barrel length for maximum velosity in 6.5x47L

[Joe Salt]

Dragman don't think for one minute that anything said isn't going to turn into a sward fight. No one has any respect or wants to believe anything someone else has to offer, so what I tell people is to try it and see if it works for you, if not try something else. I realy get a kick out of some of you that think by doing everything known to man is going to help you win every match you go too. Well wecome to the real world your still going to get beat.

Joe Salt

 

[mikecr]

The flag was rightfully thrown when someone claimed that velocity slows with barrel length. That's just what has to happen, before anyone takes bad information into basis, as the thread discussion progresses further.

You don't see 30" PPC because 30" barrels are not as accurate as ~21" barrels up close.
And given low capacity, fast powder, extreme pressure loads, nearly all powder is burned before 21", and so muzzle release of a flatbase bullet is very clean.

 

[Charles E]

T
You don't see 30" PPC because 30" barrels are not as accurate as ~21" barrels up close.
And given low capacity, fast powder, extreme pressure loads, nearly all powder is burned before 21", and so muzzle release of a flatbase bullet is very clean.

This presents a completely erroneous picture of why point-blank PPC barrels typically have the length they do.

IIRC when Roger Haney chambered up an 8-twist barrel in the 6 PPC to see if he could get it to work for long range, he used a 26 or 28 inch barrel. He was getting a bit over 2,800 fps with 115 grain bullets. His posts are somewhere back in the archives.

And even in short range, the notion of what makes an accurate barrel is changing (but not the weight rules!) As soon as you give up on the notion that the most accurate barrel is the stiffest barrel (minimize the effects of vibration) and go with tuning a load to a barrel (use tuning or compensation for vibration), many of the old truisms fade.

And that's happening. In fact, even moving from an 1.250 breech diameter removes significant stiffness. Guys are using 1.20, or even 1.1, primarily to make weight with the heavier scopes. The point being that barrel stiffness is willingly sacrificed for optics and rifle balance. Proper tuning gets it all back. Aggs, you will notice, are falling.

Etc.

 

[alinwa]

Lot's of absolute falsehood in this thread.........barrels will ALWAYS lose velocity as they're shortened. Fact.

It ain't about "losing efficiency" or "gaining heat" nor "different barrels" or blah blah blahhhhhh

The actual FACT is that a 6.5X47L will keep making velocity until you run out of barrel, even at 40 inches long.

EVERY barrel, EVERY instance EVERY time. Take it from someone who actually buys and uses 36" blanks, not from someone who guesses.

And to answer the OP, YES, the tests have been done to absolute exhaustion. This isn't an opinion poll.

al

 

[lefty o]

we're so smart now that the standard gun barrel on a U.S. warship is now 22.5 feet long. i guess the chronographs werent that accurate a couple hundred years ago.

 

[Charles E]

Here is Jackie Schmidt's text on (among other things) barrel length and velocity for the 6mm BR.

http://www.6mmbr.com/blogjan2006.html

It has nothing to do with how quickly the powder burns, everything to do with how much pressure remains in the bore. (so Al, a .22 long rifle will start losing velocity after about 16 inches).

And yes, you do gain heat, and barrel droop, and a host of less fortunate things.

Fun story: Bill Shehane once used a 40-inch barrel on a .338. He had a two-piece barrel block, sort of like a scope mount. Because of the heat differential between the two blocks, the barrel would begin stringing shots as it heated. That was the bad news. The good news was it was repeatable, so he could hold for it. Still bad news though, because nobody, not even Bill Shehane, could hold well enough to beat the people who didn't have the problem.

 

[alinwa]

Well OK lefty o, looks like maybe I misspoke

I made the assumption that the OP was about barrels readily available and used by the buying public.

My bad

I'm referring to barrels used in sporting arms.

Barrels over 40" (and cannons) will of course at some point show diminished velocity/length

LOL



al

 

[alinwa]

Looks like AGAIN I misspoke...... in answering the OP I forgot to consider that maybe the 6.5 ref'd could be construed as a .22LR

So...... to clarify........ YES the point of diminishing velocity is shorter for the .22rf case. Tests I've read indicate somewhere between the 16" quoted (I recall this was for marginally supersonic target ammunition if it's the same test...) and considerably longer for high velocity hunting ammunition, like 21 inches.

 

[lefty o]

not you Al, i had tried to quote 4mesh's post, but it didnt work. post #20 where he's mentioning ships cannons as an example of short barrels are faster.

 

[mikecr]

This presents a completely erroneous picture of why point-blank PPC barrels typically have the length they do.

IIRC when Roger Haney chambered up an 8-twist barrel in the 6 PPC to see if he could get it to work for long range, he used a 26 or 28 inch barrel. He was getting a bit over 2,800 fps with 115 grain bullets. His posts are somewhere back in the archives.

No, I said up close. To me that's <300yds where a 6PPC shines. Then you went and changed apples to oranges with this example of somebody experimenting 'for long range'.
Now, is somebody winning in point blank BR with a 26-28" 6PPC?
For that matter, is anybody winning in LR BR with a 26-28" 6PPC?
Lookin around,,, I'm not seeing any of that.

So if I'm so far off base, tell me; "why point-blank PPC barrels typically have the length they do"
Tell me about any 28" barrel, -in any chambering, that is as accurate UP CLOSE as a well built 6PPC in typical ~21-22" barrel lengths.
I must know this...

 

[Joe Salt]

How about stiffness, less vibration and weight they don't need it at short range!

Joe Salt

 

[Charles E]

So if I'm so far off base, tell me; "why point-blank PPC barrels typically have the length they do"

OK, At short range (group), everybody has a sporter rifle, because you can shoot all four classes with it, and give nothing up in three of them. Weight limit for a Sporter or LV is 10.5 pounds. You do the math.

In point of fact, I have a HV (a 13.5 pound weight limit class) chambered in .30 BR, which uses even faster powders than a PPC. It has a 25 inch barrel (again, weight). Even though I'm driving, no one likes to shoot against it, it shoots so well.

 

[4Mesh]

Lefty,

The analogy to make to todays guns on ships is that they use a different propellant. Maybe you didn't realize they quit using Black Powder. Just like is being said above, You people are all making your point showing that "XYZ ISSS Possible cause I've done it this way or this example shows it" or whatever, paraphrasing of course. Al says he uses 40" barrels. Oh yea? For 6.5's you do eh? No kiddin. So, he's probably comparing a 378 hunting rifle that shoots a couple rounds in cold weather, to a competition rifle that shoots 1/3 as much bullet. I suppose he shoots IMR 4895 in it too.

Barrel length is usually a function of the caliber. And, btw, ships use larger calibers than 6.5mm. Yep it's true.

All of you seem to think that there is 65Kpsi behind the bullet all the way to the end of the barrel. A, not only is that not true, but B, there is a $hi_load of leakage, C, that figure changes dramatically dependent on many factors including powder choice. Do not sit here and compare 378-416's with the 6.5x47 unless you're shooting 4895 in both.

Believe it or not, there ISSS friction in the barrel. Get it? Look at the test figures above with the 30-06. Now, if the acceleration has dropped off that far in 30", what do you think will begin to happen in the near future. Don't go load up a 40" barrel with R25 and then say, nope, it's still gaining, see!!!. Load your 378-416 with H4895 or H380 and now talk to me. Show me your 375 A-Max gain in velocity from 30" to 40" with that in there? Go ahead, show me. Just keep in mind, this guys not gonna shoot Retumbo in a 6.5x47. Get it?

According to you people, friction is finite, but your pressure is not. Somehow, even the people who admit that powder is done burning, seem to think it still gains on the bullet indefinitely.

How much "Loss" are we talking about. It may be minimal, but I hate to tell you folks, bullets slow down after you stop pushin on em. Especially if they're going down a press fit tube. A person could calculate how much friction there is by watching how much heat is generated in the barrel. And if you are using a powder that burns a long time, it is dirty and the barrel heat is GREATER and friction is greater. All that heat energy 'used to be' bullet momentum. Eventually, when pressure drops, the bullet will slow down. Will it do it in typically available barrel lengths? NOooo, cause they don't make them that long. Not in many calibers anyhow. When you get somewhere near the 1000psi mark, you are no longer accelerating the bullet. I say this due to evidence that if you change powders to one that produces such a muzzle pressure, velocity has ceased to gain. Not many folks try this sort of thing. H380 in a 30-416 (btdt).

Bottom line is, the OP asked about barrel length for maximum velocity in 6.5 x 47L. Anyone who tells him to keep buying barrel past the 30" mark is smoking meth. Lets see, he's at 113.6 calibers already. To equal that a 338 would have to be 38.4". A 378 needs to be 43", and a 408 needs to be 46.3. So I'll just ask again, how many of you have experience with these calibers using H4895, H4350, or faster. Oh, and with heavy for caliber bullets don't forget.

......... An inch of barrel from 30-31 gains an 06, 7.5fps, and I guess you still want to tell this guy to buy a longer barrel for a 6.5. And you people berate MY advise...?

 

[mikecr]

You are wrong.
Barrel friction and air drag on a fully engraved bullet is nothing compared to the pressure behind that contained bullet, even in extremely long barrels.
Yes, velocity gains drop off after the powder is burned up. But they are still gains, until pressure drops below needed to overcome resistance.
And don't forget, resistance itself acts to cause increasing pressure.

Haven't read anyone suggesting to OP that he go to any extremes on barrel length. All I hear is basis for 'maximum' length that is bogus.
Best length IMO falls into a balance providing competitive accuracy for this mid-range cartridge. That will be where a proven load produces low ES, low muzzle pressures, forgiving tune, and at a velocity that gives up nothing to the field with a quality high BC bullet.
IT IS NOT 'anything beyond X length causes velocity to drop'....

 

[4Mesh]

No Mike, I didn't say at what point it would loose, simply that it will. This data from quickload for 270" barrels is fantasyland. I'd love to see the real world results of this sort of thing. And, have you never seen quickload to show values that were false? Everyone else has. Using a 22LR as an example, it shows what I say to be true. No horse___ computer program, just data. Where is that point for a 6.5? I really don't give a damn. My original statement was that I agreed that past 27-29", you're gaining nothing IN THAT CALIBER. And that is correct.

Just for fun I ran numbers in QL, changing only barrel length, for a 6.5x284 using H4350.
26" = 2940fps
36" = 3147
56" = 3390
106" = 3680
107" = 3684
At 270" you just break 4000fps

Why don't you run the numbers for a 22LR and have it show the truth there. Actually agree with real world numbers. Then talk.

@Lefty,
btw, I find it interesting that your ships guns are ONLY 22' long. Why is that? Is there a barrel taper rule on them? How many calibers of length is that anyhow? Not very many methinks. The Battleship Yamato had 46cm guns with 45 calibers of length. Why not 100 calibers if there was all that "Free" velocity to be had? A primary goal of a ships guns is range. Why not gain more if it's that easy? Its longest ratio was 60 calibers of length on the 15.5cm guns. We virtually all shoot 100 calibers in 1K.

Funny how in spite of all this free velocity with less pressure, a look around the rifle range shows everyone who's winning using barrels from 26-30". Hmmmm.

 

[lefty o]

i dont know, but at 12 miles they can do groups that will make a BR shooter envious!

seriously 4mesh, you make a lot of hypothesis as the basis for your argument, and nothing of substance to back it up. i dont put a lot of faith in QL either, but you have made statements, with absolutely nothing to back it up, and yet continue to argue everyone else is incorrect.

 

[4Mesh]

Lefty,

In order to see it with stuff you can get at home, you need to move to a 22LR and simply accept that a scaled up version WILL do what the 22 does. Is someone going to go buy a 48" .264 barrel, chamber in some ridiculous cartridge and then saw it up to show what is pretty well already known. No.

Friction makes the heat in a barrel. There is heat all the way to the end of them when you shoot em. In other words, there's friction. This idea that there is no friction of significance past the engraving process is crazy. It will overcome the pressure at a point. Where is that point? Later... If it didn't have friction of note, the barrel would not get hot out at the end.

So ok, is this guy going to see this happen in a 34" barrel. I doubt it, but he might with a 47. Is anyone going to buy a >34" 6.5 barrel? I doubt it but they might. Everyone in the discussion has completely ignored the point. If the guy wanted the last .01fps from this thing, why not just build a 6.5x284 and forget the 47. It's like asking what's the fastest Suzuki Samurai package. Do ya wanna go fast or don't ya?

 

[lefty o]

the problem with your theory here is that a centerfire bottleneck cartidge with smokeless powder is not just a scaled up version of a 22lr. apples/oranges. i definately believe there's a point that adding barrel length nets you very little in return, but with the centerfire cartridges we are discussing here, its just not at the 27-28" range that your wanting everyone to believe.

 

[Tod Soeby]

I believe there were test done in P.S. magazine, can't remember what year but it has been done. Myself I like a little longer barrel so when it starts throwing shots I can start all over again. And I have one that started at 36 inches with over 4000 rounds that still shoots but it's a 30 Cal. What you are looking for is Optimum velocity don't care what the length is.. At 36" the velocity was 3080 and at 30'' It still will go 3080 with different powder. Was using R-22 now H-4350. So I guess if you change a few thing like I did you can still maintain your speed.

Joe Salt

I remember this artical, or at least one like it. If I remember they started with 40" blanks and cut them down an inch or two at a time. Don't know the calibers tested. The two things I remember...and remember well is this.....The longer the bbl the higher the velosity, And....and this really caught my intrest....Whatever the best powder for velosity in the long tube was also the best powder as the bbl got shorter (using the same bullet).....and if I remember right they took these bbls down to single digit lengths. I always figured that the longer bbl neede slower powders......I guess not.

Something in the back of my mind says the artical was written by Dan Lilja.

 

[4Mesh]

the problem with your theory here is that a centerfire bottleneck cartidge with smokeless powder is not just a scaled up version of a 22lr. apples/oranges.

Why not? If anything, I'd bet the LR leaks less around the case than does ANY bottleneck cartridge when the pressure is no longer high. Necks rebound...

i definately believe there's a point that adding barrel length nets you very little in return, but with the centerfire cartridges we are discussing here, its just not at the 27-28" range that your wanting everyone to believe.

I agreed that past 29" FOR THE 6.5x47, you will not gain a thing. This is posted in a BR forum for long range benchrest. What more must I assume about what the guy wants to do with it?

Ok, I'll re-word this. For a 6.5x47L gun, do not bother buying more than 29" of barrel because you will gain essentially no velocity and will loose a lot. You will loose a hell of a lot more important things than speed, but if you want to go there, by all means have at it.

Ok, your contention. Definitely buy more than 30" of barrel if you want max velocity from a 6.5x47. Fine, I'll go along with that.

Btw, I have owned, built, and tinkered to destruction, a 32" 6.5x300WSM. I had about double the powder capacity of a 47, yet, the extra length gained me nothing. Yes, I cut the barrel off, several times. Moreover, I could also add powder to that case and not gain velocity either. Great for ES, not so good for competition.