Bearing surface lengths of bullets

[Webphut]

so please correct me with any misinterpreted or misunderstood knowledge when reading this, I am still learning!

Ok so I think I know that the stability of a bullet is primarily relative to the twist rate of a a barrel and the bearing surface length/weight of a bullet. The base type, ogive and tip type play a lesser role, but still has their importance.

With this said, is there a chart somewhere that I can look at that shows the bearing surface lengths of bullets categorized by bullet weight?

I am not surprised if this both does or does not exist as this would be handy for fine tuning loads and also this too much work given theere are so many bullets in the world.

 

[spclark]

...stability of a bullet is primarily relative to the twist rate of a a barrel and the bearing surface length/weight of a bullet.

Bearing surface has less to do directly with inherent bullet stability (which is more a result of the combination of the factors of sectional density, center of gravity, overall bullet length, base style, etc., essentially what all goes into calculations for Ballistic Coefficient) than it does to affect pressures generated upon being fired.

It’s not so much from friction either, it’s how much metal is being deformed by a bullet’s passing from round cross-section into something else as it gets deformed when being engraved by a bore’s lands and grooves.

With this said, is there a chart somewhere that I can look at that shows the bearing surface lengths of bullets categorized by bullet weight?

Best I know of are the bullet specs published in the books Brian Litz has brought to us over the past few years. Though not ‘all-inclusive’ of all the bullets out there, he’s done a pretty fine job of describing those more commonly chosen for competition.

Other than that, Berger Bullet’s website provides a downloadable chart giving dimensional data for their products but of course this is for just theirs, not other brands.

 

[Webphut]

Boy did my thinking open up a can of worms...lol,

Thank you, I have some homework to do.

I have Bergers chart, which is how I came across the idea in the first place. In fact aside from a few things that have sparked threads I started on the forums, Bergers load data book is really saturated with a wealth of great information. So much that I think I have forgotten more than I remember. I need to say the same for Sierras load data book too, but I think what Sierra left out, Berger filled in so to say. I have yet to read the other load data books in depth information, but one books information section at a time.

Ok, thank you.

 

[ClassCat]

Look at Pressure rings also

 

[dcali]

You’ve got it backwards. The parts of the bullet furthest from its center of gravity have the most impact on stability. To get it truly right you have to account for the entire geometry of the bullet. But... you can get a surprisingly good approximation of stability using only the overall length as a substitute for the complete geometry. This is what the Miller rule does. Note that it doesn’t work very well for flat based bullets.

The more practical concerns with respect to bearing surface are that it impacts pressure, and the fact that you need to match bearing surface to an appropriate throat length to maximize usable case capacity.

 

[Murray Brook]

In my limited experience with this I found that bearing surface length of a bullet had a minor effect on stabality compared to bullet length. My 2 encounters with this was when I purchased a box of 53 gr Hornady V-max bullets for my 22/250. Loaded some up and seen right off, on paper, that the groups were bad and bullet holes were oval. Done some research and found out that the 1/14 twist would not do the job. I decided to try something. The original length of the bullet was .830. By removing the plastic tip the bullet then became .700. I loaded these up to try and shot .75 moa with nice round holes. The next case was a friend purchased a box of 168 Barnes LRX 7mm bullets. They would not stabalize in his 7mm Rem Mag. He asked me if I wanted them to try. Remembering what I had done with the 53 gr V-max I said yes First I tried them untouched in my 7mm/08 and they were all over the target and the bullet holes looked more like slots than holes. The original length of the 168 LRX was 1.587. With the tips removed the length became 1.422. Just removing the tips gave me groups of .650 at 100 yds and the holes were just that , nice round holes. In both cases the bearing surface remained the same only the length was changed. Nothing else. Just what happened to me.

 

[CharlieNC]

In my limited experience with this I found that bearing surface length of a bullet had a minor effect on stabality compared to bullet length. My 2 encounters with this was when I purchased a box of 53 gr Hornady V-max bullets for my 22/250. Loaded some up and seen right off, on paper, that the groups were bad and bullet holes were oval. Done some research and found out that the 1/14 twist would not do the job. I decided to try something. The original length of the bullet was .830. By removing the plastic tip the bullet then became .700. I loaded these up to try and shot .75 moa with nice round holes. The next case was a friend purchased a box of 168 Barnes LRX 7mm bullets. They would not stabalize in his 7mm Rem Mag. He asked me if I wanted them to try. Remembering what I had done with the 53 gr V-max I said yes First I tried them untouched in my 7mm/08 and they were all over the target and the bullet holes looked more like slots than holes. The original length of the 168 LRX was 1.587. With the tips removed the length became 1.422. Just removing the tips gave me groups of .650 at 100 yds and the holes were just that , nice round holes. In both cases the bearing surface remained the same only the length was changed. Nothing else. Just what happened to me.

Simple but very interesting experiments. Seems I read somewhere to ignore the plastic tip in some regard which I don't remember, but clearly not for stability. Thanks.

 

[barefooter56]

Boy did my thinking open up a can of worms...lol,

Thank you, I have some homework to do.

I have Bergers chart, which is how I came across the idea in the first place. In fact aside from a few things that have sparked threads I started on the forums, Bergers load data book is really saturated with a wealth of great information. So much that I think I have forgotten more than I remember. I need to say the same for Sierras load data book too, but I think what Sierra left out, Berger filled in so to say. I have yet to read the other load data books in depth information, but one books information section at a time.

Ok, thank you.

On he BERGER QRS SHEET: " Keep in mind that these numbers are for REFERENCE ONLY AND DO NOT REFLECT EXACT NUMBER FOR EVERY LOT".

 

[chop house]

The original length of the bullet was .830. By removing the plastic tip the bullet then became .700.

i recall the quick rule of thumb for 14 twist is 22 cal was 0.750 bullet length. your clever experiment seems to validate that. i only found this out when i picked up a used 22 250 without knowing the twist rate. my wide assortment of 22 cal bullets got suddenly limited when i measured the bbl with a cleaning rod.

 

[chop house]

The more practical concerns with respect to bearing surface are that it impacts pressure

i am guessing shorter bearing surface means higher velocity for same pressure? also, what affect does bullet hardness play?

I routinely measure velocities 100 to even 200 fps higher than 'expected' when playing around with speer tnt series bullets. those bullets are claimed to be thin cups and with dead soft cores.

 

[dcali]

i am guessing shorter bearing surface means higher velocity for same pressure? also, what affect does bullet hardness play?

I routinely measure velocities 100 to even 200 fps higher than 'expected' when playing around with speer tnt series bullets. those bullets are claimed to be thin cups and with dead soft cores.

Anything that changes the amount of force required to start the bullet into the rifling will change the pressure curve. I would expect harder bullets to require more force, and yield higher peak pressure. I don't know much about Speer's bullets, so I don't have anything to add there specifically.

 

[Tim Singleton]

http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_1.pdf