An unavoidable task for anyone assembling an AR-15 type rifle is torquing the barrel nut. Old military manuals instruct the armorer to clamp the barrel in special aluminum vise jaws, torque the barrel nut to a minimum of 35 foot-pounds and continue tightening the nut until a notch aligns with the gas tube hole in the upper receiver. The upper receiver is free floating in this operation.
Civilians tend to go a different route by holding the upper receiver in the vise rather than the barrel. Clam shell devices that encircle the receiver are common as are receiver blocks like the DPMS Panther Claw. This technique works well with lower torque values but as the numbers climb the upper receiver and plastic holding fixture begin to twist in the vise. I have personally removed factory installed barrel nuts that required upwards of 100 ft lbs to loosen.
I have been aware for some time that factories use a splined holding fixture that fits into the locking recesses of the barrel extension. I was in the process of designing my own similar fixture for shop use when I found the new Geiselle "Reaction Rod" on the Midway USA web site. Bill Geiselle, the trigger guru, beat me to it. I swallowed my pride and ordered one immediately.
The "Reaction Rod" is a beautifully blued piece of one inch round stock with splines that fit the barrel extension on one end and 3 1/2-inch flats on the opposite end to secure it in a vise. Push the barrel into the upper receiver, start threading the barrel nut onto the receiver threads by hand and slide the whole assembly onto the Reaction Rod until the splines lock into the barrel extension. Tighten the nut with your wrench and torque as necessary. I torqued a barrel beyond normal limits and everything felt solid as a rock with no twisting.
Kudos to Bill Geiselle for this new tool.
The Reaction Rod
The Reaction Rod is manufactured from a 1-inch piece of round steel stock and is very rigid. It's hard to imagine a torque level that this fixture can't handle.
Rod in vise
Flats are provided on the rear of the rod to secure it in a vise. These are plenty long to let a big vise's jaws get a good secure grip on the tool.
Slide the upper receiver with barrel installed over the rod until the splines lock into the barrel extension. This gives steel-on-steel contact for maximum strength.
There's no twisting of relatively soft aluminum with this setup. You can use all the torque you find necessary, and don't even have to remove sights to change barrels.