Firing pin striking primer on SP10, when auto loading ?

[rmiked]

I unloaded a chambered round this weekend using the charging handle. When at home inspecting the unloaded cartridge, I noticed a small indentation on the primer. Clearly the firing pin made contact when the BCG went into battery. I guess the firing pin spring isn’t strong enough to prevent the forward inertia of the BCG from moving it into contact upon the deceleration of BCG going into battery. I only have 67 rounds thru my new SP10 and have never looked at an unloaded cartridge before. The rifle operates flawlesssly. I guess this reinforces the rifle safety rules of never pointing a rifle at something you don’t want to shoot. Picture attached. is this normal?

 

[River44]

Yes it’s normal

 

[rmiked]

Thank you. I was hoping that was the case.

 

[diggler1833]

Thank you. I was hoping that was the case. If the FP spring was stronger, unreliable ignition might be an issue.

No firing pin spring in your Seekins, or any other AR. The hammer spring is what causes the hammer to move and strike your firing pin.

Either way, it is extremely common for the firing pin to bump the primer of the round being chambered. Some guys say to avoid softer cup primers (Federal non-"AR"is an example), others say that it is not necessary. I have never had a slam fire...but I've read enough anecdotal evidence on the interwebs that I stick to harder cup primers in my ARs just to be on the safe side (#41, CCI 200/400/450).

 

[mtrmn]

AFAIK- Armalite AR10 is the only AR I've ever seen with a firing pin spring.
Slamfires do happen. Rare, but they happen. I've had 1 in like almost 30 yrs of messing with ARs. Zero since the #34 and #41 "military primers" became available.

 

[rmiked]

Yes, I have not disassembled my BCG yet and assumed the FP had a spring. My mistake. Thanks for clarifying,

 

[bigjake83]

 

[LRRPF52]

I unloaded a chambered round this weekend using the charging handle. When at home inspecting the unloaded cartridge, I noticed a small indentation on the primer. Clearly the firing pin made contact when the BCG went into battery. I guess the firing pin spring isn’t strong enough to prevent the forward inertia of the BCG from moving it into contact upon the deceleration of BCG going into battery. I only have 67 rounds thru my new SP10 and have never looked at an unloaded cartridge before. The rifle operates flawlesssly. I guess this reinforces the rifle safety rules of never pointing a rifle at something you don’t want to shoot. Picture attached. is this normal?

I have never seen a floating firing pin auto-loader that doesn’t superficially indent the primer when going into battery. M-1 Garand, M-14, Mini-14, AR-10, and AR-15 all do it.

There have been articles about it dating back to the days of black & white American Rifleman:

Exceptions are:

ArmaLite Inc./Eagle Arms AR-10s with the sprung firing pin
Hk416 & 417 with sprung pins
Savage MSR-10 with sprung pin
New Knight’s Armament SR-25s have sprung pins

 

[rmiked]

Thanks for your detailed reply. I falsely assumed my AR firing pin had a spring. Being new to ARs, I didn’t know. My bias was to bolt actions. I disassembled my SP10 BCG today for familiarity and cleaning. No spring present as stated by others. Interesting that some ARs (you listed) have sprung pins. There obviously must be a balance between the energy delivered by the hammer (to the FP) and the resistance offered by the spring, for reliable ignition. I’m not concerned about unintended detonation based on the history of these platforms. I wonder what drove these manufacturers to have sprung pins? Eliminate reliability concerns associated with repeated chambering of unfired (but previously dented) ammo?

 

[msgriff]

If you handload/reload using 6.5 CM SRP brass, I would pay attention to primer selection. Also, don't drop the bolt on a chambered cartridge.

 

[TheOE800]

Floating firing pin

Exceptions are:

ArmaLite Inc./Eagle Arms AR-10s with the sprung firing pin
Hk416 & 417 with sprung pins
Savage MSR-10 with sprung pin
New Knight’s Armament SR-25s have sprung pins

LMT MARS-H as well.