HANDLOADING BENCH PART FOUR
Bullets
Last month we covered loading equipment and case preparation. Now, let’s move onto the other end of our fat little beauty, the projectile and we’re not exactly short of choice. Looking at my components records, I counted no fewer than 44 different 6mm bullets in my possession ranging from 55 to 115gn, though I only hold small numbers of many models where I’d bought 100 to try them out. They’re roughly equally split between match and expanding sporting models and all, or nearly all, are still on sale.
Let’s take one quick step though to limit the choices and simplify things – by eliminating the 115 grainers. Although John Carmichael campaigned a 6mmBR/115 DTAC with some success in GB National League F Class a few years ago (pre 7mm short magnums!), the general consensus is that the BR case doesn’t hold enough powder to obtain any ballistic benefit from the 115gn Berger VLD or Tubb/Sierra DTAC - the improved BC over the best 105s offset by the MV reduction.
The chamber freebore may have to be increased so much to obtain the maximum MV that it compromises the use of lighter bullets in the rifle. Some people also reckon that the extra jacket length in a 115gn VLD form bullet produces an only marginally balanced combination given its 6mm diameter. The upshot of these factors is that it’s not worth trying them, especially as a 1-7 or 1-7.5 twist barrel may be needed. (Larger cartridges – 6XC, Swiss Match, 6-6.5X47mm Lapua and .243 Winchester – that can push the 115s to 3,000 fps and beyond are a different matter.)
A selection of 55 - 60gn 6mm ‘varmint’ bullets.
There are yet more out there too, although not all are available in the UK, so the 6BR shooter has a huge choice and if having a rifle built or rebarrelled, serious consideration has to be given to this issue in terms of rifling twist-rate and the chamber throat form that will be specified. Of course, most users won’t want to use highly frangible 55-87gn varmint bullets, more heavily constructed 85-100gn deer bullets and 105- 115gn long-range match bullets in one rifle but I know two individuals who do just this, such is the cartridge’s flexibility – but only if the right mix is specified for the chamber and rifling twist rate.
58gn to 87gn ‘varmint’ bullets from Hornady and Sierra.
Twists and Throats Let’s look at matching rifling twist rates to bullets. Actually, before we do that, there is another choice to be made if you’re still at the planning stage – standard or ‘tight’ bore size on your barrel. Most custom US barrel-makers produce 6mm tubes in two bore diameters (the distance between the lands, or put another way, the diameter of the hole bored down the barrel centre before the grooves are cut or swaged) - 0.236 and 0.237 inch.
Shorter match bullets that work in a 1-10” twist barrel. Left to right: 70gn SMK, 66gn Berger HBC-FB, 88gn Berger HBC-FB, 90gn Lapua Scenar in both naked and
factory ‘silver’ moly-coated forms.
The ‘rule of thumb’ is to specify the smaller diameter bore for long-range rifles whose ammo will be loaded with HPBT match and VLD type bullets, especially if you plan to use the ‘skinny’ Lapua Scenar models. Choose the larger 0.237 variant if building a short- range rifle using light flat-base bullets, especially if you’re going to load hand-made bench rest quality examples whose ‘pressure ring’ diameter can be
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