I assumed the parts on an AR15 bolt would be similar, if smaller, than the parts on an AR10 bolt. I sold my AR15 years ago, and maybe my memory is foggy, but...

...I don't recall that the firing pin on the AR15 was "spring loaded." But the firing pin on the AR10 is.

Might someone with knowledge on this subject tell me if my memory of the AR15 bolt has faded, or whether just th AR10 firing pin is spring-load. And, if it is only the AR10, just what is the purpose of the spring on the AR10 bolt?

Thanks!

You're remembering right.

There was some trialing of spring loading the .223
AR, along with several different pin designs, to
deal with pin-primer cycling impacts, early in
development. The current design was selected,
and no return spring was needed.

Ahh...thanks, Steve. So, pin-primer impacts were determined to not be a problem in AR-15s, but are a problem in AR10s? That's kind of scary...and I wonder if the spring sometimes leads to light primer strikes?

No knowledge on situation with AR-10...just the
Defense Dept. had concerns over the dimpling of
primers in the M16, and time and effort was put into
it. Don't recall if anything I've read even said there
were any cases of slam firing...may have just been
something someone didn't like, you know how that
can go!

Actually, at one time, as noted above, slam fires were an issue with the M16. The firing pin was redesigned to eliminate/minimize the issue (made lighter, IIRC). The minor ding you see on a primer in the AR15 isn't an issue, but you don't want to keep chambering the same round over & over.

I expect the AR10 firing pin is more robust and needs a retraction spring/uses a floating firing pin. The M16 to be was a scaled down AR10 and they may originally skimped on changing the firing pin or at least changing it enough.

Both my Armalite AR-10 and Savage MSR-10 have the spring. So far no light pin strikes.

__________________
Stay safe people!

As I understand the issue, the mass of the AR-10 bolt carrier, bolt and firing pin combined with a stronger recoil spring was either believed to be or proven to be a combination that could lead to a slam fire; hence the addition of a firing pin spring to dampen the forward inertia of the firing pin.

I've not had any negative issues with this arrangement on my M&P 10.

I haven't had any issues, either...but I'm only using good quality, 168-grain brass case .308 ammo.