Building a benchrest AR-15

[yorketransport]

All of the other AR threads got me thinking about a project that I'm slowly building.  The goal is an AR-15 which will hold .5 MOA to 1000 yards. The caliber is already decided and a matched upper/lower receiver and the barrel are already sitting in the safe. I still need all the other parts though.

The goal is to have the  most accurate and consistent bench gun possible. Keep in mind that this is essentially a  heavy varmint gun and weight is no real issue. So throw out your parts list for what you'd use for triggers, forends, stocks, mounts and everything else. Since I'm completely out of my element when it comes to gas guns I don't really have any bias towards one brand or another. 

Andrew

[Dan-o]

I can't help ya, but I'm curious what caliber?

[TRD1911]

I don't own anything spectacular but I've always been happy with Geissele triggers. If you havnt already, check out some of the top builders webpages and duplicate their build. They list the parts in detail and the good thing about ARs is they are pretty much all drop in parts (with some exceptions in larger caliber). Two good manufacturers that come to mind are GA Precision and JP. Looking forward to the build results. Are you handloading?

[fly-by]

A few of the parts that I used on a long range AR build:

CMC trigger.  About 3 pounds.  You say benchrest so may want to go lighter.
Luth-AR MBA stock - About half the weight and cost of the MagPul.  Good range of adjustment but more of a "set and forget" setup vs Magpul
CTK ultimate rail-pod - Rock solid and does not get in the way when folded. Wide range of coarse and fine adjustments.  Added after picture taken.
DIY spikes for bipod feet.  There are a couple of aftermarket makers out there for Harris and Atlas.  Makes a big difference in ability to load the bipod.
Plain carbon fiber tube with camera shoe bedded in epoxy.  Drops straight into tripod without a hog saddle.   

Base rifle is a DPMS lite hunter in 260 Rem.  0.5 MOA without much load development.

[yorketransport]

I can't help ya, but I'm curious what caliber?

I'm thinking 5.45x39. I've heard pretty good things about that in an AR.

Since I always need to have something a little different, it's going to be a 6.5 BRX. It's a 6mm BR with the shoulder pushed forward .100" and necked up to 6.5mm. It's essentially a 308 case cut down to about 1.5" and necked down to 6.5mm. The 6 BR has the shoulder at 1.0748" and the BRX moves the shoulder forward to 1.1748". Its a simple matter of necking a 6 BR up to 7mm then necking it down to 6.5mm to create a false shoulder, then fireform. It's easy! 

Left to right: 6.5 BRX, 6mm BR, 264 LBC/Grendel, 6.5 BRX


The shoulders on the BRX cases are a little soft because those 2  were formed from shortened 243 cases. It's a lot easier to move the shoulder forward on BR cases. The BRX gains about 20% in capacity over the LBC/Grendel and has a legitimate 150-200 fps advantage with a 123gr bullet from a 20" barrel.

CMC trigger.  About 3 pounds.  You say benchrest so may want to go lighter.

The thought of a 3# trigger kills me! I just put another Jewell HVR on an action for different project and promptly adjusted it down to 6oz.  These ARs are going to take some getting used to!

Andrew

[bullfisher]

Are they still making brx stuff? I've been contemplating a grendal build, but I might have to look into the brx.

[yorketransport]

Are they still making brx stuff? I've been contemplating a grendal build, but I might have to look into the brx.

There is still one listed as available on the site towards the bottom of the page.
http://www.ar15performance.com/barrels

The BRX is a great cartridge if you're willing deal with the fireforming. It's really the only caliber in an AR-15 that got my attention.

[jay.sharkbait]

XLR buttstock
Timney trigger
Heaviest buffer available/ JP spring

I like the Noveske selector.

SLR adjustable gas block is a must.

That barrel is threaded?

I like the Lancer HG but the cheap alloy round tube would work too.

LaRue SPR mount.

[yorketransport]

XLR buttstock
Timney trigger
Heaviest buffer available/ JP spring

I like the Noveske selector.

SLR adjustable gas block is a must.

That barrel is threaded?

I like the Lancer HG but the cheap alloy round tube would work too.

LaRue SPR mount.

Great, now I need to get around to buying all that crap!  This is stupid. I want to go back to building bolt guns out of parts I have sitting on the floor in my garage!

Andrew

[300rum]

If you want a true 1k plus rifle, go with an DPMS style LR build, the AR15 type platforms just don't have enough umph.
I think the JP Trigger is hands down the best.  I have had a chance to try many of the triggers out there and the JP is the best. 
I use an SLR gas block and Comp.  The rifle is very flat in recoil, I can watch the bullet impact.
Larue makes the best scope mount.  Mine has 20moa built into it for the long stuff.
JP makes a barrel and bolt to match, it is very expensive though.  Black Hole Weaponry makes a very, very accurate barrel and they usually headspace off a DPMS Bolt without any adjustments. 
Make sure that you get the longest forearm you can, it needs to at least cover the gas block so that you can put your bipod out farther.  Diamond head makes a very nice smooth surfaced forearm.
I would start with an 80% lower so that you can machine the lower to fit perfectly tight to the upper.  Basically, I want to have to use some force to get my upper to fit into my lower.   

[Bill W]

you could always check on this site and see if anyone's ever used a semi of any sort and what their results were.

http://www.pa1000yard.com

My initial thought would be it would be a waste of money.  But then at one time everyone thought the world was flat.  I may be one of those people.

[WoodlandShooter]

243WSSM???

I am using the following.

1/8 twist tube, PRI 6.5mm Brake.

OA upper and Lower. I trued the reciever face on the upper.

added some weight to the buffer to keep from ripping the cases out too early...using 4831 is a little slow for a rifle length AR, but it is working

For magazines, I am using modified PRI mags originaly for use with 6.8 SPC. These allow a COAL of 2.30.

Pushing a 105 Grain Hornady Match BTHP ~ 3075FPS

all other AR Accuracy mods apply....

[yorketransport]

I probably should have given a little background on my shooting.

1000 yards is what we consider a mid range shot. I have a 19" Striker in 6mm BR that can hold .5 MOA to 1000 yards with a 90 gr Berger VLD at 2680 fps. The 18" 284 Striker can hold .5 MOA to 1300 yards with a 168 VLD at 2680 fps. The 260 Rem Striker shoots a 123 A-max at 2750fps from the 19" barrel and will hold .75 MOA to 1000. I spend a lot of time shooting pretty mild calibers to the 1000 yard mark.

The 6.5 BRX with a 123 A-max will hit 2750-2800 from a 20 " barrel. In longer barrels the 260 will beat it by 100 fps but at the cost of added weight and powder burnt. The whole goal was to do this off of an AR-15 to keep the versatility of the smaller platform. We've shot my buddy's 264 LBC so 750 with decent results from his 20" gas gun, but his isn't really setup for precision work.

If I really need more long range "umph" than than the little BRX can dish out, I'll grab one of the real calibers like the 6.5 Badger, 375 BME, 338 Edge, 7mm RUM, 270 RUM or (if it's ever finished!) the 338 Big Baer! The little calibers are like bird hunting with a .410. It's done just for sport.

[WoodlandShooter]

this thread is quite timely!!

so, 6BR , 6LBC, 6ARturbo or 6wssm???

I know you already know this, but it is hard finding a case short enough to fit the AR15 mag and also let you run a long bullet.

I am kind of in the same boat here. Looking to build a 6mm AR also to replace my 243WSSM...This would work great except I cant get the billets seated without damaging the ogive due to the excessively thick necks. I need help here so any suggestions would be great. already have a sinclair collet die, but even with it, there is ~4 thou of neck tension after running them thru.

I may just bite the bullet and build a DPMS/SR25/R25...Mk11 Clone type setup in 243Win.. Not looking for Bench rest accuracy, but it would be nice to get under 0.5 MOA like my 270 winny is.

I have been asking around, and from what others say ($0.02) JP barrels are so-so. the JP bolt is good, but Kreiger or Bartlein, or Benchmark would be my barrels of choice.

[Bill W]

Shooting a 5 inch group at 1000 yards is a worthy achievement.  The Williamsport crowd shoots 10 shot groups at their matches.