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Stiffest upper receiver for long heavy barrel

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Baron85

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Mar 18, 2012
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Building my first precision AR, have another post about it but looking for more feedback directly about the upper receiver. Using a 24” heavy lilja barrel and silencerco 7.62 spec war can and want a stiff upper to prevent impact change when loading bipod.

Im looking into
seekins irmt-3 ( built in handguard mount so handguard is not mounted to the barrel nut)https://www.seekinsprecision.com/product/ar-uppers/seekins-precision-irmt-3-upper.html

Vltor mur

Dpms lowpro

Nordic extruded upper https://nordiccomp.com/categories/nordic-components-nc15-extruded-upper-receiver-stripped/

Bear creek side charge.https://www.bearcreekarsenal.com/bca-ar-15-side-charging-stripped-flat-top-upper-receiver

looking online, the dpms and Nordic look significantly thicker than the other options but I have read that the vltor, being forged creates a stronger/stiffer upper when though it’s thinner because of the forging process.

I have a vltor mur and seekins normal upper already and the seekins appears to be thicker.

I personally like the looks of the seekins but I’m building this rifle for performance and accuracy as biggest concern, not looks.

Please help me choose Hide!
 
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I'm not sure which one to pick, but from a shooting technique perspective....

When you're loading a bipod, you're putting just enough pressure forward to take the slack out of the pieces of the bipod. That's it. You dont need to drive it forward like you're shooting a belt-fed machine gun on qual day.

Just something to think about.
 
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I have not really shot precision AR’s so maybe it’s over rated, just read that there is point of impact changes when on bipod, barrier, sling ect and would like to minimize the the effects and make the most accurate AR I can within reason.
 
I used a matching Seekins billet SP233 upper and lower for my heavy 16in barreled RECCE build and run a sico Specwar on it with no problems at all
F13154A2-8519-49E5-9189-B5462E38298A.jpeg
 
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Baron85 said:
I have not really shot precision AR’s so maybe it’s over rated, just read that there is point of impact changes when on bipod, barrier, sling ect and would like to minimize the the effects and make the most accurate AR I can within reason.
Click to expand...
You're correct in a way. The key is consistently doing the same thing each time. So there is the same tension and therefore microscopic flex in the handguard each time. Loading the bipod the same each time. Adjusting your loop sling to the same tension and place on your arm the same way every time.

Consistency is accuracy.
 
I’m hoping to use the rifle to play at some local positional shoots so I fear that since I won’t always be shooting off a bipod, or always shooting with a sling, or barricade, or tripod ect, that the flex COULD, cause problems for me.
 
Baron85 said:
I’m hoping to use the rifle to play at some local positional shoots so I fear that since I won’t always be shooting off a bipod, or always shooting with a sling, or barricade, or tripod ect, that the flex COULD, cause problems for me.
Click to expand...
I personally think it's a non-issue. As long as nothing is touching the barrel, there would be minimal point of impact change from the different types of support you are going to be shooting from. The biggest variable is the shooter, how they build their position to steady the rifle and control the recoil from all the different positions.
 
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Why the 24"barrel?
Most higer end uppers with a free float hand guard will get the job done.
Back to that barrel length, there's a lot more to it than picking a 24" barrel.

A gass gun has a ton of stuff going on and that extra 4" to me isn't going to help you.
I think you should read up on barrel harmonics,gas ports and timing the gun then trying to make it all work.

Just something to think about before you commit to something you're not going to be happy with.
 
Why the 24"barrel?
Most higer end uppers with a free float hand guard will get the job done.
Back to that barrel length, there's a lot more to it than picking a 24" barrel.

A gass gun has a ton of stuff going on and that extra 4" to me isn't going to help you.
I think you should read up on barrel harmonics,gas ports and timing the gun then trying to make it all work.

Just something to think about before you commit to something you're not going to be happy with.
[/QUOTE]

I was honestly not planning on building a precision AR but ran across in my mind a great deal on a 24” lilja barrel and some other AR stuff that I could not pass up so here I am. I would much prefer a 20” barrel in probably 6.5 Grendel but figured this would be a good way to try and see if I like precision AR stuff. If this barrel doesn’t work out but I like precision AR I will likely build another upper or pull the barrel and swap it out. But I want to pick the best parts.
 
davsco said:
other than more weight, which isn't necessarily a bad thing in prs, what's the downside(s) to 24" vs 22 or 20?
Click to expand...
The Aero M5 as suggested above is a soild choice,I have many of them.

I'm not trying to say there is a downside, but what I will tell you there is no standard with this platform.

Unless you are in the CM arena the 308 will do everything you need it to do with a 20" barrel and parts to make it all work are had easily.

Matter of fact, if you choose someone like Areo perssision it's pretty much a one stop shop,with the exception of the barrel manufacturer.
BA makes their barrels BTW and can be had for pennies on the dollar if you watch Primary arms sales.

Go to accurate shooting and read up on what you are really getting into with a longer barrel on a gas gun in 308.

There are people a hell of a lot smarter than me, that took the time to figure it all out.
 
He isnt asking about AR10s

If you like the handguard on the Seekins, I'd get their upper.
 
Baron85 said:
This will be a 223 FYI.
Click to expand...

Well that charges things,a lot it was something about the 7.62 spec can

I'd still go with Aero without getting to deep into this,spending money elsewhere.
Trigger
Barrel

Now we are back to square one mentioning the Grendal.

If you reload a Grendal can be a very fun round.
 
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Either Seekins or Vltor. Another option like the Seekins is the Spikes BAR 2.
What lower are you using?
You can get matched Seekins or Spikes.
What length gas tube?
 
Cost really isn’t a big concern, I will save up as needed to get the “best” and best to me means performance. I don’t want to spend a ton of cash for the “cool” factor but will spend money for performance.

I have a spikes hellbreaker lower already that’s been in the safe for years, planning on prs stock, Timney calvin elite trigger or another hyperfire. Just need to figure out the upper.

Like I said, this will be a test run for this type of gun for me, have other precision bolt guns and other AR’s but figured this would be an easy way to try out the precision AR since I already have all the reloading stuff and if I don’t like it a simple barrel swap gets me another AR like I’m used too.
 
If it's a 223..... Geissele handguards are some very rock solid pieces of gear. About a year ago I made the mistake of buying a Geissele Mk4 13" handguard.... dude, it's really an amazing piece of precision machined equipment. The extra length the barrel nut has and how the handguard fit and is secured with steel bolts. Awesome
 
Pick a billet lower that has the features you need and proceed. Any billet will do what you want
 
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VLTOR MUR1 is what I use on a lot of rifles, it's just a damn solid upper. If you use a KAC URX4 handguard, it's a one piece tube that doubles as the barrel nut and turns the upper into what is essentially a monolithic upper. They torque on at like 160ftlbs or some shit so they're SOLID.

For the lower, dude, get a good forged milspec lower and call it good. I like KAC, LMT and Noveske. They have higher resale values I guess but more importantly they pay attention to detail and there are less deviations between receivers. Ie, they tend to fit better.

I have a Noveske gen2 or 3 lower, it's nice I won't lie. But I wouldn't pay that much for another I don't think. The gen 3 upper vs. the VLTOR MUR1, well, I guess I just don't get it, the MUR1 is damn near the same thing (I guess Noveske got tired of buying 'em?).

Look at JP FMOS for your BCG if you want ultimate reliability.
 
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There's more than receiver rigidity in play when we're talking about precision.

There's also the interior dimensions of the receiver to consider. Some are "tighter" inside than the standard Mil-Spec dimensions. This is a two-edged sword, in that it provides the potential for increased precision through better bolt/bolt carrier alignment, along with the guarantee of lower reliability when things get dirty.
 
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Smart people who have already chimed in are smarter than me and have more experience with ARs

I have a BCM upper which thermo fits to get barrel super snug. That rifle is an 18 WOA SPR build with a Nordic handguard and shoots very accurate.

Another build I am finishing now is a Nordic upper with Nordic 10.5 .300 BO barrel and Nordic handguard. The rifle is almost completely together, I hope to shoot it soon. It is a pistol build off of a Stag lower. I expect it to be fairly accurate for what it is.

Another upper could be the BCM Gen 2, maybe some of the gents in here could give us some real world feedback on those as I am curious as well.
 
An interesting theory about AR accuracy which has been touched on here already is flex induced by the hand guard. The thinnest part of the receiver using any normal/milspec threads is the barrel tenon. Since the hand guard is also attached at that same point uneven pressure shot to shot on your bipod/rest/whatever may flex the tenon, and your barrel will move with it. If you buy into that (it seems reasonable to me) you should look for a receiver that has the most material at that point as possible. And for a handguard who's stresses are directed into the receiver rather than into the barrel tenon. So of the ones you have listed above, I think the Seekins is least likely to effected by this potential issue. Aero's M4E1, LMT's monolithic, and old Mega monolithics (I have one I love aside from the keymod) are all similar. There are probably others I'm leaving out.
 
Aero M4E1 is the budget choice. A Seekins or monolithic type upper might be a tiny bit better.

I would (and have) go M4E1 upper with matching handguard and lower. Add other parts to suit.
 
LMT MRP would be the stiffest. There’s a new guy doing barrel conversions as well as Marvin Pitts. It’s hard to beat LMT’s stainless barrels though.

There’s a used rifle length MRP quad rail chassis on GB for $500
 
MSTN said:
There's more than receiver rigidity in play when we're talking about precision.

There's also the interior dimensions of the receiver to consider. Some are "tighter" inside than the standard Mil-Spec dimensions. This is a two-edged sword, in that it provides the potential for increased precision through better bolt/bolt carrier alignment, along with the guarantee of lower reliability when things get dirty.
Click to expand...


I asked this question (same question as the OP) a couple months ago on 2 other forums and didn't really receive any first hand info, just a few opinions on what might be best.

I eventually decided on a Noveske marked MUR upper (because it has a little more material around the barrel extension than the standard VLTOR upper), a Knights URX4 handguard and a JP FMOS bcg. This build will be getting a Bartlein barrel from Craddock.

In regards to upper and bolt fit, my sample of 1 JP FMOS is no tighter in a Noveske MUR than a standard mil-spec bcg (toolcraft in this case) and a BCM MK2 upper receiver. I was hoping the JP bcg would have less play in the upper but no such luck.

MSTN, a question for you specifically: in your experience, have you found that a tighter bcg to upper fit (less carrier tilt) results in better accuracy/consistency, even slightly? I am considering buying a Youngs NM bcg as well in hopes for a better fit in my Noveske marked MUR but I wonder if the fit will be the same or if a tighter fit will make no difference.
 
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Well I picked up a 25% off coupon from the PX so looks like I’m going with the seekins setup. I’m very curious about how much the different uppers really play into the accuracy and consistency. I have a handful of uppers and might play with trying all the same parts and lower but change the upper receiver and see if I can actually tell a difference. We will see if I end up doing it but is intriguing.
 
Baron85 said:
Well I picked up a 25% off coupon from the PX so looks like I’m going with the seekins setup. I’m very curious about how much the different uppers really play into the accuracy and consistency. I have a handful of uppers and might play with trying all the same parts and lower but change the upper receiver and see if I can actually tell a difference. We will see if I end up doing it but is intriguing.
Click to expand...

Very cool; the Seekins set is one that I considered (also considered the M4E1 and BCM MK2). I'm very curious to see your results. I can't wait to compare my MUR/URX/Bartlein combo vs your Seekins/Lilja combo. Not trying to make a competition out of it, just genuinely curious if there ends up being a statistically significant difference in accuracy.

My build is following a similar philosophy as yours - willing to pay for any real (or perceived) increase in performance without wasting money on "cool looking" etc. I have a handful of other ARs, but none that are built for precision so this is also my first foray into (hopefully) highly accurate semi autos - like you I have some bolt guns for stacking holes.

Please keep us updated on the build and your range reports, I'd like to compare notes.
 
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jhr1986 said:
Very cool; the Seekins set is one that I considered (also considered the M4E1 and BCM MK2). I'm very curious to see your results. I can't wait to compare my MUR/URX/Bartlein combo vs your Seekins/Lilja combo. Not trying to make a competition out of it, just genuinely curious if there ends up being a statistically significant difference in accuracy.
Click to expand...
So if there is a statistical difference, are you going to attribute it to the barrel, upper, trigger, shooter, ammo, handguard, bcg, or environmentals?
 
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srt-4_uk said:
So if there is a statistical difference, are you going to attribute it to the barrel, upper, trigger, shooter, ammo, handguard, bcg, or environmentals?
Click to expand...

None of the above. Obviously this is not scientific. Still interested in seeing the results from both rifles though.
 
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Jhr1986 - I can't tell you what I can scientifically prove, but I can tell you my theory. Tighter is better, up to a point that reliability is affected. The Young's N/M bolt carrier is one fine product, in my experience. You'll need to become an expert on keeping that host weapon scrupulously clean, doubly so if shooting suppressed.
 
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MSTN said:
Jhr1986 - I can't tell you what I can scientifically prove, but I can tell you my theory. Tighter is better, up to a point that reliability is affected. The Young's N/M bolt carrier is one fine product, in my experience. You'll need to become an expert on keeping that host weapon scrupulously clean, doubly so if shooting suppressed.
Click to expand...


Thank you Sir. I'll give you a call tomorrow about the possibility of buying one of your upgraded Youngs bcgs.
 
Carrier tilt is at most a very tiny part of AR accuracy.

The upper is a much bigger issue. It is what connects the barrel to the scope rail. If it flexes, the POI is going to shift from the POA. In a conventional AR upper with a male threaded snout and a long free float handguard attached to the barrel nut, that creates a big lever arm to bend the upper receiver at that male threaded snout.

The solution to flex is adding more material between the barrel seat and the scope rail. That is what the inverted barrel nut setups like the Aero M4E1 do. It makes it so the stress on the upper/handguard flexes the handguard rather than the upper and probably makes the whole thing more stuff because the handguard is on the thicker side of AR free float tube handguards.

By comparison, the only forces that might be tilting the bolt before a gun fires is gravity and the buffer spring pushing forward. After it fires, it's going to align itself to the barrel extension lugs, no tilt unless something was machined wrong.

The reason why people are concerned with carrier tilt is that the rear of the carrier can hit the edge of the buffer tube because the force on the gas key wants to push the rear of the carrier down. If you have a buffer tube with anti-tilt feature, it's pretty much solved unless you are running a gas piston system but then you are more likely to have cam pin issues than carrier tilt and gas piston isn't good for accuracy so don't do it.
 
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In the process of building a seekins. I went with the seekins upper with the IRMT-3 (Triangle shaped handguard) upper and the seekins skeletonized lower and a JP Barrel and adjustable gas block. Waiting on a silent captured spring, but I like the way it all fits together, seems really solid.
 
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I have a Seekins 3G2 and it’s stiff. I like it and the triangle handguard. I’m not sure why more folks don’t use it.

If you want to mix upper and lowers, then I’d get a Seekins upper and an AmericanDefense lower. It’s full ambidextrous. I like being able to drop mags and lock-unlock the bolt on both sides. Just something to think about.
 
What do yall think about barrel nut size and material in relation to any affect on accuracy? Obviously bigger means a better heat sink, but beyond that..?
 
Forgetful Coyote said:
What do yall think about barrel nut size and material in relation to any affect on accuracy? Obviously bigger means a better heat sink, but beyond that..?
Click to expand...
gas tube limits barrel nut diameter. unless you go with the swiss cheese version.
 
Reviving an old thread.... hopefully someone somewhere has some incite!

@Baron85 & @jhr1986 - What have you fellas determined after your builds?
I have an 18" heavy match barrel in my cabinet I've been wanting to purchase a nice upper for. I've been doing DMR/SPR/Sniper matches all over here lately, with thoughts about dabbling in PRS gas gun. I think it's time to quit competing in those styles of comp with my 14.5 BCM and get into something a little mo betta!

The Seekins IRMT3 V3 has been on my radar and I've almost pulled the trigger on it several times. I'm only hesitant because I want to do all of my due diligence in getting the most potential for precision out of any upper I spend my money on. It may one day host a 6ARC if the barrel is a dud, who knows but I want it to be a be all end all precicion rifle upper.
The VLTOR MUR is second on my list just because that's all I see people talking about in other threads and forums. I just don't understand how the MUR can be considered anywhere near as rigid as the Seekins, considering the handguard mounting.
This whole handguard/barrel nut flex thing is significant in my mind because of the different complex shooting positions we face in some matches.
 
Wow, it’s been a while. I ended up with the seekins, never tried the MUR. The results have been fantastic. Took 3rd at the steel safari special ( tied for 2nd and lost tie breaker and I think we were 1 point behind 1st), I think 11th at the team steel safari, and won a local teams match that went out to 1k with the rifle so far. I have mostly used the rifle for prairie dogs and it just hammers them!!!

Build ended up seekins upper and lower (I swapped to an aero standard lower because my brass catcher wouldn’t fit on the seekins lower).
Larue MBT 2 stage
Lilja 24” fluted 223 barrel
When I built the rifle the JP bolt I wanted to run was out of stock so I put a spare bolt I had in the rifle and haven’t changed it, not sure what brand it is.
Kgm r30k suppressor
Arca rail added to the bottom of the hand guard.


I am beyond please with the rifle. By far the most accurate AR I have ever been around and consistently shoots under 1/2 moa with 53vmaxs. My match load runs hornady 75 otms and I get occasional flyers but for the most part is under 1/2”.

I played with impact changes with different pressures on the hand guard and shoulder pressure. I still get more shift than I do with my bolt guns but significant reduction from my other standard AR upper builds.
 
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@Baron85 Wow! Awesome info dude! Congrats on your placements as well.

After the reading I've been doing I'm not sure the barrel I picked up will compliment either of the recievers I've been torn between (MUR & IRMT3) However, I'm glad to hear the Seekins is treating you well. The barrel is a Faxon 18" 223 Wylde 1:8 "heavy profile" 5R, nitrided. Got it on sale for $150 shipped. I've been seeing horror stories about their barrels shooting like garbage ever since I snagged it...😅😕 but it's what I got so we will give it a whirl🤷‍♂️
I'd be coupling it with an Aero Enhanced lower from the 14.5 I currently use so I'm pleased to hear that upper pairs well with it.
How dramatic are your poi shifts with what kind of handguard pressure?
 
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