123 grain SST and 123 HPBT Match are .264, 143 grain ELD-X and 153 ATip are .2645.

quote:

Originally posted by pbslinger:
123 grain SST and 123 HPBT Match are .264, 143 grain ELD-X and 153 ATip are .2645.

What’s the 4th digit on the first billet? 0? Isn’t there more variance than that on most bullets?

I don’t recall a bullet diameter stated as “correct” past the thousandth.

quote:

Originally posted by OttoSig:

quote:

Originally posted by pbslinger:
123 grain SST and 123 HPBT Match are .264, 143 grain ELD-X and 153 ATip are .2645.

What’s the 4th digit on the first billet? 0? Isn’t there more variance than that on most bullets?

I don’t recall a bullet diameter stated as “correct” past the thousandth.

The 123 grainers are .2640.

I used a Lee Collet die to squeeze a piece of fired brass enough to hold a bullet so I could test C.O.A.L when the bullets touch the lands. I did two of the bullets with one squeezed piece of brass and it worked perfect for the test. Then two bullets dropped right in and I had to squeeze more to do the same test. That is why I was alerted to check the diameter of all my Hornady 6.5 bullets.

Is it supposed to measure exactly .2640 ?

All my bullets measure exactly .2630 which includes Hornady ELD-M 140, Sierra TMK 130, Berger VLD Target and Hunting VLD both 140's.

Maybe my Mitutoyo Calipers is off?
Although my Sinclair mandrel measures .02620 and that is what they specify?

Hornady customer service said there are tolerances with everything, and that bigger bullets have greater velocity and usually shoot better.

I'll surmise the bullet forming dies wear from use, and start out small and are used as long as they can. Whatever specification they've decided that is.

I’m far too inexperienced to help Pbslinger, but for my education what is a normal tolerance for bullet diameter? +\- .001?

I know length can vary a bit.

I wonder how much a cup and core bullet "bumps up" to fill the bore like a lead bullet does. I'd guess a mono bullet doesn't do it much if at all.

Of course these numbers don't mean much without knowing what your barrel truly is as well.

According to this wiki article on "obturation" jacketed bullets are larger than bore and don't obturate.

https://en.wikipedia.org/wiki/Obturation


"To prevent excessive deformation in high pressure rifle and magnum pistol cartridges, lead bullets are often covered in copper or another harder alloy. These bullets are generally designed to be compressed upon firing as they leave the chamber and enter barrel. This seals the bullet to the interior of the barrel and engages the rifling."

That as a blanket statement would be incorrect, but perhaps accurate in regards to modern jacketed bullets.

And because they're larger than bore diameter doesn't necessarily mean they're groove diameter or better. If everything's right, yes. Life has taught me everything is often not right.

This an old post froma Campfire forum:


A two diamster bullet is caliber size at the base and bore size towards the ogive, most are divided at a cannelure. How many diameters I don't know, but two if you omit the taper. This was in deference to the short throat on the .264 and later the 6.5 RM. It was an effort to reduce pressure but caused problems for reloaders who were not aware of this and switched components. Bob Hagel was the first person I recall to write about this in Handloader magazine (can't find the article though). It led to the rumor that the 264 produced erratic pressure which didn't help it's popularity.

The Hornaday 160 was a two diameter bullet that may have gotten changed to a conventional design, I'll have to measure them again. I was not sure about the 129 and 154s though, but don't have any of the old 129s around to measure.