I have finally completed my AR15.
One question looms on my mind.
How durable is a lower receiver. Since this is the part that is required by law to register in my state it is now the most important part to keep in good order, whats the average abuse it can take in terms of bullets being fired from it to the point it just warps 
If it helps I have an MP15 lower 7075 T6 Aluminum hard coat black. I dont plan to be dropping this on the dirt, cement or being to *rough with it 
its a non stress part, unlike the upper. It wont warp under normal use
Are you sure with this answer? If this is true this is GREAT news if not this is BAD news 
So would you say that it can last almost a lifetime with proper care??
I doubt this slightly? So after dumping 10,000 to 15,000 rounds of 5.56 I am to see no wear on the lower per say?
Bushmaster had one in-house about ten years ago that they estimated had over 250,000 rounds on. It was used to test completed upper reciever assemblies.
They said they had replaced FCG parts but the reciever was still in-spec.
I am curious if they still have it.
You might see some enlarging of the FCG pin holes. You might see some slop develop between upper and lower from slight enlargement of the takedown and pivot pin holes. All easily remedied without throwing out the receiver. And even if you do, just get a new one. If youâre worried about it, buy a replacement now and stick it in your safe. It would cost you about $60-120 for that piece of mind.
It should last you a long time. Ive seen heavily dinged and worn down to bare aluminum M16A1 lowers from years of no-care-use that are still perfectly functional. No egging out of the hammer and trigger pin holes, whatsoever. Personally, Iâd be more worried about an improperly installed RE.
the lower doesnt take the stress of firing, the upper and BCG do.
Wearing and warping are two completely different things. No, your lower wonât warp. It will wear in certain areas, like the pivot and takedown pin holes, but not nearly enough to render the lower useless. The FCG and buffer parts will also wear, but are all easily replaceable.
It will last you a lifetime of shootingâŚ
You should even be able to hand it down to the next generation of shooters!
Think of all the pre 86 m16a1 lowers out there in private hands, a number get shot often. Almost 25 years worth of FA and most havenât fallen apart.
Considering that when I went to basic, both times, we were using a whole bunch of Vietnam era M16s that had been upgraded to a1 (I saw Colt AR15 marked guns, Hydramatic Division guns, etc.) over the years I never worried about the lowers at all.
Even abused they last a very long time.
We have discussed this before. Lower receivers get damaged due to people improperly disassembling and assembling the FCG. Especially using steel punches to remove and install pins.
I can almost guarantee that if you learn the correct way to maintain and disassemble/ assemble your lower it will probably last longer than you.
Why the âalmostâ and âprobablyâ? If itâs a sure thing, then why the uncertainty? Not trying to troll or nitpick, but it seems that, if the best answer is âprobably,â then the OP has a valid question and it would make such things as KNS pins seemingly valid.
Well, Iâm not Iraqgunz but being itâs best to avoid absolutes itâs âalmostâ always smart to use the terms âalmostâ and âprobablyâ - because stuff happens. Nothing is a sure thing.
A lot of people use KNS pins and thatâs fine for them but itâs âalmostâ never necessary. Good milspec parts should work fine, not walk out nor oval out the receiver.
Anyway, Greyman, I also have a M&P-15 stripped lower receiver that I built up with a milspec LPK and BCM RE/stock kit and havenât had any problems with it. Iâve dinged up the finish a little but otherwise the receiver is as strong as anything else Iâve seen and I expect it to outlast me. Iâve tried a couple uppers on it and the fit was snug while function was 100%. Be happy with yours, itâs a fine start for your rifle. Get a BCM or other quality upper and youâll be GTG.
Edit: if it has the standard weight carbine buffer you might need to replace it with an H-buffer and maybe stake the castle nut but thatâs about it.
Bushmaster seems to have managed a couple hundred thousand rounds before KNS pins were available.
First off, the OP makes no mention of KNS pins. Second, I say almost guarantee because there are no guarantees in life.
Anything man made can fail and people can find a way to damage anything. I have seen M16 lowers that probably should have been in a museum and they were still working 20+ years later.
I have yet to see a lower receiver that had trigger or hammer holes that were damaged by a rotating pin. I have seen plenty of dicked up ARâs damaged by morons who decided to bang on pins, improperly remove and install their FCGâs and a host of other problems.
I find it curious that even to this day there are old M16âs being loaned out to police depts. that are probably 30+ years old and still seem to be functioning. If anyone has any proof of holes being worn by simple rotation of the hammer or trigger pins I would love to see it.
From someone whose armed forces that still uses the old M16A1 as in really old (40-30 years old) Colts, H&Rs, GMs and not so old Eliscos, the lower receiver does last a long time.
These rifles are probably older than the soldiers carrying them.
Skyyr,
Just curious, what is a moving mechanical device, that you have, that you will absolutely positively guarantee will always work?
.
Oh, I donât have one, nor do they exist, but that wasnât my point. Let me digressâŚ
There is purposeful slop (i.e. âtolerancesâ) allowed in every receiver, meaning that virtually every piece thatâs in the lower receiver can move. Movement = friction, be it a lot or a little of it, and therefore an educated person can deduct that a lower receiver WILL eventually egg-hole or the like over time. How many rounds until then? Half a million? Two million? Who knows; my point is that logic and deduction would say it IS possible, which brings me to my next pointâŚ
Many people state that the lower receiver will âout-liveâ the owner, many times using the argument that they can always buy a new gun if their current one wears out. Thatâs true⌠for now. What if another AWB were to pass? Is that statement still valid? Buying new receivers may not be an option. If you only had one gun, and couldnât get another, and shot competitively, then whoâs to say that it would still last a lifetime?
My point is that the people that typically state âit wonât wear outâ are usually ones who approach it from an armorers standpoint, meaning that theyâve seen âreally old onesâ that arenât worn out⌠and they replace the ones that are. Thatâs something the average Joe canât always do. The other thing is that while Iâm sure there are many VERY old rifles still in service, no one really keeps a true round count on them. Yes, you can try to guesstimate the count, but even then, itâs still a guess at best and can be completely wrong. And even if you can come up with 5 guns with â259,374â round counts, thatâs still only a sample-size of 5, which isnât significant.
Everything has a designed projected life span. Whenever I see someone make a comment about âit will outlive youâ followed by âmaybe,â thatâs a contradictory statement. Either a receiver WILL outlast a human life on average (~80-120 years), or it wonât. Thereâs no middle ground.
Sorry for the long post.
Hmmm, Iâm 62⌠Yeah, my M&P-15 lower is gonna outlast me! 
Maybe - if it doesnât get run over by BHOâs machinery.