lowering ES/SD in .308

[wolfman]

In the past I've never paid attention to ES/SD in my .308 F/TR loads. I'm fortunate to get to shoot 600-900m matches most of the summer, so I'd find a load that shoots well at distance, and then go with it. I started running a new rifle last season and while it shot well enough to win pretty much everything last year, there always seemed to be a shot or two in each string that would drop or climb out- sometimes up to a minute. Now I'm trying to sort figure out the stray verticle, and so would love to hear how folks tighten up their .308 loads.
For refrence, I'm shooting unturned lapua brass, sorted by neck consistency, 155.5 bergers, and h4895, w/ Win primers. Varget showed even more vertical variation. I'm also trying N150, but those experiments are in early days. I've got enough Fed GM and CCI Br's to get me through the season if I discover one of those are the ticket. Thoughts?

 

[RDavies]

I also found Varget gave me more verticle and also found that Winchester primers gave the 2nd most consistant velocities. The PMC primers were just a bit better in my rifle. Some peoples firing pin/spring combinations dont like the PMC primers, while other do.
Most people will say jam 0.01000' into the lands or keep them 0.043284' of the lands or whatever, but each combination likes something different. Others here with more experience than me on 308s would be able to say what sort of neck tension works best. What neck tension are you running?

 

[fdshuster]

wolfman: My son & I have both been working with our 308s' at the 'longer' distances, so your question caught my attention. There was recently an excellent in-depth article in 'The Handloader' magazine, December-January 2009 edition, page 72, titled 'Developing an Accurate .308 Load', by Gary D. Sciuchetti. You may find it interesting: we both did.

 

[wolfman]

New brass is running about .003 teck tension. 1 fired is around .001. I'm going to compare the once fired to the new brass results, and try milder primer.

 

[wolfman]

Thanks Lynn,

Funny, but that is the strategy I had come up with on my own as well!

 

[RDavies]

I would use that strategy if the rifle had a tuner or if the low ES/SD velocity happened to line up with a barrel node velocity. But if it happened right between 2 accurate nodes, it might not work too well.

 

[MikeyG]

There was recently an excellent in-depth article in 'The Handloader' magazine, December-January 2009 edition, page 72, titled 'Developing an Accurate .308 Load', by Gary D. Sciuchetti.

I'm justy starting to load 308 for palma and would like to read this article, unforyunately we don't get this magazine in New Zealand. Does anyone out there have a link to this article or could someone scan the article and email. it to me. Cheers

 

[Shotist]

Can't say it'll work for everybody, but this is what I did to get my best ES/SD numbers and tightest groups when testing at 600-1000 yards:

1.5 degree throat angle on the reamer.

Jump bullets .025-.030',and it didn't matter if they were tangent or secant ogive design using that 1.5 degree leade).

Faster burn powders with 155gr bullets,Benchmark, H4895, N135, N140), particularly in a shorter tube.

De-burring flash holes is SOP unless using cases with drilled flash holes. My case lots would be +/- 1.5 grains as ready to load.

Consistency in neck tension,try to hit that .0015-.002' interference fit).

STRONG firing pin strike! This often overlooked detail can give elevation strings at distance, no matter what else you do.

Test your primers and expect to try several/many lots. F210M's seemed to never quite give me what I was seeking. CCI BR's would occasionally be VERY good with lots of so-so lots. WLR's seemed to give best overall consistency on a lot-to-lot basis, but were never quite as good as the very rare lot of good CCI BR's. WLR's are what I normally used for Palma as they were very reliable for me. My only issue with the WLR's was that once they switched to the non-plated variety, they did not fit the fired cases nearly as snug.

YMMV, but I could always hit my personal criteria of sub 1/2 MOA elevation for long shot strings at 600yds using the above when settling on a recipe during testing.

 

[davegh2o]

Hi wolfman,

Just thinking outside the box, but I had one or two verticle flyers every now and then, right up until I started Meplat trimming of my projectiles,175 SMK).

Regards Dave.

 

[wolfman]

Thanks Dave- yet another thing to consider. Ironically, the rifle that I started shooitng F/Tr with really liked 175 smks, and held incredible waterline.