Is COAL the same in different rifles with the same bullet

[roob]

With different bullet shapes the ideal COAL to match a rifle has to change between loads, I get that.

Are the chambers and throats in all or most brands of rifles cut to the same specs though so that the right coal for a load in one rifle will be the same in another rifle?

I'm making these numbers up but say you have the following.

308 175gr Berger Match VLD bullet.

You work out in your Tikka that the COAL for the bullet to be 10 thou of the lands is 2.815"

If you put the same finished cartridge in a Remington or a Winchester rifle, will the bullet be sitting 10 thou off the lands still or will it have changed?

If not, why don't they do make them different?

[Baldrick314]

Short answer, no. Rifle makers use the SAAMI specs as a guide so factory ammunition will function in their products but there will always be variations caused by different people making them, tool wear and differing designs such as some manufacturers like to have excess freebore in their rifles.

[Westy]

I have 2 Tikka 6.5 x55 T3 lite and super varminter both have a oal different to each other can't remember now what they are will check the book and post them here later

[Westy]

I have 2 Tikka 6.5 x55 T3 lite and super varminter both have a oal different to each other can't remember now what they are will check the book and post them here later

This also is the same for the 223's

[MeccaOz]

the COAL, varies from rifle to rifle, even the same models sometimes. Like Baldrick said though there is a Standard to follow and the most common one in use for us, the Americans and Brits is the Sammi Standard.

http://www.saami.org/

[1290]

saami shmaami.... CIP, think metric!

COAL is just the measurement of whatever youre loading, unless your talking actual spec. which consists of a cartridge Maximum and chamber Minimum. Some of these dimensions provide a tolerance as such there will be slight differences not only between manufacturers but even within production runs...

I think I posted this drawing some time ago... its the 5.56x45 (5.56Nato) with Milspec bullet inserted to COAL... its all relative.


(Mil=green, blue =CIP cartridge and bullet, Red = chamber and rifling)

[Chronos]

So what's the ideal COAL? 2 thou off? 10 thou? 20?

And what happens if you change the powder charge .5 gr? Of its hot, or cold?


There must be a hundred variables and combinations that can make a particular load and seating depth or COAL is only one ( or more correctly cartridge base to ogive length)

People get hung up on loaded length as the second most important part of load tuning (after powder charge) but in reality most cases these guys are using secant ogive bullets that aren't all that sensitive to seating depth.

I believe this has filtered down from target shooting where secant ogive VLD bullets ( low drag) and custom throat reamer depths and angles are often used and these are much more sensitive to seating depth and adjusting it is a way to reduce group sizes.

Chronos

[newsteadvic]

Are the chambers and throats in all or most brands of rifles cut to the same specs though so that the right coal for a load in one rifle will be the same in another rifle?

As others have said, the short answer is no although there are industry guidelines about chamber size and pressure limits.

This image is two chamber casts of two 35 whelens - on the left M98 Mauser, barrel re-bored by Peter Davern, middle is Winchester M70 Whelen and then loaded round. It is obvious how much more freebore the M70 has.

[Chronos]

newsteadvic,

Out of interest where did you get your cerrosafe? I see northern smelters has is but I haven't priced it.

Chronos

[newsteadvic]

out of interest where did you get your cerrosafe? i see northern smelters has is but i haven't priced it

Chronos

That is not cerrosafe, the chamber cast is made using powdered sulphur and graphite, a method set out in Hatchers Notebook. Oil chamber and first part of barrel. Stand rifle up, barrel down. Poke scrunched paper or cotton into barrel 5cm on from chamber. Make a paper cone to fit into chamber. Dangle twine into chamber for the mix to solidify around and help with removal of cast.
Mix 4 parts by volume sulphur (garden shop/chemist/volcano) and one part by weight graphite powder (hardware). Melt on electric hotplate (not flame). Pour molten mix in, allow to cool for a few minutes then tap with cleaning rod from barrel end, pull on string at chamber end.

[Chronos]

out of interest where did you get your cerrosafe? i see northern smelters has is but i haven't priced it

Chronos

That is not cerrosafe, the chamber cast is made using powdered sulphur and graphite, a method set out in Hatchers Notebook. Oil chamber and first part of barrel. Stand rifle up, barrel down. Poke scrunched paper or cotton into barrel 5cm on from chamber. Make a paper cone to fit into chamber. Dangle twine into chamber for the mix to solidify around and help with removal of cast.
Mix 4 parts by volume sulphur (garden shop/chemist/volcano) and one part by weight graphite powder (hardware). Melt on electric hotplate (not flame). Pour molten mix in, allow to cool for a few minutes then tap with cleaning rod from barrel end, pull on string at chamber end.

i see, thanks NSV, i've never heard from anyone who's used that process so i assumed t was one of the commercial chamber casting products

thanks

steve

[Tiiger]

If not, why don't they do make them different?

a) Allowable tolerances.

+

b) Everyone thinks their way is best.