Bearing Surface Lengths

[cstarr3]

Hi All;

Does anybody know of a website that lists approximate, target, or average bearing surface lengths for various bullets, especially those made by common brands (Hornady, Sierra, Nosler, etc.)? How about for base-to-ogive length? This information is, as far as I have seen, never listed with other advertised bullet information. I certainly haven't really found any source, manufacturer-published or otherwise, that seems to have any broad set of data listing bearing surface or base-to-ogive lengths. If you know of any, please let me know.

I know that JBM has a bullet-length list of most popular bullets, and it appears to be taken empirically.

Anyway, again thanks for your help.
-cstarr3

 

[stringnut]

What is the need for such info? Not trying to be a smart ass. You can't change it , so , why worry about it? Bearing surface length does have a correlation to pressure, but, so do a lot of other things. Doubt it affects accuracy much. Just my 2 cents. Maybe only 1 cent. OK maybe completely worthless thoughts

 

[JimKirk]

I do not know of a list .... but here is a little info on the subject ....

http://www.6mmbr.com/medlerTUBBBSC.html

 

[243winxb]

Berger Bullets http://www.bergerbullets.com/pdf/Quick-Reference-Sheets.pdf

Bearing Surface are listed at the link. Not sure if produced by Berger?

I measured some bullets, using 2 sized cases, not a very accurate method. But gives an idea of the difference.

Your measurement will be different.

 

[Bart B.]

A bullet's bearing surface is determined by its diameters that will touch the barrel's land and groove surfaces. Without the barrel's dimensions for them, precise bearing surfaces cannot be determined.

For example, 30 caliber bullets of all lengths have diameters from .3070" to .3092". Barrel bores from .2970" to .303" and grooves from .3065" to .3090". Plus, barrels can have 3 to over 10 grooves and lands.

Get an undamaged bullet pushed through your barrel then measure its surfaces rubbed by that barrel. Or find your barrels bore diameter then mark both ends of a bullet at that diameter. That's the longest bearing surface length it might have. If it's a .3092" bullet that'll be shot in a .2970" bore, .3065" groove barrel, actual bearing surface will be a little longer as the bullet is squeezed down.

 

[cstarr3]

Thank you to those who have responded. I actually started looking around for this information because my brother got ahold of some 62 gr. FMJ bullets for his AR. He is even newer to reloading than I am, and I was a little hesitant to use the manual's OAL suggestions from one bullet on another.

Stringnut: I was curious because I thought it might make things easier when using a load developed for one bullet on a different bullet. I know that it is usually a safe practice (given similar weights), but more information can't hurt. I figured that knowing something about the bearing surface lengths of the bullet in the manual and the bullet one is using might cause one to tweak the load data a bit (maybe drop it down a tiny bit if the bearing surface length is longer on the bullet being used). However, the part that I would actually be most concerned about is seating depth. Similar seating depths might result in OAL differences from one brand of bullet to the next, and similar OALs might give two different seating depths. This, I think, has significant effects on pressure. This is also why I am so curious about base-to-ogive lengths.

JimKirk: Thanks for the link. I have taken a peak at this article before, but it never hurts to read it a second time. In my case a third or fourth probably won't hurt much, either.

243winxb: Thanks for that link. The measurements you took are a great illustration of the kind of info I was looking for. I recently took some base-to-ogive measurements using a Hornady caliper and comparator set on some left over 55 gr. .224 V-Max bullets; they averaged about 0.297", .304" being the longest and .2925" being the shortest.

Bart B.: Wow! I didn't know that bore and groove diameter varied so much. I will have to look into seeing what I can do to get an undamaged bullet.

 

[macgrumpy]

"Ballistic Performance of Rifle Bullets" 2nd edition by Bryan Litz has that info for more than 500 bullets. Tell me the specifics (brand, diam, weight) and I'll see if it's in the book, if it is I'll post the info.

 

[cstarr3]

macgrumpy: Thanks! You're the man! The two I was looking for this particular time was the 63 gr. Sierra SMP .224" and the 62 gr. Swift Scirocco .224".

If this book has this kind of information in it, whether or not it has these specific bullets, I might as well pick up a copy the next chance I get. Having more information can't hurt.

 

[macgrumpy]

Well Litz's book didn't have those exact bullets so I resorted to using photos of the bullets and comparing their features. This isn't the most accurate process as far as the actual dimensions go but it gives a good relative estimate of the differences between the two bullets. I calculated that the bearing surface was .018" longer with the Swift bullet but due to photo resolution and other errors I'd guess that the bearing surface could be plus or minus a couple of thousandths from that number but if you were to assume a .020" longer dimension I doubt that you'd be very far off.

The numbers below were calculated from the images so any errors are a reflection of the roughness of this technique.




One dimension I didn't display was the nose radius but I had to use a circle to help identify the end of the bearing surface and that circle represented the radius of the nose. The Swift bullet definitely has a larger radius (around 9.5" compared to Sierra's 8"). That radius combined with the boat tail indicates that the Swift bullet will have far better long range accuracy but if your intentions are to stay under 400 yards with these loads I don't know if I'd be concerned with that accuracy potential, I think I'd rather chose the bullet that is built for the job - short range hunting vs. long range hunting? The Swift will produce improved long range performance but I have no idea how it performs on the kind of game you're interested in taking.

 

[Bart B.]

What's the BC for both of them?

 

[macgrumpy]

Sierra
.231 @ 2800 fps and above
.235 between 2800 and 2000 fps
.240 @ 2000 fps and below

Swift
.307

 

[Bart B.]

25% more BC does not guarantee better accuracy.

I and others get equal accuracy at long range with 30 caliber bullets having a 33% spread in bullet BC shot from 308 Win cases

 

[macgrumpy]

Whatever