The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Hi all,

Quick question, does changing the C.O.L. effect pressure & muzzle velocity?

If so do calculators exist that help work this out?

Thanks,

Mick.

Yes.
The closer the bullet to the leade the higher the pressure. This is one of the reasons that many off the shelf rifles have long throated chambers, often in excess of SAAMI dimensions (especially firearms of American manufacture). Not sure of any calculators out there for this.

I am not aware of any calculators either and even tools like Quick Load do not take into account the jump or jam of the bullet with none SAAMI/CIP chambers.

Ok, thanks guys.

It was the lack of reference to C.O.L. in QuickLoad that prompted the question.

I use Silhouette Ballistics http://home.comcast.net/~jesse99/interior.html - you can adjust the COAL/seating depth and see the effects. According to the results, a shorter COAL increases the pressure with a given weight of powder compared to a longer COAL - see this article for more info http://bulletin.accurateshooter.com/201 ... -to-ogive/

Surely there are (at least) two different answers to the original question?

1. Assuming the bullet is not going to touch the rifling, increasing COL with everything else being equal will generally result in lower pressures and velocities. Software like Quickload can be used to calculate this, assuming you have calibrated it with some real-world data first. Decrease the COL and the pressure and velocity will generally increase.

2. If you are starting with the bullet close to, or touching the rifling and increase the COL so the bullet is now jammed, then the pressure will certainly increase but the velocity may not.