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Must Have M4 Specialty Assembly Tools
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Quote:
Originally Posted by
Rifleman_04
I’d skip the geissele reaction rod and get standard receiver blocks. Seen too many tweaked uppers from the reaction rod style.
I use a reaction rod to assemble and a clam shell to disassemble. The nice thing about a reaction rod is the massive flexibility in positioning your work.
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Use a MI URR or 2Unique barreling spud instead of a G Reaction Rod and you won’t twist up your upper. And its compatible with the Vltor uppers, etc., unlike a clamshell.
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Quote:
Originally Posted by
Rifleman_04
I’d skip the geissele reaction rod and get standard receiver blocks. Seen too many tweaked uppers from the reaction rod style.
The problem with receiver blocks is that they made from plastic and flex when torquing the barrel nut. The flex makes lining up the gas tube harder than it needs to be.
Receiver blocks do not prevent the barrel from turning while torquing the barrel nut. Six to one. A half dozen to the other.
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Quote:
Originally Posted by
prepare
I wouldn't consider the fitting pin a "must have". It would be nice to have for popping pins out, but useless for installations. By the time I got the holes lined up to insert the fitting pin, I might as well as insert the trigger/hammer pin.
When it comes to installing a trigger, my "must have" tool is a slave pin for the trigger disconnect.
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Quote:
Originally Posted by
Rifleman_04
The flexibility is nice for sure but the reaction rod style puts all of the torquing force on the aluminum upper and the index slot and deforms it. Not a good tool especially for people who prefer running a fixed fsb on the barrel.
Not necessarily true.
You have three parts, the barrel, the barrel nut and the upper, you can hold any one of them still and turn one of the others to torque the nut, since the nut is rarely held stationary, we only need to look at holding one of two parts, the upper or the barrel, stationary.
So, let's look at the loads on the various parts when torquing the barrel nut:
1) Hold the upper and turn the nut - the nut will contact the flange on the barrel and the barrel will try to rotate with the nut, the only thing keeping the barrel still is the index pin, so what is the load on the index pin? Assume maximum torque of 80 ft-lbs, lubrication on the barrel flange and threads.
The torque on the barrel flange trying to turn it will be the clamping load times the coefficient of friction between steel-on-steel, if greased that will be .016, times the moment arm (approx 0.5 inch). Calculating the clamping load yields 960 pounds. So the total load on the pin is = 77 pounds.
2) Hold the barrel (either by reaction rod or clamping in a vise) and turn the nut. The drag of the nut on the aluminum threads will try to turn the upper and, again the only thing preventing rotation will be the pin.
The drag on the upper will be the clamping load times the coefficient of friction between steel-on-alumium, if greased is again 0.16, times the moment arm. The clamping load is the same, the moment arm is the same so the load on the pin is the same 77 pounds.
The only time problems arise is when you do not grease things properly. If you omit the grease the load on the pin in Case (1) jumps to 216 pounds, and for Case (2) 312 pounds.
If you use grease and assemble as described in TM 9-1005-319-23 & P, there is no difference in the loading of the index pin no matter how you hold it. If you really have to reduce the load on the pin hold both the barrel and the upper still when you torque the nut.
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The reaction rod lugs go into the steel locking lugs in the barrel. Not the aluminum upper.