As many know, I recently received my BM LE account. Well today I got my first shipment of their super light carbines. (http://www.bushmaster.com/catalog_xm15_BCWA3F16SL.asp)
Since this is my first order, I thought I would take the time to document what I found.
On initial inspection, the weapon looked very good and clean. No dings, scratches or blems. I did notice two things though, the castle nut was NOT staked and the FSB was not F marked. Upon field stripping the gun, I found that the gas key was barely staked (meaning that that the stakes were not actually touching the screws) and that the screws used in the gas key were on the small size (head diameter was undersized). This issue can result in a gas leakage problem. I then removed the extractor from the bolt and found a blue extractor insert.
The gun came with M4 feed ramps, carbine buffer and a commercial receiver extension.
Un-staked Castle Nut
Poorly staked Gas Key
Blue extractor insert, no Crane O-ring
M4 Barrel extension and M4 upper receiver
The small gas key screws really needed to be addressed so I went about removing them. I was interested in seeing how much inch pounds of torque it would take to remove these screws. The first screw came out at about 36-40in lbs.
Torque setting for removal of gas key screws
Once the screws were removed I looked at them and the gas key for any signs of adhesive. None was used. Using light torque, no adhesive and light staking is a recipe for disaster IMHO.
As I said earlier, the gas key screws looked on the small side to me. I was right. My calipers tell me that they were on the small side and no amount of staking was ever going to get the sides of the gas key to touch the screws. So I changed them out for heat treated, aircraft certified torx screws.
Size of the BM factory gas key screws
Size of Torx bolts we replaced the factory gas key screws with
I followed the following steps for the installation of the gas key:
1. Degrease the gas key, bolts and bolt carrier.
2. Verify that the gas key base is square.
3. Apply a THIN coating of rocksett onto the torx screws.
4. Torque down the screws to 60in lbs.
5. Stake the gas key properly.
Degreased bolt carrier, gas key and Torx screws
Rocksett getting applied
Torque setting for re-installation of gas key screws
Gas key getting staked
Finished product
After the gas key was re-installed, I moved onto the bolt extractor. I changed out blue extractor insert for a black one and added a Crane O-Ring. I then upgraded the carbine buffer to an H buffer. Moving onto the castle nut, I double checked the torque setting on it and then staked it.
Upgraded extractor
Staked castle nut
Factory Carbine buffer and installed H buffer
The last issue that seems to plague many shooters is the low front sight base. This one was NOT rated for a flattop (F marked) and so I went ahead and installed a taller front sight post.
Comparison of the two front sight posts (factory post on right)
Taller front sight post installed
Now we are all done and everything is good to go and back together. That wasn't so hard now was it?
C4
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