Best barrel profile? hey there. In the next few weeks, I'm going to be building up

[Jmanwit]

In the next few weeks, I'm going to be building up a precision AR, from a JD Machine receiver set. I am debating which barrel profile I will want. I was leaning towards an .825 at the gas block, but will I want the .936 later? It's a 20", and I want it to stretch to 1000 yards eventually. What say you?

 

[ORD]

I say if its a standard AR-15 in .223/5.56 and you aren't shooting in a vacuum, you are going to want/need a GOOD BIT more barrel LENGTH to get to 1k without having to call for air support. Joking aside...you are REALLY sacrificing a good bit of MV by only going with a 20" barrel and while I know that there are trade-offs with going 6-8" longer, if you really want to accurately put rounds on target with an AR in .223/5.56 at 1k, you'll need every advantage you can muster. Obviously, you also aren't going to be achieving that goal with mag-length ammo for the most part which tops out with the 77gr SMKs and like bullets. You also need to consider how you are going to have the barrel chambered as you'll want to run some of the LONG match bullets with higher BCs (like 80gr to 90gr match bullets from the Hornady AMAX line, Berger Match VLDs, SMKs, etc.) that may or may not lend themselves to being run properly in your average 5.56/.223 chamber (most off the shelf barrels these days are .223 Wylde or 5.56 NATO chambers), even if you are single-feeding them (try running a search on some of the throated match ARs out there just as one source of info). Finally, with respect to barrel contour, it doesn't sound like you are envisioning this build as a rifle you'll be humping around a whole lot and if that's the case and weight/portability isn't of too great a concern, I'd be getting a long (like 26-28") and heavy contour (1" or so under the HG, 0.936" at the journal, etc.).

Now, I'm not saying that you can hit 1k with an AR...not at all. But it generally requires more than your basic, stock components to do so consistently and accurately.

 

[SomeOtherGuy]

I agree with ORD. A 5.56 or .223 Rem AR with a 20" barrel is not a great 1000 yard gun with ammo that can fit into a magazine. I think a 20" AR only makes sense for 1K if you are shooting service rifle in high-power and are planning to single load 80-90gr bullets, as stated.

Soooo.... if you are shooting service rifle division, I would optimize for that, and maybe just buy an off the shelf upper for it from someone like White Oak. If you are not shooting service rifle, I'd go 26"+, or just treat the AR as a 600-800 yard gun tops.

 

[Jmanwit]

Silly me, I forgot to mention it's a .308 build, with a Broughton blank. I want it to be portable enough to be competetive in "Tactical" shoots, (potential to ruck moderate distances etc.), not quite a bench rest behemoth.

 

[ORD]

Silly me, I forgot to mention it's a .308 build, with a Broughton blank. I want it to be portable enough to be competetive in "Tactical" shoots, (potential to ruck moderate distances etc.), not quite a bench rest behemoth.

Well @#$%!! That does make a WHOLE lotta difference now, don't it!

Ok...forget basically everything I said above.

A 20" tube, with a medium to somewhat heavy contour barrel should get it done just fine. I tend to stay clear of the 0.936" journals unless absolutely necessary as they tend to limit, somewhat at least, the selection of gas blocks out there without going the custom route.

I'd still go 1" or so out to the journal, then 0.875" (NOT 0.825" as you indicated in your OP as that is an off size journal) at the journal if it were my build.

 

[Jmanwit]

How would the weight be approximately? Would fluting be in order? I meant .875, just typed wrong on my phone (see title lol) .

 

[ORD]

How would the weight be approximately? Would fluting be in order? I meant .875, just typed wrong on my phone (see title lol) .

Just too many variables to give a reasonable guesstimate of total weight, but with all things considered, likely ~3.5-4.0lbs (stripped...no block/gas tube/etc.). Fluting is your call and will save SOME weight depending on how aggressive you go (deep/wide) with the flutes, but it isn't going to save an appreciable amount of weight so much that you'll really notice it if you are humping the rifle around all day. Its generally more cosmetic than functional in terms of its effect for the most part.

 

[Jmanwit]

Always been my assumption of fluting. Well, as it stands now, I'm looking at the PRI delta 15" handguard, A2 stock, Aadmount and a Weaver tactical scope. I'm wondering if it will balance right with that, or is a PRS in order?

 

[ORD]

Your call on the stock as it completely comes down to personal preference/fitment. Depending on your optic/mount and your particular body habitus...the A2 stock may fit you just fine and give you proper cheek weld, LOP, etc. If not...the PRS is a worthwhile investment at ~$200. If the A2 fits ok and you just need more weight in the rear of the rifle to "balance" things out a little, then there are a multitude of different options for remedying that from buttstock compartment lead weight wedges to epoxying in some lead shot into the compartment to...well...you get the idea.

With the 15" Delta, and I'm sure you probably realize this already but I'd be remiss for not saying it, you will need a low profile gas block whether you go adjustable (which I'd highly recommend) or not as it'll cover the journal by ~2".

 

[Jmanwit]

Was definitely looking for low pro gas blocks, but why is adjustable recommended? Tuning for proper function with different loads?

 

[ORD]

Was definitely looking for low pro gas blocks, but why is adjustable recommended? Tuning for proper function with different loads?

Adjustable blocks have many functions/uses, but primarily, they allow you to finely tune your particular ammo/shooting conditions/etc. for not just "proper," but optimum functioning of the rifle. Most factory production rifles these days are overgassed from the get go which can pose a variety of issues. An adjustable block slows down the cyclic rate, reduces wear/tear on rifle components, cuts recoil (at least perceived recoil) somewhat, can keep the rifle cleaner, and just generally makes the rifle function better overall. It is of arguably critical need for rifles that will be run suppressed as the significant increase back pressure/blowback from the suppressor can and will speed everything up and can really take a toll on a rifle (again, especially one that may already be overgassed), including leading to failure to function properly and wear/tear/breakage of components.

There are a variety of different makes/models of blocks out there from infinitely adjustable, set-screw and click/detent adjustabe type models like the JP, PRI, Syrac, etc. models to positional (ON-SUPPRESSED-OFF) type units like those from Paladin Machine, etc. Only you can determine what's best for your particular needs or whether you even want/need one at all.