I like the rifle. Once an initial bolt tightness was alleviated after a break-in period, the rifle has been rock solid reliable and digests even really cheap low power reloads consistently. I equally enjoy using the rifle for target shooting, hunting coyotes and occasionally plinking.
One thing I did not like about the rifle was the Reno-Era fixed stock. It is a flat-top rifle and I shoot it with both the carry handle sights and a large 10x fixed-power scope. Since the scope is large, fitting eye-relief to both it and the carry handle can be awkward. And, to be perfectly honest, the fixed stock does not look right on a rifle with a carbine-length barrel and Bushmaster Dissipator front end.
Luckily, Bushmaster makes and sells their factory-fit six position stock as a direct replacement. It comes with everything needed for the swap and is a bargain at a bit over 100 clams. I originally tried to buy the stock from a large Midwestern company that sells shooting supplies, but in today's political climate, keeping these in stock was apparently not possible; my purchase was cancelled by the vendor after a considerable back-order dealy. I ended up purchasing it directly from Bushmaster, part number F1000360.
As mentioned, the kit comes with everything needed for the swap, sans instructions. While it isn't needed, an AR15 combo wrench is a handy thing to have.
We start with ensuring the rifle is not loaded and the gun secured in a vice.
I've heard horror stories about how hard the stock can be to get off of a factory Bushmaster rifle. I do not have copious upper body strength and so I was prepared for the worst, ready to use an impact driver if needed (or possibly even cut off the old stock). However, a twist with a large screwdriver easily removed the upper screw on the stock; the factory nylon locking material only marginally resists turning the screw. Once the screw is out, the fixed stock slides off of the existing buffer tube.
The lower receiver can then be removed from the rest of the rifle per factory manual. Once the two halves are separated, the existing buffer can be removed from the buffer tube by pushing down on the buffer retaining plunger and pulling out the buffer. Then push down on the buffer retaining plunger and unscrew the buffer tube. This will be snug, but shouldn't be too tight. An AR15 combo wrench or standard 5/8 wrench is used to remove the buffer tube. Once unscrewed, be careful not to lose the buffer retaining plunger or the rear take-down pin spring.
The rear take down pin detent spring is held on by the fixed stock. In this picture, the spring is put back in place prior to reassembly.
Install the included castle nut on the new buffer tube, then slide the buffer plate on the buffer tube as shown in the picture. With the new stock, the buffer plate holds the take-down pin spring in place.
Install the buffer plunger and hold the plunger down while screwing in the buffer tube until the plunger is appropriately held in place by the cut-out in the tube. This is where buying factory parts is nice as the buffer tube has a small cut-out which perfectly holds the buffer plunger in place while also allowing it to retain the buffer. Some after-market parts may require a bit of fitting.
Hold the plate against the rear of the receiver and tighten the castle nut against the plate. Use an AR15 wrench to tighten the castle nut securing the new stock, plate and receiver all together. The castle nut needs to be tight, but not threadstripping tight. It does not need locktite, nor does it need to be "staked." Channel Locks or the like can be used to tighten the castle nut, but that is gorilla gunsmithing. The AR15 wrench is really nice here.
The new stock can now be pushed onto the buffer tube by pulling down on the pin that holds the stock in position. To install, it needs to be pulled down farther than can be accomplished with the stock adjustment lever. Once installed, the adjustment lever can be used to slide the stock for and aft.
Push down on the buffer plunger and install the new buffer spring and new buffer. Once released, the buffer plunger should securely hold the buffer and spring in the buffer tube.
The stock is now installed on the existing receiver. This entire operation should be doable within about 30 minutes. It is a good time to clean the rifle since it is apart anyway, stretching the time only marginally.
Finished, the adjustable stock is functional.
And, with a ridiculously large fixed 10x scope (which is almost as long as the barrel), it is ready to make some noise.
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