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Post by tisme on Sept 18, 2014 16:32:23 GMT
Anyone tell me how to measure and adjust neck tension and what I should be aiming to achieve. Using FL dies
Ta
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Post by sako75varminter on Sept 18, 2014 17:08:17 GMT
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Post by Admin on Sept 18, 2014 17:10:16 GMT
Measure the neck on a full-sized case then measure a neck on a seated bullet the difference is your neck tension. You are aiming for about two thou. Regards Pete www.varmintinguk.co.uk |
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Post by tisme on Sept 18, 2014 17:34:23 GMT
So bumping it back about 3 thou should give me a 2 thou tension.
Thanks
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Post by Admin on Sept 18, 2014 17:40:04 GMT
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Post by triggersqueezer on Sept 18, 2014 19:02:34 GMT
i could be wrong but to controll neck tension you need a bushing die so you can buy different sizes.if you measure a sized round then a loaded on the difference should be a good indicator.what makes you want to change it?
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Post by tisme on Sept 18, 2014 20:35:39 GMT
Off to do some measuring then
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Post by Mildot on Sept 18, 2014 21:32:43 GMT
You need neck bushing dies! my .260 Ack Imp has 2though neck tension i use a .284"thou bushing. with a .264 bullet and neck thickness of .11thou so a loaded round will measure across the neck of .286"thou
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Post by davet on Feb 14, 2016 20:47:22 GMT
Gents
Following through a thread over on That other forum (apologies but I do look and post there also!) confirms my long-held understanding that an expander mandrel should leave enough neck tension to retain a bullet satisfactorily....but...
I have used the K & M mandrels in 260 Rem (6.5mm) and 6mm with good results but when using a new 308 mandrel the other day to ease excessive neck tension on virgin Lapua brass the result was that the bullet slid right through the case with very little hand pressure !
Suitably bewildered I went on to use a neck sizing bushing die to correct matters.
I measured the mandrel and it shows .308 to .3085 depending on my level of dexterity with the calipers.
I would have expected enough spring-back after expansion to give me .001" or more of NT but clearly didn't get that result in this case.
I am thinking that either the brass is not exhibiting the expected spring-back (batch problem?) or the mandrel actually IS that little bit over-sized OR I simply have misunderstood their usage all these years!
Any thoughts or experiences very much appreciated.
Either way I will be neck-sizing as a precaution after using an expander in future as I was lucky to get away with the neck sizing operation having already charged the cases and had to take out the decapping assembly.
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Post by tisme on Feb 15, 2016 9:12:16 GMT
Are you FL sizing first. I ask because if the necks were made smaller first then you used the mandrel to open out to .308 they would spring back but the new brass being already nearly .308 might not.
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Post by c18rch on Feb 15, 2016 10:30:47 GMT
What does the mandrel on your neck sizer measure?
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Post by davet on Feb 15, 2016 12:46:52 GMT
Pete...could be that but in the past new Lap brass in 308 has been way too tight for me as I prefer .001 or .002 of NT.
Perhaps they have changed manufacturing processes...will go back and check.
Rich....the mandrel is .308 as measured with a decent caliper so I was expecting a spring-back to net me .001" NT
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Post by c18rch on Feb 15, 2016 14:10:43 GMT
Yeah, I meant what is the diameter of the expander in the neck die. If you compare that to the diameter of the new mandrel, and the new mandrel is bigger then that is your problem. Doing it that way also cancels out any inaccuracies in whatever you are using to measure them with.
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Post by davet on Feb 16, 2016 17:58:14 GMT
Rich
I use a 308 Redding Comp bushing neck die without any expander....bushing is .336.
Lapua necks measure out at 14.5 to 15 thou per side so I get neck tension of about 1 thou.....enough that the bullet won't seat deeper if pressed against side of bench.
I think my expander is a bit too wide diameter.
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Post by tisme on Feb 17, 2016 9:04:08 GMT
Just for some comparison I use lapua 308 brass neck sized to .334 my case necks measure .014 and with Berger 155.5 bullets in them they measure .335.
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