Dmr/sdmr build and testing report.

Discussion in 'AR15/10 Rifles' started by pondskipper, May 19, 2017.

  1. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    First and foremost I am a bolt gun guy, I have never really had any love for the AR or any other semiautomatic platform for that matter. I am a long range shooter and hunter first and foremost and the semiautomatic platform in my mind allows for the potential for too many things to malfunction and also theoretically shouldn't be able to compete with its bolt action counterpart in terms of accuracy. I get asked quite often by friends, friends of friends, and family members what it takes to make an AR more accurate and aside from the things that would usually transfer from a bolt gun such as free floating the barrel, having a good quality barrel, shooting high quality match ammo, a quality trigger, and a stock with good ergonomics that allowed for a proper cheek weld and length of pull adjustment, I couldn't really help them out anymore than that because I wasn't very versed with the design. Well about a month ago, I decided it was time that I got my feet wet and learn more about them, more so out of a necessity than a desire. Coyotes in my local area have become a huge problem and hunting them with a bolt gun when they are running in packs will limit you to basically getting one or possibly two simply due to having to break position to cycle the action and once the lead starts flying they don't hang around to find out what's going on and why their buddies are blowing up next to them. Which brought me to the AR platform.

    I decided to purposely buy a run of the mill complete PSA upper and lower receiver sets to give myself a baseline as many people would do and systematically start shooting, swapping parts to see what helped or hurt accuracy in an effort to make myself more familiar with the platform inside and out. I started at the barrel and worked my way back throughout the gun, shooting, changing/upgrading parts then shooting again and documenting the results.

    (see next comment)gun)gun)gun)
     
  2. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    For a barrel I decided to consult with my friends who shoot military rifle matches and see who had the best reputation for making high quality AR barrels and to my surprise the almost all suggested a brand I've never heard of called White Oak Armament, claiming they were by for the biggest bang for your buck as well as exceptionally accurate in comparison to other brands of barrel makers that consistently cost 2-300 dollars more. I decided to go with an 18" DMR contour stainless 1:7 twist barrel with the rifle length gas system. Prior to installing this barrel the gun was normally shooting 1.2" to 1.5" groups at 100 yards, with multiple different types of match ammo. After the barrel swap, which I did myself mind you, the groups shrunk down to an average size of .5-.75 after barrel break in and the new barrel seemed to actually prefer the Hornady 75gr match ammo, so from here on out this was the only ammo fed through the rifle to alleviate variances in different ammunition. When I installed the barrel I also installed an adjustable gas block so I could restrict the amount of gas enough to where it was just enough to cycle the action open and lock the bolt back on the last shot, I do believe this does help accuracy but I can't say how much as I did it with the barrel swap so the effects it had couldn't be measured.

    My next task was to address ergonomics as well as reliability which ill get into in the next comment.

    At this point the gun was still wearing a standard A2 stock, standard crappy grip, and that lame excuse they call a trigger that has what felt like a 1 ton trigger pull with a 1/2" of creep before it finally went BANG! Knowing exactly what I wanted in all these parts I selected each one according to their feature set and what I already knew they needed to be for me. For the stock I selected the newest generation Magpul Prs stock, so I could fine tune the length of pull and comb height so that I could get a good cheek weld on the scope, it is a fair amount heavier than others but it is a very good quality unit and seeing as how I'm use to caring around bolt guns that weigh in excess of 21 lbs I honestly don't mind it, it also moved the rifles center of gravity further back which makes it more handy in both prone from a bipod as well as shooting offhand. For the grip I decided to go with the ergo tactical grip as I have pretty big hands and I was able to wrap my trigger finger around the trigger with the stock grip all the way to the third joint if I really tried. For the trigger I went with a Timney single stage straight shoe drop in unit because I am better with single stage than two stage and they feel better to me, and the straight shoe moved the trigger out even further and I am now able to use the tip of my trigger finger like I'm supposed to.

    (see next comment)gun)gun)gun)
     
  3. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    After changing the stock, grip, and trigger out I was able to maintain .5-.6" groups with the rifle on a regular basis now that I wasn't having to fight it and was able to get much more comfortable behind the gun, these things didn't make the gun more accurate, it made me more accurate with the gun.

    Every now and then I would still get an unexplainable occasional flyer that always opened the group up to 3/4" and would simultaneously have a failure to completely feed the next round, and with a light push from the charge handle, the bolt would slip right into battery just like it was supposed to, this was also always accompanied by an audible difference from the shot. I always keep the action and barrel clean and well lubricated with frog lube so I knew that wasn't the issue, what I did find is that between the super rough parkerized finish on the factory BCG along with having excessive slop in the upper receiver raceway that that the BCG rides in that it would from time to time cause enough of a problem cycling. What I did to solve the cyclic issue was replace the factory BCG with an Aero Precision nickel boron BCG and install a JP enterprises silent captured spring and from then on I never again had any failures to feed and the groups also stayed in the .5-.6" range from then on and the flyers were gone, the gun was always capable of that but due to cyclic issues and inconsistency's it would cause the occasional flyer, another added benefit of adding the silent captured spring was it no longer sounded as if there was a hobo playing an out of tune banjo inside the buffer tube lol.

    (See next comment)gun)gun)gun)
     
  4. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    After all was said and done I had finally gotten the gun to be a consistent .5-.6 shooter time and time again, knowing I had hit a barrier as basically all major parts and components had been changed out with the exception of the forged milspec upper and lower receivers.

    I did notice that when I was installing the new barrel in the gun that there seemed to be an excessive amount of play between the barrel shank and upper receiver barrel socket when the barrel was slid into place and I knew that this plus the sloppy fitment of the bolt carrier group in the upper receivers raceway were what was likely holding the rest of the system back from what it was really potentially capable of and I decided to get a billet upper and lower receiver set that was designed from the ground up to be the foundation of precision rifle platform, I looked at many brands and ended up going with a Wilson combat matched billet upper and lower receiver set to install everything into and I am glad I did! it was pricy for sure but it was money well spent, installing the barrel into the new upper I instantly noticed if you weren't holding your mouth right the shank would not slide into the socket, moving forward I also noticed just how little play there was between the bolt carrier group and the upper receiver raceway, which was roughly 1/3 the amount of its milspec counterpart, those two things plus the increased rigidity of the billet unit being thicker and stronger, I'm pleased to announce that the rifle is now shooting 5 shot groups that are seldom larger than 3/8" in diameter and just look like a single .375 cal bullet hole at 100 yards with factory 75gr Hornady match ammo.

    I learned a lot doing it this way, sure I could have just gone out and purchased all top of the line parts, put the gun together, and been done with it but I wanted to know for myself as well as for others, the things to look for and what gives you the biggest bang for your buck when it comes to trying to turn an AR into a rifle that's that is more accuracy oriented rather than the spray and pray at 75-100yds. I now feel completely confident that any coyote within 600 yards or closer, is going to be in some serious trouble. I'm sure it would still be accurate at 1000 yards and maybe in a few weeks I will load it up and take it to the range and find out, but for hunting and taking a shot at something with a pulse, I'm not going to press my luck on a cartridge this small to have the energy to humanely kill a coyote any further out than 600 yds, I know they are a pest but I wouldn't want someone to shoot me from a long ways off and let me lay there and suffer.
     
  5. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    Things to take from this are if you want accuracy form one, find HIGH QUALITY MATCH ammo it likes if you don't reload, after you install a good high quality stiff barrel, keep the gas system rifle length, use an adjustable gas block to meter the amount of gas going through the gun, get the ergonomics down to where the gun fits you not the other way around, if you are building from the ground up with a billet receiver try and find an upper receiver that has very little slop in the BCG raceway and that the barrel socket fits the barrel shank very well without the barrel nut installed, keep it clean and well lubricated and use a bolt carrier that has a smooth finish.

    I believe a reasonable accuracy expectation from a rifle using a run of the mill forged milspec upper and lower receiver with top of the line parts installed will be anywhere from .5-.75" with quality ammo depending on shooter and weather conditions.

    With a super high quality billet upper like mine which is a much, much tighter fit in every area and is thicker and stronger where it really counts, accuracy could be in the .2-.3" range possibly better.

    If you are new to AR's and are reading this and have an interest in buying one or building one from the ground up, I hope all this helps, the good news is that you can do it little by little at a time, which I'm sure most people probably do in some form or another and you'll still have a gun to practice your fundamentals along the way, and yes, AR/s really are like Legos for grownups for the most part.

    I will put together a price list for everything I have done to the rifle from the time I purchased it to what it is now along with photos showing groups as well as how it the guns looks changed along the way later on tonight.

    James S.gun)
     
  6. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    A side note. Fitment between the mil-spec forged upper and lower receiver, as long as the are within tolerance and function properly, does NOT matter or affect accuracy, I did try several different things to get rid of it with my forged receiver and in the end all they did was make it more difficult to get the upper and lower apart, the accuwedge took the slop out but accuracy didn't improve at all and over time the compressive force exerted on it was enough to cause it to have permanent marks left in it and became loose over time. The jp enterprises locking rear takedown pin was another thing I tried, which did firmly lock the two together with no slop anymore but again, accuracy was not improved and taking it out to clean the gun was more trouble than it was worth to me from a maintenance standpoint and seeing as how there was no gain in accuracy so I took it out and pit the original takedown pin back in and just lived with the play. The billet receiver set has no slop or play between the matched upper and lower set when you push the pins in but for the price it shouldn't and I know this is not something which improves accuracy for a fact.

    Honorable mention would be the radian raptor charge handle, for a scoped ar that's used for hunting purposes and may likely be shot from your strong side at times or you need to rack a round in quick this things a life saver, its well designed and executed, as well as being aesthetically pleasing to the eye. With the diameter of the pins used on the latch handles I HIGHLY doubt ill ever have to worry about it.
     
  7. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    Sorry for not getting back on here sooner but I had a friend of mine call literally when I was getting off work this afternoon to tell me that coyotes killed one of his calves so I went over to his house to help him get rid of the carcass before his kids got home, it was their cow.. Anyway, it looks as if I'll be spending my weekend over there trying to kill some coyotes, I wasn't kidding when I said they have gotten extremely bad. I'll post photos on Monday but I will get a price list together for everything involved in the build.

    PSA 18" lightweight m-lock upper with bcg and charge handle $339.99

    PSA classic lower with A2 stock 199.99

    White Oak armament 18" SPR barrel 1:7" twist rate and rifle length gas system $315 with shipping.

    AR stoner adjustable gas block $65

    Timney 3lb straight shoe single stage trigger $190

    Magpul PRS stock $214.99 on sale.

    Aero Precision nickel boron bolt carrier group $199

    Jp silent captured spring $135

    Ergo Deluxe grip $29 on sale locally.

    Radian raptor ambidextrous charge handle $80 on sale

    Total for completely decked out rifle minus optics, optics mount and billet receiver $1762

    Keep in mind a few of the things listed wouldn't be totally necessary if all you were doing was hunting with the gun and not trying to milk it for everything it was worth, like the prs stock or the silent captured spring so that would save you about 350-375 depending, but you would still have a rifle that was fairly easily capable of groups in the .5-.6" range at 100 yards which is still very respectable for a semiautomatic rifle, I've seen a few factory AR's that are in the 2500 dollar price range that still struggle to achieve that kind of level of accuracy in real world conditions consistently.

    Price with the wilson combat billet receiver after all was said and done $2372.00

    If you are thinking about building an ar from the ground up with nothing but accuracy and strength in mind, this, as their website states, is the best foundation for a precision build and I can't disagree due to the results I'm getting from mine, that said, I won't say it's the absolute best because it's the only billet AR receiver I have any experience with. I'm sure something like the JP billet receiver set would be fantastic as well and I'm sure there are other good ones out there too.

    Price with optics, $3572.00

    I didn't go into optics in this thread till this point because this was to be about building a precision AR and I didn't want to stray too far off topic, for accuracy testing I used my Burris XTR II 3-15X50 FFP and will likely swap it out with my 2-10X42 Burris XTR II for hunting, the reticle is fatter in the smaller scope, the zoom goes down lower and lets in a bit more light after the sun is practically completely gone, and a lot can happen with a few extra minutes of hunt time, especially with coyotes. Only having 10x max magnification for mid day work isn't a drawback either for long range, less problems with mirage and I've made consistent hits on steel at 1000 yards more times than I can recall with a fixed 10x scope when I first got into long range shooting about 15 years ago.

    The scope mount use was initially a Burris 34mm but mine actually failed, the studs that ran through the mount actually started to pull through the mount, I don't know if mine was just faulty or if others have had this problem but it was 114 dollars completely wasted, and yes, before anyone asks I only torqued the two 1/2" nuts to 60 in-lbs, which is not an excessive amount of force by any means and I was using a 1/4" drive snap-on inch pound torque wrench, the same one I use to torque the rings and bases to my bolt guns, specifically the ones that have scopes that are as expensive as this AR I've built. Anyway, I've replaced that mount with the JP Enterprises 34mm AR optics mount, its twice the mount the Burris is for sure but is also twice the price, its way more solid and uses 5 torks bolts running through the mount to attach it to the upper receiver, I highly doubt it will ever give me any grief.

    Again, I hope all this helps anyone looking to get into ars or anyone who's already familiar with them but wanted to make theirs more accurate, I still plan on posting photos but will have to wait till Monday, got coyotes that need to be taught a lesson! gun)
     
  8. budlight

    budlight Well-Known Member

    Messages:
    846
    Joined:
    Sep 30, 2004
    You don't need an adjustable gas block on a rifle length gas tube. I can't find the test article, but max pressure is achieved very early in the bullets travel down the barrel. So don't quote my numbers. They are from memory. on a round loaded to about 53,000 psi The gas port on a carbine length gas tube gets about 30,000 psi The mid length was 22000 and the rifle length was 17,000. They did state slow burning powder and bullet weights could change these up and down.

    I have friends with carbines and light weight BCG and when you open them up for cleaning after a few hundred rounds on a new AR the buffer tube weight face is marked up from getting slammed by the BCG. The small piece called a “cam pin” located underneath the gas key is already visibly warn already.

    My mentor told me to use the heavy full auto bolts, longer gas tubes, and possibly even heavier buffer tube weights. It all slows down the cyclic rate. I've even messed with the buffer tube end hole diameter and using flat wound springs to quiet the cycle.

    You want everything in harmony to eject your rounds every time. I have some that put all the casing in a pile about the two O'clock position and others clear back to around to nearly 5 O'clock
     
  9. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    I think I read the same thing somewhere at one point or another but what I found out was that running an 18" barrel on a rifle length gas system, and shooting very heavy for caliber bullets that it was getting too much gas initially and chewing up cases really bad and ejection was never consistent even though the original BCG and the one I replaced it with were both full auto profile and weighed the same. The reason for this was mainly due to the fact that both 18" barrels had intentionally oversized gas ports. The reason for this was because with 18" barrels with rifle length gas systems have an obviously shorter dwell time from when the bullet passes the gas port to the time it exits the barrel and the pressure drops, they compensate for this shorter length of time by oversizing the hole to let more gas through. I believe this may only be a problem in 18" barrels with rifle length gas systems and wouldn't be an issue with 20" barrels with rifle length gas systems as the gas port isn't oversized in them and they get a much longer dwell time. When I installed the new barrel and adjustable gas block I intentionally left the gas block wide open to see if it still wiped case faces and crushed case necks when it ejected spent cases and it did. Once barrel break in was done I immediately started working on getting the gas block adjusted and once it was finished it threw cases into a 12" diameter circle at about the 4-5 o'clock position and the cases came out basically unharmed, just minor scratches from the rough finish from the original BCG but even those are now gone thanks to the slick finish on the new BCG. To say that everything works in harmony now is an understatement but I've also invested a pile in it to make it what it is and once my tax stamp finally comes back I can't wait to see what it's like with a suppressor on it!
     
  10. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    These photos are to show basically how the rifle started and how it looked with the new barrel and furnature, apparently I didn't take photos of it with just the barrel swap out but I did do a before and after of how it was shooting with the stock barrel vs the new one
     

    Attached Files:

    • ar1.jpg
      ar1.jpg
      File size:
      133 KB
      Views:
      16
    • ar2.jpg
      ar2.jpg
      File size:
      118.9 KB
      Views:
      18
    • ar3.jpg
      ar3.jpg
      File size:
      170.5 KB
      Views:
      16
  11. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    The bottom target in the first photo is a good representation of the accuracy with the stock barrel and was taken just before it was changed, the top target in the first photo was done after barrel break in of the new barrel and getting the gas block set, the next two photos are representative of what the gun would consistently do with the new barrel, the last one was after I had done the stock, trigger, grip swap and are 1/2" square graphs.
     

    Attached Files:

    • ar5.jpg
      ar5.jpg
      File size:
      121.2 KB
      Views:
      12
    • ar6.jpg
      ar6.jpg
      File size:
      139.3 KB
      Views:
      12
    • ar7.jpg
      ar7.jpg
      File size:
      108.4 KB
      Views:
      11
  12. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    just more photos of the gun as it was going through transformation and buffer spring photos, also a before and after of the case heads after the gas block was set for illustration as to the affect it had on my gun, you can clearly see where the bolt face was wiping the case heads very hard prior to getting the gas block set, if you look closely you can even see the bur left by the ejector plunger.
     

    Attached Files:

  13. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    These are the latest photos of the gun after installing everything into the Wilson Combat billet receiver set, as you can see accuracy dramatically improved and I guess the stars aligned with this Hornady ammo. My gunsmith and I are actually very good friends and I was able to talk him into coming over and bringing one of his home brew registered suppressors that he makes for himself which is totally legal come to find out but he can under no circumstances manufacture and sell them. anyway, with his suppressor attached we shot some groups yesterday seeing as how the weather had basically gone to crap and hunting coyotes was pointless. I guestimated way to much for POI shift which is why the first shot is so high, but heres how it did.

    By the way, I did do all the work to this gun on my own, including checking the headspacing and installing the new barrel, when I told my gunsmith/friend how well it was shooting he had to come see for himself.gun)gun)gun)
     
  14. pondskipper

    pondskipper Well-Known Member

    Messages:
    251
    Joined:
    Aug 23, 2010
    photos
     

    Attached Files: