THE HANDLOADING BENCH
6mm NORMA BENCH REST (Part 5)
measure the first two or three rounds produced using the callipers and comparator and readjust the die if there is any variation from the seating dummy’s comparator-COAL – being five to ten thou’ out is not uncommon. If you’re loading very long-nose bullets such as some VLDs, it’s always a good idea to check they fit your die’s seating stem before your first loading session. If there is insufficient room inside the stem to accommodate the bullet tip without ‘bottoming out’, this is instant death for ammunition concentricity. The bevelled bottom edge of the stem must bear evenly around a point on the bullet nose well down from the tip. Fortunately, my Forster die suits every 6mm bullet I’ve loaded to date but I have heard of problems with other makes.
Powder Choices
Forster custom neck dimension full-length sizer alongside a Sinclair Gen II expander die body and E24 mandrel.
After ascertaining the ‘into the lands’ COAL, I use that individual bullet in an inert dummy round at the adjusted setting I want my loaded ammo at (ie 15 thou’ shorter or longer as appropriate) using the comparator again to adjust the seater die. On using the OAL Gauge to get a handle on throat wear, I did a comprehensive re-measure of my heavy match bullet comparator COALs at the 1350 round-count mark and erosion was only in the 0.025-0.032 inches range depending on the bullet and the round count it had first been used at, not all having been loaded throughout the barrel’s life. A measured erosion rate of around 0.020 inches per 1000 rounds is modest, especially as initial ‘wear’ on a newly chambered barrel is relatively rapid with the nice sharp leade the gunsmith gives you quickly smoothed out.
Here are some bits of advice on comparator and seating die settings that are not 6mm BR specific, for what they’re worth. First, should you acquire more than one comparator insert in any calibre, don’t assume as I did that they have identical diameter holes! My long-range 90gn BTLR 223 Rem rounds produced a distinctly iffy performance at 900 yards in the Scottish RA Long-Range Meeting in July and I subsequently discovered my two 22 cal. inserts were different enough to produce a 0.016 inch COAL variation and, as I’d loaded the ammo. up in several sessions, I had a mixture in my ammo boxes depending on which insert I’d picked up.
Secondly, I’ve sometimes found that setting the seater die by screwing its stem down onto the seating dummy’s bullet isn’t accurate enough. Always
Anyway .... onto powders. Before I get onto what the websites and loading manuals recommend, I did QuickLOAD ‘Propellant Charge Table’ runs for a selection of different weight bullets. This facility lists powders and maximum charge weights in descending MV order, the outputs calculated to meet criteria that you input – in this case a 102% (slightly compressed) maximum fill-ratio and 58,000 psi PMax value with my fired cases’ water capacity of 38.7gn.
A close watch was kept on headspace during sizing, shoulders only knocked back marginally.
For heavy bullets, I did runs for the 95 and 105gn Berger VLDs at 2.375 inch and 2.4 inch COALs respectively. Combinations that give the highest MVs are not automatically the best ones as we want consistency - small MV spreads, minimal barrel fouling and more – especially in precision shooting applications. Nevertheless, the MV produced within a fixed pressure envelope is as good an indicator of internal ballistics efficiency as we’re likely to get and a potentially useful pointer as to which powders suit the cartridge configuration with any particular bullet.
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