Hammer Bullets and twist recommendations

[DoneNOut]

Brad,

Hang tight; the Hammer guys will be here shortly to give you some insight into your query.

Oh Ok, I was looking at this,

Length contraction is the phenomenon that a moving object's length is measured to be shorter than its proper length, which is the length as measured in the object's own rest frame.[1]​ It is also known as Lorentz contraction or Lorentz–FitzGerald contraction (after Hendrik Lorentz and George Francis FitzGerald) and is usually only noticeable at a substantial fraction of the speed of light. Length contraction is only in the direction in which the body is travelling. For standard objects, this effect is negligible at everyday speeds, and can be ignored for all regular purposes, only becoming significant as the object approaches the speed of light relative to the observer.

 

[eoperator]

I understand this is maybe not the best test medium.

An observation I have made while digging bullets from sand backstop (I always do this) is bullets fired near or at minimum listed twist rate have inconsistent expansion sometimes. All samples in pics are through 2 layers of cardboard into sugar sand backstop at 100yrds. Samples to the left are spun well over listed rate. Samples on right are at or near minimum twist rate.

 

[northhunter]

I'm fairly new to reloading and have a few questions on stability factor. Is it the same as gyroscopic stability? Another thing, what would be a more accurate number to use in a calculator, the air pressure or my altitude? I have entered my info into two different calculators (Bison Ballistics and JBM), only one of them allowed for elevation. I was given two completely different numbers between air pressure and elevation. Thanks for your help

 

[Pdvdh]

Yes, stability factor is gyroscopic stability. One in the same.

Station pressure = air pressure at the shooter's location. Station pressure would be best, if you have a Kestrel or equivalent instrument that will read actual air pressure at your shooting location.

 

[GLTaylor]

I understand this is maybe not the best test medium.

An observation I have made while digging bullets from sand backstop (I always do this) is bullets fired near or at minimum listed twist rate have inconsistent expansion sometimes. All samples in pics are through 2 layers of cardboard into sugar sand backstop at 100yrds. Samples to the left are spun well over listed rate. Samples on right are at or near minimum twist rate.
View attachment 317565

Are these Hammers? They didn't perform like typical Hammers - even given the media?

 

[northhunter]

How crucial is the stability factor under 500 yards? I don't think I've ever shot that far before.

 

[eoperator]

Are these Hammers? They didn't perform like typical Hammers - even given the media?

Yes random 6.5, 7, and 308 hh&ah

 

[HARPERC]

How crucial is the stability factor under 500 yards? I don't think I've ever shot that far before.

It's important to me, as it benefits terminal performance at any range.

 

[northhunter]

Ok, thanks for the help.

 

[DoneNOut]

Baro pressure seems to affect the DOPE pretty significantly. Leupold says elevation changes are in the 2000ft band. Baro changes things much quicker.

 

[Rich Coyle]

BFD Guns,

Someone suggested to me to think about spinning a pencil on its end and spinning a top. The top will stay upright at a much slower rpm than the pencil.

 

[DoneNOut]

BFD Guns,

Someone suggested to me to think about spinning a pencil on its end and spinning a top. The top will stay upright at a much slower rpm than the pencil.

I understand your illustration, but don't understand the relevance of RPM on atmospheric condition influence.

 

[northhunter]

From what I have read today, higher barometric pressure equals more drag on the bullet causing it to use its energy at a faster rate. The higher RPM helps to keep it more stable as it slows down. Does this sound correct?

 

[DoneNOut]

I'm not going to argue RPM when the barrel twist rate is effective/matches the manufacturer's recommended rates. Just punch in different baro conditions on a ballistics app. You'll see the influence.