repeatability issues

[wtx]

Good morning guys, advice needed, long post.

Having trouble with repeatability in load development. I won’t get to every detail but ran through a test in a Tikka 7mm-08 using varget//win WLR primers//starline brass//140 nosler ballistic tips. Started 3 round groups in 0.5 grain increments and identified a node to dive into. All groups were sub MOA with decent speed and some ES numbers that I could work with. I then loaded up 5 shot groups in 0.3 grain increments and landed on two loadings with 15-16 ES and about 10 SD. Couldn’t be going any better at this point.

Here’s where I’m needing some help. I haven’t been able to repeat since. I’ve loaded up two separate 10 shot groups in the “sweet” spot and seeing velocity numbers through the roof, as in 30-60 ES. The accuracy is still there (0.5 to 0.7 moa) but frustrated with the spreads.

The load isn’t intended to be anything over 500yards, and I’ve run some ballistics test to show the ES doesn’t make more than an inch or two difference at that distance, but would like to tighten the velocity up.

Brass was new when I started, and ran through about 75 rounds of the star line before switching to Lapua. Lapua actually made it worse. Scale is the same and calibrated (hornady auto-loader), seating depths are all the same (redding type s set), primers seated as best I can (hornady hand primer) . All rounds were opened up with a expander mandrel to begin and tension should be 0.002. Havent resized any yet, still working though the lot.

Any help from you guys? Sorry for the long post.

 

[Erict]

If accuracy is about the same I would not be concerned. Look at it this way - 60 fps / 2900 fps = 2% variation. The animals/targets will never know the difference.

Different brass will have different internal capacities, hardness, etc. so I would not assume the Lapua will give identical results. I would also suspect that you will see similar variation once you begin using resized brass vs. the new stuff. Good luck!

 

[Ram94]

Are you keeping track of the round count on the barrel? I have a very similar setup (Tikka SL in 7-08) and I had a similar thing happen. Found a good velocity node and then at around 150 rounds, fell out of it. I backed down on the powder charge by 0.3gr and I am back in business.

Lapua Brass
41.6gr Varget
162gr. ELD-M
CCI200 Primers
2690fps
ES 16
SD 4

 

[wtx]

When I started LD for this rifle I estimated 200 rds through the tube, now up to 280. Could've just caught it an an unlucky time I suppose.

If accuracy is about the same I would not be concerned. Look at it this way - 60 fps / 2900 fps = 2% variation. The animals/targets will never know the difference.

Different brass will have different internal capacities, hardness, etc. so I would not assume the Lapua will give identical results. I would also suspect that you will see similar variation once you begin using resized brass vs. the new stuff. Good luck!

Good point on the variance. Being relatively new to the hobby, most of what you hear is all about <20 ES and geared for the "long" range guys. I'm not to that point yet, just now getting comfortable out to 500 (which is still long, but its all relative). The variance makes it tough though to feel confident in taking it out to "my distance". I am going test out a Labradar with the same loads just to verify my MagnetoSpeed isn't the culprit. Also considering a scale upgrade (RCBS?, cant justify the A&D set up yet).

 

[Rob5589]

New vs fired brass. Different brand of brass.

 

[Lawnboi]

Try some once fired and sized brass. I think you might see a difference.

 

[willfrye027]

Did you get into a new powder keg? I’ve seen pretty big changes in my loads when I crack a new jug open.

also what chrono? Could be different lighting conditions or something causing erroneous readings.

 

[wtx]

Did you get into a new powder keg? I’ve seen pretty big changes in my loads when I crack a new jug open.

also what chrono? Could be different lighting conditions or something causing erroneous readings.

Powder has all been from the same lb that was new when I started on these loads. Magnetospeed is what im using, on a covered bench. Temps were different, that I do know. However took extra time on the warmer day to ensure better cooling, even through the gun in the truck for some AC. I did notice that the cold bore shots are all very close over a few different testing sessions. I might test that theory over a week or so just shooting one shot.....slow process ha. Its a factory tikka pencil barrel. I'm going to test over a lab radar also to see if perhaps its the Magneto.

 

[Hiwayman92]

I had a gun like that once. One hole gun one day, 2@ gun the next. I ended up having a loose barrel! Scopes, stocks, triggers, brakes, bullets, powders, cleaning, and chasing my tail.

However, Tikka barrels are usually so tight you can’t get them loose If you tried. Have you stripped the barrel of all carbon and copper and bore scoped it?


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[MidGAHunter]

Remember this saying....If you change one thing, you change everything. Changing brass changes your load completely. Same thing with powder, primers, and bullets. That also can apply to lot numbers within each category. When something, anything, changes you have to re-verify the load looking for the velocity you found your barrel likes in that particular bullet weight. Also, have you shot your rifle enough to have sped up the barrel so it settled in? Did you fire form your brass? Both of these will make a difference.