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OAL variance

12 Feb 2018
@ 12:50 pm (GMT)

Andrew Murray

Hey team,

Similar to Lane I though I would ask the collective wisdom rather than ping Nathan again,

Doing my first reloads over the weekend and came up with some variances in the COALs for the finished products.

In fact I noticed the same kind of difference in the projectiles themselves. These differences at their most extreme came to 0.11mm or 0.005". Projectiles were the Z Max (A Max with green tip). 168gr 30cal.

The variance on cartidges were ranging from 71.15mm (2.801") to 70.92mm (2.792")

The majority were significantly closer to the target of 71mm (2.795") being around 70.98mm-71.05mm (2.794"-2.797").

My question is... is this normal variance for projectiles and normal variance for COALs?

What kind of effect does this have on accuracy and velocity? (If any...)

This may be straight forward but it's my first time round and I am wondering if I have done something wrong or this is par for the course...

Thanks everyone.


12 Feb 2018
@ 06:15 pm (GMT)

Andrew Murray

Re: OAL variance
From Nathan, via a different channel. Good advice for those looking

Regarding your question, the bullets are cheap mass produced but they will still be accurate. The big jump will even out pressures / harmonics. So simply measure one projectile (as you have done), set your die and go for it. But do take note that when setting up the die, there can be some spring back. So it can pay to have a second projectile of the same dimensions to check how the OAL is when seating in one pass (or three if you are rotating when seating). Otherwise, don't go any further with measuring, will just do your head in. For now, just plan on getting to the range.
13 Feb 2018
@ 02:50 am (GMT)

Bryan Webster

Re: OAL variance
bullets vary a lont if mesured from their point. When doing COAL I measure from the ogive to the base. The ogive after all is what first touches the lands if you seat out that far. This measure is talked about in Nathan's reloading book if I recall correctly.
13 Feb 2018
@ 09:40 am (GMT)

Martin Taylor

Re: OAL variance
You will find a SAMMI spec 308w to be a very forgiving cal to learn on, develop your skills & tune. The rifle shoots some factory rounds extremely well so follow the steps in the book and have fun.

Keep a good set of notes on the work up so you can refer back to what makes this combination work in your rifle.

Nathan's advice you have listed is spot on as usual!


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