Barrel Length Conundrum

[shcal]

In my search for more loads for my new 6BR I ventured over to another forum,yes, I confess, I do read other forums and sometimes post on them). Anyway, I motioned that I was shooting out of a 28" pipe and it seems as though I started a small firestorm with a couple of folks over there. A Savage expert states that you really only need about a 24" pipe on the 6BR because the short fat case is so efficient.

Now Moderator I believe you my want to give some input here since I understand a dissertation on the proper length of barrel for the 6BR has been discussed, guess it was the Goldilocks approach, "not too short and not too long, but just right". How about it guys, where do you weigh-in on this subject?

Is 28" too long or is 24" just right? Lets hear from you.
shcal

 

[Caduceus]

IMHO, the answer is "it depends....."

I think it is reasonably clear that you can get more velocity from a 28" barrel than from a 24" barrel. There is a law of diminishing return to play with here because this doesn't necessarily mean that 32" will go faster than 28".

There is also a general consensus that from a pure accuracy point of view, short and fat is where it's at, meaning that short barrels are stiffer and therefore more accurate than long barrels of the same profile. If you read Precision Shooter, you might see that this concensus is seriously challenged as barrel tuners become better understood but....I digress.

So now the question for you is what rates higher on your scale of importance - maximum velocity or maximum accuracy? I'd certainly prefer accuracy. All other factors being equal, I'd opt for the shorter end of the barrel length spectrum. If you really want extra velocity, use a larger case rather than adding inches to your barrel.

That's the theory anyway. At the end of the day, too many other factors will confound the results anyway. I mean, you'll prabably still find a guy who's 28" barrel rifle is more accurate than his mate's 24" tube. At the same time, you will find the occasional dude with a short tube gun with unexpectedly high velocities and he won't appear to have excessive pressures.

Have fun deciding. FWIW, my 6BR has a 26" barrel so I'm truly a fence sitter.

 

[Rust]

A rule of thumb is 45-70 fps difference for every 2" of barrel if you are starting in the 24-26" range. There have been some strange results cutting down barrels though, sometimes they hit a node where there is virtually no change in velocity when chopping off another 2", and then the average decrease when chopping off another 2". Not an exact science by any means.

It is more difficult to produce a match barrel in longer lengths, on reason that most barrel makers price barrels at 26" and charge a premium for anything over that. Longer barrels can be a little more finicky to develope loads for too.

it all depends on whether or not you feel the extra velocity will do anything for you. One thing that can help you make a decision is to use Quick Load to determine the Optimum Barrel Time which predicts what time and therefore what velocity would be needed to have the bullet exit the barrel at a null node. Some OBTs are not attainable unless you load really really hot. Play with the numbers and you may find the length barrel that should work with a load you feel like using.

Opinions vary on that though but I figure if you plug in good numbers it ought to get you pretty close.

I figure it's a little better an idea than getting a long barrel and then trying to find a load that works for it and then finding out you could just as well take a couple of inches off the barrel and still get the same results.

 

[Forum Boss]

I can only give anecdotal responses because I don't know anybody that has published a progressive cut-down velocity test for 6BRs or Dashers.

32" -- Lynn's 32" barrel gave no more velocity than his 30".

31" -- Scott Parker is getting 3100+ FPS with his BRX in a Palma,relatively skinny contour) Broughton and it is insanely accurate, capable of shooting in the Twos at 200 yards. It appears the added length gives him more V than a 28". See: http://www.6mmbr.com/gunweek020.html

30" -- Darrel Jones is getting superb velocities with his Blackstar 30" barrel--3050 fps or better with Sierra 107 SMKs and a standard 6BR case. This is definitely faster than anybody I know with a 28" barrel. It is 1.25" tapering to 1.10" at the muzzle--big and heavy. There is something amazing about that barrel though--he can run a very stout charge of Varget, way too hot for most rifles. See: http://www.6mmbr.com/gunweek013.html

28" -- John Brewer won the US F-Class championship shooting his 28" 6BR in the 600-yard leg. He says a 28" definitely delivers more Velocity than a 26".

27" -- Harold Seagrove's Hickory Shoot gun is one of the most accurate 6BRs ever built. The rifle features a 1.250"-diameter straight-contour, fluted Spencer barrel finished at 27", with a big honkin' brake. He's getting 2950 fps with Danzac-coated bullets, and again, a Varget load that is way too hot for most rifles. See: http://www.6mmbr.com/gunweek026.html . My PacNor 27" is delivering velocities in the 2920 range with 105s,what Brewer is getting with his current 28" Krieger), and extremely good velocities,3060) with the Berger 95s. Load changes respond very closely to QuickLoad predictions. FWIW, Quickload predicts an extra 20 fps or so per inch out to 30".

26" -- Appears to be enough for a Dasher or improved 6BR case. Richard Schatz set a 6-target world record agg at 1000 yards with a 26" Hart-barreled Dasher running Reloader 15. And get this, he was jumping the bullets about 15 thousandths. His barrel had over 1500 rounds through it.

25" -- David Stripling just set a pending 600-yard world record shooting his 6BR Ackley Improved,6BRDX) with a 25" Kreiger barrel. It is a 10-twist shooting Berger 88gr FB bullets. Case capacity is 39.0gr of H20 according to David, not a lot more than a standard case.

What can we conclude from all this?

30" is probably not too much, if your barrel is big and stiff, unless you're Scott Parker of course, LOL--his Palma contour shoots like a Point-Blank PPC. Then, 27-28" seems like a nice Sweet Spot. That should get you to 2900 with 105s and a standard case. Maybe 2950. And there seems to be an interesting accuracy node going on in the 27-27.5" range. For an improved case, 26" is probably enough.

I'll leave you with this bit of advice from Bill Shehane "For a BR I'd start at least 28-29". That way you can set it back or re-chamber it and still have 26" which is as short as you want to go."

 

[lawndart]

This is from the perspective of a varmint hunter and plinker. I own and am the sole physician at a rural clinic. I am open on Saturdays and Sundays are for family, hunting and fishing only. So, competition is not in the cards until I retire, which will likely never happen.
For a purpose built rock chuck/coyote varmint rig that isn't too heavy or awkward to carry around the local hills, cliffs and mountains I think 24" is about the max. For shooting near the truck I am looking at a new barrel for my Blaser LRS II. I believe that will come in right at 26".

lawndart

 

[sparker]

That skinny barrel is still shooting like a house on fire. I hope the next one is just like it.

Scott Parker

 

[Wild_Bill]

Hi i have a Remington 243 VLS that was cut back and rechambered to 6mmBr when brand new to 22" i use it for spotlighting and other varmint shooting i find it perfectly ballanced for the lighter projectiles. Now i have just had my 6mm Dasher built i will pick it up Thursday and it has a 26" #7 profile barrel i think a stif heavy barrel is better as i will have it under the 17 ld limit for 600 and 1000 yard benchrest it also wears a Stiller Tuner. i think a 26" barrel is all you nead for any of the br cases.

This is only my opinion
Cheers Bill
Australia

 

[Forum Boss]

Lynn,

Thanks for the excellent report. I just want to add for the readers out there who are thinking of trying Varget in their guns that they may not be able to load anywhere near 31.5 grains, especially with naked bullets. Shooting the 105gr Scenars, I definitely was at MAX at 30.7 grains or so--the primer pockets were opening up and I got one pierced primer at 30.8. But I have a fairly short throat,.080) and it may be that guys with .100+ freebores can use more powder.

But quite a few folks, like me, are maxing out at around 2900-2920 with 30.5 Varget or less. Just stay safe and realize that each barrel's pressure tolerance level is different. When loading Varget with the 105-107gr bullets, I recommend starting at 29.5 grains.