I am looking to build two uppers for my M16 that have a heavier barrel especially near the chamber to help dissipate heat. Do any of you have suggestions on a durable 12.5" or 13.7" barrel that will hold up to sustained fire without premature throat erosion? I was looking at the Noveske 12.5 switch block barrels or the 12.5 low profile gas block barrels. I have also looked at the Geissele 12.5 CHF Chrome lined barrels and think they may be a viable option.

I’ve always ready that CHF barrels with a chrome moly lining is the best. Regardless you will have to let the barrel cool after ~100 rounds of full auto. A heavy profile barrel will absorb more heat, but will also take longer to cool down once hot.

The cheapest option is to swap uppers, but if you’re really planning to run hundreds of rounds through it in quick succession you might want to look into and MCR so you can just swap barrels.

As far as 12.5” vs 13.7” that’s up to you. I’m sure a 12.5” will be easier to find than a 13.7”. Also if you’re just sending lead down range I wouldn’t put too much money into the barrels and treat them as disposable.

FWIW the upper that stays on my M16 is a 10.5” pencil profile made of 416 stainless. Probably the worst barrel possible but it’s meant to be light weight and compact, it’s not a LMG upper.

As above, go with a couple of cheap, lightweight, chrome lined barrels and build more than one upper.

One cools as you shoot the other.



Or get another machine gun and shoot one while the other cools


RCA

P.S. Personally, I like a 20 inch barrel with rifle length gas for slower ROF.

RCA

Nice thing about the M16 platform is that you can tune it to run slow even on a short barrel if you want to.
The 10.3" upper below has a rate that is slower than a 20" upper w/ a standard configuration.

I have read a lot of your posts and am impressed with your abilities to get sometimes uncommon and seemingly mismatched parts/caliber combinations to not only run reliably, but at the rate of fire you prefer.

I tend to run my Colt A1 with a Colt A2 upper receiver mated with a Brownell's A1 1/7 chrome lined barrel assembly along with a hydraulic buffer.

Prefer the old school look of the pencil barrel and triangle handguard, but prefer the A2 rear sight  and as a lefty for long gun, really like the shell deflector of the A2 upper.
Also like 1/7 twist for the times I fire M855.

Haven't run a 9mm upper since I got my double push pin RR HK 94/MP5.


RCA

Thanks
I don't know which hydraulic you are running but note that they behave quite differently in my experience.  I only like a few of them.
My buffer experiences here: https://c3junkie.com/?page_id=325
You can see my MP5 in the background I am testing against.  
The new MEAN Arms bearing delay with the M lifter w/ my lower configuration has a nicer cyclic rate than my MP5 and way better ergonomics.  I would say it is softer than the MP5 but the MP5 is more straight back recoil.  Very hard to beat the MP5.
Will have to see how it holds up.  Only about 1K through it so far.

The hydraulic buffer I run is the Kynshot RB5001, for rifle length buffer tube.

RCA

Ah, that is one I do not have as I do not like fixed stocks.  I have a friend that has one and I did test it in conjunction with a Colt LMG upper.  

What were the results of your testing?

My impression is that it spreads out the recoil and somewhat slows rate of fire, but without a means of quantifying the ROF, it is just my impression.
Definitely an improvement.


RCA

I tried to find it but couldn't.  I probably didn't save the data since like I mentioned I don't care for fixed stocks and if I am able to achieve the smoothness and the cyclic rates I want with a collapsible stock, I see no point in the fixed stock.
Here are some pics of the testing I did with my friends LMG which I probably tested with the 5001 but didn't save the data:
Baseline:


Now my preferred setup which is right around the rate I like.