Bullet bearing surface question

[jmason]

Originally Posted by royinidaho

Yur darn right. That'll keep ya off the streets awhile.
I've not had much luck with the SMK in the Winny. Nolser Ballistic Tips out done them every time.

You're right! I don't see too many streets! I am going to try another bullet after I burn these up. I'm looking to do and learn anything that will help. It don't sound like it matters for the distances I'm shooting, but I'll stretch further. My 600 yd groups look like my 300s used to...

[jmason]

Originally Posted by jmason

My problem is that the .277 cal insert for my comparator tool doesn't come up the the crease at the boat tail of the bullets. Is that the way I should go at it or should I use the .277 on the top for ogive and the.284 for the boat tail? The .284 seams to come just a hair past the crease. It is closer to it than the .277. For got to mention that is a 270 win.

anyone have an idea if this should work alright?

[Forester]

Originally Posted by jmason

anyone have an idea if this should work alright?

Do you have a tubing mic. you can use to find out what the actual inside diameters are of the comparator inserts?

[jmason]

No I don't. I'll end end up getting another .277 insert next time I order some things. I just don't see how I can get an accurate bearing surface measurement with it on the boat tail side since it doesn't actually fit over the crease. For now I know I'm measuring a portion of the bearing surface, maybe not all of it though. I really don't imagine I'm seeing any benefit from it with a factory rifle and shooting the distances a 270 is useful for deer. Maybe I'll learn something in the process. If not it will be something I won't have to learn when I shoot further with or have a custom rifle.

[Mikecr]

What you're running into is normal and not a bad thing really.
No doubt the 277 gizzy is drilled to ~.271, which correlates with bore ID rather than groove. A 284 would likely be drilled to ~.277(it's bore ID), which is why it mates very closely to 277 bearing begin.

It depends on the bullet diameters(which vary with brand and lot to lot) as to how consistantly you can measure. The closer you get to actual bearing, the tougher it is to get consistant measurements because slight changes in contact pressure start affecting the readings.
You might use 284 gizzys front and back, if your bearings are large enough and you control contact pressure with a bit of precision. This wouldn't be something done for damn with calipers.. You would need a Tubbs/Buhay comparator.