Downsides of building an AR15?

[Justice06RR]

Do any of you that has "built" AR's (or more like assembled them as I call it) run into some issues?

I'm on my third AR15 build, not a lot by any means but I have come across a couple of small issues when you build an AR15 from different parts manufacturers.

First, there is a chance that some of the parts you build may not be completely compatible, or not completely in-spec. By that I mean that things like trigger pins or take down pins that are too loose/tight or just not fitting at all without a little modification. For example on my 2nd AR15, I bought both upper and lower receivers stripped from one company (Spikes Tactical), but the LPK from another (Palmetto). The trigger pin seems to be 'walking out' when first shot 40rds to test the rifle. In comparison to a factory built AR15 like my M&P, pins are all very tight fitting and will not wobble or loosen with recoil.

Of course i'm looking to add the KNS anti-walk pins so its not a big deal, but compared to a factory built gun you will most likely not have that issue.

Secondly, any problems you run into like I mentioned above may not be necessarily covered by warranty. In the issue I had with the trigger pin walking out is not necessarily a major issue, but if that happend to your factory AR15 it will be covered by warranty. With AR builds, YOU as the builder are responsible to choose good quality parts that will hopefully fit when you assemble them together. And if they don't work/fit 100%, you have to fix it yourself

On the flipside of all this, the advantages are more significant than the disadvantages. I was able to build my Spikes AR at a good price--below or at the same cost as a factory built gun. After finally completing my Spikes Tactical AR even during the panic, I was still able to keep it under $1k.
Prices for example:
Stripped lower receiver - $115 (bought the day after Sandy Hook)
Upper receiver - $99
BCG - $175
Barrel - $140

Another advantage is that you can pick and choose every part/upgrade you want to install on the gun already while saving a lot of money. I chose Magpul parts (AFG, CTR stock, mags, etc) so they all match perfectly along with a Noveske rail that I got for less than a bill.

Just wanted to share my experience with anyone thinking of building an AR15. Parts are becoming available and cheap again so its a good time to build if you have been thinking of doing it instead of buying a factory built gun

[eastbank]

i thought about building,but just bought a colt WMLE-6920 with sights to boot, for a little over a thousand dollars at walmart. my last one bought was a colt LW target match for 800.00 several years ago. when the parts to build were on the cheap it made more sense to build,but not now. eastbank.

[Justice06RR]

thats an excellent deal! I have been keeping an eye out for a Colt6920 myself. I believe they are around $1200 in my area--if you can find them.

here is my Spikes Tactical build with my M&P15 Sport. The M&P was $839, and the Spikes is right below $1k.

[Quentin2]

I've put together four ARs and had no incompatibilities. Never had FCG pins walk out either, including a fifth lower I completed recently. As long as quality parts are used and you select the right parts for your configuration I wouldn't expect issues.

As far as warranty, that's not been an issue either but it's a good point if something does go wrong. To me, in order to get exactly what you want it's a slight risk worth taking. Now if someone slaps together a cheap, poorly conceived thing, then a $700 factory AR makes more sense.

[Fishbed77]

In my opinion, the only downside to building an AR today is just finding the parts in-stock that you need!

I bought both upper and lower receivers stripped from one company (Spikes Tactical), but the LPK from another (Palmetto).

I've mixed Spikes and PSA parts before on two occasions with no problems whatsoever.

Neither Spikes or PSA actually manufacture their stripped lowers in-house. Both get their lowers from companies like Aero Precision and LW Schnieder. Many PSA lower parts come from the same suppliers that supply FN, and supposedly Spike's parts do as well.

[BillyJack3]

Sounds like you had some pins that might have been out of spec. I have 2 PSA LPKs and the triggers are completely different. The first one was smooth as can be and had a nice crisp break. The second feels like someone duped a shovel full of sand into my lower. That's the only issue I've had in assembling lowers though and it's not really an issue. If you get quality parts that are in spec, you should be fine and not run into problems.

On a side note, my first AR is an M&P and then I assembled a Spike's lower with PSA kit. I did however get a complete Spike's upper to slap on it. They make a great pair!

[smarquez]

I bought a S&W M&P and a Mega Arms lower at the same time. I can't believe how simple it is to put the lower together. I did enjoy putting it together but I am a hopeless DIYed and tinkerer. I have an Aero Precison upper waiting and am shopping barrels right now. I don't see a downside.

[Metal god]

What type of trigger did you put in the gun that the pins are walking on . I could be wrong here but I thought the hammer spring sits down in the notch in the pin and keeps them from walking . yes , no ?

[madcratebuilder]

First, there is a chance that some of the parts you build may not be completely compatible, or not completely in-spec. By that I mean that things like trigger pins or take down pins that are too loose/tight or just not fitting at all without a little modification. For example on my 2nd AR15, I bought both upper and lower receivers stripped from one company (Spikes Tactical), but the LPK from another (Palmetto). The trigger pin seems to be 'walking out' when first shot 40rds to test the rifle.

The FCG is not installed correctly. The hammer pin is secured by a spring (J or D) in the hammer and the trigger pin is secured by the hammer spring legs. Hammer pin has a groove in the center and the trigger pin at each end. Spring tension in these grooves is what keeps the pins from walking.

[Justice06RR]

Metal god, It was a PSA lower parts kit installed in a Spikes Tactical lower.

I know these companies don't actually make these parts but gets them from larger manufacturers, so I don't blame them. Both companies are A+ in my book.
There is a possibility that the trigger pin is installed wrong, but in the 3 builds I had, this is the only one that had the walking out issue and I installed all the parts the same exact way as described in many youtube videos.

Also comparing the pivot/takedown pins of the M&P and Spikes, the M&P pins are definitely tighter and harder to take out manually. the PSA pivot/takedown pins on the Spikes lower come out nicely and easily by pushing with your finger

I will verify that the spring is actually locking/catching the trigger pin and preventing it from walking out. But I hear this is a minor issue with certain AR builds which is why they sell KNS anti-walk pins to begin with. I've never seen a factory AR like a Colt or M&P with anti-walk pins, usually only builds.

[Spats McGee]

Not that I've ever built an AR, but my impression has been that the biggest downside to building one is the fact that you'll just want to run out and build another. And another . . . and another. . .

[CTS]

These are the same things that you would run into if you were working for a "manufacturer". The difference is they have access to more parts if they run into a problem. It is not uncommon to have to do a little "fitting" on occasion. I ran into that on my last upper. The Pivot pin fit very tight and I had to take some fine sandpaper to the pivot pin hole to get it to slide in and out like it should. Probably could have done it with some lapping compound but the sandpaper was handy. The only downside I can see is as was mentioned. If you do it yourself there is no warranty but I don't see that being much of an issue to someone who knows how to build one to begin with.

[riggins_83]

I ran into an issue of parts tolerance a few years ago; an LMT lower and BCM upper were very loose against eachother on the pivot pin. Installed an Armalite oversized hinge pin and it was great.

[Mike40-11]

..you'll just want to run out and build another..

Yeah, there's that. But see, they come in all these different calibers now and I already have one in 5.56 (okay three), so I have to look at the numerous varieties of .30 cal, then there's your big bore stuff like the .458 and the .50 Beowulf, and you can go with pistol caliber carbines... and... and... and......

[Mobuck]

I've assembled more than a dozen AR lowers and 1/2 dozen uppers. I've found numerous combinations of parts that didn't fit together in a way that satisfied me. I also found several combinations of upper to lower that were just a no-go. With several in the rack, it's usually fairly easy to get a good fit by trial and error. Most of my lowers came in lots of 3 to 5 and it seemed each lot(even of the same brand) was slightly different as far as pin holes, parts fitment, and deck height. It's all about tolerances and whether they stack or cancel each other out.

[Tangentabacus]

@Justice

What optic you have on your spikes build? Also why didn't you go billet?

[eodinert]

KNS pins are a waste of money. Your problem would be solved by replacing the defective part in your rifle.

As mentioned above, there is a spring inside the hammer that retains the hammer pin. Most likely that spring is bad/broken/missing. Take the hammer and pin out of the rifle, and insert the pin in the hammer. You should feel it engage the pin as the pin slides through...and catch on the groove in the pin.

[Justice06RR]

The FCG is not installed correctly. The hammer pin is secured by a spring (J or D) in the hammer and the trigger pin is secured by the hammer spring legs. Hammer pin has a groove in the center and the trigger pin at each end. Spring tension in these grooves is what keeps the pins from walking.

(update) I took the lower apart and saw that the spring was not catching the trigger pin correctly. I adjusted the pin/spring and This seemed to have remedied the issue. Thanks for the advice. I will skip the KNS pins if I don't have any further issue.

Yes, the problem with building them is you want to build more! I'm looking (again) at 300Blackout since I have two 5.56 rifles now. I initially wanted a pistol AR but I'm throwing that out the window until I find cheaper pistol barrels.

I've also come across many other parts that are not fitting properly. I have an ATI complete polymer lower with takedown pins that are super tight it becomes a pain installing the aluminum upper receiver on and off .

[madcratebuilder]

Originally Posted by Justice06RR

(update) I took the lower apart and saw that the spring was not catching the trigger pin correctly. I adjusted the pin/spring and This seemed to have remedied the issue. Thanks for the advice. I will skip the KNS pins if I don't have any further issue.

Glad it's fixed. I encountered this the first time I took a FCG out, very easy to do. KNS pins do serve a purpose. They stop the hammer pin from rotating, that stops any wear in the lowers pin hole. They can improve the trigger feel by eliminating any slop. Lowers can have .001-.002 slop between the two pins. KNS pins have zero movement, can make a significant improvement on how the trigger feels on some lowers. It's even more noticeable with a precision FCG.

[Dondor]

A little bit off topic but I want to know if Justice has more in that drift RC than one of his rifles