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Posted: 9/30/2004 6:14:33 AM EST
[Last Edit: 9/30/2004 6:15:23 AM EST by _DR]
A friend of mine just bought a new Bushmaster M17S and was hand cycling live rounds to check magazine feed (yes, I told him it's not generally a good idea to cycle live rounds because of the risk of an AD/ND, but he is prior service infantry and a big boy, so I did not berate him too much).

Anyway, he noticed the ejected rounds had a dimple on the primer from the firing pin, presumeably from when the bolt group went into battery and the inertia moved the firing pin. He was wondering if this was normal for ARs with free floating firing pins such as the AR15.

Myself, I generally don't lock and load live rounds unless I am preparing to shoot at something, and have never experienced a no-fire incident, so I have never noticed the particulars on any unfired primers/cartridges after they were ejected.

What's the consensus? Is the primer dimple normal, or Slam fire risk? Is there any reason to be concerned?
Link Posted: 9/30/2004 6:19:59 AM EST
[Last Edit: 9/30/2004 6:20:27 AM EST by mr_wilson]
Normal, as AR15/M16s have floating firing pins...... not a concern.

Mike
Link Posted: 9/30/2004 6:41:05 AM EST
Normal.


www.ammo-oracle.com/body.htm#slamfire

Q. I chambered a round in my AR and then unloaded it later. The primer has a small dent in it, apparently from the firing pin. Should I be worried about this? Won't that cause a slam-fire?

A gas-operated semiautomatic operates on gas bled from the barrel. This gas is channeled to the bolt operator, which blows the bolt open and ejects the spent shell casing. A heavy spring then returns to bolt carrier to the closed and locked position on the next round. In the case of weapons with free floated firing pins (SKS, AR-15, etc.), the inertia of the firing pin carries it forward and it strikes the primer as the bolt closes. (The "slam"). Generally this will dimple the primer and leave a small indent. This isn't anything to worry about as primers for centerfire .223 and 5.56mm are pretty "hard" and aren't likely to be set off by this impact.

Early M-16s had a problem with slamfiring because of the firing pin design. Eventually Colt redesigned the pin to be lighter and therefore carry less energy into the primer.

Slam-fires are pretty rare in modern ARs provided they are well maintained but they can be caused by a broken or protruding firing pin, foreign matter on the bolt face that is carried into the primer, foreign matter in the firing pin assembly that prevents it from retracting sufficiently, overly soft or poorly seated primers, or other malfunctions.
Link Posted: 9/30/2004 6:44:09 AM EST

Originally Posted By _DR:
A friend of mine just bought a new Bushmaster M17S and was hand cycling live rounds to check magazine feed (yes, I told him it's not generally a good idea to cycle live rounds because of the risk of an AD/ND, but he is prior service infantry and a big boy, so I did not berate him too much).


You should - prior military/LEO is no excuse for stupid safety behavior


Anyway, he noticed the ejected rounds had a dimple on the primer from the firing pin,

He's prior military and just noticing this? (Trust me he's not the first - there was a report from Afghanistan on it last year - seems those people didn't know about it either even though it's been going on for the last 40+ years).


What's the consensus? Is the primer dimple normal, or Slam fire risk? Is there any reason to be concerned?

It's perfectly normal. But it's also the reason why I don't cycle live ammo through the rifle (that is what snap-caps are for); if you have commercial ammo with a light primer there is a small chance of detonation.
Link Posted: 10/1/2004 10:18:32 AM EST
Well, as long as people are going to talk about me - I figured I should respond...

First, I want to say thanks for the responses - I hate to admit that after 14 yrs of military service I had never noticed this during my 6 yrs in the Army as a Scout or 8 years as an SP. As an SP we did carry live ammo at all times (180 rnds state-side and 240 overseas), but we didn't carry on duty with one in the chamber of the M-16. (the Air Force version of lock and load is to lock the bolt forward THEN load the magazine - I know this as I received a LOR my first day on an Air Force Range at Lackland for performing the Army lock and load on the firing line - thanks to the AF range master for explaining that one prior to going on the line, I really enjoyed the *** chewing)

Also, with regards to safety - What _DR didn't know was that since I do not own a clearing barrel at home, I had lined up several cut plywood & OSB sheets, with a final backstop of two full brick pallets (and ultimately drywall and another layer of brick of my garage). Make shift at best, but I wouldn't have messed with live rounds without some type of backstop that was capable of stopping the round should an unexpected event occur. I felt confident that my NATO ball ammo could not penetrate that brick pallet backstop... Good point on the possible lighter primer on Commercial Ammo - I will definitely keep that in mind if I ever purchase any instead of NATO surplus (not that being NATO guarantees a better/safer primer)!! I have used snap caps in the past during Police training, but find that they do not do a good job of showing smaller scrapes/deficiencies during chambering as the plastic on mine was of a very good quality. and I wanted to see any feeding marks on the ammunition from some new magazines that I had recently aquired.

Thanks again to everyone for your quick responses!!
______________________________

Eagles may fly, but weasels don’t get sucked into jet engines.
Link Posted: 10/1/2004 10:29:15 AM EST
pigmypuncher welcome top the board


What up with your screen name ?
Link Posted: 10/1/2004 10:30:42 AM EST
Normal.
Link Posted: 10/2/2004 8:07:53 AM EST
[Last Edit: 10/2/2004 8:10:31 AM EST by pigmypuncher]
Originally Posted By u-baddog:
What up with your screen name ?

A friend of mine hacked my QII Chaos character name several (read many, many) years ago and changed it to PigmyPuncher. I didn't know for weeks, but thought it was funny so it stuck as my gaming name since I used the Marvin skin and later as my online name :)
Link Posted: 10/2/2004 11:32:50 AM EST

Originally Posted By pigmypuncher:
Originally Posted By u-baddog:
What up with your screen name ?

A friend of mine hacked my QII Chaos character name several (read many, many) years ago and changed it to PigmyPuncher. I didn't know for weeks, but thought it was funny so it stuck as my gaming name since I used the Marvin skin and later as my online name :)



He means Quake 2 (the computer game), with Chaos modification for those of you who are not into online gaming. Actually the name Pigmypuncher is kind of funny since he is about 6' 4"
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