From what I understand, it is pretty common to order a chamber reamer with a shorter than SAAMII spec freebore; however, I would like to get a better understanding of some of the risks. I have two builds that I'm currently working on that i would really like to feed from the magazine.
From reading Long Range Long Time's review of the McMillan EOL Outdoorsman, I found out that McMillan along with EOL have made a modification to their 300 RUM chamber (300 EOL Long Range) that allows it to feed from the magazine and still touch the lands. In addition, it can still fire factory 300 RUM cases safly. The only way that I can figure they modified the case was by shorten the freebore a bit. That being said, could I order a custom reamer with a shorter frebore and get the same results?
Please let me know if I'm on the right path, or if I'm missing something.
Here is a link to the review.
Mcmillan EOL Outdoosman Family Outing
At the same time, I understand that Remington and Weatherby both use excess freebore on their larger magnums to gain velocity without excess pressure. If I start loading rounds .020 off the lands like my other rifles, will I be able to reach expected velocities without excess pressure? I have read that by using a shorter throat, or seating the bullet close to the lands, the pressure can be greater.
Mike E's comment in the attached link gives me some concern. match chamber or not?
I had a similar experience to his with my other custom 300RUM where it was a match chamber with I believe a standard freebore. I was seating the bullet at .020" off the lands and getting book velocities with almost 10 grains less powder. The accuracy was excellent, so I left well enough alone and forgot about it until now.
The other rifle that I'm building is going to be a 7mm SAUM on a Stiller Short action. With this rifle, I would like to reduce the frebore from .3077", which is the standard SAMII in the 7mm SAUM down to, or close to .1884", which is the SAMMI for the 7mm WSM.
My goal is to have the cartridge under 3.1" OAL which would would allow me to feed from the magazine. What should I expect from this and in a pinch, would I be able to use factory ammo?