Bushmaster Acceptance Inspection (8/07)

[ST911]

Highlights from an initial acceptance inspection of an officer’s Bushmaster carbine. Photos included below are of anomalous items, or items of particular common interest. Photos copyright by me, all rights reserved.

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Manufacturer: Bushmaster
Type: Carbine
Model: Undetermined (Pending)
Serial Number: L452###




Lower Receiver:

L-prefix serial number. Standard single stage semi-auto fire control group. Note seam on hammer and possible mold mark on left side of hammer. Mil dim receiver, hammer, pivot, and takedown pins. Drain hole in magazine fence. Hex bolt in grip screw.








Buttstock Group:

Common Bushmaster type. Commercial dim receiver extension. Circumferentially larger and longer (3/4") than mil dim. 6-position. Hole spacing uneven. End of extension cut at angle. Buttstock plastic. Form of current mil type . Loose fit. Receiver extension (castle) nut unstaked. Nut could be unscrewed without tools after two attempts. Standard carbine buffer, correct weight.






Upper Receiver:

Flat top. Eotech 553 mounted. BUIS is flip-up, Bushmaster OEM, retained by allen screws. No addressing on rails. Extended feedramp machined pre-anodizing.






Bolt Carrier Group:

Bolt bears “CM” engraving. Extractor spring assembly 4-coil spring with blue insert. Carrier key bears small rectangular indents for staking with no material intrusion on carrier key screws. Bolt carrier includes shrouded firing pin and semi-auto rear tang.










Barrel Assembly:

16” barrel, marked “B MP 5.56 NATO 1/9”. Chrome lined chamber and bore. M4-type step on barrel. A2-type flash hider installed and timed correctly. Gas block shaved style with Bushmaster OEM flip-up front sight installed over the top of the gas block. Sight retained by allen screws. Gas block and pins installed prior to parkerizing. Sling swivel installed with rivet. Barrel extension cut for extended feedramps prior to parkerizing. Handguards M4-dim, lightweight plastic, single pair black heatshields.








Gauging:

Passes pertinent gauges.


Other:

Michiguns Ltd. 5.56mm NATO chamber applied to chamber. Small amount of material removed from chamber.


Function Testing / Live Fire:

Pending


Required corrections:

Stake carrier key screws. Stake receiver extension nut to receiver end-plate. Replace OEM extractor spring assembly with carbine extractor spring assembly. Replace grip screw with slotted screw. Apply thread locking compound to all sight components supporting optic. Corrections for Eotech optic as per standing order concerning same.


Recommendations:

Conditional approval. Return for inspection at every 500 round and 60 day interval(s).

*END*
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[rob_s]

Those kind of look like M4 feedramps in there.

[Robb Jensen]

Those kind of look like M4 feedramps in there.

You're right. The only Bushmaster upper receiver I've ever handled that had M4 feed ramps was a Bushmaster piston upper.

[jmart]

Highlights from an initial acceptance inspection of an officer’s Bushmaster carbine.

Other:

Michiguns Ltd. 5.56mm NATO chamber applied to chamber. Small amount of material removed from chamber.

Ned posted his reamer specs over on a another site and his neck reamer runs a tad larger than even NATO specs. It has a longer freebore dimension (.0750 total length compared to .0500, .0566 standards) and it runs on the high side of the freebore diameter tolerance (.227). I know it's hard to characterize what constitutes "a small amount of material" but it's very possible the BM chamber was cut properly to NATO dimensions and the reamer removed a tad more. No real way to tell though.

Good writeup and good pics. While it's not terribly comforting seeing the flaws in the product, luckily they are easily correctable.

[shooter521]

Recommended corrections:

Replace bolt. Replace hammer. Return for inspection following live fire.

Why replace the bolt? Other than having the incorrect extractor spring and insert, what's wrong with it?

[Pat_Rogers]

My assumption is because it is not MPI

[dangertree]

Do I see CM on that bolt? If so, CMT bolt, likely is MPI.

[Pat_Rogers]

Bushmaster has publicly stated that they "batch test" bolts, meaning that they "test" one of a group. In other words, they do not test every bolt (and another shortcut taken)
If you have more accurate information as to their testing of bolts, please share it.

[Moose]

Bushmaster has publicly stated that they "batch test" bolts, meaning that they "test" one of a group. In other words, they do not test every bolt (and another shortcut taken)
If you have more accurate information as to their testing of bolts, please share it.

Pat, you are correct.

Out of interest, BM do in fact check the chrome plating on every barrel with a bore scope for what it's worth.

[ST911]

Those kind of look like M4 feedramps in there.

You're right. The only Bushmaster upper receiver I've ever handled that had M4 feed ramps was a Bushmaster piston upper.

They are indeed. In my experience, however, they're the exception not the rule. They have been seen on the Texas DPS guns, some NFA guns for gov end-users, and other special contract guns. Not the norm, esp for the commercial side.

I would still consider your chart accurate, Rob.