How much stability is needed

[RockyMtnMT]

I always thought that 1.1 was the floor for stability of a bullet to work accurately. I am not sure that is true now. I am guessing that it must have something to do with the form of a bullet.

So my next question for the smart guys is.....How much stability factor is needed for accurate flight?

Steve

 

[MudRunner2005]

According to Berger and Bryan Litz, you need at least a 1.5 SG to be considered stable.

 

[RockyMtnMT]

According to Berger and Bryan Litz, you need at least a 1.5 SG to be considered stable.

The 1.5 or higher is considered fully stable. That does not indicate a lack of accuracy if the number is less than 1.5. The question is more complicated than that.

Steve

 

[MudRunner2005]

I have a couple of loads that are below 1.5 that shoot very well. Not quite sure where the threshold is for accuracy to drop-off, but these 2 loads shoot very well.

My .308 Win 210 VLD load is around a 1.39 and it shoots 1 ragged hole.

My 7mm STW 180 Hybrid load is around 1.42 and it shoots 1/2 MOA groups.

 

[RockyMtnMT]

I have a couple of loads that are below 1.5 that shoot very well. Not quite sure where the threshold is for accuracy to drop-off, but these 2 loads shoot very well.

My .308 Win 210 VLD load is around a 1.39 and it shoots 1 ragged hole.

My 7mm STW 180 Hybrid load is around 1.42 and it shoots 1/2 MOA groups.

Exactly. I just did testing/load development on a .234 with a stability factor of 1.37 that shot less than an inch at 200 yards. Then as we were packing up some deer came out on the range at 150 yards. What better opportunity for terminal testing.
Shot intentionally quartering away just behind the ribs and out just behind the off shoulder. Bullet tracked on a perfect straight line through the deer. 1.37 is technically marginally stable but performance is perfect. This bullet is not very aggressive in the ogive compared to the 7mm we shot at the same session. It had a stability factor of 1.18 and printed oblong holes at 200 yards.

Steve

 

[B-P-UU]

Reference guide for Berger bullets now lists two 'stability' numbers:
http://www.bergerbullets.com/pdf/Quick-Reference-Sheets.pdf

min twist = needed for accuracy
optimal twist = fully stabilized (with respect to BC)

good explanation on stability:
The State of the Art in Rifle Bullet Stability | Berger Bullets