need advice plz

[MacDonald]

Hi to all out there, I am in the process of breaking in a new barrel, have fired the first 20 roungun)ds cleaning after each shot. Am now at the point of shooting 3 shot groups before cleaning.My first group showed a weird thing, at 50 m and at 100 m the bullets are key holing.
I have not chronographed, shall do so on next outing.
Is this some thing to be alarmed about?, does it indicate anything or must I obtain more info, ie speed of bullet etc.
I would welcome any input please.
The rifle is a custom 270 , the rounds are 150 grn Sierra game king and I have started the loads at the minimum recommended for our powder which is Somchem
S365
Thanks all
Macdonald

 

[Grumulkin]

The bullets are key holing because that haven't been stabilized adequately. There are two possible reasons:

1. The twist on your barrel isn't fast enough to stabilized bullets that long.

2. The bullets are going too slow.

Actually, barrel twist is a bit more important than velocity. After all, if you have a 1:12 twist barrel, that means that for every 12 inches the bullet travels, it will rotate completely one time. It doesn't matter if the bullet is going 1,000 fps or 3,000 fps, it will still only rotate once for every 12 inches it travels.

Increasing bullet velocity will increase bullet RPM though which can help in stabilization. As long as you're not having signs of excess pressure, I would increase the load until:

1. Best accuracy occurs.

2. Signs of excess pressure occur.

There is no need to shoot light loads while breaking in a barrel.

 

[MacDonald]

Thanks a million! Tomorrow I shall fire rounds over the chrony, just to determine where i am at regarding speed.The twist is 1 in 12 , as soon as I have some figures, I shall contact you again.
Thanks

 

[bigngreen]

A 1-12 twist might have issues with a 150gr bullet, the norm is a 1-10 twist thou they do well out of my 11 twist 270 WSM. I would load some 140 gr bullets and see if they will stabilize. In my experience, if your not stabilized at 100yrds with a reasonable load then velocity isn't going to fix it, if there wobbly near transonic then a bump on velocity will sometimes keep them straight a little longer.

 

[MacDonald]

Thanks for that,
as soon as I have a starting velocity, I should be able to work things out.
I shall indeed try my other bullets which are 130 grn Sierras, marvelous bullets!