Home AR-15 Smyth Busters: AR-15 Small Parts Kits Are NOT All the Same

Smyth Busters: AR-15 Small Parts Kits Are NOT All the Same

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There’s an old saying, “Part is parts.” So all AR-15 small parts kits are pretty much the same, right? That’s the notion going around on the Internet. But is it true? Let’s get some truth today from Brownells Gun Tech™ Steve Ostrem and Mike Mihalski, founder and owner of Sons of Liberty Gun Works (SOLGW), a guy who knows a LOT about AR-15 parts. AR-15s rarely break down because a major component fails. Stoppages are usually the result of a little $2 spring breaking and bringing the whole rifle to a halt. Mike says the difference between a highly reliable AR-15 and one that’s iffy IS those small parts. Even a “mil-spec” AR-15 trigger is capable of delivering a consistent pull with a clean break, heavy hammer strike, and a positive reset – all hallmarks of a “good” trigger – IF it’s manufactured to strict tolerances. The most problematic part from the generic small parts kit is the bolt stop, which has to take the stress of stopping the bolt with all the mass and energy of the action spring behind it. Put a substandard bolt stop in your AR, and you’re headed for trouble. Inspect parts before you install them in your rifle. If a part doesn’t fit well, it’s probably out of spec. So the myth is BUSTED. Small parts kits are NOT all the same! Do yourself and your rifle a favor: get a high-quality AR-15 small parts kit, such as one from Sons of Liberty Gun Works.

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35 COMMENTS

  1. As a career long auto mechanic it never ceased to amaze me how many high end auto owners chose to go with the cheapest possible parts found . But many once big brand names anymore are just that . A name . With firearms I choose O E from the maker .

  2. I did a build a while back with a CMMG lower parts kit and took it to the range and it had multiple light strikes. The range boss who was a former marine armorer broke it down but couldn`t find the problem. But once I got home I went over it with a fine tooth comb and found it to be a weak hammer spring witch I replaced with one from Brownells.

  3. Best trigger group I've found is the Rock River Arms 2-Stage National Match. It drops in, has a powerful hammer spring to take on hard Russian primers with a faster lock time than mil-spec. It's beautifully crisp at 3 to 3.5 pound, that only gets smoother better the more it's used. All Mil-spec triggers there after will feel like your dragging a dead cow across a 4-lane highway (long, rough and heavy as hell). For all other internals and springs I use genuine Colt. Buy the best, forget the rest… As to the hammer/trigger pivot pins I use KNS Precision, Inc. Non-Rotating pins with keepers (NRTHP Mod.2 – 1555 kit). This way the receiver never suffers any hole wear… ^~^

    edit: my spelling is utter rubbish at the best of times… 0~o

  4. I like to build with ambi parts kits and the only one's I've found on the market are CMMG. Still though, I prefer to toss out the hammer and trigger pins and go with KNS anti-walk, anti-rotational pins. I also dislike the standard A2 grips and swap them out with an Ergo Grip rubber grip. I like to throw in an XMR extended mag release, the Odin Works Gen1 works well and just clears the KNS bar between the pins. It would be nice if someone made LPKs that came standard for ambi use and gave the option of picking out a different grip.

  5. Glad someone finally speaks up to the mass about this lol. That’s why I only use cmmg LPK’s for the most part because everything from their mag catches to their springs are great in fit and finish. I’ve used SOLGW and CMC LPK’s and they’re good (better than most) but some of the parts have finishes that are a bit too thick for my liking.

  6. Is there a list of parts that breakage of will absolutely prevent the gun from firing semi-auto? I realize that breakage of a non-essential part like the bolt hold open can tie the gun up. I almost did not install one last night on a new receiver I purchased the other day (Better get one now while still easily legal to buy). My AK does not have one and all is good with it. Besides it does not work with my conversion .22 kit that I am using it for anyway. A pistol grip in one receiver kit just plain would not fit my new anderson receiver. I dipped into a PSA kit for a standard one it fitted perfectly.
    A list of the most vital small parts would be handy and I would order them say from brownells and retrofit them to my ARs just to be sure.

  7. Producer: *kicks in the door
    OK people! Let's get started!
    …..wait….. You're not Caleb.

    Steve: Actually this is…….

    Producer: QUIET STEVE! I'll ask the questions here.
    HEY NEW GUY. Take off your hat.

    SOL: *takes off hat

    Producer: Sweet Jesus! PUT THE DAMN HAT BACK ON! Ok I can work with this.
    Let's get started filming people!!

  8. The last build I did was on a KP-15 I ordered through Brownells. Everything went together well, except I used an ALG ACT trigger I had on another rifle I was cannibalizing for parts which had the lighter hammer spring on it. When I took it out the first round fired, but then click. Everything cycled, but out of about 10 rounds only one or two rounds fired. I knew the ammo should be fine and it was dimpling the primer, but looked kind of weak, so I packed up for the day and picked up a stouter spring from one of my local shops since I lost the original and next time out, worked like a champ.

  9. I always had good luck with Spikes Tactical and Daniel Defense LPKs, not so much with CMMG or Aero Precision. The CMMG takedown pins were a slightly smaller diameter than those from Spikes or Daniel Defense and there was a noticeable amount of play between upper and lower receivers because of it. Aero Precision mil-spec triggers were terrible. If you're using a different trigger, then probably not a big deal. Small parts from Radian Weapons and Geissele have also been great.

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