Need help to tighten the group

[BarryL]

I been working up a load with Lapua 139 in my 6.5-284. I got the ES down to 21 and the SD to 6 over 6/5 shot groups. At 200yds. the groups are all averaging .7moa. Im at 51.5gr. of H4831sc, Lapua virgin brass turned necks 1.5thou per side. Fed210m, Im at .025" jam and Im thinking that might be a bit much. Velocity is 2925. What Im looking for is a quick fix so I can load tomorrow and head off to a match. Barrel is a Gaillard 8 1/2 twist. PGW Action. McGee stock, Shilen trigger 2oz.

 

[chris308]

Was thinking pull the oal back??..My past experience with the 139`s and the 142`s is mine shot best just touching or a few thous off. That`s just my stuff though as every gun is different.
I think the powder charge is ok,??) I myself never shot 4831 but 2900-2950 is about were everyone else,including me shot a 6.5/284 accuarately.
I`m gonna open a can of worms here but sometimes .7moa might be all the better it will do at 200 yards. might shhot that well at 600 too.I burned up my shillen barrel before i figured that one out.
Maybe do a search on here and see if your 4831 powder charge is on par with everyone else...hope some of this helps chris 308

 

[chris308]

After going through my notes, I got 52.0-53.0 grs of vv n165 for my 6.5/284 which is a much slower powder than 4831. So i`m thinking,stress thinking!) maybe drop your charge down a tad??

 

[BarryL]

I worked up to 51.5 and 51.2 is where the groups started to come in and the ES dropped considerably. 51.5 is where they actually came in under moa and 20fps. If I had more time to dick around with Id probably play with the seating depth at this point. Also Im at 900rds down this barrel so Im thinking this might be as good as its going to get until I set back. Just wish the snow ould leave earlier in this neck of the woods so a guy could get in more range time before the matches started.

 

[jb1000br]

I was running 0.1gn more powder with a 142...

nearly 1.5" groups at 200? What discipline is this for? IMO to be competetive in 1K BR, you need to really be holding 1.5",vertical at least) at 500...

I'd switch bullets personally....but not before I at least tried 10-20 thou off and increase and decrease the powder charge a bit to find your happy spot...

FYI - pushing the bullet 35-45 thou back in the case WILL increase pressure...so reduce and work back up accordingly.

There is no quick fix except hoping for something better to happen at longer range...

ETA: OK, re-reading this looks like a prone setup due to the McGee stock. How are you shooting these 200yd groups? Bench?

JB

 

[BarryL]

This is all on the bench. Just got back from the shoot. 11 3/4" 5 shot and 16 1/4" 10 shot. A fair bit of vertical in both. Got a chance to have a look at the throat with a bore scope. Barely noticable fire cracking for the first couple inches. A little elbow greasw would clean it right up. No hell for groups though.

 

[jb1000br]

Yup, you need to change the powder charge, and the vertical will usually go away...

 

[BarryL]

This weekend I was figuring on doing a couple groups at 200yds with 51.8gr. same jam and seeing if that lowers the es even more and maybe tightens up the group. What figures you?

 

[jb1000br]

my normal practice when closing in on a sweet spot is 3-shot groups in .3gn increments surrounding the load.

JB

 

[BarryL]

Im hearing that Im running these bullets a bit slow. What seems to be the velocity the 139 likes to move at?

 

[ceylonc]

I'm shooting 139gr. Scenars through my 6.5x284 also. My best load with 4831sc is 50gr. powder, 210M primer, Lapua Brass and bullet seated 2-thousanths off the lands. At 100yds, 5-shot groups in the .2's & .3's are pretty common,when I do my part) and at 600yds groups run about 2.5". For my rifle,Lothar Walther varmint contour 26" barrel) the load is almost always sub .5 MOA with me being it's biggest handicap.

I came to 50gr. 4831sc after running up to 51.5gr. during load development. I couldn't get my rifle to settle in consistantly @ 51.5gr. so I started working down. I also got some pressure signs which no longer is the case at 50gr.

A previous reply mentioned that Scenar bullets liked being off the lands just a tad. This is my experience as well & might be worth trying in your rig.

 

[BarryL]

Do you happen to know what velocity your moving them at? With a 26" barrel it must be considerable slower than most posted.

 

[ceylonc]

Do you happen to know what velocity your moving them at? With a 26" barrel it must be considerable slower than most posted.

I haven't been able to shoot any of my loads over a chrono to get exact velocity. I would have to agree that my loads are not as hot as those mentioned by many other users of the 6.5x284 here. I guess I never worry about velocity so long as the accuracy is there...

 

[BarryL]

I did the same thing with 142MK's. Worked the load up trying to hit that magic 2950-3000fps mark and as I went up the load ES and group size opened considerably. All that matters is how it looks on paper.