A day in the life of a BM LE Dealer

[C4IGrant]

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 so I dialed my torque wrench to 40. The first screw came out at that setting and I believe that it would have come out with even lighter torque (maybe 36). The second screw came out at 48. What I find interesting is that each screw had their own DIFFERENT torque setting. This leads me to believe that BM is NOT using pre-set torque wrenches.

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

[C4IGrant]

All done and ready to go!





C4

[markm]

Very thorough indeed!

Are you sure the FSBs needed the sight post changed? I mean... is it possible they just didn't have an "F" stamped into them?

[C4IGrant]

Originally Posted by demigod

Very thorough indeed!

Are you sure the FSBs needed the sight post changed? I mean... is it possible they just didn't have an "F" stamped into them?

I measured it and it was shorter than an F marked FSB. The taller front sight post just gurantees that the end shooter will be able to use whatever BUIS they want.


C4

[gotm4]

Very cool.

[JB2000]

Excellent work! You should offer that as an upgrade package to all of the Bushmaster and other "tier 2" owners out there. My Stag came with the blue insert, standard buffer, and un-staked castle nut. I've fixed the first two but need to torque and stake the castle nut still.

[C4IGrant]

Originally Posted by JB2000

Excellent work! You should offer that as an upgrade package to all of the Bushmaster and other "tier 2" owners out there. My Stag came with the blue insert, standard buffer, and un-staked castle nut. I've fixed the first two but need to torque and stake the castle nut still.

I often times do, but generally BM owners tend to believe that their weapons are perfect and need no "upgrades."


C4

[Paulinski]

Excellent upgrades Grant.

This is the way Bushmasters should arrive from factory.

[markm]

Originally Posted by Paulinski

This is the way Bushmasters should arrive from factory.

They should be matching the correct FSBs to flat top receivers. I can't believe they don't do so.

[AMMOTECH]

Good Job!
I'm glad to see that you took the suggestions of AR users and fixed BM's mistakes.
If only BM would take those few extra steps and put out a properly assembled M4.


I now know where my next major gun/accessories purchase will come from.

[C4IGrant]

Originally Posted by AMMOTECH

Good Job!
I'm glad to see that you took the suggestions of AR users and fixed BM's mistakes.
If only BM would take those few extra steps and put out a properly assembled M4.


I now know where my next major gun/accessories purchase will come from.

It may look like I put a lot of time into this, but it realy only took me 10 minutes to do.

You are right though, there is no reason why BM cannot do this stuff in house as it is all very simple.


C4

[Wayne Dobbs]

Is there a fixture out there (other than the Mk I, Mod 0 eyeball) that can also tell you if the FSB is mounted squarely? I've seen quite a few BMs that wouldn't zero without using up most of the windage adjustments due to FSBs that were mounted off-square.

That should be another issue addressed in your inspection/upgrade process.

[C4IGrant]

Originally Posted by Wayne Dobbs

Is there a fixture out there (other than the Mk I, Mod 0 eyeball) that can also tell you if the FSB is mounted squarely? I've seen quite a few BMs that wouldn't zero without using up most of the windage adjustments due to FSBs that were mounted off-square.

That should be another issue addressed in your inspection/upgrade process.

I am aware of this issue, but know of no tool to measure cant. I do my best to eyeball them and am usually good at spotting issues.


C4

[M4arc]

That little carbine is ready to roll now!

Nice work C4.

[jhs1969]

My last two BM M4's needed the taller sight post. After calling BM to complain and order the sight post they sent it twice in two years with no charge. They seem willing to adress any issues their customers have. They offered to hand stake my BCG but instead of the shipping expense and downtime I did it myself. I'm certainly not going to make excuses for them but their rifles seem GTG after a few simple mods. I also strongly feel they should not need any mods for the price they are sold for. I haven't stake the castle nut yet as I plan to eventually add a different stock and mil spec tube, in the interim I check for any looseness everytime I use it. Instead of upgrading the bolt I plan to shoot it till failure then replace it with an upgraded MPI bolt. My wife now claims the BM M4 and had me put it back to it's original config. She likes the KISS principle of iron sights and standard M4 handgards. I transfered the KAC RAS, Aimpoint ML2/ARMS, Troy BUIS, GGG vert. grip to my new LMT with SOPMOD stock and am happy I also feel lucky to have two smooth running M4s for her and myself Next big decision will be ACR or SCAR

[Skintop911]

Looks like a pretty typical Bushmaster on arrival. The standard continues to be mediocrity.

A gun with that PM should be quite serviceable when live fire testing verifies function.

Grant- Did those come with a "CM" bolt?

[C4IGrant]

Originally Posted by Skintop911

Looks like a pretty typical Bushmaster on arrival. The standard continues to be mediocrity.

A gun with that PM should be quite serviceable when live fire testing verifies function.

Grant- Did those come with a "CM" bolt?

Negative on the CM bolt.


C4

[C4IGrant]

Originally Posted by M4arc

That little carbine is ready to roll now!

Nice work C4.

Thanks. It is a nice and light weight carbine. A good entry level AR I think.


C4

[Razorhunter]

Grant,
I don't know what kind of machines you've got (if any), but I assume if you are pinning FSB's (as I've seen in the past), you've possibly got a mill?
If so, a number of jigs can be made to align and check the alignment of FSB's.
I know that Kotonics advertises that they "laser align" their FSB's before and during installation.
Might be something to look into.
Like you, I'm good at eyeballing them, and I can catch a FSB that's off by only a couple degrees with my naked eye.
Just a thought. I'm a total freak when it comes to the FSB being straight, after having a couple 6920's with crooked FSB's. (granted, I don't think Colt pinned them crooked, but rather, the torquing of the bbl nut caused the indexing pin to allow the bbl to rotate in the upper).
Anyhow, it's always nice to have a perfectly aligned FSB.
I know AR15Barrels.com (Randall I think is his name?) has a simple jig that he milled to check and re-align FSB's for customers.

Got your email. Contact info sent. Call ANYTIME tonight or tomorrow.

[C4IGrant]

Originally Posted by Paul Cataldo

Grant,
I don't know what kind of machines you've got (if any), but I assume if you are pinning FSB's (as I've seen in the past), you've possibly got a mill?
If so, a number of jigs can be made to align and check the alignment of FSB's.
I know that Kotonics advertises that they "laser align" their FSB's before and during installation.
Might be something to look into.
Like you, I'm good at eyeballing them, and I can catch a FSB that's off by only a couple degrees with my naked eye.
Just a thought. I'm a total freak when it comes to the FSB being straight, after having a couple 6920's with crooked FSB's. (granted, I don't think Colt pinned them crooked, but rather, the torquing of the bbl nut caused the indexing pin to allow the bbl to rotate in the upper).
Anyhow, it's always nice to have a perfectly aligned FSB.
I know AR15Barrels.com (Randall I think is his name?) has a simple jig that he milled to check and re-align FSB's for customers.

Got your email. Contact info sent. Call ANYTIME tonight or tomorrow.

We do not pin/install FSB's and yes you are correct, there are custom made jigs for that.


C4