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Problems Sierra TMK seating

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I’m having problems getting a consistent seat on my 260 with 130 TMK. I’m using redding  dies with a VLD stem in it and getting up 10 thou difference with Hornady compactor. Never had a problem with 140 ELDM. Any thoughts. I’ve cleaned them and  sat the other stem on the bullet Tip but it looks like it will squash the tip. 

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IME, the TMK's have a very soft jacket, and when seating, you can easily crush/deform the ogive if there is too much neck tension.  So, you need either a better fitting seating plug, or you need to set a lighter neck tension, via an expansion mandrel/die.  

Dealing with the same thing in my CM, but haven't ordered the mandrels yet.  Had the same issue as well in my 224 Valkyrie, and the expansion mandrel did the trick quite well.

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Some die manufacturers will supply a polished seater to prevent this, or you can do it yourself with lapping paste

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If your using a compressed load this could cause it too..

Try the lighter neck tension method first though 👍

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4 minutes ago, No i deer said:

If your using a compressed load this could cause it too..

Was going to say the same, often hard to get consistency seating over very compressed loads

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My 6.5x47 with 139gr scenars sat on 41grs of RS62 doesn't usually seat to the desired length on the first stroke of the ram. Sometimes it needs 2 or more..

Try it.

Seat and measure.. Seat and measure and see if measures shorter each time but don't force it. The powder is compressing a bit more each stroke.. scenars have a thick jacket so less likely to dent it..  if I had a long drop tube it may help.. I do tap the case a few times on the bench top with my finger over the neck to stop powder flying out to get powder too settle down a bit more before seating.. 

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I use the 130 tmk is my 6.5x47 and they seat spot on, no marks, less than 1 thou variation in ogive length, 

 

I'm using foster benchrest dies don't know if they make any difference? 

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12 minutes ago, rhhudson said:

I use the 130 tmk is my 6.5x47 and they seat spot on, no marks, less than 1 thou variation in ogive length, 

 

I'm using foster benchrest dies don't know if they make any difference? 

The 139gr scenars have a long bearing surface and seat really deep compressing the powder. I imagine the base to ogive measurements are much longer than the TMK's 🤔. I could be wrong though..!!

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I wonder if it will cure it’s self as I’ve just just started reaming inside doughnuts out as they have started forming. I’ll try some in the cases I’ve just done. I’ll give it a bash and see if there is a difference and report back. Cheers every one

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I don't think the donut will stop the bullets seating consistently. They could cause inconsistant neck tension.

Does the bullet seat above the donut area..

If you resize your brass as normal and get a K&M neck tension mandrel these so say push most of the donuts back out but neck turning the cases cutting into the shoulder helps against donuts. If the cases haven't been necked up or down I didn't think you get donuts..

Only inside neck ream fired cases.

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They are Lapua 243 brass necked up to 260. There are definitely there

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I thought you could buy 260 brass nowadays 

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Backing up brass 243 to 260 is an act of desperation nowadays......it will create donuts 100%.

It causes havoc with bullet seating.

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18 hours ago, rhhudson said:

I use the 130 tmk is my 6.5x47 and they seat spot on, no marks, less than 1 thou variation in ogive length, 

 

I'm using foster benchrest dies don't know if they make any difference? 

Likewise for me.

I use 130gn TMK in my .260 with Forster benchrest dies.

They seat perfectly for me with no marks or deformities.

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6 hours ago, No i deer said:

I thought you could buy 260 brass nowadays 

I had a load of 260 brass that came with gun and thought I’d use 243 so I can keep an eye on what’s what. And gun shop always has 243 in stock

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