View Full Version : Spare parts

December 31, 2012, 02:47 PM
Anything mechanical has a failure rate, what are the most commonly replaced worn parts on the AR15 platform (S&W M&P), what would be reasonable to try and acquire to make sure the one I own lives forever.

Obviously two of everything on it would be grand, but now likely more like 3 grand...:(

I would just like to know if something breaks I have one in my closet, not have to scour the web after the fact.

Any resources on duty cycles on the individual parts would be great.

Thanks in advance.

December 31, 2012, 03:05 PM
Look at what is critical to operation and what takes a beating or heavy use:

- firing pin
- bolt, lugs can break off but more likely the extractor, extractor spring, ejector spring
- bolt cam
- bolt o-rings
- hammer spring
- trigger group
- buffer spring
- buffer retaining pin

Then I would look at what could easily get lost during field or detail strip:
Pretty much every pin and spring, and the cotter pin that secures the firing pin.

To make it easy, maybe a lower parts kit and a spare complete bolt. Might want to add a gas tube. The bolt would be my top priority or a bolt rebuild kit.

Sure I missed a few things but that is my first thought.

December 31, 2012, 03:12 PM
Aside from just some manufacturing fault or freak accident, any idea what the duty cycle on any of these are?

I have not owned it long, < 1k rounds since it was new, cleaned meticulously after every range visit.

I see things that were once black are now shiny, but cannot see any visible signs of anything other than cosmetic wear on anything.

essentially is there a point where something should be replaced because of use *Just to be sure* like changing the oil, or keep it clean then run it till it breaks?

December 31, 2012, 03:40 PM
A spare bolt, firing pin, and complete lower parts kits will keep your AR running for a very long time...

Before the craziness, ~$130 of parts.

January 1, 2013, 07:19 PM
Ok, thanks folks.

Metal god
January 1, 2013, 07:34 PM
Here is a similar thread


January 1, 2013, 10:52 PM
If you keep spare parts you are much more likely to need one because you lost something than you ever will be because you wore something out or broke it.

January 2, 2013, 12:56 PM
A complete bolt should be in every AR owners range bag. After that, a lot of it depends on the specifics of your build.

Bolt carrier with a new cam and firing pin would be good parts to add after the bolt.

I would probably go with a gasblock and gas tube next.

Next a charging handle.

Then a complete set of springs.

Then a bolt rebuild kit.

I don't use buffer retainers or forward assists at all. They are prone to breakage so I just strip them out if I end up with a lower that has those parts and never buy them when I build new.