Im about to put together an ar build and cant decide between the two. I want a rifle i can reach out and touch with while also having sub moa accuracy. The rifle needs to be light and have the use for self defense if the problem arises. and ballistics wise would a .223/5-56 be better than a 7.62x39. Main reason im comparing the two would be because the 7.62x39 has a bigger bullet and is cheaper overall.

If you are looking to build an accurate rifle that could be used for longer ranges as well as close in then .223/5.56 would be a better choice IMO.  Reason being is that 5.56 is a much flatter shooing round than 7.62x39 this would allow you to engage targets at varying ranges easier.  Also, as far as I know there are much more factory mach loaded ammo choices out there for .223/5.56 than 7.62x39 that should give you the sub moa accuracy that you are looking for. As for barrel length I personally prefer 16" over 18" barrels, you do loose a little bit of velocity for those longer range shots though.

Ever thought about a 6.5 Grendel? $8.99 a box from AA.

Get both.

But seriously,  I have an 18" Spr and a 16" recce type. I built the recce to be lightweight and have used it in carbine classes. No way would I try that with the Spr. So, the 18" spr gets pulled out for prone or bench duty only, and that isn't very often.

16" with a good 1-4× scope is a decent compromise.

+1. I'd go recce all the way. I always thought of the two as follows:

RECCE: An accurized M4 with a 16" free float match barrel and variable power scope such as a 1-4x.

SPR: Bench gun. 18" FF barrel and much more powerful scope. More of a "sniper" setup like the M110 SASS system.




So isn't that what a recce is??

I agree.

Make one that can do it all

Yes, in my opinion. But I've seen 16" rifles with long handguards and a flip to side magnifier called a recce too.


Edit: old pic of mine. I recently ditched the UBR stock for weight.

The next AR I build.

The 16inch covers a lot of ground.

Scott killed this antelope with one shot at 486yds.

Get both!

What cartridge?

What size free float rail for a 16 inch barrel for a RECCE build?

Most will say 12" but I've seen them as short as 10" with a mid-length.

I built an accuracy/hunting rifle a couple years ago and actually started with a 7.63x39 barrel setup from AR Performance.  Then after looking at ammo pricing and realized that the x39 was cheap to shoot if I was just shooting crap ammo.  Anything decent and readily available (locally for a quick stop at the range for example) was the same price as 6.8.  Reloading ran the same price and the 6.8 was ballistically better and the mags were much better as well.  After realizing all that, I sold the 7.62 stuff and replaced it with AR Performance 6.8 parts instead.

That is something to consider.  The price for good ammo for most common AR calibers is all about the same so why not pick something with a little more power and range?

Let me put it this way. I tore apart my SPR and sold off the longer pieces in order to begin assembling my 14.5 midlength recce. I shot a similar one with sub moa accuracy so the recce is my choice plus it is much lighter.

Yes, but for how long?   Wildcat or semi-standardized wildcat cartridges tend to become rare and expensive after just a few years.  If you hand load, that is different.

I'll give you two great examples of almost obsolete centerfire hunting cartridges that are technically superior to their competitors, yet have fallen into disfavor and are difficult to find on shelves.   The 6mm Remington is superior to the 243 Winchester in just about any measurable way.  The 280 Remington is superior to the .270 in just about every way.  I own rifles in both calibers and appreciate the benefits.   But, I handload.  Were I dependent on factory ammo, which used to be very plentiful for each of them, I would have few choices and none that is inexpensive.

On the other hand, standard military ammo is extremely plentiful, available in bulk at attractive price points, and will remain in inventory in good supply virtually indefinitely.

.223/5.56 is going to be with us for a long, long, time, just like .308 and .30-'06.   Stick with that unless you hand load., or are adding a unique chambering to an already broad collection of other rifles and don't mind the risk of ammo becoming scarce or obsolete.

BTW:  I vote for a RECCE 16" lightweight but precision barrel with 12" free float rail and a QD mounted 1-4 or 1-6 scope with illuminated reticle and true milrad turrets and reticle.   Very versatile and easily to carry about.   My build is that way except that I deviated by going with a slightly higher magnification scope, a 3-9x40, because I use it more for hunting and not so much home defense.  But, I put the scope in a true return to zero QD mount and swap with a QD mounted red dot when the rifle is performing HD duty.

Were either of those calibers in mass production by the major ammo producers in both the USA and Russia?  Do any of those calibers offer significant advantages over the comperable calibers in their class?

Grendel isn't going anywhere but up.  The support for it is already outstripping the 6.8 and other non-military calibers in the AR platform and the availability of cheap russian ammo is HUGE.

not the answer you want, but the truth is an RRA entry tactical will shoot 1moa , in fact is guaranteed by RRA I shoot mine out to 250 yards regularly it has a heavy barrel  weighs under 9lbs with no rails. If you want a midweight 16" carbine its hard to beat.  

what you want to debate is the optic not the barrel leagnth

if you want to shoot past 500 meters go 308 win