.260 Rem turned vs unturned necks

[JimSC]

disclaimer - I am a rookie F class shooter who scores low to mid 190's most matches, never "cleaned" a target. I am not a expert shooter nor a benchrest shooter. I doubt you will see me on stage at any national event any time soon and probably never will. I do this for fun and as a retirement hobby

A bit of background. With the recent primer supply situation I decided I need at least one rifle that used LRP's to practice with in order to conserve my SRP supply for matches only. I had a Shilen barrel in .260 Rem for a large shank Savage action with about 500 rounds down it sitting in the corner and the 6CM on my FTR gave up the ghost at around 1000 rounds, the throat looks like burned toast. So the 6CM went away and the Shilen got spun on. No action screw tuning has been done, all three screws are at 25 inch pounds.

I started last week with a rough load test using 140 SMK's and H4350. All the SMK's were seated at .025 from the lands for the initial test and at 42.0 gns 4 out of 5 shots went into the same hole with the 5th about 1/2 inch high. I wondered if the flyer could be caused by the case necks.

I proceeded to turn the necks on 25 cases to see what would happen. All cases were full length resized using different bushings to get .002 expansion after bullet seating. I normally prefer .003 but I did not have a bushing small enough to give me that on the turned necks and I wanted a apples to apples comparison. They were then loaded with 42.0 gns of H4350 checked on my A&D to be within .02 gns, seated .025 from the lands.

Wind conditions were mild about 4 - 7 mph, targets were at 300 yards and shot round robin. Fifteen rounds on each target. First shot was target 1, second was target 2 , third back to target 1 etc. After each ten shots the barrels were allowed to cool and the next string was started with the opposite load han the last. Here are the results using Ontarget analysis. The turned necks are the top target, the bottom unturned necks.

First thing I noticed was the horizontal stringing on the turned necks and the 2 "high" flyers on the unturned neck group. Since the groups were shot round robin I do not think wind could have caused the horizontal stringing. Nor do I think it was shooter error because if you look at the horizontal and vertical offsets for both groups they are almost identical which leads me to believe my POA was consistent.

My takeaway is that the turned necks may solve the flyer problems. I have some new bushings in the mail to play with neck tension some more and will play with seating depths to reduce or eliminate the horizontals. I am hopeful that with a bit of work I can get this barrel down to a decent sub .5 MOA shooter.

Just posted this for the fun of it, but feel free to comment and offer suggestions

 

[jepp2]

I proceeded to turn the necks on 25 cases to see what would happen.

If you mentioned what brass you were using, I missed it. What was the case neck variation range before you turned the necks? What about after you turned them? And how much did you remove?

for the initial test and at 42.0 gns 4 out of 5 shots went into the same hole with the 5th about 1/2 inch high.

Your basis for arriving at the accuracy potential for the load/rifle setup was 1 group consisting of 5 shots?

 

[JimSC]

Triger time and wind reading will make more difference then neck turning. Just my two cents Tommy Mc

You won't get any argument on the trigger time, that is why I put this barrel back on so I can use up those LRP's. If you look at the group offset numbers you can see my point of impact was consistent between the two groups. On the group offset vertical it was .634 vs .646 MOA. Horizontal was .297 vs .294. The two groups shapes are what I found interesting as well as the two "flyers" up near the POA in the unturned group. Normally I would blame myself for the horizontal on the turned group , but shooting the two groups round robin insured wind effects were consistent between the two groups. Therefore I believe the horizontal stringing was most likely caused by something in the load. The only difference being the thickness of the brass in the neck. Both loads expanded the necks a equal amount so I am leaning toward the .002 thinner brass having less tension on the bullet being the cause.

Or maybe I am just down the rabbit hole too far lol. Anyway as soon as the smaller neck bushings are in I will repeat the experiment with different neck tensions using the neck turned brass before changing anything else.

 

[JimSC]

If you mentioned what brass you were using, I missed it. What was the case neck variation range before you turned the necks? What about after you turned them? And how much did you remove?



Your basis for arriving at the accuracy potential for the load/rifle setup was 1 group consisting of 5 shots?

As I stated in my OP , this was a rough load workup. I figure that if five rounds won't group well, twenty won't either. The reverse being if five rounds do shoot well there is a chance that twenty will also. The only purpose of this test was to see if I could reduce or eliminate the vertical flyers with more consistent neck thickness. I found that I could. At least a 15 round group had no vertical flyers so that is a improvement. Now I need to tune the load to see if I can eliminate the horizontal and hope the vertical flyers do not return. I still have not touched the seating depth or primers selection. That's two other areas I can play with to try and tighten the group size.

Worst case scenario is I get more trigger time and I don't impact my SRP and powder supplies for my 6BR and I may even get a load this barrel will shoot with a bit of persistence and experimentation

The brass is Lapua, 12 times fired never annealed. Full length sized and shoulder set back .003 using a Redding S type bushing die

 

[dstoenner]

I turned all of my Lapua brass for 260 rem fclass. Then i started a load work up. 42.5 h4350 with berger 140 hybrids.

 

[JimSC]

Main reason I posted this was the horizontal on the target with the thinner necks. The only difference was the neck thickness and my point of aim. Targets were shot round robin so the wind was not a factor. I was using a Sinclair front rest and using the windage knob to switch between the points of aim, but I could have screwed up and canted the rifle slightly when switching from the left target to the right. Looking at the V shape of the horizontal I am beginning to suspect that a canted scope may have been the reason for that V shape

On the original test I had some good numbers down around 41.7 so I decided to decided to load 10 each at 41.5 and 41.7 before messing with the seating depth. I will shoot them at 100 tomorrow along with some of the 42.0's I had left just for the heck of it. At 42.0 I had no pressure signs on either the primer or in bolt lift so I may go up some if needed but I can drop back 100 FPS and still be supersonic past 1000

Anyway, I am having fun with it, getting some good practice, and learning some new stuff and that is what it is all about for me

 

[dstoenner]

I believe that tuning the seating depth will round the groups

 

[JimSC]

the V shaped stringing at 42.0 was all me. I put a cheap anti cant level on the scope rail and the grouping tightened up. Live and learn

Went back to the range today, it was sunny but still a decent day to test with a mild wind about 5MPH, just enough to make the mirage tolerable. Shot 8 shots at 41.5 gns bad horizontals again so I stopped at 8 shots. Then I did 9 at 41.7 gns with one fail to fire, and 10 at 420 gns and the groups tightened up nicely. No real flyers thatcould not be attributed to mirage/wind. Same seating depth as the previous test @ .025 off lands. Group width on the 42.0 load was 2.6 inches and the group height at 1.4 inches for ten shots. Eight of the ten were 1.4 inches in width.

I did a Ontarget analysis of the 41.7 and 42.0 grain groups combined. All 19 shots of the .3 gn spread grouped at just at 1 MOA wide and .6 MOA in height. I can load at 41.8 or 41.9 and not have to worry about the charge being off by .1 gns. I may tweak the seating depth a bit and use another .001 or .002 neck tension but overall I am pleased with how the barrel shoots at this point. It will definitely suit the purpose as a F class practice rifle. Next week l plan stretch it out to 600 and 800