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Reamer design for 338 Norma Mag for 250gr Berger

 
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  #8  
Old 03-06-2013, 09:52 AM
Platinum Member
 
Join Date: Jul 2004
Location: Texas
Posts: 5,442
Re: Reamer design for 338 Norma Mag for 250gr Berger

Quote:
Originally Posted by Machann View Post
JEC I would consider +50 years of experience a expert.

The amount of experience you guys are blessed with over there is huge compared to what we have over and thanks for sharing. We don't have the powder over here to push the 300gr bullets fast enough, will be able to get 2650fps max out of the 300gr vs. 2950fps on the 250gr. That is a 7MOA drop difference at 1500m.

I’m looking to build this rifle as accurately as possible. An old bench rest legend over here designs all his reamers so the bullet kisses the lands with the base of bullet bearing surface between 0.02-0.07 above the intersection of the case neck and shoulder. Thus my thinking behind the reamer design. If you seat the Berger 250gr correctly you have close to a +0.22 jump in a chamber designed for the 300gr Berger kissing the lands. Is this too much jump to get optimum accuracy out of the rifle?


There are some that think that the bullet has to touch the lands to be accurate and some that don,t.

The logic behind touching the lands is sound for small cartridges like the 6mm PPC (Or most bench
rest cartridges) very few bench rest cartridges use over 50 grains of powder because they are for shorter ranges. Only the long range (1000 yard Bench rest use more) and these rifles have the same requirements as Long Range hunting has (Velocity, Ballistics and accuracy).

This type of shooting has a different set of rules than short range bench rest. Short range bench rest
bullets are normally a Flat base design, cases are loaded down for best case life and accuracy, Barrels
are normally short and heavy because velocity is not an issue. All of this is just the opposite for a long
range rifle (Long barrels, boat tail bullets with high BCs,heavy loads of powder for velocity, And yes,
Free bore to achieve high velocity without excessive pressure).

Years ago bench rest shooters had to try many rifle/ barrel and chamber combinations to get a winner.

Many of these guys became barrel makers because of poor quality barrels and chamber reamers were
not as good and most had small home type Lathes to work with., So in order to have a consistent load/
chamber combination, seating the bullet against the lands helped to center the round.

Now with good barrels,reamers,equipment and a good Smith this is not as important as it was in the
past.

I felt it necessary to bore you with the details of the different needs and my reasoning because of
the different requirements of long range hunting.

Don,t get me wrong, there is nothing wrong with seating the bullet against the lands except the velocity
and pressure issues and the ability to use many different types of bullets.

I have 4 personal rifles that I am happy with the accuracy (5 shot groups of .034, .053, .077. and
.092 and they all have free bore over .185 to .756 they can handle max loads with no heavy bolt lift
(High pressure) and the trick is a perfectly concentric chamber with little or no head space,good
load quality, great barrels and a little luck.

I hope this has not talked you out of anything, I just wanter to give you my reasons.

J E CUSTOM
__________________
"PRESS ON"

Last edited by J E Custom; 03-06-2013 at 10:38 AM.
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  #9  
Old 03-06-2013, 11:45 AM
Junior Member
 
Join Date: Aug 2011
Posts: 26
Re: Reamer design for 338 Norma Mag for 250gr Berger

Please JEC, you are not boring me with anything and thanks for sharing!

Suppose the best place to go have a look is the 1000yrd bench rest and how those guys do it and thanks for pointing out the differences. Guess what bench rest discipline our legend shoots.

Thanks for helping JEC. Got a 338 Norma Mag reamer print on. http://http://www.elr-resources.com/...in%2032448.pdf
From my calcs it looks like I'll have a 2.6mm jump if I use the 250gr bullets. Doesn't sound to bad given the advice provided.

Regards
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  #10  
Old 03-08-2013, 10:18 PM
Platinum Member
 
Join Date: Dec 2009
Location: NW MT
Posts: 2,587
Re: Reamer design for 338 Norma Mag for 250gr Berger

A friend of mine shoots 1000 bench, Penn rules.Actually a few of them.They shoot on or in the lands.The one guy has 6-8 world records,his mentor.that I used to shoot archery w/has several also.That is w/6mm dasher.They have also shot 300wsm,their reamer design for comp.The one guy just built a heavy 300 wsm w/promise.Their load prep. and method would take a book to describe .
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  #11  
Old 04-14-2013, 07:05 PM
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Join Date: Dec 2009
Location: NW MT
Posts: 2,587
Re: Reamer design for 338 Norma Mag for 250gr Berger

I got a box of 250 elite hunters by mistake, so Im going to shoot a few. On my comparator the 300 is 1.970 and 250 is 1.860, difference of .11 , on ogive not as much as it lookes when side by side
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