Commercial and mil spec receiver extensions do have different outer dimensions and therefore must be paired with the appropriate sized butt stock.
For all real world use, quality uppers and lowers will all work together, and there’s no such thing as a “commercial” lower, a “commercial” upper, or a mil spec lower that doesn’t require NFA paperwork.
Let’s clarify something. Forget buffers, unless you are confused on compatible carbine, rifle, or A5 recoil systems. Let’s focus on uppers and lowers. If made to correct specifications, they should be universal. Meaning, you can swap uppers and lowers with other uppers and lowers. I can do this with all of my AR’s no problem. Are the resultant configuration optimal? No. But, they will all go bang. So, I don’t know what ARFCOM is trying to tell you. The only issue with “commercial” versus “mil-spec” is the compatible carbine stock choice based on what type of receiver extension you bought and installed. For my money, I always go with “mil-spec” type RE’s and stocks. No brainer.
When you say buffer I think this is what you are misinformed on… commercial vs Milspec buffer Tube , the diameter of the commercial buffer tube is different than the outer diameter of a milspec buffer tube. Also many commercial buffer tubes are made of lower grade aluminum than true milspec buffer tubes. Do some google searches on what milspec means, I doubt many here want to go to the lengths to completely explain it when there are hundreds of threads about it on the internet.
A commercial lower and milspec upper work fine together.
Every once in a while you will run into an upper that won’t fit in a lower. If the lugs on the upper are to the maximum allowable tolerance, and the corresponding pockets in the lower are on the low side of the tolerance, you can have two pieces that meet the range of tolerances allowed but will not fit together. Tolerance stacking will get you sometimes.
This ^
Yep, no argument there. Thanks for pointing that out.
So what you are implying is that FN has lower quality control standards?
I really have trouble believing they would make their commercial lowers to different specs than their lowers sent to .mil . Yes I understand the colt TDP situation, however it just doesn’t make sense to make lowers to different standards, it would be a poor choice financially.
Actually it wouldn’t. You have lowers that have to meet U.S. Govt standards of tolerances between X and Y or you won’t make spec. You know that lowers that miss these specs by .001" (hypothetical measurement) will still work just fine in the civilian market, so those are set aside for civilian use. You have a separate acceptable tolerance for the civilian versions. Ones that don’t make either spec are recycled.
I’m not saying this is happening anywhere, but the scenario would still make sense if you had both .gov and .civ production.
I have in no way, shape, or form implied that FN has lower QC than Colt. I’ve gone into way with FN weapons, and they have served me admirably. In my mind, FN is a very highly respected name in the weapon business, at least as much so as Colt, and more than just about anyone else.
Well, that is pure speculation, and by that same train of thought there is no reason that Colt isn’t doing the same thing.
I was just hoping there was some empirical data points that prove Colt lowers truly are better than FN lowers, so far I have yet to see that.
The only real difference I have been informed of is that Gen 1 FN lowers did not stake their castle nuts, which I really don’t consider a big deal. From what I understand Gen 2 FN lowers do stake their castle nuts.
Why…?
Just for my personal knowledge so I can make informed choices for firearms purchases, and share the knowledge with others.
Maybe I should have worded it better, something along the lines of the actual differences of FN vs Colt lowers.
I’m still trying to decide if I should buy an FN Tactical II or a Colt Combat Unit, I can buy them both for about 1,200$.
( the FN link price only applies to LE/Mil )
https://www.midwestgunworks.com/page/mgwi/prod/35-36312
https://www.budsgunshop.com/catalog/product_info.php/products_id/719014177/Firearms/Rifles/Colt/Colt+Combat+Unit+M4+5.56+16in+30%2B1
I would be more interested in the gas port sizing of the Colt vs. the FN.
FN has answered emails pretty fast for me in the past. I don’t know the answer to that question, and also I don’t even know what the appropriate size for a mid length gas port would be? Somewhere between carbine .063 and rifle .0935 ?
IMO for a 16 inch midlength you would want around .076-.078. many manufacture will go .08 plus so the guns will run under powered ammo
I don’t think you are going to find enough data to categorically say one way or the other.
Perhaps if one were to get a look inside the warranty repair records for each company you could spot trends.
Other than that most of the evidence you will hear/see is anecdotal and often tempered by bias. We are prone to remember and over-emphasize flaws in products we believe are of less value and discount the discrepancies in brands we value.
This is not to say that some brands do not deserve their reputations for shoddy QC, etc., just that in some cases it is overstated.
FN buffer tubes (even though they are mil-spec diameter) are likely made from 6061 aluminum since they have never advertised which aluminum they are made from.
I believe that FN does use 6061 on the buffer tube at least with the gen 1. I tried to ask them but they wouldn’t confirm. I have seen another form where someone said that it is in fact 6061 apposed to 7075. Does that make a big difference?
Yes. The receiver extension material is critical (7075T6). I’d buy the Colt CCU, without hesitation, over the FN offering. Just me.
FN’s use of 6061 makes no sense to me, and I’d be surprised if it is correct.
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