Quoted:
The clam-shell block will work pretty well to hold the upper without significant risk of damage to the upper beyond what any upper blocks pose.  I say that because these tools are still going to put any torque from barrel installation or muzzle device installation on the upper, and this can be a problem.  A barrel vise is both simpler and more secure.  It may leave smears of aluminum on your  barrel, but they come off with a good bronze brush and some solvent, and ALL of the torque is applied to the barrel (the toughest and most resilient part of the system).  It is especially important to use a barrel vise when installing or removing muzzle devices because the barrel is supposed to be kind of springy, and it will turn into a torsion bar when you crank on that flash hider - and transmit ALL of your torque somewhere else.  You NEED a solidly held barrel when installing the muzzle device or your torque (and maybe timing) will be way off.

Then why did the Colt instructor from the armorers school tell us that the clamshell is the best thing to rebarrel one of these things because it reduces the torque on the locator pin and groove in the upper?  Now a muzzle device still needs a  barrel vice.

Quoted:
Then why did the Colt instructor from the armorers school tell us that the clamshell is the best thing to rebarrel one of these things because it reduces the torque on the locator pin and groove in the upper?  Now a muzzle device still needs a  barrel vice.

Quoted:
I am not an armorer, but I understand the mechanics of this assembly task.  Compared to a bottom mount upper receiver block, a clamshell reduces the torque applied to the index pin and upper index slot.  But if you are using a barrel vise, there is almost no torque applied to the pin and slot.  This is because by the time you are putting any real torque on the barrel nut, the barrel is already locked up on the upper enough to STOP any movement of the index pin in the slot.  This happens at something like ten foot pounds, long before the pin could do annoying to the upper.  Not to say anything bad about the armorer instructor, but you don't have to be an engineer to teach a course about mechanics.  Having been a technical instructor, and having critiqued a fair number of other instructors (including military weapons training instructors), it doesn't take much to add good information to a course but to do it ineffectively and make things confusing or inaccurate.

Go ahead and use a clamshell, but it is still not superior to a barrel vise for holding the barrel and upper for installing, and especially removing, the barrel nut.

Quoted:


This the stance from the Colt instructor.
"More locator pins have been damaged due to using barrel vices than can be recorded"

I have changed literally thousands of barrels personally on this platform as well as watched other in the unit change thousands more and seen many many barrels screwed up and having to use maximum windage to zero when using the barrel vice but have never seen one utilizing a clamshell.  

Coincidence? maybe but since it goes in line with what we were taught by Colt, I'll will always stick with this opinion.

Quoted:
My cousin bought an upper vise block and it didn't come with an insert to fill the BCG area. Is this right?

I have owned the same block for a long time from Brownells so I figured I would ask.

Thank you.