DPMS .260 build finally complete

[Ledzep]

I've been collecting parts for this build for a little over a year now. I finally made it home and got it put together last week. I've only made it to the range once with it and fired 20 rounds just to make sure everything is kosher.

13 rounds:
41.0gr H4350
140 Amax @ 2.800"
R-P brass with .0035 neck tension
CCI #200
Avg Velocity was around 2630fps

Then I did 7 rounds starting at 41.5 through 44.5gr of H4350 to see how high I could go without pressure. There were no signs of pressure on the brass through all of those, however, the gas system had issues with 44.0 and 44.5. By the time I got to 44.5gr I was around 2850fps. I forgot to really check after each round through the pressure test, but I remember seeing 2724fps at 42.5gr. I have loaded up a few more rounds in .2gr intervals between 42.7gr and 43.7gr to test at 200 or 300yd. I'm not trying to chew up brass any more than I have to with this gun and anything over 2750fps is good with me. Mostly looking for accuracy. Speaking of which, the last 8 rounds of 41.0gr plinkers I shot into two 4-shot groups. One was about .7", the other was just under .5" at 100yd. I have great confidence that this gun will shoot

I was a little surprised that the velocity was 100+fps slower than what people report with their bolt guns, but my chrono may be off as well. We'll see when I get settled on a load and take it to longer ranges.

DPMS A3 upper
Kreiger 1:8 26" SS Barrel
JP Recoil Eliminator
JP FF tube
JP .936" adjustable gas block
JP "Enhanced" bolt and BCG parts (dpms carrier)
DPMS LR308 lower
Jard 1.5lb trigger
Magpul MOE stock
Larue LT-158 mount
NF NXS 5.5-22x56mm NP-R1 High speed, no ZS.
Danner boots

Everything else standard parts.

Edit: By the way, with those low-power 41.0gr loads, I noticed I had some gas blowback around the primer, and my bolt face has some sweet new pits. They're tiny, but it's still.. "interesting". My guess is that there wasn't enough pressure to obturate the primers.

 

[T-Hoe]

Re: DPMS .260 build finally complete

Good looking rig. As far as your load, try some 4831sc with some 142 match kings. That combo has been the best for me in my 260s.

 

[longrange223]

Re: DPMS .260 build finally complete

that's kinda like what i'm wanting to build,trying to decide if .260 is what i want or stay with the .308,keep us filled in on how it's doing

 

[Ledzep]

Re: DPMS .260 build finally complete

Thanks T-Hoe. I have a 1lb jug of H4831sc, but no 142 smk's. I have 95gr Vmax, 123 Amax, 123 Scenar, 120 smk, 123 smk, 140 amax, and 140 berger VLDs.

I think my H4350 loads will give acceptable accuracy and velocity. I don't really want to use the lighter bullets either. They're for my 6.5 Grendel.

Longrange, it really depends on how far you want to shoot and if you reload or not. If you're an avid reloader and want to push it beyond 600yd often I would suggest the .260.

I'm going to the range in a few minutes. I was going to do a ladder test, but I think I'm just going to go off of group size at 200yd (farthest the range goes to). I like to go out into the NV desert to shoot, but don't have a vehicle that will make it down those dirt roads. I'm working on that as well.

 

[longrange223]

Re: DPMS .260 build finally complete

let us know how it does when you get to stretch it out a little

 

[-Snyper-]

Re: DPMS .260 build finally complete

Bump your load of H4350 up to around 43.0 grns and you'll see a major improvement. My DPMS just like yours loved the 139 scenars with 43.0 of H4350. Now go have fun with her, now that she's complete.

 

[IslandTime]

Re: DPMS .260 build finally complete

Nice job on the new rig!! Ive shot many a .270 and I'm sure you will enjoy the .260 round when you find the sweet load. Nice work!

 

[Ledzep]

Re: DPMS .260 build finally complete

Major flop today.

I wasn't able to get to the range like I had planned yesterday, so I went today. I shot 6, 5-shot groups at 200yd from 42.7 to 43.7gr 4350. Results were not impressive-- approximately 1.5 MOA for each group. I proceeded to sight in my NV scope on my .308 upper for this lower, and plinked around with some other guns.

Usually when 6 different loads perform equally bad there's a weak link in the chain. So the first thing I checked was the crown, then scope rings. Concentric, clean and tight. Then I grabbed the upper and the Larue mount and torqued them back and forth. It wiggled. Great. I suppose I'll rinse/repeat some time later this week or weekend now that it's tightened up.

I'm going to try to take my scale and Lee hand-press with me out to the desert so I can find a load and immediately crank a few more out and try it at long(er) range.

 

[tylerw02]

Re: DPMS .260 build finally complete

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ledzep</div><div class="ubbcode-body"> Then I grabbed the upper and the Larue mount and torqued them back and forth. It wiggled. Great. </div></div>

I've had the same thing happen to me with LaRue mounts. Then I tried my GDI mount and got the same thing. I was so frustrated, but after an adjustment, the GDI seems to be holding fine now.

 

[Ledzep]

Re: DPMS .260 build finally complete

This is the first time it's happened to me. I think the problem is that i took it directly off of my ar15 and put it on this rail without checking the fit. It's tight now and I haven't had any issues with them self-loosening.

I'm thinking now that the previous sub-moa results were luck. We'll see.

 

[SD26]

Re: DPMS .260 build finally complete

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ledzep</div><div class="ubbcode-body">
I'm thinking now that the previous sub-moa results were luck. We'll see. </div></div>
Nice build!

Are you going to put some results on the 30 round/6 group threads?

How long is your JP tube? 15" or 12"

 

[Ledzep]

Re: DPMS .260 build finally complete

Thanks. I will probably do a string for the 6x5 thread once I get a good load. The jp tube is the 15" model. Unfortunately it doesn't have holes in the right place to adjust the gas system. I think I'm going to put a 3/8" hole in it once I find my drill.

 

[Ledzep]

Re: DPMS .260 build finally complete

I retested my loads today at 200. 42.7gr was about 0.6moa. 42.9 and 43.1 were around and just over 1moa. 43.3 was 0.66moa, and the last two opened up again.

I'm going to load up 50 with 43.3 and stretch the legs some time in the next week.

 

[Ledzep]

Re: DPMS .260 build finally complete

Got it out in the desert a couple days ago. I set up a 2/3 scale ISPC plate at 565yd (3 degree incline), and a 45% ISPC plate at 655yd (5 degree incline) on a hill side. I was going to reverse their order to put the bigger plate further away, but I got tired of carrying 50lb up a hill

I also didn't check my plate placement for the 45% at 655 and it was about 30degrees sideways to the shooter.

I also forgot magazines for the .260 (Duh...) so I only shot about 30 rounds, single loading before I got tired of it. The first 10 were a 100yd group/velocity test. I pulled two shots (not applying technique) but the remaining 8 were sub-MOA (~.8", whole group was 1.3" with the 2 called shots). Velocity ES was 18 FPS, avg velocity of 2795 FPS.

On to longer distances. I was testing Strelok for the first time on my cellphone instead of printing out JBM sheets. I also give the disclaimer that I am by no means experienced shooting at long range, and have very very little experience observing, and shooting in the wind. That said, I shot two rounds at the 565yd plate while the wind was calm. It was a little high and I over-adjusted down and fired 6 more shots at first in calm conditions, then the wind kicked up a little and I kept holding in the same spot to see what would happen. Quite a bit of lateral spread, but not much vertical.

I then moved on to the 655yd target which was very small laterally. My first two shots were hits in the lower right corner, but with mirage and the plate face being a shadow I couldn't see where. I shot 8 more rounds. Those that missed were just off the right side.

EDIT: picture should be good now.

I then shot at a couple bigger rocks at 840yd and 973yd. Strelok was within 1 MOA at all distances but I need to tweak it some to try and get a closer match.

Then I went on and blasted at the targets with my 6.5 grendel AR-15. It's got a cheap(er) button rifled barrel and is about a 1-1.5 MOA gun at 100yd. I usually don't shoot it beyond 400yd, but wanted to see what it was capable of. It had more issues with Strelok. Hit low at all ranges I shot it. I may chrono it again and see if something has changed.

 

[leadbullet]

Re: DPMS .260 build finally complete

looks like you got a shooter, right on.
congrats.

 

[Ledzep]

Re: DPMS .260 build finally complete

A little more on this. My chronograph numbers and JBM/Strelok did not agree. After playing with the MV in strelok yesterday I was getting something more like 2880fps, which is right in line with bolt-guns running similar loads (vs. 2795 from the chrono).

I shot at 400yd, 500yd, and 600yd on paper and corrected from the strelok calculations to get my actual dope for those ranges, then fiddled with MV to get Strelok to agree. I then took a couple shots at 1188yd at a rock to verify. Impact was within 1 minute.

I really don't think I need to be running things that fast. I'm happy with anything around or over 2750fps, so I may try to find a cooler node and test it at 400yd now that I have a vehicle that can get me where I can get that extended range.