Home Forums Hunting & Shooting Ask The Gunwriters Slow Barrel 6.5-06

What makes a barrel slow ? By my records I got 2888fps. and I would say I might be pushing it at that. 54gr of RL25 and Hornady 140 SP . 24" barrel. 2850 max might be more sane. This is about a 100fps off what would be expected.The rifle is a Husqvarna 1600 that I picked up at a gun show and then shipped off to Greydog to check over. It did require some fixing. Just out of curiosity, what are some of the causes of " slow barrel" ?

Yeah, I know 100fps is nothing in the field. 1600s are sweet rifles so I'll hang on to it.

One of the reasons could be that its not loaded nearly hot enough. What pressure are you running ?
Charlie

Long freebore and not upping the loads will cause this.

What are your expectations based on?

I think this matter of slow barrels and fast barrels is interesting and little understood. (Just for the record, I’m not claiming to understand it.) Let’s look at some, if not all, the factors involved. Pressure pushes the bullet down the barrel. The more pressure, the faster the bullet goes, but only within certain parameters, and only up to a point. We have to keep in mind that resistance is required to build pressure. Without resistance there is no pressure. (If, for example, we tried shooting a 7mm bullet down a.308 bore, we probably wouldn’t generate enough pressure, once the bullet left the case, to get much speed. At the other extreme, if we fired our.308 bullet down our 7mm barrel, we might generate a lot of pressure, but it might not make it to the muzzle.

So, given a “correct” bullet:bore size ratio (which is to say both within acceptable tolerance, what factors influence the degree of resistance the barrel affects on the bullet. There’s the bore size across the lands and the depths of the grooves. How deep are the lands digging into the bullet? What’s the microfinish of the lands and grooves (which potentially and usually, is going to be different, top, bottom and sides.) What’s the width of the lands, how much material is being displaced? How does the rate of twist affect the amount of resistance? How does the throat configuration affect the pressure curve? We know that, generally, a longer throat allows a greater initial pressure, but is there a point of diminishing returns?

What about variations in bullets? Some bullets of the same caliber can be found to run slightly different in diameter. Some bullet makers use different alloys and alloys can vary from lot to lot, just like powders can.

I’m sure that variations in all these things, and more, that are way to small for the industry, much less the gunsmith or handloader, to reasonably measure can have an effect and these effects can cancel each other out, or in some cases, stack together to create a fast or slow barrel.

You’re right abo100 fps. In the final analysis, it’s just a number.

Where did you get the data to use RL-25? Alliant's data doesn't list the 6.5-06, and neither does Hornady. In fact relatively few current sources of data include the 6.5-06. While it was accepted by SAAMI after the defunct A-Square company submitted the cartridge, it's no longer listed by SAAMI.

As a result there aren't any consistent chamber measurements, including throat length. The rifle could also have been shot enough before you got it to erode the throat.

Another comment: Since SAAMI switched to electronic transducer pressure measurement some years ago, none of the new manuals show muzzle velocities much above 3000 fps with 140s from the .264 Winchester Magnum from 24" barrels. Some don't even show 3000--and the 6.5-06 has considerably less powder capacity than the .264.

Also, the SAAMI maximum average pressure for the .264 is 64,000 PSI, which is only 1000 PSI less than they allow for ANY cartridge.

I had done a fairly extensive load developments with a 264WM before when the only data available was for when it was introduced. My method was a full case of a slow powder ,a Shooting Crony, and a target maximum velocity.Targets are involved, too, chuckle. The left over RL25 was from that. I have also done 338-06.Different powders ! I have reams of notes on both. With the 264WM, each shot of a three shot group markedly increased in velocity with RL-25 . Others had noticed this too. The more usual was a slight decrease as the action got looser. With the 6.5-06 ,RL-25 behaved itself. In fact I picked up a couple more pounds just for the 6.5-06 . Unlike for some, temperature between spring load development and fall hunt varies at most 10 degrees C. for me.

To answer the question of pressure. I don't know the number in psi, but I do know too damm hot. Loose primers for one.

One of the things Greydog found was the first gunsmith had left the barrel one thread loose to headspace. I'm glad I had him check it out. He fixed that. He couldn't do anything about the Huber Concepts trigger, I had installed though. I got a note in capitals letters, trigger sux. LOL Greydog is a magician in metal. I trust his chambering. I measured his 308Norma he did for me on a P-17, the fired brass was only 2 tenths out of round. I thought that was pretty good.

This gets back to the question of factors that make for a high pressure/slow rifle. That's my long winded question, Why ?

I have a little experience with the 6.5-06, more with the improved version and lots with the 6.5-284 which is basically same capacity.

Never had any luck with R25. 3150fps from the improved version using several powders.

Based on my experience, i would expect 2900-2950 from the 24" barrel with modern powders. You aren't that far off.

As far as fast and slow barrels, i had a 340 Wby barrel that pushed factory 250 grain loads to 3200 +. No idea how or why. Had no discernible pressure signs but surely it was hot. Brass still has tight primer pockets. Never had a " slow" barrel.

One of the several "slow" barrels I've encountered over the decades was on a Browning A-Bolt .270 Winchester, a first-year production rifle sent to me for a test-shoot article. At the time (1986 if I remember correctly) it was one of the lighter factory rifles available, and Eileen was looking for a lighter yet more "powerful" rifle than my grandmother's Remington 722 .257 Roberts she'd started hunting with a couple years earlier.

I worked up two handloads, one with IMR4350 the 130-grain Hornady Spire Point Interlock, and the other with the 150 Nosler Partition and the original H4831 military surplus powder. Had tried the same loads in other .270s, and have since as well. Both got around 100 fps less than they do in most .270s--and as in most other .270s shot to the same POI at 100 yards. She used the rifle with both loads for several years, at one point taking 10 big game animals with one shot each, including a buck pronghorn at over 400 yards (using a 4x scope long before laser ranger-inders appeared) and bull elk and moose at "average" ranges. The 130s were used on deer-sized game, and the 150s on the bigger stuff.

Don't know why the barrel was "slow," but also never could tell any difference in "killing power."

Mule Deer;
Good afternoon John, I hope that you and Eileen are well and that it's decent enough weather down there to get some seeds into the ground.

It seems like eons ago now that I was quizzing you about a slow velocity 22" Parker Hale barrel .270 I was fooling with at the time. You suggested that I might be more happy with a 6.5x55 barrel on it and that's the path I took.

Regarding that barrel, since I didn't and don't have anything other than a chronograph, I could only say that by the time I was approaching "book speeds" I was getting really flat primers and smearing the back of the case along with sticky bolt lift. I want to say back then too it was you who suggested I try to measure the twist and it ended up to be a tad slower than "normal" .270 barrels were.

Whether or even how that'd result in slower speeds of course is speculation.

It's interesting as well what you wrote about the .264 Win Mag as that mirrored the one and only '90's Model 70 that a now gone buddy and I fooled with. It just wouldn't push a 140gr much past 3000fps without those old school pressure signs showing up. Again pressure testing would have been interesting, but besides not being able to produce blistering speeds, it just shot okay, so it ended up going down the road in fairly short order.

All the best to you both as we head into warm weather.

Dwayne

All my life I have asked why did that happen. It was a great mind set as a millwright.

I wonder if the barrel had been a 6.5x55 and the fast twist might have something to do about it ?

Hi Dwayne,

We have risked putting part of the tomato plants in, and hope for more warm weather, as it can freeze here just as late as it does in your country!

A few other comments on this subject:

I have owned and shot a bunch of 6.5s, and velocities not only depend on the barrel but the magazine length. This is obvious, but the difference ain't as much as some believe--partly because of the 4-to-1 Rule, which I developed by crunching the numbers of pressure-tested data. What is basically comes down to is that any gain in powder capacity results in about 1/4 as much gain in velocity, at the same pressure from the same barrel length. This is NOT with the same powder, but the "fastest" (as in producing the most velocity) powder.

Have considerable experience with not only the "antique" 6.5x54 Mannlicher-Schoenauer, but the 6.5x55, 6.5 Creedmoor, 6.5-.284, 6.5-06, .264 Winchester Magnum, 6.5-.300 Weatherby and 26 Nosler, often in more than one rifle.

What I have found is they all pretty much adhere to the 4-to-1 Rule, though individual rifles can vary a little, probably due to the throat length and/or bore/land dimensions of the individual barrel.

Probably the 6.5 Creedmoor has resulted in the most consistent velocities, and in seven rifles. But some others have varied considerably.

One is the 6.5-.284, which has two versions--the "short-action" Winchester, which is designed to fit into the more-or-less standard 2.85" overall length of the .284 Winchester. But the Norma version, designed to fit in a ".30-06" length magazine, results in about another 2.2% in powder room. This does NOT, however, result in another 2.2% in potential velocity, due to the 4-to-1 Rule.

And even the Norma version does not have the case capacity of the 6.5-06. I have measured the water capacity of fired cases, using the same 140-grain Hornady Interlock seated to the cannelure. (This is the most accurate way to measure relative powder capacity, regardless of the bullet, rather than filling the case all the way up to the mouth.)

The 6.5 PRC comes closest to the 6.5-06, both holding around 61 grains of water. The 6.5-.284 holds around 56-58 grains, depending on whether bullets are seated to 2.85" OAL, or the longer Norma length. My present 6.5-284 is a New Ultra Light Arms Model 20, which has a magazine allowing bullets to be seated out to not quite 3.1 inches--about halfway between the Winchester and Norma versions. The same sort of thing happens with varying throat-chamber lengths in the 6.5x55--as I know you know.

But my main point is that a lot of this doesn't make all that much difference. As an example, my NULA 6.5-.284 gets around 100 fps less than my Charlie Sisk 6.5 PRC, using the same bullets with the "fastest" powders. (Both have 1-8 24" barrels, the 6.5 a Douglas #2 stainless, the 6.5 PRC a 1-8" Lilja #4.) This is about as much velocity as the 6.5 PRC loses within 60-65 yards from the muzzle--which of course is considerably less at 400 yards, or whatever range anybody chooses. Whether that makes any practical difference is another question.

Best to you!
John

It is an unsolvable mystery to me. I have a .338 Ruger 77 tang safety w/ 24"bbl. that shoots 210 NP's at 2900, 225 NP's at 2820 over 72 gr. of H 4350. but will not push a 250 NP past 2550 with H 4350, even though the book says 2700 should be expected. I went from 68 gr, to 69, to 70 gr with no velocity change and at 70.5 started to flatten primers so I quit. That was 30 years ago and I still load the 225's for elk. No idea why the 250's stopped at 2550.

Limapapa;
Good afternoon to you sir, I hope your part of Colorado had a decent day and you're well.

Thanks for twigging my memory on another rifle I had that didn't seem to want to hit "book speeds".

It was a Liberty Model 77 in .338 Win Mag and I got similar speeds or as far as I can recall that's about what mine did.

I'm in the same boat of it being a mystery to me and the lackadaisical velocity was one of the reasons it's now a .308 Norma.

All the best.

Dwayne

After reading this thread a few times, what comes up is that it could be a tight bore, and , or a rough bore, or maybe my guess, a fast twist 6.5x55 barrel rechambered 6.5-06 .

BTW, I checked Nosler on-line, (thanks for the heads up Mule Deer)they list 2900 as a max, so a 2850 wouldn't be too far out of line. As in bang on. After repairing the travel trailer soft floor, I can get up to the range .

Contrary to popular believe, rifling twist doesn't have much effect on pressure.

Peak pressure occurs as the bullet moves forward from the case and is engraved by the rifling. By the time it's engraved and starts moving down the bore, pressure starts droping considerably, regardless of rifling twist.

It has been a while since I did the calculation, so I don't remember the numbers, but only a very small fraction of the energy from the powder goes into spinning the bullet.

Thanks John,OK, my guess was wrong . One less factor. But much more to the point, my sweet 1600 isn't that slow.

A story for amusement, my canoe rifle has a blistering fast barrel. Canoes can tip. I have a Clipper 15'6" Mackenzie Sport V-stern freighter, grossly over powered with a 4.5hp Merc. It's pretty easy to dump her. So I needed a moose hunting rifle that wouldn't break a my heart or my wallet,if it fell in, preferably another 30-06 . I found a BSA P-17 30-06 sporter, for $100. He said it really kicked, which seemed strange to me,it's only a 30-06 and they are light like a Sherman tank is light. I mounted an old Bushnell Scopechief 3-9, added an aftermarket trigger and ejector spring, and glass bedded it. I mistakenly loaded the standard 180gr IMR 4350 load that everyone says shoots great.2700fps like the factory load. Headed to the range to sight in and clock the load. This thing really did kick. But it went 2900fps +, whoa, that's 300WM speeds. Can you imagine a hunting 220gr factory load ! ! I saved a fair bit powder loading it to a more sensible velocity. But I don't have interchangeable 30-06 loads any more. We did dump in the Dease river, BTW. Dried it out and put another scope on her. Hunted on the lake instead. The cross hairs were on the floor. I sent it in and got a Scopechief II 4x back. Much better scope.

I know your story was just for amusement, but now you've got my curiosity piqued. Did you ever slug the bore or cast the chamber with cerrosafe on that BSA? Seems like something could be out of spec with that rifle. Assuming your loads were OK, a 200 fps increase seems like an awful lot for just a "fast barrel."

I don't think the high 2800's is necessarily slow, for a 6.5/06. I also think 54 of Rl 25 is a bit light. I have loaded that amount of 4831.
I knew one fellow who was pushing 3000 in a 6.5/06. There were some factors in play. The barrel was 26" long, the barrel was throated long and the magazine was long enough to allow him to seat bullets out. The primary factor though, was that he was perfectly happy with case life of three or four loadings!
When I built my 256 Newton, the only load data I had was a Speer No. 1 manual. It listed 57 of 4831 as being maximum. I loaded a couple at 55 grains; the first shot saw a little smoke come out of the action, and the ejected case left the primer on the bench. I don't know what kind of brass Speer used to develop their loads, but it was a lot tougher than the Hornady brass I had.
Art Bourne shot a 6.5/06 AI in "F" class and he was able to exceed 3000. His barrel was 28 inches long and his loads required the use of Winchester brass. Anything else and the primer fell out. I believe he loaded H1000. GD