Copied from another thread:



The ER scopes are first focal plane or front focal plane. That means
that the reticle gets bigger or smaller relative to the target size
depending on the power setting. In doing this it keeps the mil spacing
correct on any power so it has advantages in that you can range, use
holds for wind or hold overs or holds to shoot movers on any power.



With
the standard second focal plane scopes ( LR/T) the mildots are only correct on
one specific power as the reticle's size doesn't move but the image of
the target does get bigger and smaller as you adjust the power setting.



 

You still would benefit from a sloped mount. Scopes work better near their mechanical zero (middle of the scope) so pretty much anything past 300 yards you're getting out of that area with a .308.

Just got finished building this guy...

Mega Arms MATEN Megalithic upper/lower receiver set
Rainer Arms Match Barrel 20" 1:10 twist
Magpul UBR stock in grey
JP Enterprises low mass chrome carrier and enhanced bolt
JP enterprises muzzle brake
Heavy buffers carbine buffer, spring and tube
CMMG lower parts kit
Geissele SSA-E trigger
American defense mount
Viper Vortex PST 2.5-10x32 glass

The pics are with the ADM Recon mount but it was too tall so I'm exchanging it for the Recon SL which should be delivered in a few days.

https://farm4.staticflickr.com/3918/14437575261_2a6926753f_b.jpg

https://farm3.staticflickr.com/2927/14417801916_b1c322cff8_b.jpg

https://farm4.staticflickr.com/3889/14439589842_91126c0ece_b.jpg

Very nice!
Welcome

YES YES YES!!!!  I love it!  0 inch with the UBR is what I am working on now!!!  I love it!



 

I'm not a fan of the big muzzle brake, but the rest of the rifle is nice. I don't like the looks of the 2 port style brakes, but definitely can't argue against their effectiveness. Nice build, job well done!

Agreed, it's a personal taste type of thing.  Also it's one of the easiest parts to change out so I can rock a different style if wanted!

Surefire 7.62 would be sweet....and you don't have a huge diameter barrel so you don't have to make shoulder shield like i did.

















 
 

Looks like they have a "Rifle Length" and "Extended Rifle Length" option for hand guards, but I don't see exact lengths for either.  Any idea?

If you are talking about mega mkm receiver hand guards the rifle is 12" and extended is 14" I believe it is the same for the megalithic

No go for gap making the collar. Looks like I am going to have to pay out the ass to have a machinist make it.

Or just don't get one.

DAMN!!!  Are you running the Surefire like mine or are you running the other one?  Also: see my incoming IM.



 

It doesn't work like that. It NEEDS IT. It's just an look that I prefer.

I agree.  I think the collar is essential for protecting the geometry of the barrel shoulder.



 

Do yall shoot these things or look at them?

Shoot



...but trust me when I tell you that a barrel is a lot softer than people think...I have no worries about scratches and gouges, they don't bug me at all...BUT the shoulder of the barrel is a critical feature.  Not as critical as the muzzle...but critical.  I protect that end of the gun at all costs...that's why I prefer muzzle breaks or FHs that fit across all dimensions.



 

Ya!! What he said

LOL...IM on the way w/ good news/.



 

How much torque are you guys putting on your barrel nuts?

I put 65 ft-lbs on my JP 20" barrel and am having about 2" groups at 100 yards. JP suggested re-torqueing the barrel and possibly going a little higher.

I would also reccomend a fair amount of Loctite around the barrel extension inside the receiver.

I originally put anti seize compound on the barrel extension.

Should I remove that and put Loctite 271 (red) on the extension?

If the shitty toque wrench I got from OReilly is correct, I put 80lbs on mine. The damn barrel nut would not line up, after trying 10 times to get it at 60lbs, I said screw it and torqued it til it lined up. Haven't done any real accuracy test, but is grouping about 5" at 50yds with irons. Zeroed the sights in at 25, and have been pretty consistent during break in. I'm only at 100rds or so, all got another 5 mags before consider it broken in.

My guns seem to shoot better with the extension bedded in.

All the guns I've worked on that have a reputation for accuracy, have an extremely close/interference fit on the receiver and extension.

I wouldn't change anything just yet.



My barrel nut is at about 55lbs.  How tight did you torque your brake/fh?  Those don't need to be so tight.  Mines at about ten ft pounds with plenty of rockset.  I shimmed it to about 15 to 20 degrees from TDC and then tightened it up.  Didn't take a lot, like I said, but the rockset holds it plenty fine.



By they way, if your barrel nut is plenty tight ( which it is ) and your FH isn't crazy tight, I suggest getting in a bit more shooting.  With my 308 Mega and my 5.56 DSA build I had initial issues with interfacing with my optic correctly and that caused me plenty of issues.  When I marked my stocks and did a lot more practice getting my optical alignment correct....my groups shrunk a LOT...and fast.



My Mega, by the way, is a JP barrel....a fantastic shooter.  I suggest you gather some more sessions at the range.  Focus on technique.  I mean, do make sure your scope mount and rings are tight, etc., etc., but once that is done....just shoot.  More data will really help you out.  I know one thing...you don't have a loose barrel.



 

What type of ammo? What type of rest? If this your first large frame AR? Barrel torque isn't the first thing I would look at when trying to diagnose accuracy problems. As stated, 65 ft/lbs should be plenty. Go over your equipment again, change ammo, read about proper shooting fundamentals, dry fire using those fundamentals, make sure the barrel is clean, dry fire, and try dry firing some also.

Done... will break it in on Saturday

NICE NICE NICE NICE!!!!



 

My best guess is, assuming he's using good parts across the board:  scope/eye interface.  I am having the same issue but am slowly getting things dialed in.  I had much better results today.  I lengthened the pull, adjusted my cheek piece carefully and also added an MDT Anschutz style adjustable butt plate in order to get proper shoulder interface also.  I've shrunk my group size by over 75 percent.  I also brought the gun in to fifty yards so I can really focus on everything from my technology to my technique.



I still have a lot to learn on AR-10s and scoped ARs in general; so I am taking my time and being really scientific.  I make only one change at a time and I do a lot of dry practice before I go hot.  I'm still having some alignment issues but it's getting better every session.



My groups have gone from two inches to one inch and the ONLY reason they aren't one third inch is that I am still having some interface problems.  I'll put two bullets in a single hole and then one a half inch or so out.  I need to work on my sight picture more as I am still getting too good of a picture when my face has shifted.



That being said, the repeatability has increased many fold.  After working on consistency all morning, I went out to 300 yards and swept the field. BANG-DING-BANG-DING-BANG-DING, etc.



 

In fact, this might be good for any of you guys who are new to the scoped AR game.   If any of you are frustrated, angry or just bewildered if you are having issues with your scoped AR...you aren't alone.





In the past, I have NEVER had a problem with scoped sporting guns be they auto or bolt.  I would install the scope, align everything, set up my eye relief, tighten the works and head to the range.  3 to 10 shots later...done.  I rarely touched the scope again.





Scoped ARs have been a nightmare for me...and for a while I thought I had improper equipment, lousy ammo, etc.  In fact, on my 5.56 bench gun...to add insult to injury, my gunsmith DID NOT torque the barrel correctly which DID cause a big problem and a LOT of unnecessary time.  Once the goofy barrel nut issue had been resolved...I thought my problems had been resolved.





HA!  No such luck.  I was STILL shooting shotgun like patterns.  As an experiment, I put a rubber appliance dot on my MOE stock on my 5.56 gun when I got a good picture.  I used it as a reference point to make sure my face was in the same place every single time I squeezed the trigger.  My group size and repeatability improved IMMEDIATELY.





I began to understand that my physical interface with an AR is different that with a sporting rifle and when coupled with a scope that has a generous eye relief, I could get a perfectly good picture through the scope even though I was technically not correctly aligned with it.  I n other words, my optical path allowed for a good picture that was not necessarily aligned with the optical path of the prior shot.  I  started picking up on it with the help of an observer noting that the position of my face was changing from shot to shot.  Sometimes, imperceptibly...and those shots were repeatable...other times it was VERY noticeable.  Those were the shots that were fliers.





That is when I started to focus on optical alignment.  There's a lot more to it...but let me show you what my groups look like as my setup and techniques improve:





Here is a 3 shot group typical to both my 5.56 and my 7.62.  This was shot with my Mega:





''





Note the bullseye shot.  That was actually a MISS.  I had not adjusted for windage yet due to my inconsistency issues.   The bullseye shot SHOULD have been with the other two you see.  My sight alignment changed inbetween shots.  The the first shot was to the right.  The second was in the bullseye.  I backed off the gun and set up my third shot freshly.  That went back to the right where it belonged.





So, I added more length off pull, I also adjusted my cheek piece.  What I did was make my sight picture more critical.  My eye MUST be properly aligned before I get an acceptable sight picture.  Only proper alignment results in a good picture.





So much easier said than done when you have an optic with a generous eye box.





Here's a subsequent group.  Now prior to this, I had finally started getting enough consistent data that allowed my to adjust some left windage into my shooting.  Note that this group is 4 shots instead of 3 as it was the end of the box of rounds.





''
Two round were in the main group and so I didn't refresh my shooting position, even though I felt it was a bit wrong ( BAD MISTAKE ) ....shot 3 is the flier.  SO, I backed off the gun and set up for my last shot...that goes into the original group.  Alignment....optical alignment.





As you can see...I am GETTING there, bit by bit.  I need to do some more tweaking and practice.  If I can get the picture so that I can SEE that I am wrong without having to back fully off the gun...then I'll have perfect repeatability.



So, if you guys are getting hiccups in your groups....some of my issues...may be your issues.
 

Well I made it 10 whole pages in this thread before I broke down and ordered a ambi receiver set from Rainier . Now that I got that out of the way, I can continue through the rest of the pages for some ideas on the direction I want to head with this build!

Sounds familiar.
I don't owned a 308 yet and may follow suit and order an upper/lower set this summer and start a gradual and slow build.
What did you get for upper/lower from Ranier? They anodized or nickel set?
Question - is this DPMS bolt based or AR10 based?
I like the Ambi set using std AR15 parts.

I got the anodized set. From the research I've done so far you can use either dpms/sr 25 or ar10 bolt as long as the barrel extension matches.

First official post , been lurking here for a few years.  I'd like to thank everyone on this thread for getting information out there on these builds.  You guys saved me a lot of time and money by me just researching this thread.  So here's a list of parts and my contribution to it.


Mega Maten MKM
Mega Barrel 16 inch
BAD ASS Safety
Rubber City Armory BCG
JP Captured Spring
JP Syrac gas block
Melonite Gas Tube
PWS FSC30
Magpul UBR
Magpul MIAD Grip
Geissele SSA-E
Zeiss Terra3 4-12x42mm
Larue LT104
Atlas Bipod BT10-N

He also had a little brother in the process of this build
" />" />" />" />

Well holy shit, look what the cat dragged in! Maybe you do know how to operate a computer after all. Glad to see you've finally made it on here, bud!

Excellent first post, BTW!

Wow, slick looking rifles sir. Welcome!

JohnY516:
Thanks for the info. I guess it the barrel extension + bolt.
I think I'll decide once I find a decent 20" SS barrel and base the bolt on the extension type.

If you can't find it in this thread...I don't think it exists!!!!!



 

I have tried several different types of ammo.

Winchester 168 gr. Match
Winchester 150 gr Power Point
Winchester 150 gr Power Point Plus
Remington UMC 150 gr.
PMC Bronze 147 gr.

I know only one of those is high quality ammo, but some of the groups were up to 4" at 100 yards, with the smallest being 2". I figured they would be smaller than that.

I am shooting using a Cabela's rest. It has a base with a rest for the front and rear of the rifle. I put a sandbag in the base to keep recoil to a minimum.

I have a Vortex Viper 4-16 in a Larue Mount. The optic was mounted per Larue instructions, and the mount levers were adjusted to spec as well.

I increased the torque to 85 ft lbs, cleaned the rife, and went back to the range.

After getting frustrated with the results, I threw the mount and optic onto my Larue 18" 5.56 OBR and shot sub MOA right off the bat using 69 gr match ammo. Since I had good results with the second rifle, I am confident my shooting technique and setup are adequate.

I also threw on a different optic with a mount that was not quick detach, but the results were the same.

So, I have ruled out the possibility of an optic or mount issue.

Twice, I have shot 3 shots that were touching, but the 4th and 5th were all over the place.

I have about 200 rounds through the rifle so far.

Point: what muzzle brake/FH are you using?

The JP Medium brake that came with the barrel. I put some anti-seize on the threads and screwed it on. I torqued it with a dowel rod until the top was flat like JP instructs.

Thanks they cost enough,  I had no idea what I was getting into with the cost of the .308 until I added it all up.

Okay, cool...so that's not crazy torqued.  Honestly, I think going to the top of spec in this instance was not really the best answer but obviously you didn't do any damage either.  I just know that 85 pounds of torque on the receiver is a heck of a lot.  Goodness, the bearing caps on my 4.0 Jeep are at 92 ft lbs and those are steel on steel.



Anyway, I just hate running things like that to top of spec....



Man...I am so at a loss here.  I, myself, am VERY new to the scoped AR game so my input as far as optical issues is minimal.  You can see my post above that I am still struggling a bit with much simpler issues than yours.



I SO HATE BEING STUMPED!!!!



Okay...what trigger are you using again?   and what weight.....



 

this is gonna sound stupid but here is what I think you should do next.  Yank the brake, clean the muzzle, put on the thread protector if you have one and go shoot another set of groups...just a couple....you'll know in a heartbeat if that is or is not the problem.



What I am good at is this: problem solving.  The best approach to solving issues in a complex system is a scientific approach.  Right now we only have theory SO our best bet is to ONLY change one thing at a time.  Start with Occam's Razor...simple solutions are often the best solutions.



I will be honest..I do NOT think it is the brake....BUT we MUST be scientific.  Just shoot two or three groups.  You'll know right away if that's the problem.



 

The trigger is a Geissele SSA, which is the same great trigger Ithat did so well in my OBR.

I think I have ruled out the following problems using the scientific approach

Barrel not tight
Mount not secure on rail
Optic not tight in mount
Ammo (I have only tried 147, 150, and 168 grain but come on...)
Shooting technique ( I shot sub moa with an OBR)

I will try removing the break and report back.

I called them and they said to:

Re-torque barrel
Clean barrel
Try match 150 or 175 grain ammo
Shoot with a mount that isn't quick detach

I have done all of those and it didn't solve the problem.

I will call on Monday.

Man...if it ain't the brake....there's only one thing left....okay...two things.....the barrel...or the nut behind it.    My problems are all from barrel nut 2.  



 

...

About how many ounces was shed with the dimpling? Also who's gas block is that?