Hey guys I have a complete FN15 tactical gen 1 rifle and I was wondering if anyone knew if the lowers on those rifles are mil spec? If so do you think it will work with a bcm upper? Reason I ask is because I have a bcm complete upper and it is just sitting and I would like to put it on my fn15. I sent a message to fn a while ago regarding it and still haven’t heard back from them. Thanks.
Yes and yes.
No, they are not milspec, yes, they will work fine with your BCM upper.
What about them are not milspec? Also I thought that you could only use milspec lowers with milspec uppers?
i believe he is referring they are not built off the TDP because Colt is the only manufacturer that can build to the exact TDP specs because they own it. FN can only use it for the rifles they provide to the military. All manufacturers other than colt have to reverse engineer the specs, so they are not truly milspec. The FN lower should work fine with any ar15 upper though. Hell, i dont recommend it, but a bcm lower would “work” on a $100 polymer lower.
Your FN lower should work fine with the BCM upper. I believe it would make a better overall rifle than with the FN upper especially if you have a BCM BCG
An FN lower with a BCM upper would be an awesome gun. I would personally consider it a ‘‘tier1’’ gun if it is loaded with proper parts, but that is just my opinion.
FCG, selector, and receiver are not “milspec”. None of that matters for your intent, and it is GTG.
What part did you think was milspec?
Wouldn’t a 6920 lower and fcg not be considered milspec either, since they can’t use happy switches? Isn’t the FN lower made of the same aluminum and anodizing as a 6920 lower?
I thought the only main difference from the FN lower and a 6920 lower was that the colt stakes their castle nut to TDP, which I wouldn’t consider a deal breaker for the FN. (I also thought that new FN lowers do stake their castle nuts).
I also wouldn’t be very concerned about the selector, but technically the 6920 selector isn’t milspec either because it can’t go to the third position?
Am I completely wrong here? I would like to learn as well, and am genuinely curious.
I asked similar things in a thread last month and all anyone really said was colt is better because they are built with TDP, but if that were the case then nobody would be buying danial defense or other ‘‘high end’’ AR’s?
Correct, the Colt 6920 isn’t milspec either.
I’m sorry that all you got out of your previous questions was that Colt is built to the TDP. At some point you will understand the quality and standards which go into certain manufacturers components. A lower receiver is much more than simply a forging with holes. If you are ever in a factory and see all the rejected receivers, you will understand that standards are important. Good manufacturers aren’t saying something is “close enough”, they are keeping a standard or throwing it in the recycle pile.
I think some folks equate “mil-spec” with quality/durability/compatibility/etc… Similar to “match grade” in that there is a heightened expectation of performance when labelled as such.
I think it’s become a generic term in the commercial market.
I guess I really dont understand what mil spec means. I know it has a mil spec buffer tube for stocks so I just assumed that it would be a mil spec lower but as long as the quality is good and it will work with the bcm upper no complaints from me. One more question then if fn lower isnt “mil spec” is the bcm lower considered “mil spec” or is it the same as the fn lower? I thought the reason fn couldn’t use the tdp was because they make the rifles for the military. Can companies such as bcm, dd, noveskee, ect… use the TDP?
Please correct me if I’m wrong.
My understanding was that the patents have expired and therefore reverse engineering the parts wouldn’t get you in court trouble. This snippet seems to reinforce my thoughts:
1989: Jim Glazier and Karl Lewis of Lewis Machine and Tool Company (LMT), operating a new entity called Eagle Arms, begin producing complete AR-15 rifles for the consumer market. By this time, many of the earlier AR 15 Rifle related patents had expired, thereby opening up the market for complete AR-15 type rifles
Beyond that I don’t know the exact date when the field opened up, Olympic Arms was making them in 1982.
I’d also be willing to bet that a lot of companies have a copy of the TDP, they just don’t advertise that fact.
Other than the ar15 lower not being capable of full auto fire what constitues as mil spec? The fn15 lower is 7075 t6 mil spec buffer so is it the same as a bcm lower or a colt 6920 lower? If not how do they differ? I was under the impression that if it was 7075 t6 with the right buffer tube it was considered mil spec.
You might as well flush the words mil spec from your mind.
BCM lowers are good.
Colt 6920 lowers are good.
LMT lowers are good.
FN lowers are good.
Daniel Defense lowers are good.
etc
etc
etc
None of these can be considered truly mil spec, and it doesn’t matter. Any differences between any of the above will be in areas that don’t affect function, like the amount of mag well flare.
Double-tap
In the case of the receiver extention (buffer tube), milspec denotes the manufacturing process that produces a certain form factor (size/dimensions) that preclude which type of stock is compatible: commercial or milspec.
…and nobody here should be buying a commercial receiver extension. None of the above mfgs use them with their complete lower assemblies.
That doesn’t mean that a home builder couldn’t.
I am new to the platform and what I was told was that things labeled mil spec is more of a tolerance thing as to figure out what will work with what. So is there no difference between a commercial and so called mil spec lower other than the buffer? People on arfcom told me a mil spec type upper would not work on a commercial type lower. I came here to ask because I trust members of this board more and I tend to get the same ol’ people answering questions over there.
For all intents and purposes, quality and price point aside, a lower is a lower. Purchase a known quality lower and the rest will fall into place.