix

[Hickory]

I just thought the added information on the length of the barrel might be helpful.

[Bullshop]

I believe the reference to 308 caliber is just that to caliber and not cartridge. They were most likely shooting a 30 BR or something similar with much less case capacity than a 308 Win. Still the magic may apply but as I said earlier for a field gun its not likely anyone could ever realize an accuracy advantage. But still there is the confidence factor knowing that your gun is all it can be even if you are not.
I like the idea of a 21" fluted heavy but I would have to send it out and cough up some bucks. I better start working on my best puppy eyes begging face.
Love Life
I forgot to answer this ""How far are you shooting Bullshop?""
I am shooting at coyotes so always want to be prepared for the Buzz Lightyear shot, to infinity and beyond.

[Reciprocate]

Adding a suppressor will defeat the purpose of shortening so that is not an option. Pick up portability is not a concern only shoulder portability.
I have a rifle that is a dedicated "shoot off the truck" gun but this 308 project rifle/carbine is strictly a walkabout gun.
Kir Kenix
So it sounds like at 18" you aren't giving up anything for velocity. With that in mind dropping another 1.5" should not have too great an effect on velocity. If the drop from 18" to 16.5" lost 100 fps velocity it would still be acceptable at 2400 fps from the match load.
I wouldn't go less than 16.5 as I want no question as to it being legal.

I'm using a Ruger Scout (16.5) - and it just spits fire with normal loads. So I'm thinking that most current powders just are tweaked for 20in or greater? Not certain this affects accuracy much because short barrels are stiff and may be more tolerant to ammo variations - but that flash must be seen to be believed (varget) :(

Someday, short barrel powders may be more common? But right now - the price must be paid.

This 16in barrel is right for me...but only because I don't sweat the warts.

[Artful]

Hickory's statements above are 100 percent accurate about what happened in the warehouse. Also, Artful's statement above about fluting is incorrect. Fluting takes off weight AND stiffness together. Tapering a barrel into sections might or might not help accuracy, but sure lightens the gun for snap shooting purposes. This was once popular with German smithies making guns for running boar shoots? I have a European Browning made up this way, and really like it for beer can snap shooting. The gun is 22 inches, but will be cut back to 21.75 when re-crowned in the future. ... felix
Really?
Let's see what I said
Instead of tapering you could also loose weight by fluting it - makes a stiffer barrel with same weight as tapered

- My understanding of lightening a barrel by tapering vs fluting

http://en.wikipedia.org/wiki/Fluting_(firearms)
The main purpose of fluting is to reduce weight, and to a lesser extent increase rigidity for a given total weight or increase surface area to make the barrels less susceptible for overheating for a given total weight. However, for a given diameter, a non-fluted barrel will be stiffer and be able to absorb a larger amount of heat at the price of additional total weight.[1][2][3][4]
^ "The Real Benefits of Barrel Fluting" by Joel Avila, 1LT(P), EN, USAR, 12 August 2004
^ Fulton Armory FAQ: "What's the deal with fluted barrels? Do I want one?" by Clint McKee and Gryffin


A engineer's perspective on fluting:

These discussions on fluting are guaranteed to produce lots of controversy!

All you really need to know is that as you take material off you reduce the stiffness.

So long as the material properties remain unchanged (specifically, the material strength), you CANNOT remove material from ANY shape, and make it stronger! A clever engineer, however, can move material to make the part stronger...

Anyhow, in a humble attempt to end this controversy for once and for all, I've decided to try a cold, hard, mathematical analysis of a typical real-world situation.

Given:

* Weight is directly proportional to cross-sectional area. (Specifically, the weight is equal to the cross-sectional are times the length, times the material density.)

* Rigidity (stiffness) is directly proportional to Area Moment of Inertia.

* Surface area is directly proportional to the outside perimeter. (Specifically, the surface area is equal to the perimeter times the length.)

Both "givens" are per every basic engineering Statics text.

Test subject barrels:

Remington 700VS:
outside diameter: 0.850"
bore: .300 bore with six .308 grooves, 50% grooved
flutes: none
Cross-sectional area: 0.493 sq.in.
Area Moment of Inertia: 0.02489
Perimeter: 2.666"
Remington 700VSF:
outside diameter: 0.850"
bore: .300 bore with six .308 grooves, 50% grooved
flutes: six, 3/16" wide, 3/16" deep, full radius
Cross-sectional area: 0.312 sq.in.
Area Moment of Inertia: 0.01411
Perimeter: 4.276"
Hypothetical barrel for comparison:
outside diameter: 0.7005"
bore: .300 bore with six .308 grooves, 50% grooved
flutes: none
Cross-sectional area: 0.312 sq.in.
Area Moment of Inertia: 0.01127
Perimeter: 2.197"
Comparisons:

0.850" Fluted vs. 0.850" Plain:

Cross-sectional area (weight): 36.7% less
Area Moment of Inertia (rigidity): 43.3% less
Perimeter (surface area): 60.4% more
Conclusion: the fluted barrel is much lighter, much less rigid, and has much more surface area than a solid barrel of the same diameter.

0.850" Fluted vs. 0.7005" Plain:

Cross-sectional area (weight): *same*
Area Moment of Inertia (rigidity): 25.2% more
Perimeter (surface area): 94.6% more
Conclusion: the fluted barrel is significantly more rigid, and has much more surface area than a solid barrel of the same weight.

Notes:

* All section properties are courtesy of the 2D Properties module of Ashlar Vellum 3D version 2.70 (my favorite CAD program), based on my layout of the sections.

* Measurements of the 700VS were taken from an actual 700VS from my personal collection.

* I didn't actually have a 700VS on hand, but have recently compared one to a 700VS side by side (while deciding which to buy), and verified that the barrel outside diameters are the same. Flute dimensions are approximate, but should be fairly accurate. After ten years as an engineer, I have a good eye for dimensions; I know for sure that the flute width was much more than 1/8", and definitely less than 1/4"; 3/16" should be quite close. Likewise, I noted for certain that the flutes were full radius, and deep enough that the radius started approximately 3/32" below the outside diameter. Despite any minor errors, the fluted barrel described is certainly representative of the Real World, and the trends are quite clear from the analysis; the effects of fluting are significant. A 1/16" here or there would not noticeably change the results.

* The weight and surface area comparisons hold true only for the fluted portion of the barrel. On every fluted barrel I've seen, the fluting does not begin until well forward of the chamber (6"-9"), and ends from 1"-4" from the muzzle. For example, on the Remington barrels presented, only approximately 65% of the barrel is actually fluted, so you will only realize ~65% of the weight savings and surface area increase. Also, I've seen some fluted barrels where the fluting is more shallow and/or narrow than the examples presented. Hence, the effects of the fluting would be less than reported above.

* I also did a quick analysis of a fluted barrel with shallower flutes; I won't present the entire analysis here, but in summary, a barrel of the same weight also had a larger diameter, and the differences in stiffness and surface area were simply less pronounced than the barrel detailed above. Extrapolating: as the flutes become smaller, the effects diminish; as the flute dimensions approach zero, the fluted barrel (and the barrel of the same weight as the fluted barrel) simply becomes the original bull barrel, and there's no effect. Conversely, as the flutes get larger, the effects become more pronounced; eventually, though, one would run up against a geometrical limit (the flutes colliding, or reaching the bore). Under NO geometrically possible conditions can flutes make a barrel MORE rigid than a plain, unfluted barrel of the same diameter.

* Before someone asks: no, the number of flutes has no real effect on these conclusions. Four (or fewer) flutes of the same size would simply remove less material and hence reduce the effects shown. Eight (or more) flutes might increase the effects, but would tend to collide more easily (less room for material between the flutes), so in reality they would tend to have less depth, and hence limit the effects achievable.

Editor's Note: A fluted barrel has much less rigidity than a plain barrel of the same diameter, and more rigidity than a plain barrel of the same weight. But those comparison barrels are not, cannot, be the same. The plain barrel of "same weight" will have a necessarily smaller diameter than the corresponding fluted barrel. The material in the fluted barrel is arranged, due to its greater major diameter, more advantageously to resist bending than the plain barrel's material. So you can have your cake or you can eat it, but not both!

^ Jon R. Sundra "Weighing In On Fluted Barrels". Guns Magazine. FindArticles.com. 17 Jun, 2010. http://findarticles.com/p/articles/mi_m0BQY/is_8_46/ai_63772599/
^ Barrel FAQ at 6mmBR.com

http://varmintal.com/aflut.htm


CONCLUSION ON BARREL FLUTING....

When comparing two barrels of equal weight, length, and material but one is solid and other is fluted, the fluted barrel will have:

A larger diameter

Greater stiffness (depending on how the extra diameter/weight is distributed)

Vibrate at a higher frequency (depending on how the extra diameter/ weight is distributed)

Less muzzle sag (depending on how the extra diameter/ weight is distributed)

Fluting a solid barrel will:

Reduce its weight

Reduce its stiffness

Increase its natural frequency of vibration

Decrease its muzzle sag.

Reducing the weight of a barrel by fluting makes a stiffer barrel than reducing the weight by decreasing its diameter.

A shorter barrel of the same section, solid or fluted, will sag less and vibrate at a higher frequency.

http://benchrest.com/showthread.php?54515-Fluted-Bull-Vs-Smaller-Barrel


Fluted Bull Vs Smaller Barrel?
I was wondering why exactly a fluted barrel is better than a barrel with a more narrow taper that has the same surface area as the fluted one?

If they had the exact same surface area, wouldn't they both weigh the same? I suppose the fluted might have more stiffness than the smaller barrel?

But also wouldn't the fluted barrel be less stiff with the extra material removed?

The rifle would have a goal to be lightweight, fired about 5 times rapidly max, and have a short 20" barrel (so stiffness might not be an issue?) It would also be chambered in 308.

Several searches seem to be debatable at best, any opinions?

Adam--
A fluted barrel is stiffer than a solid barrel of the same weight.
A fluted barrel is lighter than a solid barrel of the same diameter.
A fluted barrel will be lighter than a solid one for the same section modulus.
....which, according to Wikipedia, means:

"In structural engineering, the section modulus of a beam is the ratio of a cross section's second moment of area to its greatest distance from the neutral axis.

The section modulus is directly related to the strength of a corresponding beam. It is expressed in units of volume, e.g., mm<cubed>."

I guess that says it all.

http://www.sniperforums.com/forum/rifles/58-barrel-fluting.html


I called and talked to someone at Hart barrels about fluting, rigidity, and accuracy when I was having my 6.5x284 built. This is what I was told.

If you compare two barrels of the same weight, outside diameter and length, and flute one of these two barrels. The fluted barrel will now weigh less and be less rigid than the non-fluted barrel of the same length and outside diameter.

On the other hand if you compare two barrels of the same weight and length, but one is already fluted, the fluted barrel will be more rigid than the one you are comparing it to.

Fluting stresses the metal of the barrel, but if properly relieved, is not a problem for accuracy.

The key is to compare barrels of the same weight and length. The fluted one will be more rigid. For example a 26" #6 taper barrel will be more rigid than a Fluted 26" #6 taper barrel. But will be less rigid than a 26" #7 fluted barrel (assuming they are now virtually the same weight)

http://www.riflebarrels.com/products/barrel_length_fluting.htm


Fluted Barrels

Fluting barrels for both competitive target and hunting rifles is quite popular. There are two advantages to using a fluted barrel. Improved accuracy is one advantage because of increased barrel stiffness. If we compare a fluted barrel to one that is not fluted, both weighing the same, the fluted barrel is stiffer. This is because the fluted barrel will be of a larger diameter than the unfluted barrel of the same weight and length. Increasing the diameter of a barrel greatly increases its rigidity. Fluting may also allow for a longer barrel, if weight is a consideration. Another advantage to fluting is the increased cooling rate of the barrel because of the greater amount of surface area exposed to the air. Please look at our FAQ section on fluting too.

We machine 6 flutes that are .219" wide into the barrel. The amount of weight removed by fluting depends on the length of the barrel and the flute depth. The depth of the flute is determined by the contour of the barrel and the caliber. Flute length depends on finished barrel length. Normally the flutes stop 1.50" short of the muzzle. When ordering a fluted barrel, please specify the finished length of the barrel so we can machine the flutes to the correct length. Fifty caliber barrels are fluted using a .312" width cutter.

If you have a question about weight removal from fluting, we can help, but here are a few examples: A fluted .243" caliber barrel of NBRSA HV taper and 24" long weighs approximately 5 Ibs. - 6 oz. A fluted #6 contour barrel in .308" caliber and 24" long will weigh approximately 3 Ibs. - 14 oz. A fluted #5 contour .284" caliber barrel 24" long will weigh approximately 3 Ibs. - 5 oz. Fitting and chambering a barrel will remove approximately 3 oz. We only flute stainless steel barrels, the exception being chrome-moly steel fifty caliber barrels. Barrels suitable for fluting include any of the straight taper benchrest contours, straight cylinder barrels, #4 contour sporter barrels (or larger) up to 30 caliber and #5 or #6 contour barrels (depending on caliber) over 30 caliber or any of our three standard fifty caliber contours. The maximum length barrel that can be fluted is 36". We can also flute 15" long XP 100 type barrels of suitable diameter. You may also be interested in downloading a free copy of an Excel file we have available that will compute the weight removed by fluting.

So felix please point out in the above where a fluted barrel won't remove weight from the original bull barrel
and where a tapered barrel of the same weight will be stiffer than the larger diameter fluted barrel of the same weight or where tapering a barrel from bull will increase stiffness.

[felix]

A full barrel is the stiffest. Start trimming it in any manner chosen, except length, makes the barrel LESS rigid. Chopping the length will ADD rigidity, and how much to trim should be calculated to compensate for the amount circumferential trimming (to be) done. First course in Physics, Artful! ... felix

[Artful]

So your saying a 20" barrel will be stiffer than a 21.75 inch barrel if everything else is the same, correct?

[waksupi]

I'm with Felix. Fluting and other gimmicks are just that. If you want a stiff barrel shorten it. Go with a bull barrel for the best results, with a slight taper.

Absolutely, Art.

[Artful]

I don't consider Fluted barrels a gimmick ... What makes you think it is?

Let's get back on track Gentlemen...


I searched the forums three times to find the right place to post this so hope this is it.
This project has to do with choosing the best or optimum barrel length for a 308 rifle that will be used for long range coyote hunting.
I don't want to give up much by way of velocity potential but I want the barrel as short as possible. I want it short because it will be varmint taper and I will be packing it.
I built one two years ago in 221 FB with a 17" heavy barrel and it worked out great. Plenty of barrel for the cartridge since the cartridge was designed for a 10" barrel, very accurate and legal length.
I would like the 308 to be about the same but don't want to limit velocity too much. I don't want screamer loads I just want to at least be able to achieve mil match performance of about a 168gn bullet at about 2400 fps.
I also shoot a lot of cast in the 308 but because I use powders in the 2400 burn rate area and shoot for about 2000 or slightly + fps velocity with 200gn ish boolits I doubt I will loose anything from this type load by shortening from 24" to ? and possibly may gain velocity.
Going way back to some articles from Precision Shooting I remember reading about the Houston warehouse testing. In the windless environment of the warehouse and plenty of time to shoot they found that for the BR type guns they were shooting there was indeed an optimal length for best accuracy. I think they determined that 20 3/4" was optimum for accuracy. With that in mind I am wondering if there is an optimum length for the 308 Win cartridge.
I understand that for a given case volume as bore diameter increases so does expansion ratio. As expansion ratio increases optimum powder burn rate must also increase, or get faster to produce gas fast enough to compensate for the increased per inch bore volume.
A good example with the 308 case would be to look at the 243 win, 260 rem. 7mm/08 rem. and 308 win. If the 243 is at optimum length at 24" all things considered then a 260 can/will be slightly shorter, a 7mm/08 shorter still, and the 308 shortest for optimum length. This because the optimum powder burn rate for the 243 will be much slower than for the 308 and so on.

Sooooooo with that in mind I would like to know what would be the best compromise in barrel length for the 308 for best accuracy and minimal velocity potential loss.
If 17" turns out to be best for both that will be just wonderful.

So the OP wants a short lighter weight barrel - NOT A HEAVY BULL BARREL
from the carry it in the field all day point of view what is the optimal configuration to achieve a light barrel that is as stiff as possible.
Barrel length seems to be a consensus of 20-22 inches. As we all agree the shorter the barrel the stiffer and handier in the field.

[ABluehound]

You have already narrowed down the range and energy you need. You have an idea of what projectiles and speed you want. Using off the shelf ammo then yes stick with the longer barrels. If you reload using faster burning powders you will generate the desired energy in shorter barrel lengths. Don't write off suppressors, The "Reflex" style does not add much overall length. You can build suppressor to run from the action out just a couple inches beyond the barrel which gives you a large first volume (heat dump) to trap unburned powder and followed by multiple conical or funnel shaped baffles to slow exit gas escape. That is just one idea, you can also go the route of SBR and screw on can if you are concerned with length (two tax stamps though). Several years ago there were manufacturers that made integral barrel/suppressors in .308 that had a HBAR profile that were not much heavier than standard weight (titanium tube and light weight pressed sheet metal baffles) that only required a single tax stamp. With an integral system you can end up with a short stiff barrel surrounded with a 20 inch moderator, tuned with the right load you could be in business.

Fluting is to increase the ratio of surface area to mass allowing the barrel to more quickly and efficiently dissipate heat decreasing thermal distortion in the barrel which in turn tighten groups. Weight loss is a minor bonus, this can also increase the resonant frequency at which the barrel "Rings" (in theory it may be useful l if you hit a bad harmonic), but then so can also shift phase by adding a tennis ball.

[W.R.Buchanan]

OK boys, you've made your points.

Dan: My .02 on this subject comes from my experience with my Ruger Gunsite Carbine. 16.5" bbl length over the last two years.

My standard load of Recycled M80 147gr FMJBT's over 45.0 gr of IMR4895 produces 2600 fps from the 16.5" bbl. This is verified by my Chrony and the trajectory which is dead on as downloaded from the ballistic calculator. The idea of losing 25 fps per inch of cutoff is pretty close as the Lyman book calls this load at 2800 fps from a 24" bbl.

Obviously it will make 2400 fps with a 168gr bullet.

The shorter the barrel the stiffer it is, and the stiffer it is, the less the shock wave is going to affect it.

I was leary about the shorter bbl at first however 2 years of fiddleing with this gun has changed my mind permanently. I can hit a mansized target with every single shot at 600 yards off a rest. That should be good enough for shooting bad dogs.

This Gunsite Scout is a generic factory .308 cal rifle with a Leupold VX-R Patrol 3-9X scope. My best groups have been 7/8" at 100 yds.

I just installed a muzzle brake in place of the flash hider that came with the gun but I think it will only make the gun louder and not affect accuracy at all.

So there's my .02.

For what you want to do I would have not even thought of using a 17" bbl 2-3 years ago. Now I wouldn't consider anything longer. just no point in lugging around more barrel.

Things change. Shooting is no exception.

Randy