vld short range accuracy

[bruce moulds]

we hear that vld bullets need to go to sleep to achieve full accuracy, and that this does not happen at closer ranges.
the recent purchase of rsi shooting lab allowed me to examine some targets shot at 100 mt while running in a barrel.
target 1, 3 shots , 0.24 moa
target 2, 5 shots, 0.36 moa
target 3, 5 shots , 0.31 moa.
all targets overlaid came to not surprisingly 0.36 moa.
what is amazing is that this was 3 different loads, 2 powders, and 3 seating depths, one jumping and 2 jammed to different depths.
not much of a hint here as to which direction to go.
while this wouldn't be competitive in a benchrest match, it does suggest that vld bullets aren't too bad in accuracy while still awake, let alone asleep.
the above moa was for group centres overlaid.
using the same point of aim, the overlaid group blew out to 0.42 moa, so either conditions changed from string to string, or each load had a different zero, or a bit of both.
bruce moulds.

[johnk]

Bruce,

I've had similar results with my MR with 210 Berger VLDs & (original) Hornady 208s. I suspect that the issue is the quality of gunsmithing & the attention given to loading consistently straight ammo.

If the projectile starts & runs coaxially up the bore, why shouldn't it go bye byes straight away?

John

[bruce moulds]

john,
i agree with you about runout and its need for minimization, but over the years i have had acceptable accuracy with 0.008" runout when fireforming new brass. quite a shock really.
possibly the running in targets mentioned previously lend credence to the argument that the most accurate barrels are new ones..
bruce.

[RDavies]

Have you had other barrels in the same caliber? Were they this good with all loads?
I think it could be a case of one of those hummer barrels that shoot just about everything well.
The next one you get might be one of those tempermental ones which will only shoot if loaded while facing mecca, with your tongue held just right, and with only one load, one bullet.
As for VLDs at short range, the smallest group I have ever shot was with a 284 using 180gn Bergers, but then my next 3 barrels wouldnt shoot the 180 Bergers at any range. The one which did shoot 180 VLDs well though was a very tight barrel with a fast twist. Maybe these combination help with VLDs at short range???

[bruce moulds]

rod,
it has been a trend with 2 of 284 barrels, and numerous 6.5/284 barrels.
all the 6.5 were 8 twist, and the 284 were 9 and 8 1/2. the big problem seems to arise as distances increase.
i have had a load in a 6.5 that shot lights out good elevation at 600m, but give poor elevation at 300. obviously it had poor velocity s.d, and the slow ones were shooting higher than the fast ones, coming back together again at 600. as with all the 6.5/284 barrels i had, increasing the pressure made the problem go away.
just goes to show, long range accuracy is a different ballgame than short range.
bruce moulds.

[ned kelly]

G'Day All,
I've seen a mates 223 shooting 80gn bergers shoot around .28 aggs (5 shot groups) at 100 and Dazza has seen the same guy shoot another .223 at 100 agg less than .23 for 4 x 5 shot groups at 100. So 2 different guns, 2 different bullets but the same shooter and same gunsmith. Great smith and great shooter? Probably, i wouldn't bet against either.

My 6x47 lapua amazed me at 150yd shooting 107SMK's by shooting .3 groups repeatedly, not VLD's but entirely unexpected......... same gunsmith.

A properly built rifle should perform at 100yds. I would not expect anything else. However, different barrels, different gunsmiths and different bullets may not perform the same all the time but I think now, I would be surprised if they didn't shoot surprisingly well.

Yah gets wot you pay fer I s'pose!

Cheerio Ned

[IanP]

Lets play Myth Busters! This is the expression Bryan Litz uses at the start of chapter 10 of his book "Applied Ballistics For Long Range Shooting". It seems stability and a bullet going to sleep are very much misunderstood concepts. If you have his book the subject is covered on pages 152 and 153. Then again if you had the book you wouldn't be asking this question.

A bullets stability can be calculated by using Millers formula which was introduced back in 2005 and greatly enhanced the understanding of exterior ballistics. A bullet with an Sg (stability factor) of 1.0 is deemed stable but this is for a specific set of conditions. Litz recommends a stability factor of Sg = 1.4 using Miller's formula to be optimum. The Sg = 1.4 takes into account any error in Miller's formula and the conditions that could exit.

If I can cut to the chase, Litz states that as long as the bullet has adequate stability (Sg = 1.4) then the way a bullet "goes to sleep", (all bullets are launched with some minor pitching/yawing motion) will not affect its flight performance, (BC). In other words a properly stabilised bullet will be just as accurate at 100 yards as 1000 yards. The gunsmith plays an important role in an accurate rifle but only if the twist rate is sufficient to stabilise the bullet that is being used.

If you have a bullet that wont group at 100 yards but will group at 500 yards then its probably worth calculating the stability. I have two Excel spreadsheets that include Miller's formula at safclass.com.au and you are most welcome to download and use them. Hope this helps Bruce!

Ian