Tipped match bullet length question.

[RockyMtnMT]

The tip's minimal density compared to the lead won't do much to move the center of gravity of the projectile. But, the polymer tip will extend the distance between your center of pressure and center of mass increasing the moment arm that can cause instability. Either way it shouldn't drastically change the calculation. Also, its just a formula that has some amount of unknown to it. If your stability factor is close to 1.5 or lower, put holes in paper. They will tell you things the calculation won't.

Start catching bullets in media and you will learn more about how stability effects terminal performance. Through our testing I believe it to be more important to terminal performance than it is to ballistic flight. Marginally stable bullet can and will fly very well but will lead to bullet failure on game.

Steve

 

[Canhunter35]

Start catching bullets in media and you will learn more about how stability effects terminal performance. Through our testing I believe it to be more important to terminal performance than it is to ballistic flight. Marginally stable bullet can and will fly very well but will lead to bullet failure on game.

Steve

What would you say is the minimum stability you need for effective terminal performance. A 212 eldx has a millar stability factor of 1.355 out of my 308.
A 200eldx has a factor of 1.5?
Just curious how stable they should be?

 

[RockyMtnMT]

What would you say is the minimum stability you need for effective terminal performance. A 212 eldx has a millar stability factor of 1.355 out of my 308.
A 200eldx has a factor of 1.5?
Just curious how stable they should be?

After all the impact testing that we did with our bullets we came to the conclusion that 1.5sg at sea level should be the min for hunting. It is easy to talk yourself into the bigger bullets when you plug in higher elev than sea level because it increases the sg. Problem is it doesn't increase the rpm's of the bullet. It is the rpm's and how fast they degrade on impact that dictate how long the bullet stays on a straight line path with the nose oriented forward after impact. The longer the nose of the bullet stays correctly orientated the better the bullet will deform correctly. This holds true for all hunting bullets. They need hydraulic pressure to enter the nose and deform the bullet from the inside out. The moment the bullet tips or yaws then the tip of the bullet will no longer let fluid into the hp. This is how we see the pics of recovered bullets that show the bent nose and little other deformation. I used to think this was a bullet failure. I am now more apt to blame a lack of stability not the bullet.

Another point on this. The smaller the hollow point the more this problem will show up. The smaller the hole the harder it is to get fluid in the hole. Any bit of yaw in the bullet makes the hole smaller due to the angle.

Tipped bullets are still hollow points, just with a plug in the hole. With the tip they have larger hollow points but the tip has to get out of the way allow the fluids into the hole. Tips have been advertised as helping expansion, I can't see how this is possible unless the tip is of harder material than the rest of the bullet. Tips do a great job of increasing bc on an otherwise large hollow point bullet.

Lots of choices and things to think about. Keep the sg high and terminal performance with whatever bullet chosen will be better.

Steve

 

[Canhunter35]

Thanks for the detailed response. I only really plan on nailing coyotes out to the transonic range of this load. So I'll see what I get on paper. A misshapen 212gr bullet should still be hell on a coyote. A 168 in windy conditions is just too darn hard to make good shots past 600. At least for me

 

[yorke-1]

I've seen the same thing as Steve while testing bullet expansion. The higher the calculated sg of a bullet/load combo, the more consistent and predictable the performance was. With that in mind, I'd use the measured OAL of the bullet so that the calculated sg is a little on the low side. This should give a little wiggle room in your real world stability.

For a couple of years I spent a lot of time shooting big bore/dangerous game rifles and bullet stability was a constant debate in that community. Anecdotal evidence pointed towards faster twist barrels providing deeper and straighter penetration when using solids on DG. With soft points, expansion was greater and penetration followed a straighter path when the bullets were shot through a faster twist. We came to the conclusion that an sg of at least 1.6 at sea level was a good starting point.

 

[RockyMtnMT]

I've seen the same thing as Steve while testing bullet expansion. The higher the calculated sg of a bullet/load combo, the more consistent and predictable the performance was. With that in mind, I'd use the measured OAL of the bullet so that the calculated sg is a little on the low side. This should give a little wiggle room in your real world stability.

For a couple of years I spent a lot of time shooting big bore/dangerous game rifles and bullet stability was a constant debate in that community. Anecdotal evidence pointed towards faster twist barrels providing deeper and straighter penetration when using solids on DG. With soft points, expansion was greater and penetration followed a straighter path when the bullets were shot through a faster twist. We came to the conclusion that an sg of at least 1.6 at sea level was a good starting point.

Yes Sir! This is exactly what we have concluded. Altitude should not be considered in stability when it comes to terminal performance. Ballistic performance yes. We consider 1.5sg a min at sea level. So all of our bullets are rated with a recommended twist rate based on sea level and standard atmosphere. Faster twist is considered to be beneficial for hunting.

Steve