Correct C.O.A.L won't fit in the mag..

[Thegreg]

So I've just started load development on an old .308 I've had for a while. Got some Sierra 155gr TMK's which are the ideal weight for the gun.

First thing I do after setting the proper head space is make up a "loose neck" round to determine the distance to the OGIVE for said rifle, whereby allowing the lands to push back the bullet when the round is chambered. Always used this method with excellent consistency. This time was no exception, I chambered 5 rounds and they were all within .0005" of each other.

Problem is when I set the bullet .015" from the lands the C.O.A.L is 2.960"! Cartridge is too long to fit in the mag. Unsurprisingly really given the max C.O.A.L for .308 is 2.800".

Anyway it's left me thinking 3 things:

1. The start of the rifling in this particular rifle is set unusually far forward?
2. My magazine is on the short side?
3. The profile of the Sierra bullet has a shallow taper and therefor protrudes further from the case before contacting the lands, which leads me on to thinking I might need to try a different bullet?

If I set the C.O.A.L to the recommended length (and so the round fits in the mag) the bullet is going to have a massive .175" jump to the lands, which I'm not happy about at all.

Anyone else come across this problem before?

Cheers
Greg

[223AI]

What make of mag? I had an after market howa mag conversion that would not let me load to saami length, 2.812 rather than 2.825. Careful filing opened it up and now it's fine!

[DedIdick]

Quite normal I believe, 3 of my magazine rifles are similar. I just make sure I know which rounds I load to mag length.

[Korium]

Several of mine end up with a COAL over 2.900" if I seat a bullet to the rifling. I have one .308 Win with a throat so long, a bullet will generally fall out the case before it can touch the rifling - it still groups well with mag-length cartridges.

My understanding is many factory rifles are given a long throat to accommodate a wide variety of bullets, including heavy round-nose designs.

[Thegreg]

Thanks for the replies chaps.

Talking to a few guys at the club yesterday it seems pretty common, though it is the first time I have experienced it.

One thing that still does worry me is the bullet won't have full contact with the entire length of the neck, it'll just be seated a partial way down. Might not be such an issue but I bet it'll leave a visible band on the outside of the cartridge, and this I haven't seen before.

Cheers
Greg

[dicehorn]

Thanks for the replies chaps.

Talking to a few guys at the club yesterday it seems pretty common, though it is the first time I have experienced it.

One thing that still does worry me is the bullet won't have full contact with the entire length of the neck, it'll just be seated a partial way down. Might not be such an issue but I bet it'll leave a visible band on the outside of the cartridge, and this I haven't seen before.

Cheers
Greg

It is usually suggested that the diameter of the bullets seated in the neck is a good starting point ie 308 should be at least 308 thou in the case or better still start at the recommended COL of 2.800 as in your 308 using the OCW or Satterlee method to test.

Personally I have never been able to get my head around the concept of seating the bullet 20 thou or less unless it happens to be a bench rest rifle. Most rifles have as many as four sweet spots, granted the first may well be less than 40 thou but that may be the obvious node to find - against it are two points to consider - will it fit the magazine and now with this long bullet balancing at the end of the case neck you are creating quite an air gap above the powder which can delay ignition by a nano second especially as that air pocket will creep back towards the primer as usually rounds are fired on the horizontal.

I must confess to having a little chuckle when you mentioned 'a massive 175 thou jump' - a chuckle only because my 20 Tac with a custom barrel is 223 back and will group sub .2, my 22.250 at 220 thou and 6.5 at 180 thou - both well less than .5"

Tried to put a couple of scans of other people's rifles I reload for showing these 'massive jumps' but I'm not technical enough to achieve this.

Peter