I'm looking to start a discussion on what makes a good Handguard for a precision oriented AR, in contrast to general use rifles.

A few areas where the criteria for a good precision oriented handguard may differ from a standard carbine handguard:

1. Inner diameter. Super thin handguards may be more ergonomic and work just fine on a carbine, but I feel a precision AR needs more clearance. People building precision ARs tend to run adjustable gas blocks, which are larger. With a carbine, as long as the handguard doesn't touch the gas block, it's good to go. With a precision rifle, the barrel whipping when fired will cause contact and if you're fighting for that last .01MOA of accuracy, that may matter. Add bipod load to the equation and I would think twice about those 1.2"-1.3" ID handguards.

2. Handguard to barrel nut fit. Simply put, some handguards are attached more solidly than others. What may be acceptable for a carbine may not be tight enough for a precision AR. I am unsure which type of mount is the most solid. Clamp type mounts seem most popular and I have seen these done very well and very poorly.

3. Weight. I am of the opinion that weight is not as much of a factor for a precision AR handguard as it is for a general use carbine. I am already running a heavy barrel, stock, and optic so a few extra ounces on the handguard is not a big deal. YMMV

I'll list a few examples that I've personally had experience with and my thoughts on them:

BCM KMR - Mounting system is excellent and very solid. Probably the most solid I've used. However I am of the opinion that it is too thin for my preference at 1.3" inner diameter.

SLR solo (gen 1) - Clamp system is also very solid due to long barrel nut. Still a little too thin at 1.35" ID. My SLR set screw adjustable gas block will clear but barely. Absolutely makes contact when firing. Newer SLR rails use a different type of mounting system that I have not used and can not speak to that.

Lancer Systems Carbon Fiber rail - Excellent barrel clearance at 1.8" ID. Tube itself is very stiff, however it utilizes screws to directly attach the tube to the barrel nut. This system does not seem quite as solid as the clamp systems, although once I cranked down on the screws and used red locktite, it doesn't move. Still doesn't feel as solid as the two above, but may be solid enough.

Samson Evolution - Excellent clearance for gas block. However one of the least solidly attached rails I've ever used. The barrel nut + thermal bushing system just introduces more contact surfaces to slip and in actual use, I found the tube slipping quite a lot. Even with the clamp screwed cranked down way beyond any other rails'.

Centurion CMR -  At 1.2" it was way too thin. Forget about using an adjustable gas block, even most company's lo profile blocks won't fit under it. The one I had also had a fair amount of wobble. Most likely due to the relatively short barrel nut.

Does anyone else have thoughts on what makes for a good precision AR handguard? And if you have experience with one, please state how it fairs in the above categories as opposed to "I have XX and it works great".

I have 2 AR's I would consider precision rifles

1st one is a 20" Rainier ultra match SDM in .223 wylde with a 17" AP customs gen 2 CF keymod rail and SLR adjustable clamp-on gas block

I wanted this rifle to be fairly lightweight so I went with the flutted barrel and CF rail. I really like the rail it has plenty of ID space and doesn't flex very much and the CF is excellent at blocking barrel heat from making mirage in your scope.

2nd is a 19" Lilja 319 in 6.5 Grendel with a 15.5" Gen 4 SLR ION light keymod and SLR adjustable clamp-on has block.

This rifle will mostly be used for local PRS style matches so it needed to be more heavy duty. I like how the gen 4 SLR attaches it's nice and solid but the ID is tight so I might change it if it causes accuracy problems

So far the stiffest and best mounted rails I have used or installed are the Geissele MK4 but they also have the 1.35" ID

I haven't touched one but have heard good things about JP custom rails which have 1.75" ID

OP,
     I built an 18" Grendel with 15in Seekins Competition handguard, mainly for hunting with some competition thrown in.

Reason I went with the Seekins was the triangular shape, with the flat bottom for shooting of a flat surface, like out of a blind with windows.

The Seekins is very rigid, I have to put a lot of pressure on it with make it slightly flex, more than a bipod could put on it.

I have a adjustable gas block under the handguard just like you mentioned.

The rifle with scope, 1 mag, 5 rounds of ammo is just under 9.5lbs. Scope is a Bushnell Banner 4-12. The barrel is .750 and non fluted.

Hope that helps.

SY

KMR has plenty of clearance for my adjustable gas block and I won a CMP service rifle match with it a few days ago, so... yeah. KMR. Also, having 6 possible positions around the circle made it easy to remove any sling torque.

Which adjustable gas block are you running? I currently have a set screw SLR in mine, and while it clears, it's very close. Sling pressure will cause contact.

I have not read up on the most recent rules for service rifle, but I did not think the KMR was service rifle legal? Obviously I'm behind on the rules as the last time I checked, the rifle must look like an A2 or A4 with corresponding handguards (and FF tube hidden underneath).

I Seekins appears to be an excellent choice. I did not mention it in my OP simply because I have not owned one.

My experience with AP customs does not match yours. The tube itself was fine, however where the tube mounts to the barrel nut (trunnion as they call it) was horrible and I had all sorts of wobble issues. I did not mention it in the OP because from my understand AP Customs is now defunct. My rail was purchased right before they went out of business so yours may be of significantly higher quality.

I have heard the latest Gen SLR rails to be even more solid than my gen 1, which is pretty solid to begin with. Good to hear you like the mounting system.

I have yet to find anything wrong with my DPMS 13" solid float tube. 1.750" ID .

Though I did have to drill and tap for a stud.

Seekins 15" as with the poster earlier. I also combined it with the matching upper, so the force from the HG/bipod is transferred to the upper, not the barrel/barrel nut area. Extremely rigid, and the flat bottom is a must for a precision rifle for me.

Rules say no adjustable gas blocks. Do you mean you fired OOC, but still had the overall high score?



 

I am running a JP on my 22 inch JP Barrelled .308.  I started with an Apex which was really nice but due to some accuracy issues ( which I don't think the Apex had a single thing to do with ) I swapped the forend for a JP precision to cover my only other base that MIGHT have been compromised.



The JP forend is solid as a damn rock.  I mean...the Apex is solid too...but the JP is an order of magnitude MORE so.



Here is the thing with the JP forend....I swear it was designed by Germans.  It's not an intuitive assembly process BUT....by God it is solid once you have it together.



Like a lot of guys, I do NOT glue it into postion but use a 3/16ths pin to simulate a gas tube in order to "jam" nut the assmebly together.  MUCH more secure in my opinion.



This guy uses a hex key with some tape around it. Start at the 3 minute mark:









I use a piece if dill rod turned down to these specs to do the "JAM NUT" method with more precision fitting of the JP Handguard:



Total length of hardened drill rod: 2.075".



Gas tube portion diameter that fits into the upper receiver:  .1820" diameter by .700" long

Hand guard portion that holds the barrel nut in position .2020" diameter by 1.375" long.



Here's the specs.  The video will give you a good idea how to use this:







Works like a charm.  If it does not fit, have it turned out about 1.5 thousandths on the RADIUS ( 3 thou on the diameter ) at a time until each section ( obviously turn only what section you may need to ) fits as tightly but SMOOTHLY as possible.  You can take the stripped upper and the hand guard nut with you to gage the fit.

Good video. That is actually the exact same way the Lancer handguard attaches. The two nuts are very solid, however where the tube attaches to the barrel nut via screws is where I experience some wobble. It goes away if I crank down on the screws, but I think the clamp style systems are more solid.

My experience with Seekins rails is there is .015'' of clearance between the barrel nut and the ID of the rail combined with countersunk radial screws that want to pull it in all directions means if you don't shim it straight, it will end up crooked when tight.  Crooked so that on a 15'' rail the barrel is .25'' off center from the end of the rail.  My Noveske NSR has only .002'' clearance and flat base screws rather than counter sunk and you cannot install it crooked no matter how hard you try.  Much better execution of the radial scew attachment method.

My SLR rails are without a doubt my favorite in form and function and the wedge clamp attachment is in my opinion superior to anything else I have personally tried.

As for barrel whip, it depends how stiff/heavy your barrel is.  My 6.5x55 build in an AICS has that front rail, IMUNs? Whatever it's called.  Barrel is a heavy AMU profile that only has .060'' clearance and it does not touch.   I think with the right profile barrel that interference due to whip will be negligible with a typical 1.35 ID rail.

I think a flat bottom is desirable.  I was contemplating the PRI triangular carbon rail until I decided to stick with SLR.

Just so you know, the newer MK III handguard uses a different barrel nut that is more like a castle nut than the standard sprocket nut.





Here is the box end with a 1/2 inch drive.   It's a 1 and 3/8ths inch span.  Look this up on Amazon:

Sunex 97760 1/2-Inch Drive 1-3/8-Inch Jumbo Crowfoot Wrench

Most auto parts stores stop at 1 and 1/8th so it has to be ordered.  Sears never has the craftsman ones either.  This is Chinese but it actually fit and worked well....as much as I despise anything made by the Chinese.





It's actually really easy to torque up with this setup.  I prefer it to the socket tooth style of nut.





Another thing:  my Syrac low profile adjustable gas block fit under the JP Mk III very nicely.  I am sure Odin and Sentry will work just as well.
 

What I did to prevent that was to level the screws out on a surface plate so that they were all the same depth and then I turned each one the same amount in a "star" pattern as best I could.



Like I said....I think the JP MK III was designed by Germans.



 

I would say pick whatever free float rail floats your boat and go with it. I like geissele but really anything free floated shoud be fine.

You won't find anything more solid than Geissele rails. PRI worked well on Mk12's

I'm building an 18.5" LaRue Stealth with a SLR Solo handguard. Using the LaRue gas block and the fitment is great.

I've never used a Geissele rail. How does the tube mount to the barrel nut? How would you compare it to say...a KMR?

I'll add another one to the list: Diamondhead VRS-T - The handguard itself is very solid, but a little thin on the inside. I run a 13.5" on my precision AR and a friend ran a 15". While on the bipod, his had clearance with his low profile gas block. However once he preloaded the bipod like he was shooting, that clearance reduced. While firing, the whip of the barrel absolutely caused contact between his gas block and handguard. There were marks on the both the gas block and inside the handguard to indicate this.

We replaced it with a basic DPMS tube (pictured by another poster above) and accuracy became much more consistent. Previously, the rifle had been shooting around 2/3 MOA with occasional flyers that took it 1 MOA. After replacing the handguard, overall accuracy stayed around 2/3 MOA, but the flyers completely disappeared.

My theory is this (and it's just a theory):

If squeezing the barrel and the handguard by hand can cause contact between gas block and inside of handguard, then it's probably making contact during recoil. 60000psi is going to make the barrel whip more than I can apply by hand.

Whether or not this affects accuracy, is up for debate. I would imagine the bullet is out of the barrel at this point. Although if the gas block is striking the handguard, that may still have an effect on consistency. As for real world examples, my friend and I are running essentially the same setups. He saw real performance gains by switching handguards and the rifle is now shooting as you would expect a Shilen select match to. On the other hand, my rifle has the same handguard and the same issues and has been shooting quite well. Makes me wonder how it would shoot if there were no contact though.

By squeezing the barrel and handguard together, you are flexing the handguard (probably where it mounts) rather than the barrel. I doubt you're bending your steel barrel.

Barrels absolutely bend

https://www.youtube.com/watch?v=BgD6MtSBfzM

Double

You're absolutely right.


And so are you.

When squeezing, I'm sure I'm bending the handguard way more than the barrel. I'm just testing to see how much clearance I have. I did not explain it well earlier. During actual firing, it's the barrel that whips and the video posted shows it well.

Here's another video showing whip while firing. A precision AR barrel will be heavier than this and won't whip as much, but will still be present.

Seekins, SLR and Troy here. Seekins and SLR are the better of the three. No issues with the SLR and nothing with the Seekins like what was mentioned by another post

I made this thread mainly as a discussion point as I'm not actually in the market for a new rail. After thinking about it more though, I ended up ordering a URX4 to test out. The hand guard itself is the barrel nut so no worries about mounting strength. The ID of it is 1.55" as opposed to 1.35" or less of most modern rails. It should have plenty of clearance.

I'm using a low profile MI rail on my 6.5 Creedmoor build.








Clearance is pretty tight with my SLR 9.




 

Post your thoughts when you get it.  I've got a URX4 15" arriving today that's going on a new build.

Like a lot of others here, I really like the way the newer SLR rails mount. I've tried Troy, MI, BCM, and RRA handguards, and SLR is by far the most "robust" mount. It's also one of the easiest to install/uninstall. That said, we may be arguing over diminishing returns; as long as some basic criteria are met, I suspect most FF rails will print almost identical groups.

I choose SLR due to the way/ease in which they mount; the other benefits are just icing on the cake.

Has anyone tried the Aero Quantum rails? appear to be pretty sturdy but would like to know someone's actual experience with them

This thread prompted me to take a closer look at my SLR9/MI Mlok combination. Looking at it closely it was hard to see any gap between the gas block and rail. The rail would flex away from the rail when pushed and then the gap is visible.

I decided to pull the gas block out and file down the screw holding the tension spring in place. Hopefully that will provide enough clearance to prevent any accuracy issues while shooting.

Pretty slick looking rail.

And the price is decent too. For the 15", $109.99 with a BAR type nut, $94.99 if you don't need the nut (for their enhanced receiver)

1.8" ID for cans.  I am seriously thinking about picking one up.

Link for those interested

Gorgeous rail but what does the hand guard clamp/barrel nut system look like?



 

Not gonna lie, I really like that rail. Did not know it existed until this post.

It was designed for their M4 Enhanced receiver. Compatible with any BAR system handguard, but they give a barrel nut for non enhanced receivers




Barrel Nut



From their site

A friend just picked up an upper with a JP forearm.

It is really nice. I had planned to use one on my Creedmoor, but ended up with an SLR that I got for a decent price which I do like a lot. After seeing the JP, I thought I would not have made a bad choice going that route. The thought had even crossed my mind to trade the SLR for a JP, but I dont know if I will end up doing that. My only reason for the consideration of a trade is that I usually like to go with my first idea.

I have to agree with this. As long as the rail is floated and the attachment point is solid, any rail will work. After these two, just find the one that best suits your fancy or any other specific requirements. I'm dreaming up a lightweight build based around a Brigand Arms carbon fiber handguard, PROOF Research barrel, and some brand of trued up Ti barrel nut.

I didn't see anyone reply to this.

The Geissele has a longer than usual barrel nut. It is 2 1/4". A milspec nut is .85". The additional length improves the rigidity of the handguard.

The barrel nut is torqued onto the upper at 50 ft lbs. The handguard is then slid over the barrel nut. It is a VERY tight, precise fit. You will have to apply pressure to mate the two, but it will slide smoothly on. It's very impressive how tightly they fit. There is about .001" of clearance.

Once the handguard is on, there are two cross bolts that secure the handguard onto the barrel nut. You will align the receiver rail with the rail on top of the handguard, then tighten the cross bolts to 10 ft lbs.

I agree with most of your points. However my .750 SLR gas block does barely  fit under my CMR. And I mean its close. It looks crooked. But its not.

Here is it on my Noveske barrel.

Thanks for the picture. It looks like you're ok on clearance up top. How about the bottom though?

When I had the CMR, I had issues with the bottom of my gas block and ended up filing a good bit off the bottom of the block. And that was when I was running a set screw block. I am now running a clamp on which is larger at the bottom.

I partially installed my URX4 last night. Meaning the rail is on, but I haven't been able to get the gas block attached under the handguard. I will need to pick up the right size ball headed allen wrench in order to do so.

ETA: When I had the CMR, it was a few years ago, I'm pretty sure SLR's current sentry blocks are smaller than the DA-7s out back then. However the block I needed to file down on was a Troy non-adjustable.

Is your URX4 key mod or mlok?  My mlok URX4 arrived yesterday and the barrel and SLR clamp has block should arrive today.

Mine is Mlok. My gas block is at rifle length. There is an Mlok slot that aligns the perfect distance from the receiver for the two clamp screws. However, the slot is not quite at the right height, so I will need a ball headed wrench. It may have been ok if I had gotten a keymod rail due to the larger size of the key section.

In any case, I would highly recommend picking up a set of ball headed allen wrenches now.

What is your gas system length?

I like my Bondhus ball headed wrenches.  I bought a full set off of Ebay.  Brownells also sells them individually.  I had a missing key from one of my standard sets and bought the replacement from Brownells.  I think it was $1.50 and I used my edge shipping.

Mid.  It's going on a 16" LaRue Stealth.

The bottom is very close as well. Basically I should have put a pencil barrel inside the CMR. But technically my 11.5" Noveske does Fit my original 9.5" CMR.

Also the tightest clearance is the screw holding the blue colored plate on the side of the gas block. Perhaps this better shows how close I am cutting it.

Got the URX4 mounted and gas block tightened underneath.


Plenty of clearance for the gas block, more than it seems from this picture:


Slot lined up well with the clamp screws, although they were lower than I hoped so I still needed a ball head wrench


I had a midlength gas barrel lying around so placed it so you can see the length relative to the slots. If you are using a clamp on block, then the slot should line well with the midlength gas. You will still need a ball headed wrench just as I did.


I'm looking to going shooting with it this weekend. The purpose of this rifle is for DMR matches and the modularity of the URX over the diamondhead will help with shoot from barricades and other positions.

I have the Aero in M-Lok and I really like it. It is not too thin/not too fat.

I also have the SLR and would recommend that as well.

Awesome!

That looks dang good.   Thanks for the pictures.