stable enough? (pics added)

[HSNARC]

A few weeks ago i was excited to see powder valley get the Berger 140 match VLD's in stock so i quickly bought a box. Well i forgot that these bullets supposedly need a 1-8 twist to stabilize properly. I think my lilja barrel is either a 1in 8.5 or a 1 in 9 twist......shit. So this past weekend i loaded up a ladder test to try and determine if these things would even shoot in my rifle. I shot it at 100 yards because i was lazy and it was cold. Well every shot (all 13) went into a 1.5 inch group, with one node (shots 1-7) grouping approximately .75 So does this mean that these bullets are stable enough to try and do load development? or am i just giving myself false hope from performing my test at 100?

well i went back out to the range today and shot another ladder at 375 yards and here is what i got.

i shot 3 shots (sighters) that grouped about 2.5 inches looked decently stable? so i shot the rest of the ladder and im thinking my node is between shots 2 and 7 what do you think?

 

[Suasponte]

Re: stable enough?

Take a cleaning rod and put a tight patch on it. Mark the rod so when it spins you can monitor one full revolution. Then put a piece of tape at the barrel when you hit one full turn. Pull it out and measure from you first datum point (I typically use the end of the brass jag) to you second (Tape you put on) and that is your twist rate.

It sounds like you rifle will stabalize the bullet.

Terry

 

[Greg Langelius *]

Re: stable enough?

If the bullet holes at 100yd are round, it's stable. Stable enough? Try further.

 

[clmayfield]

Re: stable enough?

Stability issues start showing up further downrange. German Salazar did a test where he shot a lot of bullets through a low twist rifle. The under twist (heavy) bullets shot best at 100... and not so great at 600.

His test led me to believe that there is an ideal twist rate for different ranges. Surface drag will decay rotational speed, so a projectile that is just stable enough at 100 is unstable at 600. And a projectile that is overtwisted at 100 might be perfect at 600.

In short, you need to shoot these at distance.

 

[HSNARC]

Re: stable enough?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Carter Mayfield</div><div class="ubbcode-body">Stability issues start showing up further downrange.
In short, you need to shoot these at distance. </div></div>

That is what i will do then. What am i looking for when i perform my tests? Keyholing? Terrible arruracy? Both?

 

[MALLARD]

Re: stable enough?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Carter Mayfield</div><div class="ubbcode-body">

His test led me to believe that there is an ideal twist rate for different ranges. Surface drag will decay rotational speed, so a projectile that is just stable enough at 100 is unstable at 600. And a projectile that is overtwisted at 100 might be perfect at 600.

In short, you need to shoot these at distance.</div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">If the bullet holes at 100yd are round, it's stable. Stable enough? Try further.</div></div>

+1
these both sound good , you might want to play with your seating depths to

 

[clmayfield]

Re: stable enough?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HSNARC</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Carter Mayfield</div><div class="ubbcode-body">Stability issues start showing up further downrange.
In short, you need to shoot these at distance. </div></div>

That is what i will do then. What am i looking for when i perform my tests? Keyholing? Terrible arruracy? Both?</div></div>

Keyholing is a definite sign of stability issues. A dramatic drop off in accuracy is more likely. That is all you care about in the end, anyway. If you are keyholing X's, who cares?

 

[HSNARC]

Re: stable enough?

btt

 

[vman]

Re: stable enough?

Put that target out at 400 yards and try again.

 

[bowslngr]

Re: stable enough?

My opinion (from my own experience) is that if a bullet is right on the edge of not being stable enough you will see the results by the time you get to 300 yards. You are getting good results out to 375, so my vote is that you are gtg with the 140 Match VLDs.

 

[Greg Langelius *]

Re: stable enough?

My opinion mirrors bowsingr's. If instability isn't obvious and accuracy is relatively acceptable out beyond 300yd, you should be GTG. Some ballistic theories would suggest that stability increases with distance.

I would do load development to locate an accuracy node at this point and pay attention to bullet hole shapes if the development results in a lower velocity than what you're currently shooting.

My experience seems to suggest that bullets get their best LR accuracy in a twist which is closer to the lower end of the acceptable RPM range. You may be right at or around that RPM range right now.

Greg

 

[HSNARC]

Re: stable enough?


I would do load development to locate an accuracy node at this point and pay attention to bullet hole shapes if the development results in a lower velocity than what you're currently shooting.


I would assume because when a bullet loses stability and wobles/tumbles it increases drag and therefore results in lower velocity?

 

[bricktop]

Re: stable enough?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">My opinion mirrors bowsingr's. If instability isn't obvious and accuracy is relatively acceptable out beyond 300yd, you should be GTG. Some ballistic theories would suggest that stability increases with distance.

I would do load development to locate an accuracy node at this point and pay attention to bullet hole shapes if the development results in a lower velocity than what you're currently shooting.

My experience seems to suggest that bullets get their best LR accuracy in a twist which is closer to the lower end of the acceptable RPM range. You may be right at or around that RPM range right now.

Greg </div></div>

That seems to be the conclusion drawn by Litz. Faster twists amplify the effects of imperfect bullets and spin drift (although spin drift is very predictable). That, and the bullet is least stable when it leaves the muzzle, and gets progressively more stable as velocity decreases downrange (rotational twist rate stays nearly the same).

 

[RTO]

Re: stable enough?

I know I have heard George at GA say many times that people tend to over twist a 30 cal. I have a 10 twist on my 300wsm and shooting 190 Bergers with 66grains of H4350 I started seeing keyholing. I ran another ladder test and found I must have missed a grouping the first time at around 63 grains. Ever since I switched to a lighter load I havent seen the keyholing again. 190 Berger VLD suggest 12 twist and with that hot load I suspect that they were over stabilized. Backing it down didnt seem to make a difference in the groupings. Both the hot load and the lighter load both shot about .43 or .46 on average. The biggest difference I saw was that the lighter shot a little better throughout 600 while the hotter load shot well but keyholed until out to about 300 when it seemed normal. Seems to be same as what everyone else is saying here but someone smarter than me can probably explain this more than me.

 

[HSNARC]

Re: stable enough?

thanks for the info peoples

Its weird because its always seemed like this barrel likes the slower velocities. It likes the 123amax but its most accurate around 2800 fps out of this tube. During initial load testing i had those creeping up on 3100 fps without pressure but accuracy was bad.
My half ass ladder made it seem like there was a pretty wide node between 39.0g h4350 (approx 2600) and 41.5g (approx 2730) well see what kind of accuracy i can get next week or so.