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270 Wby reloading

18 Jan 2012
@ 01:07 am (GMT)

Arve Ringsbye

I have tried to measure the freebore ( throat length ) on my Sako AV, custom build 270 Wby, with a Shilen match grade barrel 26", by seating a accubond bullet marked with ink in prefired cases from the same rifle.

It seems that the rifle have weatherby standard freebore, ,378 inch ( 10mm).

I`ll be loading for both Hornady Interlock SP/Nosler Partition 150gr ( flat based bullets ) and Hornady SST/Hornady Interbond 150gr ( boat tail bullets ).

The large amount of freebore probably means that it will not be possible to get the bullets in contact with the riflings?

My question is what to expext / prefer, in pressure and accuracy, from either boattails or / compared to the flat based bullets with the given amount of freebore?

Arve Ringsbye

Replies

19 Jan 2012
@ 09:11 am (GMT)

Quote this

Nathan Foster

Re: 270 Wby reloading

Hi Arve, good question.

Bullet to bore concentricity is the key. Roy Weatherby was very smart when he designed his cartridges. One of the design features that really goes unnoticed is the long necks on the Weatherby cases, designed to ensure that the projectile is guided into the rifling as squarely as possible.

The freebore of the Weatherby is not really any different to the .308 Winchester. We not only expect great accuracy from the .308, we also expect it to be easy, so easy, that a single factory load can be standardized for every sniper rifle within a country or continent.

So in keeping with the goal of optimum bullet to bore concentricity/alignment, a good rule is to seat boat tail bullets in such a way that the bullet boattail/ body junction is seated to the case neck/case shoulder junction.

In worst case scenarios, it is a fact that flat base projectiles will indeed produce more uniform results. But other factors come into play here, such as how the flat base swages and seals to the bore. Quite often it is easier to get (for example), a Hornady flat base to shoot accurately where other projectiles have proven finnicky. All we can do is hope that our bore is complentary to the projectiles we want to use, that the throat leade angle is optimised for the ogive design and that the barrel vibrates in a complementary manner.

Areas to double check on the Sako AV action include:

Make sure the rifle is bedded and that the bedding is done correctly, taking critical points of relief into account. Use axle grease to check the fit for yourself and compare this to our online instructions.

Second area of consideration is the bolt locking lugs. Apply vivid marker pen to the rear of the lugs, close the bolt on a fired but not resized case. Extract the bolt and observe lug contact. It is not uncommon for only one lug to be in contact with the receiver in both the Finbear and AV rifles.

In consideration of the Shillen barrel. Study the muzzle for fouling during your load development sessions. If the barrel is still fairly new, you do not want excessive copper fouling to interfere with testing. In this regard, it can pay to take your cleaning gear to the range along with several spare fouling shots.