Reloading: Tuning by Turning
- By Wheelwrite
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- Last updated: 22/05/2018
I’m sometimes surprised by the response of fellow hand loaders to questions about methods of improving the quality/ accuracy/consistency of their hand-loaded ammo. It gets the job done, why change, is a popular reply from some hunting and pest-blasting mates? Hard to argue with that, but for me the search is always for improvement, the Holy Grail of perfection.
The quality and consistency of the fit of the bullet in the neck of the case is an important component in achieving both safe and accurate performance. Too tight and it will increase cartridge pressure and risk neck damage, too light and it can lead to movement under recoil, wherever additional cartridges are housed in a magazine. Whilst most good, quality jacketed or solid bullets are manufactured to well-controlled dimensional tolerances, the same cannot be said for cartridge cases when comparing brand to brand!
Stock die dimensions, both neck sizer and expander ball are generally very good, but should be measured carefully, especially if any fit issues are discovered during use (the manufacturers have been known to screw up!). Furthermore, chamber dimensions, although technically subject to tight specifications by CIP or SAAMI can vary beyond those tolerances, either accidentally or in a potentially dangerous ‘accurising’ process! Ergo, the ‘worst case’ sum of these variations can lead to the assembly of ammunition that is inconsistent and potentially dangerous. Buyers of second hand custom built rifles should always gauge the chamber – just in case.
In case you hadn’t guessed, an overview of neck turning is the subject. And despite the comments of some of my buddies it is not the exclusive preserve of accuracy nuts and anoraks like me. Let’s take a working example, reloading once fired 5.56x45 NATO brass for a .223 Rem rifle, (not that this is something I would really bother to do!). The 5.56x45 was designed for suitably chambered military rifles and operates at a higher pressure (typically another 5,000 psi) than the civilian ‘equivalent’. Whilst the external cartridge dimensions are more or less the same, the wall thickness of European 5.56 is almost always greater and the brass alloy often ‘stiffer’. Furthermore, Mil-spec chamber dimensions are slightly larger with an increased leade length!
De-priming the NATO cases will probably require specific tools, as will uniforming or swaging the primer pockets. Neck sizing alone will be unlikely to restore the brass to a .223 chamber fit, requiring a lube and full-length re-size. Trimming prior to turning will be necessary. Running the stock .223 expander ball through the neck should produce an orifice that gives us good tension, but the neck may then be too tight a fit in the chamber due to its increased wall thickness. Furthermore, measuring the neck wall at several points will reveal that the thickness is often not radially consistent, varying by as much as .003/.004”. Turning will therefore give you better chamber fit and more importantly, consistency of tension across the whole batch of cases.
Do you indulge in the odd spot of wildcatting or cartridge conversion? As a rough rule of thumb, the wall thickness of cases steadily reduces from the web to the neck. It therefore follows that any reduction in the length during a conversion process will reveal an increase in the resulting neck wall thickness. Furthermore, the repositioning of the shoulder to neck interface can also create an internal material bulge, popularly known as a ‘donut’ (that’s the Colonial spelling!). In such instances, an inside neck reaming operation will be essential. Yes, there’s also an external ‘donut’. This can form if the outside neck turning does not interface cleanly with the shoulder, leaving a ring that will prevent precise chambering. These two types of machining operation should not be considered as interchangeable.
Making a start on the neck-turning process begins with a simple check to ensure that the turning pilot will closely fit your resized brass. If the answer is no, then you need to decide whether the expander ball or the pilot is at fault. Your call! In order to get cutting, we need to set up the tool. The precise details of setting each brand of trimmer, K&M, Sinclair, Hornady etc., vary slightly, so we’ll just address the general points. Always back out the cutter and establish a zero, making sure that you know the amount of cut that each increment delivers. Install the pilot with a trial case positioned against the end stop, as this will allow the cutter chamfer to be set as a slight interference with the shoulder. Fine tuning will be needed, as the depth of the cut is then set. Using either the K&M and small Sinclair tool freehand is both fiddly and less accurate, so wherever possible, use a powered drive on the shell-holder body and mount the assembly in a vice or the jaws of a WorkMate-style bench.
And so, to trim! With lube on the pilot, the inside and outside of the neck, as dry cutting will almost certainly cause the cutter to chatter or gall, wrecking the finish. Having batch measured the case necks, the trimmer needs to be set to the thinnest of the wsamples and the cutter adjustment made accordingly. If the amount of material to be removed amounts to more than .002”, then I suggest that it is done in two passes. Run the Dremel on the slowest setting and keep it running throughout the turning process, as stopping or even worse, reversing will wreck the case. Take the first cut from the batch, re-lube, adjust and make a final cut. Use a fine bristle brush to keep the cutter clean. As a final finishing touch, I run the spinning neck through a fine Scotch-Brite grey pad. All that remains is to thoroughly clean the cases and at the end of the batch, the tools too.