If you’re an accuracy nut and compete at the highest level, then I guarantee you obsess about neck-tension with your homeloads.
No, we are not going to talk about neck-turning but we ran an article a few issues ago in Target Shooter (http://www.targetshooter.co.uk/?p=3921) showing how consistent neck tension is more likely achieved by upsizing the case-neck from the inside with a mandrel rather than trying to do the job (from the outside) with bushing dies – if you’re not neck-turning your brass that is.
The neck mandrels do a great job and when – like the ones from ARC Ballistics, available in solid carbide and half thou. increments – it’s possible to be very precise with your neck-tension.
But……but how do you measure it? How do you know that the mandrel has done its job and each and every case-neck has exactly the same internal diameter – no matter what your chosen sizing method. Well, you may have seen those superb – but superbly expensive – bullet seating devices made by AMP – yes, the same outfit who do the induction annealers. To read a report click on https://www.ampannealing.com/amp-press/
I would love one – having witnessed it in action at GS Precision’s facility but honestly, I couldn’t justify the cost, which is why this cleverly designed tool caught my eye at Hannam’s Reloading on a recent visit.
About the size of a small screwdriver, this little tool looks simple but it is made with extreme precision – so it doesn’t come cheap – precision engineering never does – but you get what you pay for. The one in the pic above is for the 6.5mm/264 cartridges but you can buy a 224, 6mm, 7mm and 308 – or even a full set.
So how do we use it? What does it do? How does it help with neck tension? You will see that there are four precisely ground sections on the gauge and each one varies by one thousandth of an inch – ranging from 0.260 to 0.263 – in the case of my 6.5/264 gauge.
Well, I’ve just prepped my 6.5×47 brass – full-length sizing with a Forster die with the carbide expander-ball removed – then upsizing the neck with my ARC Ballistics neck mandrel and inserted the primers. I’m hoping this will give me a two-thou. (0.002in.) grip on the bullet. So, they should all be exactly the same inside neck diameter right? Maybe. Why maybe? Well, as we all know, brass work-hardens from the firing process and if some of your cases have been fired many times and others maybe only once or twice, a certain amount of ‘spring-back’ may occur, marginally altering the inside neck diameter – and thus neck-tension. (Note – you can usually get away with up to five firings before work-hardening becomes an issue).
So let’s bring our Forster neck-gauge into play and ‘dip’ the cases. It’s simply a matter of letting the Forster gauge enter the neck until you get that ‘feel’. I was pleased to see the Forster gauge confirm my case-neck sizing method – every one was spot on. The gauge is a really nice snug fit – so much so that it provides an almost perfect seal and you can actually feel the air-pressure (providing primers are in place) as you insert the gauge – but without ‘touching the sides’.
If you are not using the ‘mandrel’ method and the gauge indicates that your sizing dies didn’t do a perfect job – i.e the necks are different diameters – where do we go from here?
Well, short of updating your dies/mandrels, I would simply ‘group’ them in my reloading box – so that if I was shooting 5-shot groups for benchrest, I wouldn’t be mixing neck tensions. For F Class, I’d try and use the ‘oddments’ for blow-offs and group the remaining rounds in my ammo box ordered in such a way that I wasn’t jumping to different neck-tensions from shot to shot.
Well I don’t doubt that some of you are reading this article and thinking “For f**ks sake, really?”
Fair point but, you are probably the same guy who looks amazed when a flyer goes suddenly high (or out of group) for no obvious reason……..?
Contact Hannam’s Reloading if you want to buy a gauge but, be warned, they aren’t cheap (£58.30p) but again you only buy one – you’ll never wear it out – and hey, if it only got you one more point in a comp, it could make all the difference.