[robocop10mm]

It does sound alot like a rotated cam pin. The bolt is held in the carrier by the cam pin. The cam pin is held in place by the firing pin. The firing pin is held in place by the FP retaining pin. If the FP is not completely in place when the retainer is installed, the FP will not travel far enough forward to fire and can fall back and lock things up. If it falls back enough to allow the Cam pin to rotate, that can lock things up

The barrel extension is a separate piece from the barrel but is not replaceable. Once properly installed on a barrel, the extension becomes a part of the barrel.

My Bushmaster specifically allows steel cased ammo under the warranty even though I have never used any such ammo.

[crockett007]

UNINTENTIONAL
DISCHARGE COULD RESULT AND COULD CAUSE INJURY, DEATH, OR DAMAGE TO PROPERTY.
CAUTION: CAREFULLY READ THIS INSTRUCTION MANUAL PRIOR TO LOADING AND FIRING
THIS FIREARM. FOLLOW ALL INSTRUCTIONS ON THE PROPER HANDLING AND SAFE USE OF
THIS FIREARM - LIVES MAY DEPEND ON IT!
CAUTION: USE ONLY CLEAN, DRY, HIGH QUALITY COMMERCIALLY MANUFACTURED
AMMUNITION IN GOOD CONDITION which is appropriate to the 5.56mm NATO / .223 Remington
caliber of your firearm. Bushmaster does not recommend the use of remanufactured or hand loaded
ammunition because it may damage your rifle.WARNING: THIS WEAPON COULD CHAMBER A ROUND if it is dropped or jarred with a loaded
magazine in place - either with the Bolt Carrier Assembly locked to the rear, or in its forward position.
999 Roosevelt Trail
Windham, ME 04062 U.S.A.

[crockett007]

Originally Posted by WalterGA

I don't quite get the point of this reply, particularly the part in red. Every manufacturer warns against the use of reloads, for OBVIOUS reasons, so I'd assume I'm missing something?

This is a copy and paste out of the Bushmaster manual, illustrating there is no language regarding steel casings (specifically) voiding any warranty. Other manufacturers state specifically that steel cases are a bozo no-no. Confirming Robo's post for any one in doubt. Sorry about not offering a more detailed explanation.

Here is the exerpt from the DPMS manual:

AMMUNITION WARNING
Due to a number of calls and comments concerning AR-type rifles, we have incurred
feeding problems with the following:
A) 1. Israeli ammunition
2. Korean ammunition
We have heard and reviewed several reports of problems with many manufacturers’ rifles
using this ammunition. The problem appears to be the bullet contour and the overall
length of the cartridge, which is contacting the rifling before firing. This is creating a gas
port pressure and chamber pressure higher than recommended, therefore causing
feeding and extraction problems due to the increased bolt carrier velocity. In addition,
there is accelerated fatigue on internal parts. There are also indications that brass may be
oversized, which could create an unsafe condition.
B) 1. PMP
2. South African produced surplus
We have used this ammunition in the past for testing purposes and found that the brass
is extremely soft and can “flow” into microscopic pores and grooves in the chamber,
creating “sticky” extraction. This had been reported in many types of rifles, but is more
prevalent in semi-automatic weapons.
C) Lacquer Coated Ammunition or Steel-cased, lacquer coated ammunition
The problem with this ammunition is the lacquer coating on the case. As the barrel heats
up, the lacquer turns to a soft, varnish substance and upon cool down, becomes very solid
and difficult to remove. This effectively creates an undersized chamber and creates
understandable problems.DPMS recommends the use of high quality, domestically produced ammunition for best
results and highest accuracy. For plinking and practice, we recommend only domestic,
commercially manufactured ammunition or high quality surplus NATO specification
ammunition. Please note that the use of re-loaded ammunition voids the factory
warranty as well as the use of the above-mentioned types of ammunition.

Even though you felt it necessary to emphasize the obvious, the manufacturer includes the obvious with each and every rifle.