Neck Tension for the Violently Chambered

[Flogain]

I’m trying to determine best neck tension to minimize the bullet jumping out more (or too much more). In my SCAR 17, the rounds as loaded measure .3375. So I round up to .338 which the LGS reloading expert recommended. I have a .335 bushing. In test rounds I chambered with this .003” neck tension about 10 times. After about ten chambers, which are violent of course, the bullet was ~.020” longer at the ogive. Now, I won’t be chambering 10 times. It’s gonna be a one or two time thing. But still, I was experimenting. I know that less neck tension is better, but neck tension is necessary. I have also read sierra’s blog post on loading for high power. But it doesn’t mention ranges of neck tension.

I redid them (sized everything again) and chambered once. Still about four or five thousandths longer. So I’m looking to increase neck tension. Of course, the .334 Redding bushing is out of stock everywhere. That would be my next test, with .004” neck tension (.0035 really, so like a real three accounting for spring back.

Any recommendations for neck tension in violently chambering gas guns?

I know, lots of what I’m doing is almost unnecessary. But as I hand load for this gun, I want to do everything over-the-top as practice.

Also, I hear people talking about using an expanding mandrel first. Then sizing the OD with the bushing. Then using a mandrel again. But that would undo the bushing on the outside would it not? I have a.30 mandrel from 21st century I use on new brass, and before the bushing on fired brass. I don’t turn necks at the moment. Some find it necessary, some don’t. I was going to buy an expensive turning setup when I fell into the not necessary camp. Anyway, the mandrel pushes my OD out to .336-.337. It undoes all my neck tension. I could get a smaller mandrel I suppose, and I too suppose this is what people do. They must oversize the OD, and slightly mandrel the ID, but then what size mandrel to get I don’t know. I would, but also I’d find it frustrating because I just got this one in the mail!

Any help appreciated.

Thanks!

And sorry, but one more thing. Why on the Forster Ultra Micrometer seater do the numbers make no sense? They are essentially reversed. Turning the micrometer to the left is backing it out, yet the numbers that appear first then are one, two, three, etc. And the plus sign is on the left too. I don’t understand. I know the Redding numbers are different.

 

[SupressYourself]

I've been down this road with ARs. .004 neck tension won't stop it completely. You can either do a crimp, or just allow for the slight lengthening. It should be fairly consistent.

 

[flyright]

.003 NT seems to hold them quite well in my .308 and 6.5 gassers and, as I remember reading somewhere years ago, trying for more than .003 NT is a fruitless effort. I'm sure if I dropped the bolt on a mil round more than 2-3 times it would pull the bullet some. Kinda the "is what it is" thing.

The Forster die numbers are simply markers - indices 0-25. I do see what you mean. Maybe that's why my friend called me all confused about how he should use them. I just told him to turn it down for deeper, up for shallower and 10 indices is approximately .001. I suppose numbered the opposite way would make more sense since we start shallow and work down unless you like pulling bullets. Or, just think of "dial it down to 20 - not deep enough? - dial it down to 10".

Edit to add: I use a honed Forster FL die to bring neck OD to .332 which works with a wide range of brass but, yes, overworks some of the thicker brass. I then use a .306 turning mandrel to expand. In most of my brass this allows a .305 pin gauge to enter with some force. My loaded neck OD's show I'm at .0025 to .003 NT. Bullet seating is smooth but the bullets won't move in 2-3 bolt drops and I can live with that. Just my .002.