I recently bought a used Bushmaster XM-15, regular stock not collapsible. I shot it for the first time yesterday. The rifle feeds, extracts & ejects okay but there is a lot of vibration and noise from the buffer tube spring when firing. I know this is not normal because I've owned 2 Colt AR's and this is my second Bushy. Can anyone help me fix this thing??? The rifle looks almost like new...no signs of neglect/abuse. Did someone wear out the buffer spring by leaving it lay around with the bolt locked back or what???
Check the end of spring coils on the buffer spring and the buffer roll pin (should be flush with the sides). Often they have a bur that will scrap down the inside of the receiver extension/spring and cause some noise.
Also a little CLP on the buffer weights (will need to drive the roll pin out of the buffer) will take down some of the clanking noise of the buffer weights in the buffer.
Another item is to use very light grease on the inside of the receiver extension and on the spring to dampen the sprang/ spring against the side of the tube (in time, the anodizing will wear in the tube, and the grease should no longer be needed).
Last item is to confirm that the buffer spring is 11.75" and not a 10.5" carbine spring (also make sure that you are using the longer standard buffer, and not the shorter carbine buffer).
P.S. Since you have few other AR's around, wouldn't hurt to swap buffer springs to confirm that the one in question in not worn out. The springs will not take a set from the action being locked back, but some rocket scientist may have clipped a few coils to solve some phantom problem.
P.S.S. Why Is everyone posting in blue font???? Did I miss one of the fashion meeting again?