I understand that I have the Spec II chamber on my bolt gun. The 110g Sierra Pro-hunters touch the lands at 2.41 inches and I seat at 2.37 which is as far out as the magazine well allows. This gives me 40 thou' to the lands.
To measure where the projectiles touch the lands I get a fired case, neck size it and then file out the inside of the neck until I can move the projectle in the neck by hand with some force. If the projectile moves too easily in the neck, you can get a false reading. If you don't file the inside of the neck, the projectile can get stuck on the lands and when you extract the case, the lands might pull the projectle out a little and give you a false reading, Also the projectle may not move down the case when it crushes into the lands and therefore also give you a false reading. I measure the reading five times to ensure it is consistent.
I drill a hole in the side of this dummy case so I know never to reload this case and I keep it in the box with my dies. I know it may sound obvious, but make sure this dummy round does not have a primer in it each time you put it in the chamber.
Thanks H, great info, hope that clears it all up for every one.
NRA Life Member
6.8 SPC (Get-R-Done)=(DRT)
(Guns, Guts, and American Pride, Will Keep our Freedom)
It would be a good idea for any new 6.8 standard to have a 0.2780 throat. Smaller throats have two problems... One is that the pressure goes up a few thousand psi:
The other is that the bullets will rub as they are often not perfectly straight in the brass, decreasing reliability and also making ammo more expensive to produce (larger ammo companies will want the loaded rounds to freely drop into a minimum chamber gauge).
I am not saying you should not make your own rifles this way - that is fine. But if you submit it to SAAMI, it will force everyone to test on that, and that will make it harder to load ammo which will freely drop into the chamber gauges.
Last edited by rsilvers; 07-24-2011 at 05:26 PM.
Just to clear up any confusion.
I have since 2009 been using the same chamber and stamping the barrels "6.8x43" dropping the Remington and SPC from the name. Some thought that was the old SAAMI chamber and I can understand why.
We now know the mil will never adopt the 6.8 or call it the 6.8x43 Nato. I am still using the same chamber from 2009 which was a result of trying to make a chamber fit some oversized ammo in the neck area. The chamber will shoot ANY factory 6.8 ammo and the hotter handloads, it is very close to the SPCII chamber that was changed closer to my design with a 45 degree cone angle in 2009. I changed toward the SPCII sized neck and the SPCII changed to my cone angle.
Now the barrels are simply stamped 6.8(chamber/ammo) ARP (manufacturer) They still have the 11.25 twist and 5R rifling with a larger than SAAMI sized bore area.
Trying to figure this out, i've done some research but just don't understand exactly what is being said. A lot of the terminolgy used is above my pay grade. I watched a video on youtube and generally understand what freebore is now, i believe when you say 2.41 for example you mean the OAL of the round, but other than that your speaking french. When talking about 80 and 45 degree angles, what are you talking about? Is there any way to stupify this so that someone with no reloading experience would understand the basic concept of what the difference is or a direction to go to find out? For the average shooter, what are the major factors/differences that i need to know?
I bought a Stag Arms Model 7 and was wondering if i need to buy any special ammo since its barrel is a SPEC II Chamber. Also i figured at some point i would start reloading, is there any special specs to go by when reloading for a barrel thats chambered in SPEC II or any 6.8 specs work for the average reloader?
P.S. please excuse my ignorance
Freebore, also known as the throat is the unrifled secton of the bore immediately ahead of the chamber. The 80 & 45 degree angle is where the lands (rifling) start and the throat ends. 6.8 ammo is dimensionally the same. Some factory ammo is loaded to a higher pressure (combat/tactical loads) like +p ammo and should only be used in chambers designed to shoot them. The chambers are where the difference is. When in doubt, contact Stag Arms on what's ok to shoot. Buy a book on reloading before you start. Safety first!
Hey! I learned something new. The 80 & 45 degree angle is before the throat. Thanks Constructor! Sorry 'bout that hotbrass.
Last edited by uplander; 04-04-2012 at 06:44 PM. Reason: correction on info
Behind the freebore. From the rear of the rifle it goes chamber, 45 degree angle, freebore, throat(angle 1.5 degrees), rifling.
All ammo as far as size will fit in all chambers, all reloading dies work with all cases and all chambers.