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Velocity Variation in 6.5X47 Loads?

22hipower
A somewhat convoluted issue but I'll make it as short as I can. Custom rifle in 6.5X47; original ammo provided by rifle maker; 37 grains Varget; 140 grain Berger VLD, Federal match primer, Lapua brass. Velocity choreographed at 2650fps. After firing at fixed ranges out to 600 yards had turrets made for scope. Problem, after firing approximately 50 rounds over six months noticed that drop at 400 yards was about four inches more than expected so chronographed the load again and found it to be at 2550 +/- and four inches lower than expected; same batch of ammo.

Trying to get back to 2650 with a consistent load, so here's the issue, three batches of ammo all using essentially the same components are providing a considerably larger than expected Extreme Spread in velocity. Got these results today (Shooting CHRONY set up in the shade about 10 feet from muzzle):

1. 2565 37.0 grains (recent load; new batch Varget; CCI 450 primer)
2. 2581 37.3 grains (recent load; new batch Varget; CCI 450 primer)
3. 2595 37.3 grains (recent load; new batch Varget; CCI 450 primer)
4. 2595 37.0 grains (my load from last year; Varget; CCI 450 primer)
5. 2596 37.1 grains (recent load; new batch Varget; CCI 450 primer)
6. 2599 37.1 grains (recent load; new batch Varget; CCI 450 primer)
7. 2604 37.0 grains (my load from last year; Varget; CCI 450 primer)
8. 2608 37.0 grains (last year ORIGINAL load; Varget; Federal Match primer)
9. 2627 37.4 grains (recent load; new batch Varget; CCI 450 primer)
10. 2635 37.4 grains (recent load; new batch Varget; CCI 450 primer)
11. 2648 37.0 grains (my load from last year; Varget; CCI 450 primer)
12. 2680 37.0 grains (my load from last year; Varget; CCI 450 primer)
13. 2655 37.0 grains (last year ORIGINAL load; Varget; Federal Match primer)
14. 2691 37.2 grains (recent load; new batch Varget; CCI 450 primer)
15. 2722 37.2 grains (recent load; new batch Varget; CCI 450 primer)

All powder loads except for 8 and 13 were on my RCBS electronic scale.
OAL on all rounds the same.
Lapua brass new or fired twice and neck sized.

Any thoughts as to what variables could account for the 157fps ES and what I can do about them?

Also the fastest loads (14, 15) at 37.2 grains where not the heaviest charge. . . .?

I realize this is a small amount of data across multiple loads but I'm really scratching my head about how to get to a 2650fps consistent load. Any help will be much appreciated.

Thanks.

Jeff
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Comments

9 comments

Date Votes
  • 22hipower
    That is "chronographed" of course, not "choreographed;" sometimes auto correct on spelling really isn't much help.
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  • charliemeyer007
    Perhaps the mag primer is the issue. Some powders/case combo don't respond well. I clean the primer pocket every time. New brass gets the Lyman flash hole de-burring uniforming treatment. I use a hand tool to prime with, Lyman 310 tool to be specific - has the best feel of any I have ever used.

    Check the scale, maybe static cling.

    Clean your bore with a copper fouling solvent. I like Shooter's Choice. Then a good work over with like JB Bore Paste.

    I try for full cases or lightly compressed in rifle loads. Powder and projectile selection subject to loading data and availability. I try and buy enough bullets/powder/primers from the same lot to wear out the 200 cases I buy at a time for rifle brass (1000 for pistols).

    Chemical reactions are usually temperature dependent - burning gunpowder and primers are chemical reactions. Back in the day I had winter loads that were marked as such. Heat leaking into the case from a hot barrel doesn't help group size.

    I like my projectiles about .003 - .005 out of the rifling. Candle soot black is a lot thicker than Sharpie black. When seating the bullet I stop 1/2 way then spin the case 180 degrees before finishing the seating process - takes out 50% of the error.

    Bullets have to fly threw the air which varies in moisture content.

    Factory data is often corrected to muzzle velocity by adding like 100 fps to the 10' data.

    Personally the best use for the chronograph is the spread. Small spread usually indicates all is well with your variables - large spread implies some component or technique isn't right.
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  • perry shooter
    What you don't show is the temp when you shot each test
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  • 22hipower
    quote:Originally posted by perry shooter
    What you don't show is the temp when you shot each test


    The 15 results shown above were all shot yesterday; temperature about 74 degrees. Don't have records, but the temperature would have been about the same when first shot the gun with the original loads last year. Probably in the 90s last fall though when first noticed the approximate 100 fps reduction in velocity.
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  • Hawk Carse
    I am not clear, was this fifteen strings or fifteen shots?

    Any road, versus the vendor's ammo, you have different primer, different powder (Varget is somewhat well known for lot to lot variation.) and used vs new brass. It all matters.
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  • gunnut505
    So is the 4" discrepancy at 600 yards, same bench, same target location?
    Try a slightly lighter bullet for 5-7 rounds & see if it comes back up.
    Not to besmirch your reloading technique, but are you using a single stage press & its' primer seater, or a separate hand-held seater?
    If all that's OK, when did you last change batteries in the scale?
    How many rounds have been down that bore?
    Also, are you using Lapua brass to form your cases, or are you buying them in that caliber?
    Inquiring minds want to know.

    I found the problem.
    Arrange your shots by load weight, then correlate that with old/new.
    Shots 1 & 4, if sorted correctly, have a +/-30fps spread.
    Similar, but smaller spreads are there, too.
    Take another look, you haven't lost much.
    Now, your choreograph might need a look-see.....
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  • 22hipower
    quote:Originally posted by gunnut505
    So is the 4" discrepancy at 600 yards, same bench, same target location?
    Try a slightly lighter bullet for 5-7 rounds & see if it comes back up.
    Not to besmirch your reloading technique, but are you using a single stage press & its' primer seater, or a separate hand-held seater?
    If all that's OK, when did you last change batteries in the scale?
    How many rounds have been down that bore?
    Also, are you using Lapua brass to form your cases, or are you buying them in that caliber?
    Inquiring minds want to know.


    Yes, single stage press with Redding dies (neck sizing only) but using a separate primer seater (Lee).

    The four inch discrepancy was at 400 yards; basically the calculated difference between 2650 and 2550 fps at that range. No, not the same bench/location. Situation was that the gun had been consistently hitting expected targets at 400, 600 and further. Chronographed again when noticed the larger than expected drop and found the 2550 versus the original 2650. At that point the rifle had about 60 rounds down the tube. It is now around 100 rounds.

    No batteries in the scale; powered from 110 and power supply. Lapua 6.5X47 brass bought new.

    Don't worry about besmirching my loading technique, I've been loading for more than 50 years but mostly basic stuff. Not a lot of longer range work so haven't, in the past, worried much about differences in velocity. But at 600 plus yards it makes a difference.

    In response to Hawk Carse's earlier question, the data is for 15 separate shots taken yesterday over a period of about an hour. Barrel got warm but not hot.

    Again, much appreciate all the thoughts and suggestions so far.
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  • Kenneth Stuart
    I've been loading for about fifty years and I'm still learning. Here's the steps I follow:
    1. new cases lubed and run through full length sizer (straightened out-of-round necks and dings)
    2. trim to same length and debur case mouths
    3. debur flash holes
    4. ream primer pockets to same depth
    5. if I believe it to be necessary I outside turn the necks but usually don't
    6. measure each powder charge
    7. make certain bullet is concentric with the neck's center (use a Lee seating die with the self centering bullet cylindrical part polished internally makes for less friction)
    8. use a medium crimp using Lee bullet crimper

    I get very consistent results and have confidence in my reload's performance but I usually load less than 50 cartridges for all my hunting/targeting needs.
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  • 22hipower
    Thanks to everyone who replied and offered suggestions. I'm going to pursue several of them and suspect I'll be able to resolve the issue. Certainly appreciate the expertise and willingness to help found here.

    Thanks again.

    Jeff
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