AR-15 DMR/Precision Build- give me guidance

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Hey everyone!

Long time, no see. Since I graduated college it has been a wild ride. But I'm starting to make my way in the world- I have a full time job working at an indoor gun range and gun shop and things (knock on wood) look stable for the next few years while I pay bills, lose some weight and get in to shape, and generally get my life together going forward.

The great thing about work is that money lets me do fun things after my bills are paid ;) and I decided to get myself my first AR. It's a Smith & Wesson M&P-15 Sport II that I have been tinkering with and turning into a formidable CQC firearm. I'll include a picture for reference. Now of course the problem is that the AR bug has bit me well and good and I'm looking to build my next gun- a DMR/SPR type rifle.

I find myself wanting to stretch out the legs on my rifles more and more, but I want to hold off on getting a dedicated bolt gun for long range just yet and get a rifle in a caliber I already have (5.56/.223), so the concept fits my objective perfectly. I want to build it myself to, in theory, save some money and help enhance my understanding of the AR-15 and its capabilities.

So, for those who have done something similar, or are doing so currently, care to share some knowledge? What should I be looking for in terms of components, tools, and accessories? What should I expect for a budget? What are ways I can save money and still get what I want?

Specwise, I am looking at 20" BBL with heavy-ish profile, mid-power optic (I get some perks on Vortex stuff from my work), and I want the end result capable of [assuming I do my part] 1.5 MOA or better as a rule.

Thoughts, comments, recommendations and advice all appreciated.

Thanks,

-Chris ar-15 upgrade p1.JPG ar-15 upgrade p2.JPG
 
If you're like me you'll end up spending more money on saving money than if you'd just bought a finished proven product. Because there's always something better that's gonna make it....better. Is that's not confusing enough?

I'll take the logistic and budgetary approach. Make a list of what you're willing to spend on what, ie stripped/complete upper/lower. Then you can decide on what tools you'll need.

Getting the inside connection on optics is a huge bonus.

Do you plan on shooting factory ammo?
 
I dont really understand the 5.56 SPR build. I mean, my LaRue 16" lightweight barrel is more accurate than many bull barrels. As for barrel length, most modern chrony results from 18-20" barrels dont read very much higher than the 16". For me, SPR makes much more sense with a larger cal such as 6.8, 6.5, .308, etc.
 
If you're like me you'll end up spending more money on saving money than if you'd just bought a finished proven product. Because there's always something better that's gonna make it....better. Is that's not confusing enough? [...]

Do you plan on shooting factory ammo?

I get what you mean, for sure. But that's a problem with ARs in general anyway, so I'm kind of resigned to that. However, that's not to say that I would be opposed to starting with a good base rifle that was already put together to about 85-90% of what I want and modifying it a little from there. However, I just don't know if there's much in the way of what I'm looking for that is affordable as a nearly finished gun.

Which is, to Jackal's point, why I have not really considered some of the built guns in the calibers he listed; that and because there's not a range long enough where I live that I could adequately stretch out the legs on a gun like that and feel like I was accomplishing anything in terms of improving my shooting ability. Also because I cannot afford to shoot 6.8 or 6.5, and while I could go with .308, AR-10 platform guns lack the same degree of compatibility as an AR-15, which is a logistics issue of sorts for me, as well as meaning I would have to add another caliber to my stable (that will happen eventually anyway, but not now).

I would, for the time being, be mostly shooting factory ammo, with an eye toward doing 'some' reloading in the future.

But anyway, as far as budget is concerned, I could reasonably spend up to $900 dollars on the actual 'firearm' itself, not figuring in optics and some of the associated accessories. I'm thinking that I'll use a Magpul PRS stock if possible, or just and A2 fixed- they fit me well enough. Lower receivers are a wash in my opinion- whatever is good quality that isn't a lightweight polymer receiver that is $100 or under. A3 upper, again, good quality under $100. I'm not sure about triggers. Barrel is ideally not a bull barrel, but certainly not a pencil either. I'm honestly fine with an 18" barrel so long as I can get a rifle length gas system on it. Is the Wylde chambering worth it? Up to $300 for the barrel. Up to $175 for a BCG, Nickle Boron a plus, but not 'required.' A good free float rail, probably from Midwest, for around $200. There's obviously stuff I'm missing, but some preliminary snooping suggests there are good parts out there that would work for this project.

However, as I don't have much in the way of armorer's tools for the AR, I am very interested, if anyone has any ideas, in a rifle that would provide that near-ready state from which I could simply 'finish' it into the gun I want.

Thanks,

-Chris
 
The heart of every SPR/Recce/DMR is the barrel. Close second is the trigger and optic.

There are a lot of good barrels out there. White Oak, Larue, BCM, etc... all make great precision barrels.

Im currently turning my SPR into more of a DMR by switching optics mostly. Either way I have a BCM SS410 barrelled upper receiver with a Geiselle SMR Mk1 rail. With Black Hills 77 grn and Federal Gold Medal Match 69 grn it consistently prints .75 inch 5 shot groups at 100 yards. Occasionally a little less and occasionally a little more. With 55 grain plain jane ammo it groups right around 1.5 to 2 inch groups at 100 yards depending on the ammo.

If you are really trying to stretch the legs of the 5.56/223 I would go with a 20 inch barrel. If you plan on staying under 800 yards a 16 inch will do just fine. Though the extra muzzle velocity of the 20 inch will help with wind at any range.
 
My Rock River Arms 16" AR will put hornady 55 FMJ into sub MOA groups as long as I don't screw it up. it will put some nosler 55g hp's into a sub 3/4" group with 8208XBR. a good trigger and barrel may surprise you with 16"

have you tested your ability with your current setup?

maybe a cheaper upgrade path is a good trigger then start assembling an upper with the parts you want. you have one lower that you are very familiar with then swap uppers when you want to stretch.

make sure you get a faster twist (not 1-9) to help shoot heavier bullets. I'm sure there are plenty of people who have done what you are wanting to do who can provide feedback.
 
I have been hearing great things about Faxon and Ballistic Advantage barrels. They seem to be a great value for slightly less than $200 with a gas block included (AIM has them). I would think the other three important features for accuracy would be the trigger, free float hanguard, and glass. Rock River Arms has a decent trigger for under $100 if you are on a budget. Larue MBT gets great feedback and is 125 if you can wait for it. Primary arms is a good place to look for optics and triggers. There are so many choices it can be overwhelming. I am In the process of a "budget spr build" I have the lower completed with the RRA trigger and think I am pulling the trigger soon on the Faxon Gunner 18inch Barrel. Been looking into their handguards as well. They are pretty reasonable about $130-140. Thinking i might try a vortex strike eagle or the Primary Arms 1x6 for glass
 
If you want an AR to shoot well for you at long range, you need a few things:

  • Great barrel

  • Free float handguard

  • Great trigger

  • Proper bullet and quality ammo

  • Great quality optics

If you want it to shoot REALLY well for you at long ranges, you also need an experienced builder to put it together for you.

For barrels: Krieger, Broughton, Shilen - with a respectable nod to Criterion and Black Hole Weaponry. $100 bargain bin mil-spec barrels don't win matches, and will typically put you in the 2-4MOA ballpark.

For triggers: Geiselle is on a plane by itself. Second place is a race between Rock River National Match, Larue, AR Gold. Triggers - largely - do not actually make firearms more accurate, but good triggers DO make firearms more "shootable," being more forgiving to the shooter to deliver the shot without affecting the position of the rifle.

For bullets: Going long requires enough bullet weight and slick enough aerodynamics to get there. Sierra Matchkings are relatively affordable and the 69 and 77 do fit in mag boxes. The long 80 and 90 Bergers and the 75 A-max will reach way down range, but must be single loaded since they're too long for AR mags. Shooting these long bullets does dictate a need for 1:7, 1:7.7, or at MOST a 1:8" twist for your barrel.

For optics: You cannot hit what you cannot see. Optics don't make firearms more accurate, but like triggers, they help the shooter deliver on target. You don't need a $3,500 Schmidt & Bender, but you won't likely find yourself shooting 10" groups at 600yrds with a $75 Walmart Centerpoint. Parallax adjustment becomes critical above about 8x, and especially critical for delivering shots beyond 300yrds. Adjustable objective or side focus scopes are the way to go. Leupold VX3, Nightforce SHV, Burris XTR, Bushnell Elite 6500/Tactical, Vortex Razor are places to look. Plan on a minimum of $500, better up to $1,000-1,200.

Free Float Handguards: Take your pick here, some are more expensive than others, but largely, they all work as well as any other. Personally, I don't like Quad rail forend tubes, hate the way they feel in hand, and I don't need that much real estate for accessories. Clamshell AR's can shoot well, but in changing conditions and positions, they WILL shift, especially at longer ranges.

Price: Plan on about $800-1,200 to build a sub-MOA AR, not including optics. You can spend more, and sometimes you can get lucky spending less and find a diamond barrel in the rough, but after spending the last two decades building and tuning literally hundreds of AR's, this tends to be the mark right now to get one put together. Buying an equivalent factory model will typically cost $200-300 more, and may not have exactly the right furniture for your taste.

For tools: Shoot me a PM and I can send you a list of tools needed, and a parts list to complete your build. You CAN build one with vise grips and a hammer, but it's not a great way to build one. You CAN drive nails with a ratchet wrench, but it's not the right tool for the job.

Accessories: In general, accessories do two things 1) make the rifle heavier, and 2) make the rifle less accurate. Lights, lasers, designators, rail covers, etc all add weight, and outside of very specific applications do not add any degree of precision, and can even degrade accuracy.

Ambidexterity: If you're really wanting this as a civilian version of a fighting rifle, add ambidextrous controls. I'm one of the few folks who hate the Magpul BAD lever, but it does work. Better ambidextrous bolt release options exist, in my opinion. The Troy mag release is great. Raptor and BCM Mod 4 are great charging handles. Seekins selector is fantastic, but cheap DPMS work fine. Ambidextrous controls are really nice on the bench too.
 
Personally I would go with a mid-weight cyro treated barrel, I only have experience with one, my RRA 18", but it absolutely holds groups as it heats up as well as the previous 20" bull barrel I no longer own. I use my 3 gun AR15 for prairie dogs also (with a different optic mounted) and the weight reduction was significant. I did quite a lot of comparison testing between this and the previous bull barrel with extended strings of fire and it really seems to give the best of both worlds for medium range (out to say 300-400 yards) shooting.
 
I was bitten by this AR Bug myself a couple or I geuss 5 times and 1upper. Mine are all nice and turned out great. It seems that the AR Market is flooded with everything one could think of so have fun and do the homework before you buy and you can stay in your budget minus the optics don't forget about Lucid optics, Giselle trigger and Lihgha barrel and all kinds of components.
 
Me personally, I bought a complete white oak upper and built my lower like I wanted. White oak will get a rock solid upper that will shoot 1/2 moa or better. Mine will shoot 1/4 moa with my 77gr handloads, they know what they're doing! And can't beat their customer service. Get one of their upper for about $650ish, nicely built lower for $500-600. And will be a precision rifle in every aspect.
 
Also because I cannot afford to shoot 6.8 or 6.5
Just an FYI from a guy who's new to 6.5 Grendel and debugging a build of his own in search of the same concept; it bangs a gong almost like 308* and you don't even notice the recoil over the boom (I also have no muzzle brake). Sounds like a 308 shooting tone-wise as well (I have to imagine it would seem like 308 NATO to anyone on the receiving end, at least unless they stopped a round to gauge its lesser momentum). Extremely fun from a shooter's perspective because of this (accurate, loud, easy shooting). I scrounged a blem barrel for $50, 100pc of brass is ~100$, dies, brass, primers, and bullets are like another hundred. So $250 --or ten boxes of quality ammo-- to get set up for reloading (find a cheap used press on craigslist). Just something to keep in mind, depending on what volume you are expecting to shoot. FWIW, the cheap steel case Wolf or recalled PPU stuff likely won't meet your accuracy criteria, so Hornady's 123gr SST and VMax offerings are your only 'budget' options.

TCB

*While 77gr 5.56 loads can now approximate 308/6.5 Grendel ballistics at range, it is worth remembering that average Grendel loads are double this mass, while the much harder-kicking (and larger platformed) 308 NATO is only ever about 50% heavier
 
On AR15 forum a guy just did a test with a Ballsitic Advantage, Criterion, and Larue Predator Barrels. They have detailed ammo testing and accuracy results. I think they are doing some additional testing as well. The Ballastic Advantage and Criterion barrels performed very well. Check out the website www.scienceofthegun.com for results. They have a fairly scientific approach to the testing. All groups are 5 or 10 rounds
 
There are two really easy ways to get pretty much what you want from a factory build.

One is Stag. Their varmint rifles are guaranteed to shoot 1".

The other is Vision Defense in Middlebury, IN. All their rifles are guaranteed to shoot 1" with match ammo. I just got an 18" upper with a Wilson match barrel. Special free float fore end. Totally mil spec. $420. They are a manufacturer so it could go to your FFL
 
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Palmato Has a Colt Competition on sale today for $699 was $999 free shipping. Looks like a good starting point to me. Also I second the Stag varmint it is a shooter. But you should check out the COLT Competition at palmetto state armory .
 
I'd consider one of the heavy wall upper receivers if you opt to assemble it yourself. Supposedly adds stiffness and helps with precision.
 
Precision testing of AR barrels has been happening almost every weekend around this country for many years. NRA-HP and CMP Service Rifle matches have been pushing the limits of AR barrels for a long time. Krieger, Broughton, bartlein, criterion, Wilson, shilen.... They all win matches. The cut rifled barrels last more shots before opening up than button rifled barrels, but they also cost around 50% more (meaning you can replace button rifled barrels twice and spend the same as begging a cut to keep shooting after only replacing once). Take your pick, shoot 3,000-5,000 rounds through it and be ready to try something else, or ready commit to another barrel from the same maker, as it's gonna be loosened up.
 
Thank you everyone for your input! This gives me a lot of good reference material to start with as I figure out how I want to proceed. The information available around here is fantastic as always, so many thanks!

I will try and make further posts on this thread as things come together with either a build or modification of an existing rifle. I have tested the capabilities of my current setup and though it is fairly accurate, between the 1:9 twist and 16" barrel it is scientifically handicapped for the work I'd want to do with it and the accuracy at range that I'd hope to achieve. So, while it will be an exceptional short-to-mid range battle blaster, it's not going to cut it as a true SPR/DMR in my mind.

Thank you all again.

-Chris
 
I've built a few rifles, one of which is my varmint gun, a sub-MOA rifle at 200 yards with 60gr Hornady V-Max bullets and 25.6gr of Varget.

Here's my advice:

Have a concrete list of the things this rifle will do well. There is no "do it all" rifle.
Heavy barrels are not more accurate than thinner barrels. Their only advantage is if large amounts of shooting are expected in a relatively short time. More mass in the barrel takes a little more heat and time to shift point of impact.
Free float tubes are advantageous if a sling is to be used. If not using a sling, they offer little to no advantage. They mitigate sling tension pulling the barrel downward.
Barrel nut torque makes a difference. When tightening the nut, follow procedure of tightening and loosening it, then torquing to final value. Use minimum needed to align the nut while still being above minimum required spec.
Buy a good barrel, that's most important. Buy a good bolt, that's second. Finally, a good trigger lets you take advantage of a mechanically accurate rifle.
There are only a handful of companies that make receivers and re-badge them for other companies. Don't get hung up on roll marks. Buy based on quality.
Decide what range and purpose you'll use the rifle for. Select a twist that will shoot bullets fitting those parameters. Every rifle is a law unto itself, but stack the deck in your favor.
 
1911 guy said it all ,I've built 5 and then bought 2 really nice pre built uppers. And they all do one thing better than the others will at certain distance and all that stuff , any of them will work just fine at killing varmint at 300 but when I need one for say 700 I've only got 1 built for that range that is accurate enough. Like said you need a quality Barrel with correct twist for the bullet your gonna shoot, a good trigger that you like and quality Bolt and carrier and to be accurate you need to be comfortable with your stock a good cheek weld and good optics then you can mess around with buffers for dwell time if needed and then any other accessories you may need or want and lastly and most important is lots of Correct Method Practice.
 
Free float tubes are advantageous if a sling is to be used. If not using a sling, they offer little to no advantage. They mitigate sling tension pulling the barrel downward.

This is only partially true - float tubes are assuredly a benefit when shooting with a support sling, but the claim to say there little to no advantage part when not firing supported with a sling is not true.

For the benefit of the OP, who is a self-proclaimed new student to the AR:

If you're firing from any position in which ANYTHING is in contact with the forend, even supporting the rifle off hand, you're exerting pressure or tension against the barrel. For extreme precision, even angled shooting with no contact to the barrel can change your POI if you don't have a float tube. A sling may pull down, but when firing without a sling, your hand presses up to support the rifle, if you're shooting down or up angle vs. level, the gun weight on your forward hand changes, even that difference in pressure can change the POI slightly. Shooting from a front rest, sandbag, rolled up coat, barricade, door frame, fence post, etc in real world positions where the supporting pressure point might change along the length of the forend can change your POI. Shooting from a bipod, any change in your preload pressure (including pressing with the same shoulder pressure with the legs short on one day vs. long on another) will exert a different pressure against the barrel. If you fire some shots with a magwell grip and some with a C-clamp and some supported on shooting sticks or a fence post, or a bipod, the pressure on the barrel will change. If you shoot some shots with your tactical DMR/SPR laying prone and preloading against a bipod and then shoot some other shots off hand with a magwell grip and the weight of the bipod hanging on the forend, your pressure/tension against the barrel will change, as will your POI. Since this is an SPR/DMR, are you going to mount a laser module, light, NV/thermal, or other accessory to your forend? Changing weight of accessories hanging on the forend will change your barrel pressure and harmonics, and will shift your POI. Shooting from a hard support like a fence post compared to a soft support like a rolled jacket, ruck, or sandbag will also change the harmonics and barrel pressure.

So there's a LOT more significance to a free float tube than only sling support applications.

Of course, this all assumes the shooter is capable of shooting precisely enough to notice the POI shift, and the application requires sufficient precision such the difference matters. If a guy is just wanting to burn powder and make noise, the POI shifts don't matter much, or might go unnoticed, but I tend to assume for a DMR/SPR, precision does matter.
 
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I dont really understand the 5.56 SPR build. I mean, my LaRue 16" lightweight barrel is more accurate than many bull barrels. As for barrel length, most modern chrony results from 18-20" barrels dont read very much higher than the 16". For me, SPR makes much more sense with a larger cal such as 6.8, 6.5, .308, etc.
I like 20" inch barrels a little better than their 16" inch counter-parts for a couple different reasons.

• It buys you a rifle length gas system which is a little bit softer shooting than with a carbine or mid/length. It's not like a 16" is all that bad, but it aids you a bit in being able to move along to your next target a little bit quicker.

• Greater velocity which translates into a larger wound channel. I hunt a fair amount and while I've taken a few deer with it I've mostly shot alot of hogs. They travel in groups and it's almost all been either at night or in failing light (dawn/dusk).

Except for trying different rifles out over the years here and there when murdering hogs and a short affair with a 6.8 SPC I've almost always used .223/5.56's. While that's enough rifle it doesn't leave a huge margin of error the way other calibers do. However I've noticed that with a 20" inch barrel the wound channel is always bigger than with a 16" inch no matter what the load is, especially when it uses modern bullets like Barnes TSX and the Hornady T2 BTHP to their full potential.

Bullets that expand fairly well with a 16" barrel always expand and often fragment with a 20".

Even loads like M-193 and M-855 will usually fragment with a 20" barrel where they often won't with a 16" barrel. That extra 4" inches of barrel makes a difference on the other end.

Just saying, a 20" inch works better for the niche that I'm using it for. To each their own, but I like 20"s.

-----------

OP : I'd probably go with a BCM. I've had really good luck with mine.

The first two AR's that I have I went with the complete package and then I added/subtracted a couple things.

After that then with the next two AR's I built the lower myself to save money and bought the complete upper on both. An upper is a little bit more difficult to build that the lower. Anyone who can turn an Allen wrench or a screwdriver and tap a hammer can build (more like assemble) a lower. I built the lower ahead of time both times and the uppers arrived in the mail, I popped two pins and they were assembled.

Then a buddy of mine who's into it a little bit more than I am is good at building uppers and I've managed to talk him into building a couple uppers for me while I've assembled the lower. Since you're an employee of a shop they probably have a gunsmith on-site, but if not I imagine if there isn't a gunsmith out of that location there's someone up there where you might know someone who can build uppers, if so take the recommendations on the Faxon barrels, they're excellent. Kept one of those for myself and gave the other one to my nephew after he turned 18.

It's kinda funny that each time I went through the stereotypical stage that every AR owner supposedly goes through. I bought complete rifles the first couple times, bought the upper and assembled the lower the time after that and then did two complete builds using custom parts. Weird.

At any rate with the complete uppers I bought one was a BCM 20" inch upper and the other was a Noveske 16" upper and then I threw them on a PSA and a Noveske lower respectively. While I love my Noveske I feel like the BCM was a better value as far as price went (you're paying a bit for the name and logo as well as the quality with Noveske).

http://www.bravocompanyusa.com/AR-15-20-Rifle-Upper-Group-s/26.htm

They don't sell the one I bought anymore (a BCM Upper with a 20" inch chrome lined barrel and a free-floated Midwest Industries Gen 1 SS-15 rail, BCM BCG and a Gunfighter Mod 3 charging handle), but that's my favorite rifle.

31354654196_ca34b1c6e5_o_d.jpg


27716209802_9dcf276978_z_d.jpg


At first I was using my Noveske lower for it, but then like most times if you have a spare upper it turns into a complete rifle at some point. So I bought a stripped PSA lower and a regular old PSA lower parts kit, stock, buffer tube and spring. Then I added a an ALG Defense ACT trigger and a Seekins Precision winter trigger guard later on.

- I topped it with a Trijicon Accupoint TR-22G (2.5-10x56 with a green triangle post).
- Used a LaRue SPR/M4 LT-105 rings/mount.
- I've always had a set of BUIS on it. I've just switched them around a fair amount. I've had everything from Troy H&K style BUIS (top pic), Mag-Pul MBUS (bottom pic), and a GG&G flip up rear and a Troy M4 style front.
- a Streampoint TLR-1 High Lumen is often on there that since I hunt at night and then I take it on and off for weight savings.
- a Harris bipod (that I also take on/off for weight savings, I have always just used my pack up and till a couple months ago. I don't know if that's staying on or not).
- a Vickers CAS/Blue Force sling w/an A2 stock attachment.
- a Sprinco buffer spring that doesn't give you that 'Spriaionggg' noise and feel like with some buffer springs.

At any rate the 20" inch precision build part of your post brought that one of my rifles to mind. I can't recommend BCM uppers and Trijicon scopes enough. Even with the benefit of hindsight I'd still get that BCM complete upper, that scope (or maybe the Trijicon Accupoint green Mil-Dot one, green works really well in poor light - the post and triangle is really quick when you have multiple targets to zap one after another) and that LaRue ring/mount set.

Like you I've also held off on getting a precision bolt gun while it's on all my lists. I used to have a really nice Remington 700P .308 Win, but sold it. At this point in time a Ruger No. 1 in .270 Win, this 20" inch AR up top and a RRA National Match A4 take care of all my long distance needs. Besides all my AR's and AK's I also have an 18" in PTR-91 .308 as well that could be used for general purpose long distance (not exactly a precision rifle), but at some point I'll likely end up getting a 6.5 Grendel and skip over a bolt action for awhile. My long distance needs/wants aren't as extreme as some and I'm not looking at getting anything to use at 1,000 yards. More like 600 yards and in.
 
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http://rifleshooter.com/2014/04/223...gth-a-man-his-chop-box-and-his-friends-rifle/
Interesting read on barrel length velocities with 5.56/223. Kind of debunks much of the DMR marketing hype. Dropping from a 20" down to a 16" only loses between 50-100 fps.

I'm not sure how this applies to here (unless the OP is interested in buying an AR with a 1/12 twist).

The rifle is a stock, left-handed Remington 700 with a chrome moly varmint contoured barrel. The bolt has been fluted and the bolt knob replaced by Kampfeld Custom. The rate of twist is 1:12″. We recognize this is the wrong twist for stabilizing heavier bullets, however, feel the velocity information gathered would be worth the effort of firing the heavier bullets.

So while what they did was interesting, most AR's out there now are 1/9, 1/8 and 1/7. Not 1/12. Although 1/8 seems to be gaining a bit in popularity from personal experience I'd venture a guess that most AR's are 1/9 or 1/7. I do have a 5.56 in 1/12, but it's not an AR ... It's a Daewoo.

At any rate here's a graph for 1/7 using M855 ...

31395605335_c280a1ed4c_o_d.jpg


http://www.sadefensejournal.com/wp/?p=1093

With a 20" barrel at least you're milking it for what it's worth. Depending on the load you might get a lousy extra 18 FPS and sometimes you get an extra 190 FPS. It just depends. That may end up being important to you with that loads performance and then again it may not be.

A 20" inch barrel keeps bullets above that 2500-2700 FPS area which seems to be necessary for fragmentation to occur for further out.

Is that extra 4 inches in length worth it to you in size and weight? To me it is just because it seems to anchor the animals I've shot a bit better possibly due to the larger wound track with some loads.

To you it obviously isn't. :Shrug
 
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Ive never seen M855 chrono that low. Its always been over 2900 in a 14.5 and close to 3100 in a 20 inch. I suspect they were using a 62 grain 223 and not real M855.
 
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