New "to me" made in Montana monolithic bullets ...

[Old Rooster]

Ok, back to cbb and stability at distance.
Iirc, when Robert first came out with the tipped 168gr version- he had some guys shoot 1000 yard groups with 308w bolt action rifles....for those guys, they proved to be accurate and stable.

As I said in prior posts, I tried both the tipped 168, and non tipped 165 and they didn't impress me. I do like his 195 mkz's for subsonic 308- but not for the cavity- for the expansion properties at slow speeds.

There are quite a few guys shooting his bullets in the 6.8spc ar chassis for hogs that like them too.

His bullets are monithic/solid copper so its a good idea to copper strip your barrel before switching to his to avoid dis-similar alloy galling (excess copper build up)

I did not experience an "ease" of load development for the 165/168 nor the 195's but others have reported quick load build up. He has been making these bullets for at least 5 years now-- if you want more info on them try the 68forums lots of guys use his bullets there

Cohunt thanks for your personal use of the Cavity Back Bullets experience.
Were you were not impressed about accuracy or bullet performance?

 

[Eddiejoe12]

Not necessarily. A shaped charge is simply that, one shaped that generally has a bullet shaped cavity in the side you put towards what you want to blow up.

Small shape charges are used in things like armor piercing rounds to create a jet of molten copper or other metal to burn through the armor at near insane speeds.

Same type of charge, different purposes.

We used to use some large cratering charges that would do more damage to an asphalt or concrete runway, bridge etc than a WWII 500lbs bomb and weighted less than 1/10th ad much.

In the service we played with C-4 making shape charges and it was interesting what a difference it made just redirecting the force of the blast, I was curious if the reverse principle would create more direct pressure in the cavity? Just trying to wrap my head around the purpose of the cavity, could be it would create a better expansion/Seal when detonated
I need to do some research as I'm not as knowledgeable in ballistics as y'all. Thanks for the feedback.

 

[asd9055]

In the service we played with C-4 making shape charges and it was interesting what a difference it made just redirecting the force of the blast, I was curious if the reverse principle would create more direct pressure in the cavity? Just trying to wrap my head around the purpose of the cavity, could be it would create a better expansion/Seal when detonated
I need to do some research as I'm not as knowledgeable in ballistics as y'all. Thanks for the feedback.

The originaly minie ball, cavity created a better seal, that was lead.
If the copper is soft enough, this can happen with the CBB too
other effects, change in center of mass/gravity
Longer bullet of same weight, or lighter bullet of same length
Other external ballistics, requires someone who knows a lot more than I do

 

[Eddiejoe12]

Thanks for the feedback.

 

[WildRose]

In the service we played with C-4 making shape charges and it was interesting what a difference it made just redirecting the force of the blast, I was curious if the reverse principle would create more direct pressure in the cavity? Just trying to wrap my head around the purpose of the cavity, could be it would create a better expansion/Seal when detonated
I need to do some research as I'm not as knowledgeable in ballistics as y'all. Thanks for the feedback.

As far as I know it's two part, one to allow the plunger/stem to travel unimpeded deep enough to start the tip expanding and, two to allow the proper amount of compression. With the C-4 charges it was the standoff distance between the charge along with the shape that directed the blast to a specific point so a different principle at least as I see it.

It's been a very long time since my explosives training but I think I remember that right anyhow.

 

[WildRose]

The originaly minie ball, cavity created a better seal, that was lead.
If the copper is soft enough, this can happen with the CBB too
other effects, change in center of mass/gravity
Longer bullet of same weight, or lighter bullet of same length
Other external ballistics, requires someone who knows a lot more than I do

A reasonable thought but copper is many times harder than lead. If it does then I'd have a concern about excessive pressures.

 

[cohunt]

Cohunt thanks for your personal use of the Cavity Back Bullets experience.
Were you were not impressed about accuracy or bullet performance?

I couldn't get the speeds he was claiming, I wasn't overly impressed with ease of load work up or accuracy--- I could get 1-1.25 moa, but I'm the kind of guy that prefers 1/2-3/4 moa or I'm not happy.

My lead core bullets were shooting faster and more accurate.... I now shoot hammers in some of my rifles and the ones I have tried, I can get as fast or faster speeds than like weight lead core bullets--- I have tried hammers in a few guns I wasn't satisfied with accuracy, but most I am.
I'm not a brand specific fan, I use what gives me the results i desire.

As far as expansion-- the cbb expanded well in anything I've tried-- they are designed to keep the pedals on ( like a barnes) --- not like the design of a hammer (pedals off) ....the cbb use a "cutting" design....the hammers have the pedals off secondary wound channels and a blunt faced penetrating projectile to create a large permanent wound channel like a hard cast wfn style bullet.

I have never seen any of the "cavity" claims proven so I'm inclined to believe the cavity is more of a marketing design than anything else.

 

[FEENIX]

I couldn't get the speeds he was claiming, I wasn't overly impressed with ease of load work up or accuracy--- I could get 1-1.25 moa, but I'm the kind of guy that prefers 1/2-3/4 moa or I'm not happy.

My lead core bullets were shooting faster and more accurate.... I now shoot hammers in some of my rifles and the ones I have tried, I can get as fast or faster speeds than like weight lead core bullets--- I have tried hammers in a few guns I wasn't satisfied with accuracy, but most I am.
I'm not a brand specific fan, I use what gives me the results i desire.

As far as expansion-- the cbb expanded well in anything I've tried-- they are designed to keep the pedals on ( like a barnes) --- not like the design of a hammer (pedals off) ....the cbb use a "cutting" design....the hammers have the pedals off secondary wound channels and a blunt faced penetrating projectile to create a large permanent wound channel like a hard cast wfn style bullet.

I have never seen any of the "cavity" claims proven so I'm inclined to believe the cavity is more of a marketing design than anything else.

What was the velocity claim vs. your actual velocity? Also, how far away to the lands are you loading them? Most of the information I have seen load them like the Barnes bullets and appears it likes a good jump, i.e., .050."

 

[asd9055]

A reasonable thought but copper is many times harder than lead. If it does then I'd have a concern about excessive pressures.

Just thinking out loud, enough pressure the reform brass cases but not expand copper? Just wondering

 

[WildRose]

Just thinking out loud, enough pressure the reform brass cases but not expand copper? Just wondering

There's very little movement in brass and it's happening at peak pressure. The cavity isn't leaving a thin long edge along the outer surface similar to our rifle brass. I guess it's possible that there's some movement but if there is enough to form a gas seal then I'd have concerns about serious pressure spikes.

 

[asd9055]

There's very little movement in brass and it's happening at peak pressure. The cavity isn't leaving a thin long edge along the outer surface similar to our rifle brass. I guess it's possible that there's some movement but if there is enough to form a gas seal then I'd have concerns about serious pressure spikes.

Like I said, I am thinking out loud...I have no idea

 

[FEENIX]

The originaly minie ball, cavity created a better seal, that was lead.
If the copper is soft enough, this can happen with the CBB too
other effects, change in center of mass/gravity
Longer bullet of same weight, or lighter bullet of same length
Other external ballistics, requires someone who knows a lot more than I do

Extracted in part from AR Build Junkie an interview:

Q: I know there are other benefits to the Cavity Back design, can you talk about those?

Robert DeBell, Cavity Back Bullets: There's a couple of things that happen with a cavity in the back of the bullet. First, it increases the square area that the powder column pushes on, this helps the bullet get moving faster and mellows out the powder spike. So, in other words, you can push them farther than what you would typically be able to push other projectiles.

Center of Gravity/Center of Pressure
What we found is, in the technical aspect of it, is there are two things that affect flight of a bullet. One is the center of gravity, and the other is the center of pressure. As the bullet speeds up, the center of pressure moves back to the ogive, towards the back of the bullet. As the bullet slows down, the center of pressure moves forward on the ogive.

One of the reasons bullets have problems going through the trans-sonic zone, like the 168-grain Sierra…where a 170-something grain bullet doesn't, is because of the difference in the weight of the bullet between the center of gravity and the center of pressure. That particular bullet becomes unstable as it goes through the trans-sonic zone.

Shifted Center of Gravity
Because our bullet shifts the center of gravity toward the center of pressure but does not put it in front of the center of pressure, our bullets are more dynamically stable as they go through the trans-sonic zone. So, that's another thing we found. All, bullets when the leave the bore…they yaw. Our bullets tend to yaw less because the center of gravity is closer to the center of pressure than another other bullets. So, that's a side benefit when it comes to accuracy that we didn't even see coming.

Bore Blast Benefits
Another effect of the cavity is something called "bore blast". There's a few different terms for it, but basically, as gasses are trying to escape around the bullet as it leaves the bore, the gasses are going faster than the bullet…that's why the bullet moves down the bore. The cavity helps disperse these gasses into a wider cone angle. So, when the bullet does leave the bore, it's not encountering as much turbulence.

 

[asd9055]

Extracted in part from AR Build Junkie an interview:

Q: I know there are other benefits to the Cavity Back design, can you talk about those?

Robert DeBell, Cavity Back Bullets: There's a couple of things that happen with a cavity in the back of the bullet. First, it increases the square area that the powder column pushes on, this helps the bullet get moving faster and mellows out the powder spike. So, in other words, you can push them farther than what you would typically be able to push other projectiles.

Center of Gravity/Center of Pressure
What we found is, in the technical aspect of it, is there are two things that affect flight of a bullet. One is the center of gravity, and the other is the center of pressure. As the bullet speeds up, the center of pressure moves back to the ogive, towards the back of the bullet. As the bullet slows down, the center of pressure moves forward on the ogive.

One of the reasons bullets have problems going through the trans-sonic zone, like the 168-grain Sierra…where a 170-something grain bullet doesn't, is because of the difference in the weight of the bullet between the center of gravity and the center of pressure. That particular bullet becomes unstable as it goes through the trans-sonic zone.

Shifted Center of Gravity
Because our bullet shifts the center of gravity toward the center of pressure but does not put it in front of the center of pressure, our bullets are more dynamically stable as they go through the trans-sonic zone. So, that's another thing we found. All, bullets when the leave the bore…they yaw. Our bullets tend to yaw less because the center of gravity is closer to the center of pressure than another other bullets. So, that's a side benefit when it comes to accuracy that we didn't even see coming.

Bore Blast Benefits
Another effect of the cavity is something called "bore blast". There's a few different terms for it, but basically, as gasses are trying to escape around the bullet as it leaves the bore, the gasses are going faster than the bullet…that's why the bullet moves down the bore. The cavity helps disperse these gasses into a wider cone angle. So, when the bullet does leave the bore, it's not encountering as much turbulence.

Thanks @FEENIX I guess sometimes I get a few things right even when I am guessing...

 

[WildRose]

Like I said, I am thinking out loud...I have no idea

We both are. It's pretty much all speculation at this point.