284 Win freebore length for 195 grain bullets.

[barnesuser28]

Hey all, i am in the process of rebarreling a savage 270 win to a 284 win and i want to be able to shoot the 195 grain EOL bullet berger is coming out with. I know i will need a 1:8.5 twist and i think i need .450 freebore to get the boatail/shank junction above the donut area when seating to touch the lands. Heres the dimensions of the 195 grain EOL. http://www.longrangehunting.com/forums/f19/berger-introduce-7mm-195-gr-eol-hybrid-hunting-bullet-85792/index23.html If im wrong will someone please correct me.

 

[Steve Blair]

No, it is .231" freebore. The 195 shank length .502". The 180 shank is .459" The difference is .043. Dave Kiff's match reamer for 180 Hybrids has a .188" freebore, minimum to clear. If you add .188" and .043", you get .231". This assumes that the ogive profile is identical.

 

[barnesuser28]

But where the bullet contacts the rifleing is farther forward than the 180

 

[Steve Blair]

How do you know that?

 

[barnesuser28]

google the dimensions of the 180 hybrid and 195 eol and you can see the difference,

 

[Steve Blair]

I see the dimensional difference. On good days, I can read a print. [br]
The ogive contact, forward of the shank, is .043" forward compared to the 180 Hybrid. Why would you need to extend the freebore more than that?

 

[barnesuser28]

you are right, i putssed up somewhere in my calculations.

 

[barnesuser28]

I copied and pasted the dimension of the 180 hybrid and 195 eol onto word then adjusted their size until the diameter and length matched up to what is spec and the ogive contact is .075 farther froward then the 180 hybrid, so .043 from the extra shank length + .075 from the longer nose profile and .188 from Dave Kiffs minnimum free bore for the 180 and you get .306 free bore. Is that correct?

 

[Steve Blair]

We don't have enough information about the "hybrid" radius or the ogive radius but the longer nose could be partially explained by the smaller meplat. The 195 is shown as Ø.055" and the 180 as Ø.068". My guess is that the two unknown radii are close if not identical to the 180 Hybrid. If you need to decide this now, send Bryan Litz and email and ask his advice. He knows the actual geometry.

 

[barnesuser28]

the line infront of the shank is where the bullet would contact the lands. It measures the same diameter as the inside diameter of my hornday comparator guage.

 

[Steve Blair]

No, the rifling leade is 1½° and the radius forward of the shank contacts the 1½° cone somewhere forward of the tangent point. I am reloading right now for Twentynine Palms and AZ LR or I would model this in Pro/ENGINEER and get you a better number. I am pretty sure Bryan will help if you describe what you need to know. [br]
p.s.: Almost all engineering drawings carry the warning "Do not scale drawing." It is there for a reason.

 

[barnesuser28]

ok, i think ill send bryan an email, i am 14 years old and just learning about the rebarreling process and reamers, etc.. so thanks for your help!

 

[Steve Blair]

Keep at it and you'll do just fine. You are getting a good start.

 

[barnesuser28]

Thanks, i sent Bryan an email asking the approximate distance from where the bullet would contact the rifling to the forward end of the shank. Whatever measurement he gives me i will probably add .010 and go from there.