6.5 CM Ladder/OCW Test Advice

[Bmars06]

Greetings,

I'm looking for some expert eyes to give me their opinions on my ladder test I performed today for a new 6.5 CM load. Three pictures are attached of the targets, shot at 200 yards. There are three target papers, each with five small targets on them. The small targets are numbered 1-15 and have a three-shot group fired at each of them. Targets numbered 1-7 are with a Berger 140gr Match Hybrid Target projectile starting at 40.0 grains of powder and going up by .3 increments to 41.8 Targets numbered 8-15 are with a Hornady 140gr ELD-M projectile starting at 40.0 grains of powder and going up by .3 increments to 42.0. The powder charges and the overall spread of the group is written next to the individual target as well. I'm having a hard time discerning where the optimal charge weight (OCW) appears to be.... I appreciate any guidance/advice!

Here are the velocities of each projective/charge:

Berger 140gr Match Hybrid Target
40.0 Grains of powder
-2609
-2619
-2614

40.3 Grains
-2609
-2609
-2636

40.6 Grains
-2640
-2624
-2629

40.9 Grains
-2677
-2672
-2688

41.2 Grains
-2704
-2726
-2704

41.5 Grains
-2766
-2754
-2737

41.8 Grains
-2777
-2766
-2772

Hornady 140gr ELD-M
40.0 Grains of H4350
-2645
-2645
-2656

40.3 Grains
-2666
-2682
-2656

40.6 Grains
-2704
-2677
-2699

40.9 Grains
-2106—Must be a misread
-2109—Must be a misread
-2569

41.2 Grains
-2732
-2801
-2743

41.5 Grains
-2766
-2760
-2777

41.8 Grains
-2777
-2772
-2777

42.0 Grains
-2801
-2789
-2789

 

[2aBaC̶a̶]

@Ledzep all you bud.

 

[Rmdashrf]

It might be helpful to graph the velocities. The spreadsheet the 6.5 guys made is fantastic.

http://www.65guys.com/wp-content/uploads/2018/06/Load-Analysis-Model-V2.xlsm

 

[Ledzep]

40.5gr H4350, 140 ELD-M (they seem to be trying harder than the Bergers)
2.810" C.O.A.L.
Don't look back.

It's enough velocity to keep you supersonic as far as you need to be for PRS/NRL, it's low enough pressure if it rains it's not going to ruin your day. I'll bet you money that if you were to shoot 20 rounds of every charge weight you tested, the SD's would be in the 7-12fps range regardless of charge, and if you were to repeat that same test (20 ea.) none of them would be the same, but they'd still all be 7-12 fps SD. Less charge weight = less dispersion IME.

 

[Bmars06]

40.5gr H4350, 140 ELD-M (they seem to be trying harder than the Bergers)
2.810" C.O.A.L.
Don't look back.

It's enough velocity to keep you supersonic as far as you need to be for PRS/NRL, it's low enough pressure if it rains it's not going to ruin your day. I'll bet you money that if you were to shoot 20 rounds of every charge weight you tested, the SD's would be in the 7-12fps range regardless of charge, and if you were to repeat that same test (20 ea.) none of them would be the same, but they'd still all be 7-12 fps SD. Less charge weight = less dispersion IME.

Would you expect the charge and OAL to very depending on the barrel length ect? I imagine the barrel harmonics very a bit where 40.5 and 2.810 works great for one gun but may very for a different gun? @Ledzep

 

[Ledzep]

I couldn't say with any certainty. Vibrations and I did not get along in college lol. I've done a couple of "by the inch" tests but nothing noteworthy ever came out of them. Accuracy seemed fairly static across the board. I'm sure with drastic changes, like 16" vs. 30" you may see some changes, but 22-26" I'd not expect anything wild. Could be wrong, though.

 

[Zack_va248]

Appears that at least 41.5-41.8 velocity stays very similar and had two drop speed and another identical at 2166. The sample size is small but the increase in cw with the drop in speed is a plateau I’d investigate more. Especially given many others have a node in that 41.5 region of cw. Seems to me that both projectiles had the same effect in that zone.

As stated graphing it really helps “see” the velocity plateau. Tune the groups with seating depth after you find the center of the node.

 

[WB300]

I agree with Ledzep and Zack. 40.5 seems to be in a lower node and 41.8(ish) seems to be in a higher node. Dan Newberry believes nodes are generally 3% apart and I've always had good luck using his method (OCW). Seating depth SHOULD tighten groups up. I usually find better groups with a lower node where I'm not getting pressure signs, but YMMV.

Hope this helps. Keep us updated.

Will

 

[Ledzep]

I agree with Ledzep and Zack. 40.5 seems to be in a lower node and 41.8(ish) seems to be in a higher node. Dan Newberry believes nodes are generally 3% apart and I've always had good luck using his method (OCW). Seating depth SHOULD tighten groups up. I usually find better groups with a lower node where I'm not getting pressure signs, but YMMV.

Hope this helps. Keep us updated.

Will

Some time if you care to try it...

Take your high node, shoot 20 shots into a single group. No time limit, just good shots.

Load 20 half way between your high node and low node. Shoot them into 1 group the same way.

40 shots to learn something that might change how you look at load development forever...