COAL at the lands too long.

[boattailed bandit]

So when checking my COAL at the lands I knew it would be a bit too long and would have to be seated a little deeper, but not this much. My rifle is a standard Browning A-bolt in 270win. Every book I have says the COAL max is 3.34in, but when I check mine to the lands it is 3.41in. I figured it would be a little bit long, but not 0.07in. Is this typical of sporter rifles and to be expected? I check my COAL at the lands by hand seating a bullet into a empty unprimed case, place it gently into the chamber with my finger until I feel resistance, and then slowly close the bolt. I can feel the bullet seating deeper in the case when I do this. I know it will be hard at the lands and I expected to back it off some, but I never expected it to be past the maximum COAL. Is this just to be expected of standard sporter rifles or am I doing something wrong, or does my barrel just happen to be chambered deeper?

 

[thatguyshm]

COAL is simply a SAMMI standardization to ensure that all rifles be at minimum length. I know that in the book it says that it is the MAX COAL, but in reality, its the max coal for a wide variety of fire arms. Not each manufacturer will use the same chamber size. On top of that, factory ammo usually won't be as exact as your hand loads, so that's where SAMMI comes in. If they make sure that the chamber is longer than the max allowable, then it will never have to worry about pressure spikes if a round is pushed into the lands.

0.070" is acceptable. It gives you something to play with via seating depth to try and improve on accuracy over factory manufacturers. Look at most SAMMI COAL's compared to actual chamber size on most Weatherby's. It will be wildly beyond max. Thast just the way it is with those rifles. If you want to keep it as a hunting sporter, and accuracy isn't measured with a micrometer, then find your max magazine length, back off it a 0.010-0.015" and use that, as long as the end results is less then 3.410" so you're not jammed into the lands.

But yes, its normal.

-shm

 

[wisdeerkiller]

I have an a bolt in 7mm mag.

the only time I reload to the C.O.A.L is when reloading for someone else.

all of my guns are reloaded just of the lands which is longer the C.O.A.L

but in doing this I have read that pressures are higher the longer your C.O.A.L is.

but you end up with better accuracy.

Just watch for pressure signs.

 

[boattailed bandit]

Thanks for the replies guys. It makes a lot more sense. Im also less worried now.

 

[thatguyshm]

I have an a bolt in 7mm mag.

the only time I reload to the C.O.A.L is when reloading for someone else.

all of my guns are reloaded just of the lands which is longer the C.O.A.L

but in doing this I have read that pressures are higher the longer your C.O.A.L is.

but you end up with better accuracy.

Just watch for pressure signs.

Pressure will spike when you get close or agaisnt. But pressure will not increase with every thousandth you seat our projectile out. Also, seating out does not garentee that the loaded round will be more accurate. It just means that your specific rifle likes it that way. Some rifles like a bit of a jump to get going and then can be tack drivers. Its expirementing with your equipment and getting to intimately know what your firearm likes/dislikes. As always, watch for the pressure signs.

-shm