Significant SD Velocity Spread..ideas?

21Bravo

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I'm shooting a factory barreled Remington LTR in .308.

I'm loading 168gr SMK with Lapua brass, CCI BR primers, 43.8 of Varget.

Trimmed to length, primer pockets reamed, neck chamfered and deburred.

Primed with RCBS hand priming tool.

Lee collet die neck sized.

Although, these loads had the shoulder bumped back prior to this loading with a Redding body die. I did not chrono them prior to shoulder bump so no data to compare to there but the groups seem to be about the same.

Powder dropped with Chargemaster 1500.

Bullet seated with RCBS Competition seater die.

I'm getting a Standard deviation of 22 FPS with Extreme Spread of it the 30-34fps range. I'm using a Pact Mark IV chrono with standard sky screens. It seems there are only a few rounds that have a significant variance to make the ES and SD significant. I chrono'd some pistol loads and my SD was in the 8fps range with ES around 12fps or so.

Any input as to why this could be and what to do to tighten things up? And yes, it seems to effect my groups as the more consistent the velocities the tighter the groups. I was shooting at 200 yds.

Thanks for helping me out.

21Bravo
aka Craig P. in MO
 

Victor N TN

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Re: Significant SD Velocity Spread..ideas?

Sometimes the group is what you need to look at. You can spend too much time chasing numbers.

In MY OPINION... and that's what it is, changing nothing but the primers can help find lower numbers. I also tend to prefer extruded "stick" like powders for lower SD numbers. In MOST loads I'm happy with 20fps SD. Not match loads. But almost anything else is good. I have gotten down to 6 or 8 SD numbers. But for most things unless shooting benchrest or groups look at the group.
 

rth1800

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    Re: Significant SD Velocity Spread..ideas?

    I do not find your #s suprisingly high. You will see alot of stuff posted on the internet better, but in the real world, you are not far off. We all hope to do better and sometimes do, but not always. Also shooting consistantly over a chrono is a bit of an art as well. You can change velocities by the way you shoulder the rifle.
    The true test is to see what your verticals are at the longest ranges you will be shooting. It will not even begin to show up until 600 yards, in my opinion.
    Seating depth is sometimes a bit of a challange that shows up on a chronograph. I have also acheived more consistant velocities with IMR 4064, but many like Varget.
     

    21Bravo

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    Re: Significant SD Velocity Spread..ideas?

    I appreciate the input. I can see that the numbers I'm seeing are not necessarily that out of line. I suppose what got me going is two rounds that chrono'd the same went through the same hole. I've worked up loads for quite a few rifles over the years and this one has been somewhat of a headache, it's very picky. I finally got a load that the gun is consistent with, around 0.8 MOA out to 275 (not much distance I know but it's all the distance I have). I'm not asking the gun to shoot any better than that I would just like it to be as consistent as possible.

    The only thing I can think of is the brass has had 8 firings without annealing. I've researched the process but have never done it. This brass has went through the load development process so some brass has been fired with a higher charge (not severe pressure signs though and primers pockets feel consistent).

    I'm wondering if proper annealing may help the issue or if it's good enough, I do get an uncalled flyer about every third group to bring it to 1.3 MOA or so. That is averaged in for the 0.8 MOA I call the gun if I could bring that flyer in tighter it would be closer to a 0.5-0.6 MOA gun.

    21Bravo
     

    Victor N TN

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    Re: Significant SD Velocity Spread..ideas?

    Try using some new brass. Yes sometimes older, harder brass is more inconsistant in the neck tension areas. I seem to get better numbers with newer brass. I also seem to favor IMR 4895 and IMR 4064.
     

    rth1800

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    Re: Significant SD Velocity Spread..ideas?

    +1 on the neck tension. Hope you try new brass and report, I do think you will see a decrease in ES but likely no change in group size at 275.
     

    21Bravo

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    Re: Significant SD Velocity Spread..ideas?

    I'm going to order some new Lapua brass and see how that does. If nothing else, out of curiosity and for future reference. I'm also going to see what the results are after I anneal some of this brass. It might be a couple of weeks but I'll post the results.

    Thanks a lot,

    21Bravo
     

    shadow4

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    Re: Significant SD Velocity Spread..ideas?

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 21Bravo</div><div class="ubbcode-body"> I suppose what got me going is two rounds that chrono'd the same went through the same hole. </div></div>

    I've seen some REALLY good groups with ammo that had high ES/SD's so this was probably just a coincidence.

    Maybe you need to bump the charge up (or down) to get better numbers. When i am working up a load, the different charge weights always have different ES/SD's. I usually pick a charge weight that has accuracy, low SD's, and prints in the same spot as the load .3gr below it and the .3gr above it. Also, like suggested above, maybe just try another brand of primers.
     

    21Bravo

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    Re: Significant SD Velocity Spread..ideas?

    After finding this article http://www.snipercentral.com/matchammo.htm

    My SDs and ESs aren't as significant as I initially thought. Although, I'm going to try to tweak some things to see what happens.

    I did shot some new Lapua brass today and my numbers were slightly worse (few FPS more on both SD and ES) than with my 8x fired Lapua brass. Although, the new brass was full length sized and not neck sized on the Lee Collet die as the other brass was.

    21Bravo
     

    madd0c

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    Re: Significant SD Velocity Spread..ideas?

    Weigh your brass and your bullets and put them in lots with weights the same or a few grains different. Then do all the other things you are doing and I think you will tighten your SDs a little.

    Also, make sure your chargemaster is on for at least 3 hours before throwing charges. If you turn it on and load you will see the charges DECREASE as the unit warms up if you weigh it out on a beam scale after throwing. You are talking 1/10ths of a grain variation, but if you are interested in decreasing SDs this should also help.

    madd0c
     

    21Bravo

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    Re: Significant SD Velocity Spread..ideas?

    Let the Chargemaster warm up for "3 hours", really? Surely, it hits it's "warmest" temperature in less than 3 hours? I can see 30 minutes or maybe an hour. Does it really take 3 hours? That wouldn't be too troublesome if I were going to load greater than 100 round lots or so, and I will once I've got this load where I want it, which will be soon.

    Honestly, at this juncture with this rifle I'm just gathering data on what helps and what doesn't with final load tweaking. I believe any greater accuracy is probably not going to happen, with any signifiance anyway. Hopefully I'm wrong but we'll see.

    I do weigh brass but not the bullets. I sort the brass and it stays with it's group. I could weigh bullets but at this point and I may to decrease the SD for nothing more than gathering data but I doubt I'll weigh them habitually, just too much time.

    21Bravo
     

    dar1246

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    Re: Significant SD Velocity Spread..ideas?

    The chargemaster does not need 3hrs or 20 minutes to warm up. Where is this myth coming from. I can put a load together with single digits SDs by just turning the unit on and loading my load.
    Single digit SDs isn't hard to get but takes a little effort. Brass prep, neck tension, seating depth, primers, and powder charge weight (42 grs may give you 16 sd, but 42.6 may give a 9 Sd). Each of these with change your SDs.

    At 1000 yards if you have a ES of 65, you will have a flyer. 600 maybe not so much but shooting farther than 600 you will notice.

    Take your time and work your load. It is not the chargemaster time to warm up that could be the cause.
     

    madd0c

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    Re: Significant SD Velocity Spread..ideas?

    dar,
    Maybe you have the lucky chargemaster that doesn't take time to warm up, but I have done the tests on MINE and it does throw heavier right after being switched on. Especially when the room is cold in the winter.

    No doubt about the 0.3gr difference between immediate on and 1 hour later when weighed on a beam scale.
    I have no idea if 30 minutes, 1 hour or 3 hours is best, I just either leave mine on, or turn it on a few hours before loading. 3 was a guesstimate
    If I leave it on for several hours then cal, it stays dead on for as many hours as I use it, or if I just leave it on it is dead on the next time I use it.

    I was just trying to help the guy, and in MY experience with MY chargemaster, it throws heavier when it is just turned on.

    Like I said, it's not much, and I noticed it because I had it on auto throw, it threw a charge and I walked off leaving the charge in the pan to do something else. It was dead on before I left an 0.2gr heavy when I came back about 2 hours later. That's when I started looking to see if leaving the machine on would help. I tested it on several different cooler days over the winter, and it did show lighter readings when just turned on.

    This assumes you calibrate when turned on and don't calibrate when it has been on for a while. I suppose if you recal every so often as it is on, then you might not get the variation.

    Just my experience.
    madd0c