VLD bullets - short range vs. long range accuracy

[StemCell]

I have heard, and read of a phenomenon where some bullets will not shoot well at less than 200 or 300 yards but will outperform others at longer ranges.

I cannot get my head around this concept.

I admittedly have limited distance shooting experience, but believe that if a bullet does not group well at say 100 yards, it will not group better at 600 yards or beyond. I can accept that a bullet may group well at lesser yardages, but have accuracy diminish due to ballistic properties at longer ranges.

But:
How can a bullet not shoot well at a lesser range, yet group well at distance?

 

[Hondo64d]

Depends on the unit of measurement for the group. Very unlikely that a load will group 1" at 100 yards and less than 1" at 300. But not uncommon for a load to group 1 MOA (about 1") at 100 yards and less than 1 MOA (a hair over 3") at 300. The theory is the bullets settle down and quit yawing at some point down range (going to sleep), therefore dispersion slows.

John

 

[Hoier]

Jim Ohara shoots all his 1k load testing at 100 and gets very small groups.

 

[markm87]

Litz had a visual of this. I've seen it posted here before. It shows the spiral motion of the bullet on a time elapse of the bullet flight.

Basically, the bullet is gyrating on it's flight axis and the gyration diameter decreases over the flight time.

(forgive me if my scientistical vocabulary chopped this explanation to bits)

 

[FeMan]

Brian Litz explains all the physics in his book. While I believe the phemonom exists, I think it is very minor. At least I haven't seen anything noteworthy in my limited personal experience. I don't believe crap at 100 yards turns to gold at 1000. My rifles that will shoot VLD's hold 1/4" 5-shot groups at 100 yards. The ones that don't shoot VLD's well don't shoot them well at any distance.

 

[lpreddick]

the benchrest shooters (some) say bullets "go to sleep" after an initial wobbling much like a child's spinning top...they wobble, then straighten up and spin stable, then wobble again and fall. i believe this especially applies to boattail bullets. there are some suggestions that a 200/300 yd group can have a smaller MOA than at 100 yds.

 

[johara1]

I think you need to understand it is a cone of dispersion, meaning it gets bigger as you go further out. Say i'm shooting a .1 at one hundred, at 300 it can shoot .3 but once in awhile it shoot a small one at 300 and they say it will shoot smaller than a 100? think what that group would have been at 100 but you can't do it at both at the same time. A hummer will be asleep as it exits the muzzle and is not effected by the wind like one that is yawing. ……… At longer ranges you have too many conditions you can't see affect the bullets, I try to control the condition that i shoot under at 100 and the further you go the harder it is to do, so i feel you don't gain anything with longer testing. After you get your gun to shoot the best it can at 100 yds. load 6 rounds shoot 3 each in 180 out conditions from the left and right and hold the same point of aim. You will see the quality of barrel you have in a hurry. A hummer will shoot a hole but an average barrel will give you a weather report. …….. jim

 

[mikecr]

Keep in mind epicyclic swerve represents bullet tip,, not pullet travel.
Once a bullet is released it does not remember the original path and head on back over there..
The whole 'going to sleep' as accounting for improved distant performance of boat tails, until proven otherwise, -is hogwash.

Boat tails are not the most accurate of bullet designs, because they don't muzzle release as cleanly as flat base bullets, and their stability requirements are detrimental to the whole system(compared to flat base). But at distance, at some point, the reduced base drag/higher BC of boat tails takes over as an advantage -from that point forward(especially in any wind above 0mph).

For example; two bullets designed of the similar form but equal in weight and one having a good boat tail while the other is flat base, a twist is chosen that works for both.
The FB will likely shoot better at 100yds and maybe so all the way out to 500yds. [Let's say .1-.3moa]
The BT will likely match FB at say 500yds, and improve on the FB further out. [say .3-.5moa]
What's happening here is superior FB accuracy(in MOA) degrading with external ballistic factors that higher BC of a BT addresses. By 1kyd the FB bullet would likely be worse than either .3moa(at 500yds) and worse than .5moa presented with the BT. So much higher, that the BT wins by that distance.
And it's not just wind, but drop as well. The more drop, the more inconsistencies in it spread.

Eventually, BC matters more than pure accuracy, which is why LR shooters use heavy for cal, hi-BC BT bullets at 600yds+, rather than more accurate(up close) FB bullets.
1kyd, competitors need only produce .5moa consistently to win(easy right?). Well, shooting in the 1s at 100 in itself, is meaningless to LR.
So even though distant shooters would like to use lighter BR FB bullets, from slower twist barrels, and with tiny little cartridges(for less recoil, torque, better pressure curve, and cleaner release), that produce 1s & 2s at 100yds easy enough, they can't and don't.

Nothing is free

 

[johara1]

Good Boat tail bullets are just as accurate as flat base with the proper twist, 66.5 gr. boat tails shot as good as his flat base and have set a bunch of records at short range. Point of bullet yaw is that the wind affects them more than one's asleep, because it isn't stable at that point.
It's funny that i just came in from trying to get my 103 Spencer BT's. tuned in a new Brux barrel and and it shot back to back .063 and .070 5 shot groups at a 100 yds., I'm glad you told me they don't shoot as good as flat base bullets, time of flight, wind drift come in to the mix…….. Jim O'Hara

 

[mikecr]

johara1, I'm glad you told me that you pulled off 'back to back' 0s from Spencer BTs. Sounds like the only bullet I'll ever need right there.
I reckon someone out there is shooting FB bullets well at 1kyd too.
Well, once in a while.

It's my contention that whatever you can do at short range, you can probably do best with FB bullets.
And whatever you can do at long range, you can probably do best with BTs.
It's not my notion that this is law that cannot be broken or anything like that.

 

[johara1]

A friend of mine made short range bullets both flat base and boat tails both were very good and at 200 and 300, the boat was way better. If somebody shoots flat base at 1000 i doubt if he ever got in to many shoot offs……. As far as back to back zero's last year i shot 6 zero groups in a row with two different light guns,with the Spencers. The year before it was the Berger 105 Hybrid, so there are a lot of good boat tails out there. Do you really think any one shooting F class are using flat base bullets…… jim

 

[mikecr]

Don't know about F-Class, but I believe Joel Pendergraft set a 1000-yard IBS record using a BIB 30-caliber 187gr FB bullet. I read somewhat recently where someone is using a 7mm FB bullet in IBS as well. But I can't find it now.
Anomalies

 

[amlevin]

the benchrest shooters (some) say bullets "go to sleep" after an initial wobbling much like a child's spinning top...they wobble, then straighten up and spin stable,

How much of this might be caused by poor crowns on the barrel or irregular bases on the bullet. If they exist, these problems should be dealt with first. Chances are that the so called "wobbling" will go away.

 

[mikecr]

Some is w/resp to muzzle pressures.
That fireball created(when folks use barrels too short for the burn), slaps across bullet bases, disturbing them. Much as a bad crown..
A 'clean release' from my perspective is that produced by a 6PPC/30br, etc -with FB bullets. These underbore cartridges already produce low muzzle pressures even with short barrels, due to their fast powders burning early INSIDE the bore. On top of that, the flat bases provide little for any perpendicular pushing.

In contrast, when muzzle pressures from a 30-06/22" barrel knocks your hat off, it's likely less of a clean release for large area boat tail bases. This area provides for plenty of shove one direction or another.
But a 6Dasher/6.5x47L in ~28" will shoot boat tails great(way less muzzle pressure).

 

[300 RUM]

Good Boat tail bullets are just as accurate as flat base with the proper twist, 66.5 gr. boat tails shot as good as his flat base and have set a bunch of records at short range. Point of bullet yaw is that the wind affects them more than one's asleep, because it isn't stable at that point.
It's funny that i just came in from trying to get my 103 Spencer BT's. tuned in a new Brux barrel and and it shot back to back .063 and .070 5 shot groups at a 100 yds., I'm glad you told me they don't shoot as good as flat base bullets, time of flight, wind drift come in to the mix…….. Jim O'Hara

Yes in deed, "Proper Twist Rate" the faster the better!!!

 

[mikecr]

But again, nothing is free.
You might consider high torque detrimental to gun movement.
I think most shooters do.

 

[StemCell]

Thank you all! I will need some time to digest your comments, do some range experiments on my own, and perhaps most importantly find a copy of Brian's book to read.

 

[orkan]

Brian Litz explains all the physics in his book. While I believe the phemonom exists, I think it is very minor. At least I haven't seen anything noteworthy in my limited personal experience. I don't believe crap at 100 yards turns to gold at 1000. My rifles that will shoot VLD's hold 1/4" 5-shot groups at 100 yards. The ones that don't shoot VLD's well don't shoot them well at any distance.

I used to believe this very same thing. The theory was sound, but I never saw anything first hand that would prove it to me.

Then I started working with 375CT, and routinely see groups of 1.5-2.5" at 100yds, that will stay 1.5-2.5" at 500yds. I have seen 2.5" groups at 100yds, produce 5" groups at 1000yds more times than I can remember.

It would appear that the longer the projectile is, the more pronounced the effect. The projo's I've worked with most are the 352 solids from cutting edge, and they are 2" long. I've not yet worked with anything else that exhibited that extreme behavior.

I have done load development for around a dozen 375CT rifles in the last year, and all performed similarly. While I do not proclaim to be able to completely explain what is going on mathematically, clearly there is something going on there.

 

[Erik Cortina]

I will not shoot a bullet that will not stabilize at 100 yards because of the BC loss due to it. I tune at 100 yards to make sure bullets are stable and accurate, this will ensure highest BC possible.

 

[johara1]

Brian Litz explains all the physics in his book. While I believe the phemonom exists, I think it is very minor. At least I haven't seen anything noteworthy in my limited personal experience. I don't believe crap at 100 yards turns to gold at 1000. My rifles that will shoot VLD's hold 1/4" 5-shot groups at 100 yards. The ones that don't shoot VLD's well don't shoot them well at any distance.

I used to believe this very same thing. The theory was sound, but I never saw anything first hand that would prove it to me.

Then I started working with 375CT, and routinely see groups of 1.5-2.5" at 100yds, that will stay 1.5-2.5" at 500yds. I have seen 2.5" groups at 100yds, produce 5" groups at 1000yds more times than I can remember.

It would appear that the longer the projectile is, the more pronounced the effect. The projo's I've worked with most are the 352 solids from cutting edge, and they are 2" long. I've not yet worked with anything else that exhibited that extreme behavior.

I have done load development for around a dozen 375CT rifles in the last year, and all performed similarly. While I do not proclaim to be able to completely explain what is going on mathematically, clearly there is something going on there.

I hate to rain on your parade but, If you shot a 5" group at 1000 you have no way of knowing what it would have did at 100 yds. It had better shoot small at 100 and repeat it to be a good 1000 yd. gun. It can not stay the same size from a 100 to 500yds. it is a cone of dispersion and it had better shoot small at 100. Conditions at 1000 dictate far more with group size than you will ever know,because you can't see it……… jim