New Barrel Time

[PhilC]

NSS offers throating for Shilen barrels but not Criterion. My Shilen 7BR was throated to dummy rounds I provided.

[charlie b]

For cast bullet shooting knowing the throat is important. The easiest to measure is to use a 'pound cast'. A slug of lead (sometimes a slightly larger dia bullet) is placed in the chamber neck. Then a rod (I use a brass one with taper around it) is used to pound the slug into the throat. Not all the way, just enough to get it into the main rifling. Then use a rod from the muzzle (again, protected from the bore with tape) and tap it back out. Then you have an impression of the throat.

But, bullet OAL is a different thing. The eld type bullets have a long ogive section so they are seated well out if you want to touch the lands. I've had some, like the 155 Hornady ELD, in my .308 that cannot be seated out far enough to touch while the 155 Bergers were just fine with a slight jam. The .223 I could seat the 77gn SMK's just fine but the Hornady 75gn ELD's were too long for the mag. And that was after 4000 rounds.

The CBTO is a decent way to determine where each bullet will touch the lands. Using the dummy case and seat it until the bullet touches, then use the gage to measure the CBTO. It gives a good reference point for your rifle. One thing to keep in mind is the bore on rifles may be different. My bore on the .308 is 0.302". So the CBTO I measure will not be the same as yours.