barrel weight vs accuracy

[ghermitage]

Has anyone tested or know of a test being done of the accuracy difference that barrel weight makes when the quality of the barrels is the same? It is easy to believe that increased outside diameter reduces the flexing of the barrel during firing, but I wonder if numbers could be put to the statistical average of accuracy difference?

The reason I ask is that I am debating whether to use a varmint weight,.85" muzzle OD at 24") or sporter weight,.65" muzzle OD at 24") for my forthcoming 6.5x47 Lapua hunting rifle that will see use from foxes to fallow deer. If the heavier weight doesn't tighten groups by much more than .25" at 100yds, I would likely go with the sporter weight. Assume match quality barrel,e.g. Krieger) in either weight.

Also, are there any issues in using a stainless barrel with non-stainless action?

 

[steveyrock]

I just got a lesson on this subject at the shooting range the other day as I was placing my targets next to a fellow testing hand loads in a 300 Weatherby.He was set up on the bench next to me and had fired at several targets before I arrived.He gave me the all clear to walk down range at the 100yd backer and as I approached the boards I couldn't help notice his string of fired groups on his targets.They were small VERY SMALL and I said to myself,damn that's one good shooting deer rifle.

We chatted after I walked back and he told me that it was a Shilen barrel on that gun and I saw it was fluted and very long and skinny,seemed to me just to be a hair over bullet diameter from what I am accustom to and that gun was doing .500 3 shot groups easily with the one load.He let the barrel cool between shots with a timer set at 8 minutes.

Yes skinny barrels will print small groups if you feed them what they want and don't let them get hot between shots.

 

[Eddie Harren]

....and make sure that big 10 pointer will hold still for 8 minutes!

 

[Sako6555]

In my opinion,as a fallow/Sika/roe & fox shooter)
a) the benchrest precision of a rifle is largely irrelevant in the field. Accuracy is controlled by how you're holding the rifle. Highseat or bipod = good, free-standing = bad, all others between.

b) ideal rifle weight is determined by how far you have to carry the damn thing. For me, my Sako Finnlight + 2.5-10x42 + bipod + sound moderator make for a reasonably portable package, which shoots straighter than I can hold it,in the field).

However, the skinny barrel is not so good a long strings of shots on the range; for that one needs a fat barrel.

In the field, barrel weight may help to your reduce the natural movements during the final "aim and safety catch-off" phase, but often I have to wait for a shot to 'come good' before I reach "safety catch off" step, and then I'm always greatful for the lighter skinny barrel!

c) if using 6.5x47 on a rutting fallow buck, please be gentlemanly - use a heavy bullet,140gr min). Personally I favour Norma Oryx 156gr in my 6.5x55,for all deer and foxes). It has lousy ballitics,on paper), but they're great at stopping sika and fallow humanely, and I've never had a fox complain the bullet wasn't fast enough!

J.

 

[ghermitage]

What twist rate to stabilize these 156gr bullets of yours?

 

[sling_n_glove]

There has been a lot of experimentation done regarding this issue. Free floating barrels are essentially cantilever beams so they get analysed that way. The problem is that barrel vibrations are somewhat complex and not especially easy to predict accurately.

As you probably already understand, heavy barrels are generally stiffer, within a certain length range, so it's thought that the vibrations cause the muzzle to deviate less from a straight line. All barrels vibrate though, even if they're very heavy. The accuracy improvements of heavy barrels seem to come mostly from the ability of the barrel to dissipate heat better throughout a string of shots.

The timing of the bullet passing down the barrel is a more important part of consistent accuracy. People seem to intuitively think that the muzzle should be at zero deflection the instant the bullet exits the barrel for greatest consistency, but that's probably not true. When a barrel is vibrating during a shot, the muzzle is moving back and forth past dead center. The speed of this motion is greatest when the muzzle is crossing this 'zero line' so slight differences in bullet speed would result in comparatively greater deviations in bullet departure angle,or whatever you want to call it). When the muzzle is at its maximum deflection from zero, the speed of deflection of the muzzle is at its minimum, reducing the possible deviation if the bullet leaves the barrel at that instant.

The gist is that a heavier barrel may very well give you some slight improvement in accuracy under certain conditions but you have to make sure the compromise is worth it. If you shoot 22-shot strings in 22 minutes, heavier contours may be best. Some people flute their barrels to get better temperature consistency but the expense only seems worthwhile to those that like the way they look. A lighter barrel isn't necessarily going to be less accurate anyway, if you familiarize yourself with the way point of impact changes as it warms up. You can easily compensate for it with experience. If you're making one shot in a day and it's at a 140-pound animal with 10-inch wide kill area at less than 100 yards, you can save yourself some fatigue by not humping a match barrel around.

 

[ghermitage]

To elaborate on the intended usage, the primary usage will be a on rabbits, hares,think of a scaled up rabbit that does not live in a hole) and foxes. When foxes are seen in daylight in this part of the world, they tend to only sit at great distance,800 yds) and while you tell yourself you can get closer than that it doesn't happen. The way I look at it, a 600 yd benchrest calibre has potential in this regard, and particularly a cartridge that is accurate shooting heavier than usual varmint bullets to compensate for the reduced velocity at those distances. More commonly, the accuracy requirement is for head shots on rabbits at ranges where the 17 HMR is losing it. The other appeal of the 6.5x47L is in Lapua's claim for barrel life exceeding that of 6BR, as the rabbit numbers are increasing in this area and the shooting can get lively.

The secondary usage is in the hands of a hunting buddy who only has narrow calibre varmint equipment at this stage and can make use of the 6.5 for fallow deer and goats when I am using my 270W,130gr from 270W seems fine on fallow, which I think is a bit smaller than whitetail). It seems reasonable to me that the weight of the gun should be optimised for the primary usage. The gun is a replacement for a 22-250 for varminting, but I notice the potential of the 6.5x47L to be more general purpose if need be. This secondary usage is interim, and when the Rem 700 SPS Stainless is chambered in 325WSM he will use that instead.

Has there been no experiment in which barrels have been successively turned down to narrower contours and put back in the action for another accuracy test?