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The installation of the Suppressor is all important if accuracy is to be expected, at the same time there is little you can do to correct issues if they are present other than try a different Suppressor.

There are differences between the USGI and Commercial Suppressors beside one being cast, actually there were some cast USGI Suppressors, Chances of having cast USGI Suppressor is remote.

For above reasons I will try to concern the installation to Commercial Suppressors, they have the most issues of proper installation when being used on a Commercial barrel. Lumping the possible issues together and some measure of over-coming them.

The Commercial Suppressors that have a cast in modification similar to the reamed USGI Suppressors is of unknown quality.. I have used them and had little trouble except the seating surfaces between the barrel muzzle and the seating surface inside the Suppressor are rough.

The barrel muzzle is easy to smooth off with a good Stone, making certain to stone a slight radius on outside edge of the muzzle. This radius is important because the 90 degree angle of the Suppressor seating surface often not a sharp 90 degrees. As a rule I chase this 90 degree angle with a carbide edged tool scraping off all unwanted left overs.

Once the above is complete trial fit the Suppressor and hand tighten the Lock Nut. there should be not rocking movement, alignment can be checked at this point. A USGI Suppressor Alignment Toll is best to check with.. Lets assume the alignment is good, being perfect is not likely, perfect is difficult to achieve and to determine in any case. If alignment is poor try a different Lock nut. USGI Lock nuts are not hard to find, they are superior to Commercial look- a- likes..

The USGI Lock nuts are machined leaving an inside collar to prevent the Nut from going past the threads on to a USGI Barrel. So it can only be screwed on so far. This may not be true with Commercial parts.

The threads used to attach these three parts is of a nature that the torque is high at lower pressure, if lube is used pressure is higher yet. I mention this because the single biggest problem is over torque on the Lock Nut..

To achieve proper torque is to stay on the side of lightness on the wrench. The USGI Lock Nut wrench is designed to butt against the Suppressor in a position that the next wrench slot is positioned for final draw up with reasonable pressure.. No grunting. I like to remove a small amount of material off the bottom of the Lock Nut so the slot meeting first resistance will move will light pressure under the Suppressor, advancing the final slot the dia. of the now hidden slot. This position works well and does not stress the muzzle. You do not want to stress the Muzzle. I do use a light coat of lube on the threads.

A poorly installed Suppressor will ruin what otherwise can be an excellent shooting rifle.

As a footnote:

When the US M14's were tested for accuracy a good deal of the poor accuracy performance was a result of improper assembly. A few M14's that preformed very poorly were later re-assembled properly by Sgt. Donovan and an amazing improvement resulted.. The proper assemble of the Gas System and Suppressor is a must... Art L.
 

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The USGI Lock nuts are machined leaving an inside collar to prevent the Nut from going past the threads on to a USGI Barrel. So it can only be screwed on so far. This may not be true with Commercial parts.
I have two castle nuts in front of me now. One I took off my 1997 SAI which I always suspected was all USGI, and a new castle nut I recently acquired (for free). The 1997 castle nut does indeed look different in the places you can't see from the outside. There is a much wider machined surface that seats against the flash suppressor and it indeed will not screw all the way down on the barrel when I tried it without the suppressor installed. I'm not so sure this is an important feature, but the wider contact area sure seems like it is; that's where all the clamping pressure is applied. The new castle nut has very little seating area... looks nil, like it wasn't even a consideration. The only way I'd consider using the new one is after machining a wider contact area on it.

Wow, this is esoteric stuff. Who would have ever thought to look inside a castle nut?

Thanks again, Art Luppino.
 
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