January 16, 2017 at 10:14 pm #50978
I was looking at some AR15 and M16 bolt carrier groups. It appeared to me that the main differenced (from a safety standpoint) is that the M16 BCG doesn’t look like it will detonate out of battery. There appears to be about a .001-.002 difference between the two type BCG’s as to where the firing pin will strike a primer. If this is indeed the case, I don’t see why all AR builders don’t use an M16 BCG during their initial build/test fire process. It just seems to be safer.
Is this indeed the case? Is the M16 BCG made differently so as not to detonate out of battery?
http://ageofdecadence.comJanuary 17, 2017 at 3:39 am #50981
The only difference is at the back end.
The full auto carrier hasn’t been cut away, both lightening the SA carrier and removing the part that trips the auto sear.
Both work fine.
Depending upon what type of gun I’m building will depend on which carrier I use. It’s a balance thing.
Go with whichever is cheaper.January 17, 2017 at 4:38 pm #50985
If the only difference is at the rear end it would seem to be a heavier vs. lighter question. I believe the original designers specified the heavier carrier but I’m not sure why. More reliability. Smoother action. Longer life …. safety? Maybe you can avoid the whole question by using a titanium firing pin.January 17, 2017 at 6:12 pm #50991
Titanium FP has nothing to do with out of battery firing. The bolt carrier moves rearward enough that the FP cannot make contact once the bolt carrier has moved @.036″. The bolt is still locked in the barrel extension at that point.
Unless you have a broken FP, there’s basically no way for an out of battery “firing”.
The full auto carrier is original, the missing section times and trips the auto sear in those guns.
Actually lighter can be better, less mass slamming back and forth, reduced recoil perception.January 17, 2017 at 11:37 pm #50996
I know that there is a difference (I broke out the calipers) between where the FP actual is able to stick out as the bolt goes into battery. I checked 4 different M16 BCG and 9 different AR15 BCG of different types such as the 1/2 moon, hybrid, etc. All 4 M16 BCG allowed the bolt to rotate totally into battery before the FP was exposed. Only 1 of the AR15 worked the same and it was a “hybrid” that my brother had purchased at a local gun show.
Update: I did speak with an Armorer (Army) that is still AD. He measured, checked, and then read up on it. It appears that per military specs the M16 BCG are designed to never fire out of battery. There is a .001-.002 difference in the length of the tube the FP goes through. This gives just enough space to ensure the bolt fully turns and locks into battery. They do this so that wrongly timed full auto rifles will not accidentally detonate out of battery and thus leave a soldier injured or without a weapon. I still have not found any reference to this, but it does make sense. He said that he referenced the Master Armorer’s book, whatever the hell that is.
My whole point with this discussion was based around the safety of having detonation out of battery taken off the table as a possible failure when building your own AR. Let’s be realistic: lots of crap can happen when you are working on your rifle. If you knew that you wouldn’t accidentally detonate out of battery by swapping a BCG, wouldn’t you consider it during test fires? Say you swapped triggers and were first testing it? ETC….
I found my answer through other channels, but it is good information to have. I know I will be picking up a few more just for the initial firing of my rifles after a build/upgrade.
http://ageofdecadence.comJanuary 18, 2017 at 1:51 pm #50997
The FP ‘tube’ has zero to do with bolt timing.
If the carrier is improperly drilled, it can effect FP depth of penetration. But that’s not a timing issue with in spec parts.
What can effect lockup timing is the can pin hole locations (and angles) both in bolt and the carrier. A properly timed BCG is rotating into lockup as the FP is just beginning to be able to move forward enough to move past the breech face. Hence the FP dimple, not enough energy to pop the primer but still marks it.
As long as the parts are within spec, you should be good, FA or SA.
The other difference in some SA carriers is the relief cut that exposes the FP ring. This only matters if your hammer follows the BCG home, meaning you have a screwed up FCG.January 18, 2017 at 10:38 pm #50998
Sledjockey, if you really want to see something detonate remove the cam pin. If you thought someone was going to steal your rifle, or you were just doing a bit of mischief to the enemy. The armorers manual may have a how to sabotage or how they might do it to you. It might pay to get one.
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