Projectile shifting in neck once loaded?

I went to the range the other day to check zero on my tikka 7mm rem mag. One round would not allow me to close the bolt, one was a little stiff and the rest were fine but showed scuff marks on the projectile like they were touching the lands when chambered.

Later that afternoon I got some calipers and measured the projectiles OAL. My load OAL is 2.740”, on average most of my rounds were now reading 2.745 - 2.746”. The round that would not let me close the bolt measured 2.749”.

I am very deliberate and measured each round individually when I made them. My load is 63.5gr IMR4831, Norma brass and the 162 ELD-X so not anywhere near compressed.

On an earlier occasion I did measure some loaded rounds and noticed they seemed to have gotten shorter measuring 2.735” when I loaded them to 2.740”.

Got me a bit baffled. They are stored in your standard plastic hard case with a lid. Sure they rattle around a bit when travelling but I wouldn’t expect the projectiles to move in the neck? On another note it didn’t affect accuracy.

Thoughts?

Brass is sized with a redding FL die.

The ogive of the bullet changes with changes in different lots of bullets (despite the best intensions of manufacturers). The bullets are made on different machines/dies and mixed up so there will be slightly different ogives in each box of bullets. Measure the ogive to base length which is the relevant measurement for the chamber. The overall length (OAL) is relevant to the cartridge length which must fit into the length of the magazine.

Did you crimp the necks at all?

@stagstalker, measuring OAL is notoriously inaccurate way of measuring projectiles or seating depth. Get a comparator and measure base to ogive (CBTO)

My first thought was compressed load, but you seem to have ruled that out.

If you are full length sizing, are you checking case length after sizing and trimming your brass ?

Sorry I should have clarified, I do use a comparator and measure of the ogive. Not base to tip.

I don’t measure each case once sized, just measured it when I first set up the die to bump the shoulder 2 thou.

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Originally Posted by Max Headroom

Did you crimp the necks at all?

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Nope

Great couple of threads here on neck tension.
As above my cartridge Oal varies by up to 0.005 and length too give around 0.003 to 0.004. You can sort Theo give measured ones out to be pretty close but the COAL always varies.
With regard to tension. Many firings on brass? Annealed?
As above..never used a crimp though this could help

Insert ogive where the above makes no sense

Quote:

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Originally Posted by stevodog

Great couple of threads here on neck tension.
As above my cartridge Oal varies by up to 0.005 and length too give around 0.003 to 0.004. You can sort Theo give measured ones out to be pretty close but the COAL always varies.
With regard to tension. Many firings on brass? Annealed?
As above..never used a crimp though this could help

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Brass is on about its 6th firing. Was annealed the home made way with a battery drill and blow torch at home after its 4th firing.

My guess is that your necks are getting loose and not gripping the projectile like they did in the first few firings. Everything gets old and tired after awhile.

If you don't have a crimp die, your seating die can be used to crimp the neck if you adjust it right. I've never done this myself, so can't explain how to do it, sorry.

Quote:

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Originally Posted by Max Headroom

My guess is that your necks are getting loose and not gripping the projectile like they did in the first few firings. Everything gets old and tired after awhile.

If you don't have a crimp die, your seating die can be used to crimp the neck if you adjust it right. I've never done this myself, so can't explain how to do it, sorry.

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I did wonder this. I was considering just getting a new batch of brass and seeing if the issue stopped.

I would of thought if projectile was seated out to far it would just push into,the case on closing bolt id look at shoulder or base of case

Quote:

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Originally Posted by stagstalker

I did wonder this. I was considering just getting a new batch of brass and seeing if the issue stopped.

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Probably the simplest way to tell. You'll use them sooner or later anyway.