6.5 CM Load Development...Next Steps??

[DiRTY DOG]

I never had an original 41.7 group. The original powder test went from 41.5 and then 41.8. If you compare the first 41.8 to the second 41.8 they are very comparable both in vertical and horizontal offset with shots from the first 41.8 impacting in almost the exact same spots as the second 41.8 group. I decided to pursue that area because on the original powder test the vertical POI at 41.5 and 41.8 are very similar. The seating depth tightened the groups but I'm concerned this may be a very small window....or it was me.

I was referring to the exact targets that I quoted in my response. You tested 41.6, 41.7, and 41.8 with a photo. 41.7 was significantly better than the others. (Which is extremely unlikely to be repeatable considering only 0.1gr difference between loads).

Then the second photo you posted in the same post (which I quoted, the post we are discussing) was 41.7 but at different seating depths. You changed the way you recorded the coal so I dunno what you changed, but it appears none of those groups in the second photo are anything like your prior 41.7 load that shot tight. Meaning, you proved yourself that it's not repeatable.

 

[Mark71]

I was referring to the exact targets that I quoted in my response. You tested 41.6, 41.7, and 41.8 with a photo. 41.7 was significantly better than the others. (Which is extremely unlikely to be repeatable considering only 0.1gr difference between loads).

Then the second photo you posted in the same post (which I quoted, the post we are discussing) was 41.7 but at different seating depths. You changed the way you recorded the coal so I dunno what you changed, but it appears none of those groups in the second photo are anything like your prior 41.7 load that shot tight. Meaning, you proved yourself that it's not repeatable.

Sorry, maybe I misunderstood. My process was this.

From the original test I felt there was a node in the 41.5 - 41.8 area with 41.8 being slightly tighter, so I loaded 5 rounds each of 41.6, 41.7 and 41.8 with the same seating depth as the original powder test (CBTO 2.241 jump 0.020). Out of these three groups 41.7 was the tightest with 3 shots clustered together at or just under 1" low of POA and 2 shots clustered together just under 0.5" low of POA giving a group size of 0.760". This clustering lead me to believe it wants to shoot in one of these two clusters it just needs some tuning to make it consistent.

From there I moved on to seating depth testing in 0.003" increments using the 41.7 charge. At a CBTO of 2.229 (jump 0.032) all 3 shots clustered just under 1" low of POA. They were a little more horizontal than I would have liked, but that could have been me. This cluster of 3 in the seating depth test is very similar to the cluster of 3 in the 5 shot group.

My plan now is to load 5 or 10 rounds at 41.7 gr using the new CBTO of 2.229 to see if the group holds together and repeats.

 

[Dave M.]

I've got another question regarding this rabbit hole I have entered.

I measured jam at 2.261" using a Hornady OAL gauge and a Hornady modified case. I started my testing 0.020 off the lands for a CBTO of 2.241" which gives me a COL of 2.760". Nosler lists the COL for this bullet at 2.805", so I'm already slightly deeper into the case than the Nosler data.

My question is, when exploring seating depth to tune the load what is a guideline for seating deeper? How do I know when I shouldn't be seating any deeper into the case?

Jam and Lands are NOT the same. My experience is there is approx 0.024-0.040” from where the lands start to hard jam.

 

[Dave M.]

42.1-42.4g of H4350 has always been a sweet spot for our 6.5’s. All three of them started to shoot smaller in that range.

And we only shoot 140’s

 

[Mark71]

Jam and Lands are NOT the same. My experience is there is approx 0.024-0.040” from where the lands start to hard jam.

Sorry...bad terminology on my part. When I took my measurements I pushed the bullet forward with the gauge until it just met resistance with the lands, so I was to just touching the lands.

Thanks for the clarification.

 

[Bc'z]

Sorry...bad terminology on my part. When I took my measurements I pushed the bullet forward with the gauge until it just met resistance with the lands, so I was to just touching the lands.

Thanks for the clarification.

Great chatting with you yesterday, looking forward to seeing it all come together.
I can't remember if we discussed neck tension/interference, it can really be eye opening what a .001 +or- can do to precision.

 

[G7BC]

Berger Hybrid Target Bullets .264 Diameter (6.5mm) 140 Grain Open Tip Match

Berger .264 / 6.5mm 140 grain target hybrid rifle bullet is a favorite among today's best long range target shooters.

www.powdervalley.com

...and start around 39 grains H4350 working up in .2 increments. Mine tuned in around 2720