Why are vld bullets jump sensitive?

[Jon D]

Why are vld bullets jump sensitive? Bergers website says they are. Bryan Litz and Emil Praslic think they are, but no one is saying why. Are the bullets just really sensitive to the speed and timing they leave the barrel at? What else does varying seating depth do to make them shoot better or worse? Are there any published books that deal with this topic on a deeper level?

 

[Old Navy]

They are not jump sensitive.

 

[338 dude]

I believe it is the transition from either a tangent or secant ogive to the bearing surface hybrid bullets are supposedly much less sensitive and it is a blend of both types of ogive but this is my opinion and it is worth exactly what you just paid for it

 

[Twdmar]

I believe it is the transition from either a tangent or secant ogive to the bearing surface hybrid bullets are supposedly much less sensitive and it is a blend of both types of ogive but this is my opinion and it is worth exactly what you just paid for it

And disturbed flight(precession if memory serves) prior to the bullet hitting the lands, due to boat tail being pushed less evenly about the base perhaps? Is there a vld flat base bullet out there? Would it be more jump tolerant?
Does it really matter with the hybrids and good tangent ogive bullets available?

 

[johnfred1965]

The VLD bullet has a secant ogive (nose) which makes a sharp, abrupt change at the shank (bearing surface). this only allows for a short, one time only chance of aligning with the rifling during firing. If you have any slop in the chamber you can have sesitivity. The tangent and hybrid ogive have a gentiler transition to the shank so the bullet can in theory, self align to some extent, easing the bullet into the rifling more consistently. I don't know if that is in LItz's books, but that may be a good place to try.

 

[Joe Salt]

Jon D This is real easy start in the lands and if you get vertical keep moving back, I've had rifles that liked 125 thou. jump and shot great. I believe Litz tell in his book or Bergers web page the same thing.

Joe Salt

 

[dogdude]

^^^^^

 

[eric32]

Berger has a test for this exact thing

Getting the Best Precision and Accuracy from VLD bullets in Your Rifle

VLD bullets are designed with a secant ogive. This ogive shape allows bullets to be more efficient in flight (retain more velocity = less drop and wind deflection). While this result is desirable for many rifle shooters the secant ogive on the VLD bullets produces another result in many rifle.

bergerbullets.com

 

[Ned Ludd]

A broader question might be, "Exactly what are we doing when we tune seating depth?". I've heard many explanations including optimizing how the bullet enters the rifling, barrel timing/harmonics, how the case neck seals, etc. But the explanations I've come across seem largely anecdotal. The answer to that question, if there even is a well-defined answer, might shed light on why VLDs have a reputation for being finicky with regard to seating depth.

FWIW - my thought is that part of the reason for this reputation may have originated years ago when VLD bullets became more commonly available. I suspect, although it is only my unsupported opinion, that many started using them in commercial rifles, such as hunting rifles, that were manufactured with chambers having an extraordinarily long freebore, such that the VLDs were necessarily loaded with very long jumps. With their rather abrupt transition from ogive to bearing surface, I can imagine how this might have caused VLDs to get a reputation for being jump sensitive that still seems to be commonplace even today.

I have used Berger's 90 VLD in F-TR competitions for a number of years. Initially, I tried seating them at .010" into the lands, as that's where the relatively small amount of information available on their use at that time suggested others had obtained successful results. However, in my hands the groups at +.010" were mediocre at best. So I started moving them incrementally out of the lands in an attempt to find a more optimal seating depth. The end result was that the 90 VLDs appeared to have at least two optimal seating depth windows. The first was with them seated into the lands at ~+.004" to +.007" (relative to just "touching" the lands). The second window was between about .018" to .024" off the lands (-.018" to -.024"). Both shot equally well, but because the second window was not only wider, but also did not involve jamming the bullets, that's where I chose to seat them. Since that time, I have observed the 90 VLDs to show that exact same pattern of seating depth optimization in different rifles and multiple barrels. So it seems to be reproducible, in my hands at least. Further, although their specific seating depth optima clearly differ from that of other tangent or hybrid ogive bullets I routinely load, I would not call the 90 VLDs any more "sensitive", merely "different".

The bottom line is that the factor(s) we are optimizing via seating depth adjustment may be very, very complex, and therefore difficult to define with any precision. Nonetheless, it is relatively simple exercise to conduct a seating depth test and determine empirically where a given bullet wants to be seated. So although we would very much like to know exactly how/why seating depth has such a profound effect on precision, we can still determine optimal seating depth for a given bullet by testing without necessarily understanding exactly what is happening.

 

[CharlieNC]

A broader question might be, "Exactly what are we doing when we tune seating depth?". I've heard many explanations including optimizing how the bullet enters the rifling, barrel timing/harmonics, how the case neck seals, etc. But the explanations I've come across seem largely anecdotal. The answer to that question, if there even is a well-defined answer, might shed light on why VLDs have a reputation for being finicky with regard to seating depth.

FWIW - my thought is that part of the reason for this reputation may have originated years ago when VLD bullets became more commonly available. I suspect, although it is only my unsupported opinion, that many started using them in commercial rifles, such as hunting rifles, that were manufactured with chambers having an extraordinarily long freebore, such that the VLDs were necessarily loaded with very long jumps. With their rather abrupt transition from ogive to bearing surface, I can imagine how this might have caused VLDs to get a reputation for being jump sensitive that still seems to be commonplace even today.

I have used Berger's 90 VLD in F-TR competitions for a number of years. Initially, I tried seating them at .010" into the lands, as that's where the relatively small amount of information available on their use at that time suggested others had obtained successful results. However, in my hands the groups at -.010" were mediocre at best. So I started moving them incrementally out of the lands in an attempt to find a more optimal seating depth. The end result was that the 90 VLDs appeared to have at least two optimal seating depth windows. The first was with them seated into the lands at ~-.004" to -.007". The second window was between about .018" to .024" off the lands. Both shot equally well, but because the second window was not only wider, but also did not involve jamming the bullets, that's where I chose to seat them. Since that time, I have observed the 90 VLDs to show that exact same pattern of seating depth optimization in different rifles and multiple barrels. So it seems to be reproducible, in my hands at least. Further, although their specific seating depth optima clearly differ from that of other tangent or hybrid ogive bullets I routinely load, I would not call the 90 VLDs any more "sensitive", merely "different".

The bottom line is that the factor(s) we are optimizing via seating depth adjustment may be very, very complex, and therefore difficult to define with any precision. Nonetheless, it is relatively simple exercise to conduct a seating depth test and determine empirically where a given bullet wants to be seated. So although we would very much like to know exactly how/why seating depth has such a profound effect on precision, we can still determine optimal seating depth for a given bullet by testing without necessarily understanding exactly what is happening.

You are right, there seems to be no clear science defining how/why seating depth does what it does. Quite surprising! Interestingly I recently revisited my 90vld loads and looks like even longer .030 jump can tighten up my groups a bit.

 

[Jon D]

They are not jump sensitive.

My thoughts are slowly going this direction. It's something else. Speed, pressure, barrel time, combustion, etc. results in the bullet behaving differently. Adjusting the jump distance is affecting another parameter. Which one, I don't know.

It's very surprising to me that someone hasn't studied this in depth. If they have, they are keeping it to themselves.

 

[dakor]

I have shot many berger vld's and in many calibers. I have jumped them over .200 in some factory rifles and have had some .003 off the lands in customs. Never had an issue getting them to shoot way off or close to the lands.