A little bench shooting.

[VaderSpade]

I have shot in a few bench rest shoots with bolt guns. Just small local shoots but I always did well. I have a couple of rifles that will make one big hole out of five shots at 100 yards.
Well I just got a DPMS 24” SS .260 Remington upper for my Tactical Machining lower, with a JP trigger group;
http://www.dpmsinc.com/store/products/?prod=1991&cat=1605
It came yesterday and it’s a heavy monster. It fit on my lower perfectly. I had several different loads ready to go and I couldn’t wait to try it out.
Yesterday didn’t go so well. I put about 50 rounds through it cleaning after every round for the first 25 as DPMS recommends, then after every five rounds. The best I could do is about a 3” group at 100 yards. Not nearly good enough for even a hunting gun in my book.
I didn’t sleep well last night thinking I had just blown a wad of cash on an upper that was a disappointment.
I took it out again today after a good cleaning, and the first group was right at 1”. There is hope for this setup after all.
I tried five different loads from 100 grains to 140 grains.
The 100’s were all over the place, too light.
The 140’s were loose, too heavy. This barrel has a 1 – 8.5 twist, and the 140 grain bullets said for 1 – 8 and faster.
The 125 & 130-grain bullets shot close to an inch over and over again. I hope I can tighten up the groups with a little load tweaking. Also DPMS said it would take about 200 rounds to break the barrel in, so time may help, and I’ve seen that with some of my bolt builds.

Anyway lets help each other out here, and maybe learn what works best in these semi autos.

[junior]

Good looking rifle!

[Hardball]

Vader,

Just curious of a couple of things.

When you received the upper, did you ensure that EVERYTHING was tight? Yes, they are supposed to torque the barrel nut, etc. but I have received a DPMS upper previously that was NOT.

Secondly, your cleaning should be done from the bolt end toward the muzzle, same as the projectiles travel. Not sure which direction you were going, and certainly not trying to insult your intelligence, just an item that will make a difference, however slight.

Assuming you zeroed the scope, where did you start with your zero? I.e. 10X @ 50 yards, then 10X at 100 yards...

There are only two things typically that make a difference in grouping these days. Ammunition being first, and the shooter second. From what you describe, the rifle likes the mid weight rounds over the light and heavy weights. What are the velocities? This can make a difference. Faster is not always better, regardless of the scuttlebutt around. Are we talking factory loads or hand loads? I have found with my 6.8 that the rifle actually likes the lighter weight projectiles at higher velocity than it does the mid or heavy projectiles, which was a bit surprising in a sense that it is rifled for mid range projectiles (.270 projectiles around 115-120 grain vs. the .270s at 130 and better). This 6.8 prefers 100 grain projectiles, and it doesn't matter which type. I am able to hold a group with 115 grain projectiles, but it is around 1"+ where the 100's are sub MOA at 100 yards.

When cleaning, did you notice, or if you strip the rifle now do you notice, evidence of stripping? Stripping being jacket material left behind. Typically stripping occurs when the projectile is moving forward faster than it is able to adjust to the rifling imparting spin.

Another thought that just hit me... looking at your photo, and Junior is right("Good looking rifle!"), is there any possibility that the lack of repetition shot to shot comes from scope flex?

Keep us up to date! Sounds like a fun problem to solve.

[VaderSpade]

Hand loads with a range of bullet weights (100g-140g), and velocities, (2600fps-3000fps).

I do clean from the back. Everything seems tight, but I will recheck.

I've only shot at 100yds, with the scope @ 25X

I’m not in love with those scope mounts, and I thought some of my trouble might be coming from there.

The shooter has his good days and bad days, but I can always shoot less than 1moa with my best bolt gun, and on good days I can make one ½” hole with 5 shots @ 100yds.

I do have it shooting at about 1moa now, but I would like to tighten it up.

Now about stripping, I did notice some stripping and this is the first experience I’ve had with it. I thought it might have something to do with barrel break in, and I can’t say which loads it was coming from. I will see what I can learn on the subject, but it sounds like I may need to slow my heaver loads down some??

Thanks for the input, I just finished loading about 12 new loads to try out.