6mm (.243) Optimum Velocity - 105 Berger Hybrid

[kilizyrag]

I'm one year into Precision Rifle shooting and I have no idea what I'm doing. I shot last year with a LR308 and swore I would build a bolt gun for 2024. The rifle is done; Tikka T3, KRG Bravo (CTR Mags) and Preferred Barrel Blanks 26" 1:75 chambered in .243 Winchester. An Arken sits on top to look through.

I broke the barrel in with 36.5gr W760 pushing 107 SMK. Slow as molasses @ 2650'/s. Lapped barrels break in fast. Next is load development.

Hornady lists the max charge of H4350 @ 37.5gr for the 105 A-MAX and 2800'/s. 37.5 grains is about 80% case fill which seems low. Of course they set the bullet at SAAMI COAL of 2.710" while I can set the COAL at 2.875 which is 0.010 off the lands and leaves a lot more space for powder.

So I did a coarse ladder test; 38.0-42.5 at .5 increment. More of a pressure test, if you will. Zero pressure signs all the way to 42.5 and all the removed primers look the same; rounded base, etc. Velocities ranged from the low of 2750 to the high of 3000'/s with the 42.5gr load. So now the questions.

Should I go faster? Out of thin air I was shooting for 2950'/s

What is a good velocity for 6mm 105 berger hybrids?

Picture is the group at 100 yards. Upper left bug hole is the 5 fastest while the lower right is the slowest. Don't know why the POI shifted. The test was to find a powder charge range and velocity only. More load development to come.

 

[Slides]

Haven't done it myself yet but guy on another forum got into 3100s with 2209 (H4350) with 108eldm in ADI brass with a 26 inch barrel. If you aren't getting pressure signs and can conveniently life cycle test a couple of pieces of brass to find when it won't hold primers that's probably best in order not to waste a heap of brass. I'm fortunate I can walk 10m between loading gear and garage to test fire so that is what I will be doing.

 

[Doom]

Looking at the target I'm betting you shot a 5 shot group, moved shifted, took a break and came back and shot another group. Different setups.

 

[Hecouldgoalltheway]

Y

Haven't done it myself yet but guy on another forum got into 3100s with 2209 (H4350) with 108eldm in ADI brass with a 26 inch barrel. If you aren't getting pressure signs and can conveniently life cycle test a couple of pieces of brass to find when it won't hold primers that's probably best in order not to waste a heap of brass. I'm fortunate I can walk 10m between loading gear and garage to test fire so that is what I will be doing.

If you take 108 eld-m's to 3100fps, you may see roughly 8 out of 10 of them explode in flight. Ask me how I know.


I found about 2,950 to be the most accurate and least brass destructive on 6mm loads with stuff in the 105gr range. I'm not a speed demon though. I'd rather dial another .10 and get 4 more firings from my brass, and maybe a little more barrel life.

 

[OREGUN]

Unless I’m seriously mistaken, 2950 is the money spot for 105 hybrids.

I think most of that comes from guys shooting Dasher so with more powder you may be able to get going a lot faster and find a sweet spot in the 3000s.

 

[kilizyrag]

Looking at the target I'm betting you shot a 5 shot group, moved shifted, took a break and came back and shot another group. Different setups.

You may have something here. I got up mid string for more coffee.

 

[kilizyrag]

Unless I’m seriously mistaken, 2950 is the money spot for 105 hybrids.

I think most of that comes from guys shooting Dasher so with more powder you may be able to get going a lot faster and find a sweet spot in the 3000s.

I may up the test to see where pressure signs start. I think I like 2950-3000’/s. Less strain on the components.

 

[MvHTjy]

You might find this video helpful:

 

[Slides]

Y

If you take 108 eld-m's to 3100fps, you may see roughly 8 out of 10 of them explode in flight. Ask me how I know.


I found about 2,950 to be the most accurate and least brass destructive on 6mm loads with stuff in the 105gr range. I'm not a speed demon though. I'd rather dial another .10 and get 4 more firings from my brass, and maybe a little more barrel life.

I'm talking from 243 not smaller 6mm cartridges. What barrel twist were you running?

I have a 6BR in 7.5 twist but my new 243 barrel is 8, I will see if Atips work out in it, if neither Atips ir eldm want to work I will buy some locally manufactured projectiles.

 

[Hecouldgoalltheway]

I'm talking from 243 not smaller 6mm cartridges. What barrel twist were you running?

I have a 6BR in 7.5 twist but my new 243 barrel is 8, I will see if Atips work out in it, if neither Atips ir eldm want to work I will buy some locally manufactured projectiles.

I'm not sure I understand why the cartridge size would factor into a bullet rupturing in flight, but mine were busting without even hitting 3,000fps in a 7 twist. You might be fine with an 8, you might even be fine with a 7.5 @3,100, but there are story after story going back years on the hide of people with the same problem.

Somewhere there was a guy who told us that "ELD-M actually stands for .extremely .low-drag, .dissappears .mid-flight". I believe I got that close. Hilarious

 

[kilizyrag]

1:7.5 twist. I’ll run some up to speed today and see what happens.

 

[kilizyrag]

You might find this video helpful:

I hate videos, but I did watch it. 2950 may be my sweet spot. Will know more after today’s shoot.

 

[MvHTjy]

Here's how I do it - decide what velocity you want to run (sounds like you're set on 2950). Then load a string of 10 rounds in .1 increments with your target estimate somewhere in the middle. Using a chrono, identify where your velocity flattens out (or decreases) even though the charge weight is increasing and choose your velocity node. I like this method because it uses the least amount of components. In my case, I like to target 2800, however my latest barrel likes either 2780s or 2830s, running 105 hybrids from my dasher with a 50-60 thou jump.

Keep in mind your charge increment depends on the efficiency of the cartridge and powder burn rate, so my suggestion of .1 works for efficient cartridges like the 6br family and Varget. For your 243 and H4350, you might need to bump that up to .2 or even more.

 

[Doom]

You may have something here. I got up mid string for more coffee.

Yep. I often see that happen.

 

[Slides]

Velocity vs charge weight nodes don't exist with appropriate sample sizes. More energy in = more energy out beyond sampling noise.

 

[LRDD]

6 creed

That 105 can be tuned to shoot wherever you want.

 

[Hecouldgoalltheway]

6 creed

That 105 can be tuned to shoot wherever you want.

Try it with a 7 twist

 

[kilizyrag]

I loaded up a bunch more just to see where this all takes me. I loaded 10 straddling my velocity goal at .2gr increments. Then I kept going at .2 gr increments for another 10. Twenty total rounds 40.8 - 44.6 by .2 increment. I had scrubbed the barrel clean so I shot 5 fouling rounds first. Fastest velocity recorded was 3227'/s with the 44.6gr load. Bullet stayed together too.

Barrel seemed to be shooting a little faster today also.

Results are confusing to say the least. Velocities don't settle down till 43.3gr which is approximately 90% case fill. No pressure signs either.
Left primer is low charge and right is 44.6gr @ 3227'/s. I faintly see minor cratering for the hotter round.

The chart shows a "wobble" around 2950'/s which is my velocity goal. I could live with 3000'/s but I don't wish to go any faster.

Would a slower powder like Retumbo or H1000 give better case fill and slower top velocity?

I have not done any seating depth tests. Currently the bullet is 0.010" off the lands. Will pushing the bullet deeper help?

Headspace is tight on this barrel. The new Winchester brass that I'm using is only 0.008-0.010 shorter than the chamber. How does that effect all this testing, if at all.

 

[kilizyrag]

I'm talking from 243 not smaller 6mm cartridges. What barrel twist were you running?

I have a 6BR in 7.5 twist but my new 243 barrel is 8, I will see if Atips work out in it, if neither Atips ir eldm want to work I will buy some locally manufactured projectiles.

1:7.5 twist

 

[kilizyrag]

6 creed

That 105 can be tuned to shoot wherever you want.

I know, but I'm retired and don't have Taylor Swift as a girlfriend. Barrels have gotten expensive so I'd like to keep it around longer if I can.

 

[OREGUN]

This thread really delivers. We’ve got nodes, exploding bullets, and .243 being described as better for barrel life (in a conversation about pushing as hard as possible for speed).

 

[kilizyrag]

Gonna try pushing the bullet deeper. Think less case capacity. Maybe heavier projectiles will help; 115 DTACS. I’m not sure where to go from here.

 

[Hecouldgoalltheway]

This thread really delivers. We’ve got nodes, exploding bullets, and .243 being described as better for barrel life (in a conversation about pushing as hard as possible for speed).

My exploding bullet episode happened at a prs match in front of a dozen witnesses. I made a thread about it probably 8 months ago and 2 of the people who witnessed it all day long were there to verify it. One guy had filmed it in slow motion, and while we couldn't get it to play on SH with enough quality to see it, his video was crystal clear. I shot an entire match with at least 8 of 10 of my 108 eld-m bullets turning into white puffs of smoke at about 100y. It was a long day.

 

[kilizyrag]

My exploding bullet episode happened at a prs match in front of a dozen witnesses. I made a thread about it probably 8 months ago and 2 of the people who witnessed it all day long were there to verify it. One guy had filmed it in slow motion, and while we couldn't get it to play on SH with enough quality to see it, his video was crystal clear. I shot an entire match with at least 8 of 10 of my 108 eld-m bullets turning into white puffs of smoke at about 100y. It was a long day.

That would suck for sure. I’m trying to keep these 105 bergers below 3000 with consistent velocity.

 

[OREGUN]

My exploding bullet episode happened at a prs match in front of a dozen witnesses. I made a thread about it probably 8 months ago and 2 of the people who witnessed it all day long were there to verify it. One guy had filmed it in slow motion, and while we couldn't get it to play on SH with enough quality to see it, his video was crystal clear. I shot an entire match with at least 8 of 10 of my 108 eld-m bullets turning into white puffs of smoke at about 100y. It was a long day.

I don’t doubt it. I squadded with a dude who blew up half his bullets pushing a 22GT to 4 bajillion rpm’s. Not sure what bullets but it was like they vanished after the gun went off.

 

[ma smith]

Is there any Hybrid bullet that doesn't like 2950 fps...