AR-15 Build Questions

Discussion in 'Black Rifle Forum' started by RustyDaleShackleford, Dec 1, 2011.

  1. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

    A few days ago I bought a stripped AR-15 lower online from Palmetto State Armory when they went on sale for $49.99 plus $7 FFL shipping. I've never built an AR-15, but I've been wanting to for a long time, and knew I had to buy since the price was right. I've been doing a lot of reading online and watching videos on building your own, but still have a few questions. I want to build a decent quality, all-around good rifle.

    From my reading, here's what I think I want:
    - 16" barrel, non-fluted, chrome-lined, 4150
    - M4 extended feed ramp cuts
    - chambered in 5.56 NATO
    - 6-position adjustable stock, mil-spec buffer tube
    - forged front sight base, f-marked, parkerized, tapered pins
    - MP tested, pressure tested, shot-peened bolt
    - flat-top upper receiver, T-marks on rail
    - staked gas keys
    - non-staked castle nut (I've heard it's not a big deal and can be a huge pain if you want to remove it)

    Now here's what I'm still a little hazy on:

    1. What's the difference in cost of building a piston gun versus a direct impingement gun? And specifically what parts are different?

    2. Is a midlength gas system, with a 16" barrel and 9" handguards the only setup which allows for the attachment of the M9 bayonet? Even if I never use it, it'd be a cool feature to have. And do you have to have a standard A2 front sight base to use it?

    3. I've heard about fully shrouded firing pins. What does this feature do, does it cost more, and is it worth it?

    4. What are material are collapsible/adjustable M4 stocks available in, and which would you recommend?

    5. Should you definitely buy your barrel and bolt-carrier group from the same place and at the same time? I've read this ensures accurate headspace. And how do you know if this is correct otherwise?

    6. I'd like to get a chrome-lined barrel for better functioning and longevity, so is there anything else that can be chrome-lined for better quality, and any that you would recommend?

    7. Will a barrel with a 1:7 twist rate reliably fire all bullet weights, since it's capable of stabilizing heavy bullets?

    8. Somebody told me that since I'm a noob to this, I should buy a lower parts kit and a stock kit to finish up my lower, and just buy a complete upper and pin it on. I'd rather build my rifle one part at a time (or one group at a time), as I browse the internet and find deals, which would also allow more customization and familiarization with my weapon. What do you think?

    Thanks in advance!

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    #1 RustyDaleShackleford, Dec 1, 2011
    Last edited: Dec 1, 2011
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  3. Good luck!

  4. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

    Specifically what parts are different in a piston vs DI build? I can't seem to find parts descriptions.

    I've heard that you actually want your castle nut not staked, while you do want your gas key staked. They say it's because the castle nut is unlikely to come loose, is difficult to remove if you decide to, and you can ruin many tools doing it.

    I'm not worried about having trouble building the upper from scratch, and would prefer it if it's at all cheaper. I've got a cousin who lives nearby who's built several AR-15's and who said he'll help me and let me use his tools. So the cost of tools isn't a problem.

    Is my thinking right? 1:7 is the fastest barrel twist rate, and since it stabilizes the heaviest bullets, that covers me for any bullet weight I'd want to use. Right?
    #3 RustyDaleShackleford, Dec 1, 2011
    Last edited: Dec 1, 2011
  5. With DI you have a gas block and gas tube. The piston system replaces these with the piston system. The BCG can also be modified depending on the system. One of the big downsides is replacement parts, all the different systems use different parts. You can get DI stuff anywhere. It also adds weight to the end of the barrel throwing off the balance unless you use a heavy stock.

    Yes, staking the castle but makes it hard to remove, that's the point. If it backs off your day is over. For a range gun it's not a big deal but it is for a fighting rifle.

    Yes, get a 1:7 barrel. Unless your going to be shooting 40gr bullets you'll be fine.

    Did your friend build his upper? It's not just the tools but the know how. If your up for the challenge and troubleshooting go for it. In the end your still not going to save much money, if any. With PSA and Spikes selling for $400-$500 complete it's hard to beat.

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    #4 boomhower, Dec 1, 2011
    Last edited: Dec 1, 2011
  6. M&P15T

    M&P15T Beard One

    I have never heard of anyone doing a "piston build". Piston ARs are not like DI ARs, where the parts are interchangeable. Piston gas systems are propietary and different from one manufacturer to another.

    Do yourself a huge favor, just buy an upper. Building an upper is pretty pointless, considering how cheap they are.
  7. IMHO, if you don't absolutely LOATH cleaning, a DI system is better. The new DI uppers, from my experience, don't have the crazy cleaning and lubing requirements they used to. Not sure if its looser tolerances, materials or what??? They will get super dirty, but don't start having jamming, feeding, cycling problems as early like they used to. Maybe I'm just lucky on my newer rifles. Of course, the longer you go between cleanings, the more time you should expect to spend getting all of the CD off of the action parts.

    Also, don't listen to anyone who tells you that cleaning the gas tube is necessary. The pressures and heat in the gas tube are sufficient to burn and blow any residue away from previous shots. I've gone countless (excess of 25k) rounds without spraying or cleaning my gas tube.

    The DI system, as noted, is fully standardized, where piston is not. This can even include BCGs, along with the expected release valve and piston. Also, adjustable piston systems may need to be tuned based on the load you are shooting. Even a slightly mis-tuned piston system will be slower to cycle than a DI, even if it cycles reliably.

    So you save some money, and some weight, and lose some potential drawbacks to the piston system. To answer your question, the gas block is replaced by a gas relief valve, the gas tube by a piston, and often the BCG, or bolt carrier is different between DI and piston. I haven't checked in a couple of years (since before I traded my last piston rifle in), but they were $400-$500 more at that point.

    Id also like to suggest getting a complete upper. While parts-count-wise they are less complicated than a lower build, you have to worry about getting the gas system aligned and pinned, barrel aligned and torqued correctly, and check head-space and bolt seating. You MIGHT save $50, if you are lucky, on a $800 upper. Not worth the ~6.5% savings, which you would, if doing it correctly, easily spend on specialty tools.

    On barrel, I wouldn't go over 1:9. 1:9 will shoot into the mid to high 60's gr. If you want to shoot heavier, go to a 1:8 or even 1:7. But don't expect a 35 or 40gr dog "poofer" to shoot well. Fast twist rates can cause wobble on lighter bullets. I like the 1:8 for the compromise. If you are a typical AR shooter, a 55gr FMJ will be 95%+ of the ammo you send through it, since it is so cheap. I have found the 1:8 shoots these better than the 1:7, though my 1:7 experience is limited compared to 1:8 or 1:9. On barrel material... chrome will give you better longevity, where a good SS will give you a hair better accuracy. Your choice there, both are good.

    On buffer tubes... all commercial buffer tubes have 6 positions, whereas true mil-spec have 4. Maybe someone produced otherwise. It is a metal tube! It will not fail on you, one place where Mil-spec is irrelevant IMHO.

    For chamber... unless you want a precision rifle, go with a 5.56 or a .223 wylde. The .223 wylde is a bit better than 5.56 IMHO. It more or less cuts the difference down the middle between a 5.56 NATO and a .223 Remington. It still shoots .223 Rem and 5.56NATO. You will find with a 5.56 action, .223 Rem cartridges will not be as accurate, especially in the cheap loads. This is because there is extra "slop" in the head-space. I've personally found that super-premium .223 Rem fires great out of a 5.56, but the super cheap stuff is below mediocre. For most shooters, .223 Rem is cheaper and much easier to find without special order than 5.56, so most of the "plinking" is with .223 Rem.

    For the stock, I also like Magpul MOE stock. They have one for Mil-spec buffer, and one for commercial buffer, just buy the one that matches what you have. if you want a precision rifle, definitely use a fixed stock... but it sounds like you want adjustable, and the MOE is the best per dollar here for me. They are all made from various plastic polymers. I haven't seen any in metal. Never heard of one failing due to UV, cold, chemical exposure, so to me they are all the same material wise.

    For Bayo... what you describe is the standard. But others have produced different specs that still have a Bayo lug. Nothing I've ever wanted, but I've seen them. Of course the mid-length gas system and the 16" barrel is the most popular, so expect to find more parts available, and more options like handguards / quad-rails available for such a setup.

    Don't care about a shrouded-pin carrier (the shrouding exists on the carrier, rather than the pin). As stated, most are, so they can be used in a select-fire weapon. They add a small bit of safety, but such a small amount it is negligible. Also adds a small amount of reciprocating mass, to aid in reliable cycling, again negligible. If you plan to cycle lots of rounds, the BCG is one place NOT to skimp on costs. But buy it anywhere that makes quality components. BCGs and Barrels are mixed and matched all the time.

    If you do build your upper... make sure to get a gas-block alignment tool, and at least a go/no-go head-space tool (or a full head-space gauge), a set of barrel-blocks and a punch set. Might be worth buying a bottle of whiskey for an experienced friend or acquaintance to check your work, or throw a gunsmith $50 under the table for a quick once-over before firing. On subsequent builds, you will know that your first one was done correctly, and might not want/need it to be double checked.
  8. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

    I've been searching the internet like mad for the last week in search of the ideal barrel, and I just can't find what want.

    I'd like 16", chrome-lined, drilled for a midlength gas system, and with M4 extended feed ramp cuts. I haven't bothered reading the descriptions of those over $200, because I've seen the cheapest barrels going for under $100. It just seems like that's too much, or is that what you've gotta pay for a decent and still budget barrel?

    Also, do they make 16" barrels drilled for midlength gas systems, or are they all just carbine length? It seems like that's all I see, and I'd really prefer the midlength. Do I need to go up to 18" for that?


    rock and roll
  10. mvician

    Lifetime Member

    Don't skimp on a barrel or bolt carrier group
  11. They make them in mid-length, I have one in that setup. I agree, the BCG and barrel are the most important parts. Also, the barrel isn't as easy to swap later like some things are.

    You can find a good quality barrel for about $180. If you have a budget, thats where I'd be looking. No need to go over $200 unless you want a comp long-range AR. Those 24in SS bull barrels get pricey!!
  12. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

  13. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

    Well, I completed my lower receiver with nothing but the tools I found in the garage. Actually everything but the bolt catch, because I accidentally got my bolt catch roll pin (permanently?!) stuck on the punch I was using, but I've got two extras on the way right now for around $1.

    I also ordered most of the rest of my parts. On the way:

    - 16", 1:7, chrome-lined, 4150, midlength barrel
    - full chrome RRA BCG
    - midlength gas tube
    - stripped upper receiver
    - upper parts kit, including charging handle
    - x2 bolt catch roll pin

    I purposely didn't order some parts yet, like a FSB and handguards, because I'm not sure yet if I wanna free-float, etc.

    People have told me that since I went with a chrome-lined barrel, there's no point in free-floating. True? Because I've also heard that your rifle's accuracy isn't made or broken on any one thing (except maybe the barrel), and that accuracy is more like making up $1 out of a dime here, a couple pennies here, etc., and that free-floating would be like adding another nickel or dime to my "accuracy dollar".

  14. Free floating will still make a difference on a chrome lined barrel, especially if you use a sling mounted to the handguard for shooting offhand, or if you mount a bipod.

    Honestly, you should have ordered a complete upper. Putting one together and getting the gas system lined up, and properly securing the gas block (assuming you don't have matched holes in barrel and gas block for taper pins) can be a real pain in the ass.

    As for the earlier question of staking the castle nut, I have never had it done on a single AR, and I have never had one come loose, even when run hard. I have one guy build all of my ARs for me, and he has built far more rifles than anyone on this board has ever owned, and he doesn't stake them. I get the feeling it becomes less of an issue when they are properly tightened.
  15. IGotIt

    IGotIt No Demlibtards

    Oh the gods of the AR world just put your name on "the list".:supergrin:
  16. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

    I know I'm missing something here because I'm an AR-15 noob, but why does putting a sling matter in accuracy?

    I'm not too worried about it. Like I said, I've got a relative who's got lots of experience and all the necessary tools and all, and I'm gonna get him to help me out when all my parts come in.

    After looking around, I know I could've found an upper for cheaper than I've already spent on all my upper parts. But I couldn't find an upper with all the specs and features I wanted, or at least not for cheap. I spend more than absolutely necessary, but this wasn't a $400 budget gun. I invested some more dough in the parts that I wanted higher quality on, and cut where I didn't think quality mattered as much.
  17. eracer

    eracer Where's my EBT?

    A couple of years ago I bought an upper with a 16" CL barrel made by Lothar-Walther (very good reputation.) I've been very happy with the accuracy (near 1 MOA with quality ammo.) That carbine has a free-float handguard.

    I recently purchased an upper from Spikes that has a 16" CL barrel made by GMP. I bought it as a relatively inexpensive KISS carbine, and put a Magpul MOE on it - not a free-float handguard. This upper suprised me by being more accurate off the bench than my LW carbine.

    Conclusion: free-float handguards are great - especially if you are using a sling - but they are not all that important to have if you are looking for decent accuracy.

    A sling helps stabilize the rifle when firing from a supported position, like sitting, kneeling, or prone. A sling attached to a non free-float handguard puts pressure on the barrel, since the handguard is rigidly attached to the barrel. A free-float handguard eliminates sling pressure on the barrel, allowing it to vibrate in its own harmonic pattern. Accuracy is all about repeatability, and a sling on a non free-float handguard introduces variability in barrel harmonics.
    #16 eracer, Dec 13, 2011
    Last edited: Dec 13, 2011
  18. :dunno:

    If your sling is mounted to the sling loop on the bottom or side of the a-frame, or on a non-freefloat handguard, the tension of cranking down on the sling to stabilize the rifle will cause a minute amount of flex in the barrel, and will screw with your accuracy. You'd probably never notice at close range, but it definitely makes a difference at longer distances. Same deal with mounting a bipod to a non-free-float handguard.

    Edit: whoops, eracer beat me to it.
    #17 WoodenPlank, Dec 13, 2011
    Last edited: Dec 13, 2011
  19. RustyDaleShackleford

    RustyDaleShackleford Giblet Head

    Got my barrel, gas tube, and replacement bolt catch roll pins in.

    My lower receiver's now fully complete, and my bolt and carrier group, stripped upper receiver, and upper parts kit should be here this Thursday.

    As for the flash hider, I guess I'll just go with the standard A2 flash hider with the closed off bottom. Should be good enough, especially since I don't plan on doing any night shooting anyway. When I buy this, should it come with a washer? And what's the difference between peel washers and crush washers?

    I'm pretty sure I wanna attach a free-float handguard, but I also like the look of the standard A2 front sight base on AR-15's. I've been doing some reading, and it seems that these are compatible, so long as you measure the handguard to make sure it allows room for the FSB. True? Again, I'm using a 16" midlength.

    But that makes me worry that I won't be able to use a scope, if and when I decide to mount one... Issue? Because I've also read that if you're looking out past x4 zoom, you won't even see a FSB.

    If I do that, I'll probably just get a rear MBUS from Magpul to finish out my rifle!
    #18 RustyDaleShackleford, Dec 17, 2011
    Last edited: Dec 17, 2011
  20. eracer

    eracer Where's my EBT?

    A crush washer is designed to compress as you torque the muzzle device to around 20 ft. lb. The problem with crush washers is that for many muzzle devices, you have to 'time' them, meaning you have to set them so that the holes are not facing towards the ground. I've found that I too often can't 'crush' the washer enough without sanding it - a major PITA. That's why I use stainless steel precision shim sets. You mix and match different thicknesses until it takes 20 ft. lb. to time the muzzle device.

    Peel washers are similar to shims, and you 'peel' away layers of the washer to get the muzzle device properly timed.

    There are some muzzle devices that don't need 'timing.' The A2 flash hider does. You may find that a crush washer will work just fine. I'd try that first.

    I use 'Rocksett' on all my muzzle devices. It's like high-temp loctite, but breaks free easily with hand tools. You have to buy it online, but a small bottle will last forever.
    #19 eracer, Dec 17, 2011
    Last edited: Dec 17, 2011
  21. Tip for crush washers with muzzle devices that need to be timed.

    Tighten slowly and back off, repeat until you have almost timed it correctly. Then make final turn to time.

    By backing off it allows the crush washer to compress enough that you can actually time the muzzle device. You should never "sand" them to make the muzzle device time properly.

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