Dmr/sdmr build and testing report.

[pondskipper]

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[budlight]

Thanks for the nice write up! I've also tried to find barrels with a .072 hole (smallest) and it seems that the majority of 18 and even some 20 inchers are mid length.

You can watch a Youtube video on polishing the barrel feed ramps.

Have you chronoed any of those 77 gr?

 

[pondskipper]

Thanks!, no I haven't stuck the chrono on it yet to see what speeds I'm getting, maybe I'll do that one day this week if I can find time, the MK262 is definitely going faster than the 75gr Hornady, but doesn't seem to shoot quite as good surprisingly, its dropping about .3 -.4mils less at 300yds than the Hornady.

Thanks for the kind words on the PM's guys but no I don't have any plans on ever selling it.

 

[pondskipper]

I got to run a few rounds through it yesterday afternoon of the 75gr 5.56 hornady superformance and was getting 2870 from an 18" barrel and it was also maintaining about 3/8" groups which is fantastic and will likely be what I start feeding it from now on, I didn't get to test anything else out because the bottom absolutely fell out on me. South Alabama/Mobile area sucks that way, sun could be out and it could be pouring buckets..

Another thing to mention is the jp enterprises scope mount, if you want a rock solid mount that will absolutely NOT give or move, it's built like a tank! I'm sure it would rip the top rail off the receiver before it turned loose of it, definitely spendy for a scope mount at 200 bucks but it's 100X better than the Burris mount I had. Well worth it for me.

 

[pondskipper]

Was able to get some more velocity testing done yesterday with the 77gr black hills MK262 and the Hornady 75 gr match, the gun still doesn't seem to care for the MK262 as much as the Hornady as far as group size is concerned which I guess when you measure the group and remember its coming from a gas operated semi auto rifle its still nothing to throw rocks at measuring just under 1/2" but what really caught my attention with it was the ES I was getting from it, the average ES is 9 fps for 10 shots and those of you reading that shoot long range will know just how important that is as distance begins to increase. The hornady is still maintaining the smallest group size in the rifle for sure but the ES is pretty high in comparison at around 32fps but it definitely makes you look a pro at short range measuring .250" center to center.

Black Hills 77gr 5.56 velocity average is 2770 fps. Es of 9 fps. average group .485"
Hornady 75gr match velocity average is 2694 fps. ES of 32 fps, average group of .250"

All groups were shot prone, from a bipod at 100yds using only a rear bag rest.

Chronograph used was a Magnetospeed V3

 

[pondskipper]

gun)gun)

hornady 75 gr match vs black hills 77gr mk 262

 

[pondskipper]

Both groups are 5 shot groups as well incase anyone was wondering.

I think this pretty much wraps up my build and testing blog for the dmr coyote gun, I do plan on finding a good hand load for it as well and will report back on here in the near future with my findings, its just hard to make myself sit down and do it especially when 223 match ammo is pretty cheap in comparison to other calibers, especially my 300wm and my 6.5cm.

As far as my feelings are concerned about semiautomatic precision rifles, its safe to say I've seen the light and that I believe now that they can be made to shoot as good as their bolt action counterparts, they are more finicky but if you have a good understanding of the system and use quality parts and ammo you CAN make them into real shooters! Obviously I cant guarantee you the same results as I've had with mine if you were to build one identical to it but I'm sure it wouldn't be far off at all, possibly even better. Hopefully anyone looking to build an accurate AR one or is new to the design will find this, and that it will be helpful for them and give an idea as to what to truly expect from one at different levels of build state from bone stock to full out custom and what problem areas to look for.

Thanks for reading,
James S.

P.S. Keep an eye on the ELR page, I'll be trying out my 300WM at 2000 yds later this summer.

 

[pondskipper]

Ok guys, I'm having a bit of trouble with the rifle maintaining zero and I'm not sure what it is. I've tried 3 different scopes on it now and they all are doing the same thing so I know it has to be something to do with the gun. I've checked, checked, and rechecked to make sure everything was right like it's supposed to be including the scope mount and barrel nut, but for the life of me I can't nail down the problem. The scope mount is a jp enterprises 34mm optic mount that's super strong so I don't think that's the issue. One thing I did notice was that when I slid the gas block and tube on when I was putting everything in the wilson combat upper was that the gas tube was pressed more tonone side than the other, I think the alignment slot for the barrel is a little off or the passage for the gas tube is off causing it to bind some and seeing as how it's basically connected to the barrel this could be causing the issue but you would think that is would cause accuracy problems and not problems maintaining zero. Any thoughts?

Scopes tested were Burris xtrii 2-10x42, 3-15x50, and
vortex razor hd gen II 4.5-27x56 from my 300wm so none of them are junkers lol.

 

[GFO127]

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

You are correct. I would never recommend anyone use a rifle length gas system with an 18" barrel, as they are always over gassed due to as you stated oversized gas ports because of the short dwell time. I always build an 18" with either a midlength or an intermediate length gas system. Now for 20" or 24" definitely go with the rifle length system, and usually I only use an adjustable gas block on suppressor builds. If you use a high quality barrel, such as White Oak, Wilson Combat (which by the way I would've used with their upper and lower and it's only 10.00 more than the White Oak barrel), and Ballistic Advantage, which I use quite a bit and get excellent accuracy out of. As a few people and the OP mentioned the key is to get everything running in harmony, which can be done many different ways, some, or even most that aren't that horribly expensive. You don't even need a Billet upper and lower matched set, just a good quality forged upper and lower set. It's all about who finishes the forged upper and lower and the QC of the company who does it. Palmetto is ok for an entry level first or second AR but there are way better quality companies out there who have excellent forged uppers and lowers, Aero Precision to name one. Also if you want to build a very accurate AR I usually recommend a 20" Heavy free floated barrel, fluted or non fluted with either a Billet match upper lower set, or a quality forged upper lower matched set. If you would like me to do a parts list for one of my custom match .223/5.56 20" barreled rifles I would be ok with listing it out for you all if you would like just let me know. I spent 15 years in the US Army and have been designing and building AR's for the last 10 years. Also I guarantee all of my rifles from 14.5" barrels on up to shoot under 1 MOA at 100 yds with quality ammo, and our match guns are guaranteed to shoot under .65 MOA at 100yds with quality match ammo. So yes AR's can easily be made to shoot sub MOA with the proper parts and combination of parts. Good luck with all you builds guys.


SSG G. OUT


"Death Waits in the Dark"

 

[GFO127]

Ok guys, I'm having a bit of trouble with the rifle maintaining zero and I'm not sure what it is. I've tried 3 different scopes on it now and they all are doing the same thing so I know it has to be something to do with the gun. I've checked, checked, and rechecked to make sure everything was right like it's supposed to be including the scope mount and barrel nut, but for the life of me I can't nail down the problem. The scope mount is a jp enterprises 34mm optic mount that's super strong so I don't think that's the issue. One thing I did notice was that when I slid the gas block and tube on when I was putting everything in the wilson combat upper was that the gas tube was pressed more tonone side than the other, I think the alignment slot for the barrel is a little off or the passage for the gas tube is off causing it to bind some and seeing as how it's basically connected to the barrel this could be causing the issue but you would think that is would cause accuracy problems and not problems maintaining zero. Any thoughts?

Scopes tested were Burris xtrii 2-10x42, 3-15x50, and
vortex razor hd gen II 4.5-27x56 from my 300wm so none of them are junkers lol.

Could be the gas block because that is what operates the rifle so with the amount of gas going to the BCG changing all the time, if that's what's happening you will get a POI shift causing your zero shift. Also what brand of adjustable gas block are you using? You also need to make sure the set screw is tight on your adjustable gas block locking it in whatever position you adjusted it to or you will have problems with operation as well. Is your JP optic mount completely on your upper or does it span both the upper and your handguard/rail system? If it spans both and the handguard is not to the same spec as the upper you could have issues with movement and then your scope would be off the next day or later in your range session. Let me know about those questions and we should be able to get this fixed for you.


SSG G. OUT

"Death Waits in the Dark"

 

[pondskipper]

It's an AR stoner adjustable gas block, I checked it all out last night again, I took the hand guard off and loostened the gas block and checked to see how much left and right play it had before it would bind and it's actually centered and nothing was loose when I took it apart so I'm at a loss. The mount does not bridge the hand guard at all, I knew better than that when I built it. The only other thing that comes to mind is the aluminum barrel nut holding the barrel on, again its not a problem with accuracy which is strange because it shoots great, but it won't hold zero from shooting session to shooting session, which consists of getting it out of the safe, going out in the back yard and shooting anywhere from 100-500 yards and going back in the gun safe unless it needs cleaning. using the same ammo every time too.

 

[pondskipper]

Ok so I figured out the problem, and I'm a little embarrassed to admit it but it is something noteworthy to mension for anyone who may be new to ar15s. They are more sensitive to differences in positional shooting than a bolt gun.. what I mean by this is that things begin to happen before the bullet leaves the barrel, I had been shooting exclusively prone with it during testing of different parts and what effects they on accuracy. Once there was nothing left to swap and I wanted to start reaching out further I started to use the large stump in some of the photos as a shooting platform and that's where my problems started. When laying prone directly inline with the gun all recoil impulses are directed straight backwards against my body and everything stays perfectly centered, when I swapped over to shooting from the stump I was doing so standing, which effectively turned my torso into a pivot point and being right handed, every time I would shoot the shots would cosistantly impact about .4 mils left because as my body absorbed the recoil on the right, the muzzle would turn slightly left. I never had a problem with it from my bolt guns because for the most part there's not much that happens prior to the bullet leaving the barrel but on an AR there's a lot going on before the bullet leaves the barrel. Embarrassing as it may be I figured it was worth mentioning for people who may not have much experience with gas guns.

 

[Lefty38-55]

Ok so I figured out the problem, and I'm a little embarrassed to admit it ...

You know, when I was reading through the "failure to maintain a zero" my mind immediately went to ... could it be the nut behind the trigger?

And I was going to ask that too, but you figured it out! Good on you! And don't beat yourself up, besides a great shooting toy - you learned a valuable lesson! Albeit the hard way, as ...

Experience is a TOUGH Teacher, as it gives you the test 1st ... and then the lesson later ...

Nice posts sir!

 

[pondskipper]

Yeah, it was something I've never noticed before now with all my bolt guns, even the magnums, I chock it up to the semiauto design in that things begin to happen PRIOR to the bullet leaving the barrel which in a bolt gun is never really an issue. It is noteworthy for people who have had little to no experience with semiautomatics though that you really have to be consistent with your position and very locked in to get the best out of them. The other thing I did learn from it was that I was very consistent from position to position, in other words I could still print tiny groups standing and prone but due to the differences in the way my body absorbed the recoil there would be a poi shift to the left when I wasn't in the prone, which is a consistent .3 mils left so if I'm ever in that position hunting I'll know to aim .3 right and I should lay them out fairly easy. I'll be going after more coyotes this Saturday now that the weather has finally chilled out. I'll report back on Monday.