260 AR 10 Build

[Herzo]

Just finishing up my first {and probably last} AR 10. Decided to go with the 260 Remington since I have a couple of bolt guns in that caliber and have had great luck with the cartridge.

Based on the Aero M5 upper/lower set and bolt carrier, I began scrounging for the required parts. My aim is to produce a 1000 yard AR Tactical, thus I went with the rifle length buffer/tube setup and an AR-15 A2 stock. The Larue trigger has been my go-to for several years {CMP and NRA competitions require a 4.5# trigger pull}.

In that no one seems to have the 260 as a standard {the 6.5 Creedmore is God}, I decided that I would machine my own barrel, thus producing the contour to my liking. I purchased a 6.5 mm, 5R, 1/8 twist 1.25" blank from X-Caliber, having had good luck with them previously. Going with an 0.875" diameter gas block allowed me to finish my 22" barrel at 0.865" on the front. A Clymer reamer from Brownells was used to chamber it.

In that the maximum magnification allowed is 16X, I mounted an SWFA 12X fixed power scope. I have had good experience with the several that I own and have used it at 1000 on my 6mm Grendel {the 30 MPH winds at Perry convinced me that I needed a little more horsepower}.

My first time out produced a couple of 1" groups at 100 yards with no load development. I hope that going from mag length to 0.010" to 0.020" off the lands will help along with a variety of loads of VV-N160.

I did manage to over-gas it with a 0.088" diameter gas port. Given the meat in the barrel, it will be easy enough to drill and tap the port to 8-32 X 1/4" deep and install a stainless steel socket head set screw which I can re-drill.

 

[ebb]

Could you just install an adjustable gas block and tune to the desired amount of gas? I have a DPMS LR in 260 REM and love it, I think you will too. What bullets are you using so far? I tried Berger 140s at first and the gun cycled hard, and brass was beat up. My friend told me to read the 260 section at JP rifles website. He steered people towards the 130 and 123 grain bullets. I've been using Nosler custom comp 123s after some testing and like them. Not sure they are the best choice for 1000yds but time will tell. I found a real good deal on a NF 4-16 so mine has a little less power than most of my rifles. after using it I am not sure if it is much of a limiting factor.

 

[Herzo]

Shooting a 140 grain Barnes Match Burner. Approaching 1/2 MOA this morning {1.2" @ 200 yards} with 0.020" off the lands. Was hoping for a little better. I may try their 145 grain MB, it's BC is substantially better and I should be able to maintain the same velocity that worked with the 140. I tried a Hornady 123 ELD-M, the results weren't encouraging plus it will fail to make 1000.

NRA rules do not allow an adjustable gas block, but the ejection pattern was close enough that I may not need to make the change.

The rifle seems to be cycling comfortably, it could be the rifle length buffer is softening it up. Recoil is only slightly more than my 6.5 Grendel. That the rifle is in at just under 12 pounds is probably helping. Ill probably add another pound or so before I'm finished.

 

[slm9s]

We used to have a 600 yards PRS style match here and I used my DPMS LR260 in those. I shot the 123 amax as it shot them well and 600 wasn't a far poke. It was a very effective tool for those matches, quick follow-up shots on multiple target stages.

 

[Herzo]

The Barnes 120 Grain Match Burners are my go-to in my 6.5 Grendel AR for 600 yards.

 

[ELR LVR]

I like your caliber choice,
I have a 6.5 Creed upper and am thinking of running my 260 reamer in
But so far it shoots 140 Eld-M's very well so dont want to mess with it yet.
But I highly recommend an adjustable gas block
Once you have it set where you like it (how far and the clocking direction it throws the brass etc
You can then forget it and let it carbon up haha, becaue you won't be adjusting it any more.
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If you like experimenting with gas ports by drilling out .001" at a time, I understand
but it's tedious and time consuming. I've done that too.
Adjustable gas blocks just make it so much easier and youre done in about 20 mins

 

[Herzo]

I like your caliber choice,
I have a 6.5 Creed upper and am thimking of running my 260 reamer in
But so far it shoots 140 Eld-M's very well so dont want to mess with it yet.
But I highly recommend an adjustable gas block
Once you have it set where you like it (how far and the clocking direction it throws the brass etc
You can then forget it and let it carbon up haha, becaue you won't be adjusting it any more.

I'm not certain that a 260 reamer will clean up the Creedmore, the 260 AI might make it though.

 

[ELR LVR]

I'm not certain that a 260 reamer will clean up the Creedmore, the 260 AI might make it though.

You may be right there, I haven't measured yet myself to make sure.
That was just my intention since I already have the reamer
a 260 AI would be better all the way around anyway.
I may have to get a 260 AI reamer

 

[Herzo]

You may be right there, I haven't measured yet myself to make sure.
That was just my intention
a 260 AI would be better all the way around anyway

4D Rentals is a good source for dimensions, 260 & 6.5 Creedmoor will not go either way.

In reality, there is no performance difference in the 260, Creedmoor or the 6.5 X 55 Mauser

 

[ELR LVR]

4D Rentals is a good source for dimensions, 260 & 6.5 Creedmoor will not go either way.

In reality, there is no performance difference in the 260, Creedmoor or the 6.5 X 55 Mauser

Yes but I already have a bunch of 260 stuff
And one reason for choosing the 260 at all (for my purposes)
is an abundance of 308 brass, range brass etc which the ability to simply use 308 brass
also makes it more economical than the Creed
Not to mention the ability to swap ammo directly from bolt gun to gas gun if needed

 

[ebb]

How about if you need less gas mill the face of the gas block so it slides closer to the shooter, That would allow the hole in the barrel to misalign with the hole in the gas block and you could regulate it that way??? I am suggesting this because if I were doing it I would be terrified to mill on the barrel of a rifle showing promise. Hope this post doesn't sound like I am know it all because i have never tried this and only think it may work.

 

[ELR LVR]

How about if you need less gas mill the face of the gas block so it slides closer to the shooter, That would allow the hole in the barrel to misalign with the hole in the gas block and you could regulate it that way??? I am suggesting this because if I were doing it I would be terrified to mill on the barrel of a rifle showing promise. Hope this post doesn't sound like I am know it all because i have never tried this and only think it may work.

The gas that shoots through there, is very very high pressure
consider the gas erosion going past the step created by offsetting the 2 holes ya know.
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one time I was trying to completely block off the gas going through the gas port and used a plate/shim over the hole with a tightened SS hose clamp also over the hole
It blew a hole right through the plate and deformed the SS hose clamp on the first shot.
So consider all the gas pressure in a barrel concentrated down to a .088" hole then try to block it even smaller.
Offsetting may just enlarge the hole back to original dimension from high pressure gas erosion in a short time.
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Not saying your idea is bad in any way, because I am all for brainstorming and coming up with new and different ways of doing things.
just informing you what's going on there.

 

[Herzo]

Actually it would be difficult to control how much reduction you would get since the hole in the gas block is substantially larger than the gas port in order to allow for some mis-alignmert. I have drilled, tapped and plugged a gas port before. You just need to be careful not to break into the bore.
If you foul that up, you are only out a set screw ($0.40 at your friendly Ace Hardware store.
Stainless steel screws are the choice to resist erosion.

 

[ELR LVR]

Actually it would be difficult to control how much reduction you would get since the hole in the gas block is substantially larger than the gas port in order to allow for some mis-alignmert. I have drilled, tapped and plugged a gas port before. You just need to be careful not to break into the bore.
If you foul that up, you are only out a set screw ($0.40 at your friendly Ace Hardware store.

What I have done myelf was, tig weld the hole in the gas block then redrill it
I have also drilled and tapped a side port in a gas block and made my own adjustable which also worked but the constant pounding of the gas tends to loosen the set screw even when loctited
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A method in addition to plugging the barrel
I think a drilled hole in the gas block with interchanegable jet inserts may be a way of tuning if it is not adjustable, but thats some machine work not everyone has access to.

 

[ebb]

I am with ELR LVR I have a history with the 260 and see no need to move away from it. The 260 is a little faster than a Creedmoor but realistically it may not be enough to matter. I took a lot of flack from friends to come into the modern era with my hunting rifles, short magnums. I was supposed to sell my 338 win mag and get a short magnum, I have no need to swap a rifle and deal with all the changes when the one I shoot is doing all I need it to do. Building a 260 on a long action makes it handle longer bullets, and faster. But we are talking gas guns. I am sure with all the gas guns being made today many come with a step in them from the factory, blocks are made from aluminum so it can't be too bad. A hose clamp? Don't say that out loud Brandon Herrera will be looking for a picture, I never let anyone see or hear of my failed gun fixes, but sometimes the Band-Aids give it away.

 

[ELR LVR]

I am with ELR LVR I have a history with the 260 and see no need to move away from it. The 260 is a little faster than a Creedmoor but realistically it may not be enough to matter. I took a lot of flack from friends to come into the modern era with my hunting rifles, short magnums. I was supposed to sell my 338 win mag and get a short magnum, I have no need to swap a rifle and deal with all the changes when the one I shoot is doing all I need it to do. Building a 260 on a long action makes it handle longer bullets, and faster. But we are talking gas guns. I am sure with all the gas guns being made today many come with a step in them from the factory, blocks are made from aluminum so it can't be too bad. A hose clamp? Don't say that out loud Brandon Herrera will be looking for a picture, I never let anyone see or hear of my failed gun fixes, but sometimes the Band-Aids give it away.

It was a nice wide beefy hose clamp

 

[Herzo]

It was a nice wide beefy hose clamp

Calling Rube Goldberg.........

 

[Herzo]

ELR LVR is showing his age.

 

[ebb]

He can't be as old as me!!

 

[Bob3700]

He can't be as old as me!!

Educate me a little here. Is there a rule that limits the bbl length on an AR Tac rifle to 22 inches?