How to reduce SD?

[_Raining]

So I have two rifles that I am reloading for. My first dabble into load development was my 308 (my 6.5 was currently being built). I used Hornady New Cases (Large Primer), Reloader 15, CCI 200, Hornady Match 168gr HPBT bullets with Hornady match dies. I fucked up a bit and did not seat the primers deep enough so I did not have all cases go off but the SD's were around 40 down to 10. I then switched to Lapua Large Primer brass, still using Reloader 15 but switched bullets to Sierra 168 gr HPBT, switched to Redding Dies, those SD's were around 19 down to 10. Now at this point my creedmoor is done so I move on and focus on that.


For the 6.5 creedmoor I was using the following components:
Lapua Small Primer Brass, Redding 3 die competition set (I have only neck sized but I have a batch that I plan to body size as it was sticky, this was after 4 firings), CCI 400 primers, Berger 140 grain Hybrid bullets. My first attempt was with IMR 3450 powder but I was having issues with chambering but the SD's were between around 25 and 10. I then switched to Reloder 16 and switched to a different set of 100 cases and my first firings had a max SD of 16 and a min of 4.5 (This was 10 shot groups). Second time testing with fire formed cases was max 7.3 and min 4.8. Twice fired was max 12, min 2.4 (This set was 5 shot groups). I then resized the original cases used with the IMR powder and my SD's were max 8, min 4.4. Since then I have chosen a load and over 100 shots, groups of 10 I have had my SD be as low as 2.X and as high as 6.X with most falling in that 4.X range. This I am happy with.

Now I just started load development back up with my 308. I switch to Varget powder and 175 gr Tipped Match Kings. Still using Lapua Large Primer Brass and CCI 200 primers. These are fireformed cases that are only neck sized in redding dies (just like the 6.5). My SD's were 20 down to 7.6 but I used .2 grain increments for the first 4 groups so they were only 5 shots which included the SD of 7.6 and it was bookended by 14.6 and 18.4 so at this point I am calling that 7.6 luck. Aside from the 7.6, the next lowest SD was 13.1 with 6 other groups in the 13-14 range (12 groups total, 8 of which were 10 shots). So at this point I am at a loss for what I should do to lower my SD. With the 6.5 after switching to Reloder 16 I wasn't really having any bad SD's but the 308 I have to get lucky just to get single digits. Varget has to be the most popular 308 powder so I am not sure why I can't get a load that works. What is my next steps? Should I mess with seating depth or neck tension, I have heard of people doing this to modify group size but no mention of it for SD. The same die brand is used, the same scale, the same hand primers aside from small vs large insert, the same idiot pulling the lever and making measurements etc. Do I switch powders or bullets? Should I try small primer 308 Lapua brass, did I mess up my brass prep somehow or is small primer cases that much more consistent (I have read this can give better SD but I don't know how factual that is)? The group sizes are more or less the same as the 6.5 creedmoor and the same gunsmith did the chambering.


In case it matters, action/barrel specs:
6.5 is defiance action, brux sendero barrel 1:8 twist and the 308 is trued rem 700 with 1:11.25 Twist Krieger M24.

-Thanks-

Edit: I have around 80 un-prepped cases of 308 Large Primer brass and a few pounds of Varget left along with three hundred 175 gr TMK's if that makes a difference in what should be my next step.

 

[spife7980]

Have you measured your necks with a micrometer and seen how much variety in thickness there is? Have you varied neck bushings to vary that? What's your cleaning regimen? Have you lubed necks? Turned necks? Tracked number of firings on the brass too see if a specific hardness works best? That along with a bushing change? Annealed? Are you letting some bullets sit in the chamber longer? Your powders aren't temp sensitive but 30 degrees in the mag and then in a hot chamber 5 seconds vs 20 could be a factor? Sure your powder weights are exact? Primer change? Sizing consistent? The list goes on and on. Get some measurements and see if you can find somewhere that you're lacking. You seem to have a firm grasp on the essentials. Do they shoot well enough at distance to meet your standards? If so say screw it and rock what you got.

 

[_Raining]

The 308 necks are turned the same way the 6.5 is, 21st century lathe. I have multiple neck bushings but I have not tried any other ones, if no1 had responded I would have repeated the same test to see if there is any pattern in the SD's and then change to a different bushing and then seating depth.

Cleaning wise I decap, wet tumble, measure necks and case length then lube up the necks and neck size then remeasure and take note. If the cases are only a few thou past minimum then I don't trim otherwise I trim, deburr, chamfer. Then I wet tumble again to get the lube off and any trim shavings out. Then I hand prime with 21st centruy benchrest priming tool (1 and 1/4 thou depth per click, take note and use the same depth each time). The primers are from a pack of 1000 so they have not changed. Scale is an entris and the Varget kernels are even smaller than the RL16 so I can get even better powder charges with Varget than with RL16. When I seat the bullet I check with my Hornady CBTO comparitor every tenth round, it stays consistent all the way through same as the 6.5. I have let my 6.5 rounds cook in the chamber and it didn't seem to have much of an effect, even round robining the 6.5 for OCW gave good results (12 down to 2) and my last 100 rounds all at 40.4gr had an avg MV of 2812 through 2815 (http://imgur.com/a/KUMDZ). I don't know how different Varget is but the M24 barrel in 308 should be less of a problem heat wise vs the 6.5 unless I just got lucky with the 6.5 barrel/chamber.

The 308 is secondary to the 6.5 so it's not a huge deal but for the sake of science I would like to figure out how to reduce the SD. This 6.5 barrel isn't going to last forever and I want to be prepared for the next one if it doesn't go as smoothly as it did with this current barrel.

I have a tube mic which isn't the best, I may order a ball mic but the necks don't seem to vary much when measuring with the tube mic although Lapua Brass is pretty damn good to begin with I probably don't need to neck turn in the first place. I'll probably mess around with the brass I have now and if that doesn't work I'll try the unmodified brass casings I have left and see if that makes a difference. I have an AMP annealer but I only used it once with the 308 brass and never with the 6.5 (I still have to get around to sending them my brass for testing) but the 6.5 doesn't seem to be effected. The avg MV may change a little bit but that is probably more from not cleaning much than it is neck hardness, the SD's seem uneffected by # of firings in the 6.5 and the 308 is only on its second/third firing.

 

[Deleted member 10043]

My only thought is with known good brass there is just a few things to do before seating. I'm losing count on your steps. SD is all about consistency in every step. And your .308 is not secondary when it comes to just tracking Chronograph data. Both setups are separated entities.

 

[_Raining]

I don't think I do much more steps than most. Neck turning is advised when neck sizing. Both the 6.5 and the 308 use the same brand of primer pocket reamer and flash hole deburrer. Same trimmer, same scale, same hand primer, same tumbler, same brand of brass, primer and dies. The only difference in my procedure for the 308 vs the 6.5 is the 308 has been annealed once and I am using:
Varget vs RL16
Sierra vs Burger
Large Primer vs Small Primer

So yes, they are different setups... with a shit load of commonalities. Perhaps something is messed up with the 308 mandrel or the 308 flash hole deburrer is crooked and created a messed up flash hole or I got less than good dies etc but the question is simply if you were me, what would be your next steps to try to lowering SD.

The 308 is secondary to the 6.5 bc the 6.5 is a better caliber, has a better stock, action, trigger and scope so I would not be devastated if I couldn't get its SD down.

 

[Sheldon N]

Why is SD the goal? You're meticulous in your processes and data gathering based upon your photos, and it looks like you have a good 600 yard range to get very detailed feedback of how loads are shooting. Why not go to the target to get the truth?

Keep in mind, SD is just a measurement tool that's trying to give you feedback on the potential minimization of vertical dispersion at distance. If you shoot at distance and find that the load has crappy vertical despite the great SD number, what use is tracking SD? I've had loads with great SD that shot like crap.

The really good benchrest shooters, the ones who hold world records and do it consistently, often don't use SD or ES to drive their loading decisions. They shoot a ladder at the desired distance and see what load gives the least amount of vertical as you change charge weights (find the flat spot). Load to that forgiving spot and then refine group size by testing seating depth, neck tension, primers, whatever you want, in order to see what maintains that minimal vertical and shrink group size further.

All the other methods (OCW, velocity chrono ladder, etc) are just tools to give you a prediction of the truth of how a gun performs at distance. If you can get the answer directly, why focus on the tools?

 

[Deleted member 10043]

Lapua brass doesn't need to be deburred. Try not neck turning, annealing or tumbling the brass. Get a nylon brush with sizing lube chucked to a drill and clean the inside of the neck. Wipe down the outside. Resize just like the instructions state. Don't do anything out of the ordinary. This should get you consistent upper single digit SD until the brass is retired. That would be the baseline to tweak. For me, I don't shoot well enough to go to all the trouble. I wouldn't know what a 4 fps SD looked like over my usual 7 or 9 SD. I'm referring to maybe 1 inch difference at 500 meters with no wind. Cut that SD in half and you're looking for that .5 inch. That would be .1 moa. Just how far do you plan to shoot?

 

[Rerun7]

What are you seeing on paper? Are you shooting enough distance with accuracy requirements that you aren't getting favorable results on target?

At one time I really stressed over my SD until I realized I was within an acceptable limit to my goals. Made my reloading more enjoyable and faster.

 

[redneckbmxer24]

As mentioned SD is all about consistency. Keep in mind that ES is just as important as SD and IMO is a better window to go off of. You can have an ES below 20 for multiple but different SD's for each string depending on exactly what the individual rounds do.

I'd ditch neck turning, especially being new to loading and using Lapua brass. There's just no real reason to and one more thing that could not be done consistently. I don't even neck turn Winchester brass. There's also no reason to touch Lapua brass flash holes either as they're drilled. I don't mess with the primer pockets on them either. The only thing I do with Lapua brass is size just to set consistency on new brass, touch the mouths with a VLD chamfer again, and load. After firing they get SS tumbled, sized, trimmed, chamfered, and demurred and then dry tumbled to remove lube and any brass shavings every firing. Trimming every firing also lowered my ES and SD's a good bit. Two different length necks will have two different size surface areas holding the bullet.

I'd also ditch neck sizing. Bumping your shoulders back a hair gives you better field reliability if any debris is introduced in the chamber. I bump mine .0015-.002. Again consistency is key.

What's your neck tension? Consistency and having enough is most important but too much can cause inconsistencies.

How are you sizing? I always got good SD's just running dies normally but when I started running the expander ball to straighten case mouths in one step, then sizing without the ball I saw a significant decrease in ES and SD. By running the expander first you can't possibly be changing anything about the brass vs it passing through again on the downstroke after sizing. I tested this very thoroughly and no matter how much lube was used and how smooth it ran, there was a difference.

How are you weighing charges? Getting consistent charge weights even if you're smack in the middle of a flat node still makes a difference. For me just using one of the big names .1gr scale whether its attached to a thrower or not isn't good enough. At the very least pick up a Gempro, they work well for the price but be patient using it, it can take a few seconds to react especially if adding or removing no more than a few kernels. You may have to pick it up off the scale and set it back. One of the best investments I've made has been the FX-120i and it's going to be even better when the Auto Throw and Auto Trickler arrive. For now throwing a touch low on a Redding BR-30 and trickling up with a trickler set on top of the draft cover pouring through a funnel set in the hole is producing consistent charges faster than a charge master would dispense and trickle as accurate as it's capable of measuring.

You're obviously doing something right with your 6.5 load and you've got a great powder and brass choice for the 308 with Lapua and Varget. You may want to experiment with primers a little, Federals (210 or 210M, makes no difference) have always worked best for me with Varget.

 

[_Raining]

The problem with seeing how it does at distance is that I am not a good enough shot to judge based on group size so my goal is to do OCW to find which charge has similar POI and then use the middle of that, which worked fine for the 6.5 because the SD's were all good so it didn't matter where my flat spot was POI-wise. So for the 308 I can still do the OCW and find my flat spot but the SD's seem like the best I am going to get is around 13, I would prefer it to be single digit. I can try other primers but with the 6.5 there was no noticeable difference in SD or group size between CCI 400 and FGMM. I am not super happy with the XLR Chassis so instead of putting more money into this rifle I may try to sell it and start with a fresh build specifically for F/TR.

 

[4sfed]

How are you sizing? I always got good SD's just running dies normally but when I started running the expander ball to straighten case mouths in one step, then sizing without the ball I saw a significant decrease in ES and SD. By running the expander first you can't possibly be changing anything about the brass vs it passing through again on the downstroke after sizing. I tested this very thoroughly and no matter how much lube was used and how smooth it ran, there was a difference.
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Would you describe your method? I'm not sure I understand how you're doing this.