Figuring out Optimal Charge Weight

[TackDriver284]

Sometimes I chase my tail chasing accuracy, and I am sure some of you do. I am pretty sure picking the wrong OCW is one of the reasons. When I do a load development, I see ugly groups or three holes but pick the nice one hole group as my go to load but when you see changes of temp, your one hole group is now a 3 shot group. Back to square 1!!
Perhaps you guys can help me with your opinions.

I did two OCW tests today round robin style, top line is the .308 with the IMR4064 and 168 VLD and the bottom line is the 6.5 Creedmoor with H4350 and 140 Hybrids.

If some of you OCW gurus could help me narrow my search for the OCW to pick,,,next will be the jump test. ( Seating depth test )

I looked at the top line on the target which is the .308 and chose #2, 3 and 4 as my OCW.
As for the bottom line on the target which is the 6.5 Creed, I chose #1,2 and 3 as my OCW.

I see those 3 shot groups I picked which are very close on the same line and POI.

Would you guys agree? Of course the jump test is after I pick the middle charge between the 3 groups. What do you guys pick?

I think this is a learning experience most of us could benefit when we do our load developments and learn to read OCW and pick the correct OCW.

 

[DrMike]

Your .308 is delivering sterling results for you. I would agree that loads 2, 3 & 4 are most promising. I would be inclined to include load 5, as well. The Creedmoor is also delivering the goods for you. For sure, your OCW lies somewhere between 41.3 and 41.9 grains of powder. Choose a load; I don't think you'll go wrong. Seating depth is your next move.

 

[RaySendero]

Your .308 is delivering sterling results for you. .....
The Creedmoor is also delivering the goods for you. .....

TackDriver,

I agree with DrM, Both rifles are shooting very well to hold those grouping over
the 15 to 21 shot strings!!!

However, I'd interject that there IS NO statistical difference in those 3 shot groupings.
And would like to see the velocities of the shots if you chronoed them?
I assume those are all shot at 100 yds - Can you confirm?
My thinking is that the average velocity and the velocity variation
maybe more important at longer ranges that the differences between those groups.

 

[SJB358]

I’m with Ray here.

I’d strap your Magnetospeed on your rifle and shoot from bottom to top of a single round a piece to see where your spot is on velocity. Chances are you’ll see where each charge flattens out, meaning you aren’t getting much deviation even with increased charges. It’s worth shooting 10 rounds through the gun.

With those two accurate rifle I’m not too surprised to see such excellent 100 yard groups. I’d shoot for consistent speeds and I’ll bet groups will hold up at distance as well.

 

[truck driver]

I use to chase three shot groups changing the powder weight between each group and would burn lots of powder,primers and bullets till Dewey introduced me to the ten shot ladder which Scotty and Ray are talking about and it does work and will save you a lot of aggravation searching for the right load.
Once you find the optimum velocity for the bullet powder combo you want to shoot and then work on seating depth to dial it in.
Sounds too simple to be true but it does work.

 

[grry10]

I've never used one but does the use of a Magnetospeed have an impact on barrel harmonics? Meaning do group sizes change when shot without the Magnetospeed attached to the barrel?

 

[TackDriver284]

Your .308 is delivering sterling results for you. .....
The Creedmoor is also delivering the goods for you. .....

TackDriver,

I agree with DrM, Both rifles are shooting very well to hold those grouping over
the 15 to 21 shot strings!!!

However, I'd interject that there IS NO statistical difference in those 3 shot groupings.
And would like to see the velocities of the shots if you chronoed them?
I assume those are all shot at 100 yds - Can you confirm?
My thinking is that the average velocity and the velocity variation
maybe more important at longer ranges that the differences between those groups.

Sorry, I did not include the velocities on the post. The test was used with a Oheler P35 and shot at 100 yards in about 65 degrees and overcast. I see a flat spot for the .308 on # 3 and #4, but its not a wide flat spot. There could be an indication of a false reading on #3 on 2nd shot but the velocity variation between shots isn't bad.
For the Creedmoor, I just don't see any flat spots. Seating depth is .020" off the lands and single fed. I need to seat about .050" off the lands to be magazine fed especially with those long 140 Hybrids.

I wanted to see how well it shoots with the Hybrids closer to the lands. A few weeks ago with virgin brass, it shot nicely out of the magazine and .080" jump when I did the first testing ( after break in ) and have not gone back to .080" jump yet.

I could do the seating depth test after figuring out which OCW to use as Mike mentioned.

Should I try 41.6 grains as my OCW / do the seating depth in .010" increments or narrow it down to 41.4, 41.6, 41.8 three shot groups and find a sweet spot first before going to the jump test?

.308:
1. 2705-2697-2685
2. 2716-2715-2711
3. 2740-2718-2735
4. 2740-2734-2737
5. 2766-2753-2761
6. 2772-2771-2764
7. 2791-2810-2733

6.5 Creedmoor
1. 2698-2728-2739
2. 2714-2742-2752
3. 2749-2751-2758
4. 2768-2773-2779
5. 2773-2807-2811

 

[DrMike]

From the data you present, I would focus on the charge weights that produced groups 3 & 4. For the Creed, I'd focus on the weights that produced groups 2 & 3. Nothing wrong with that data.

 

[AFG270]

I've never used one but does the use of a Magnetospeed have an impact on barrel harmonics? Meaning do group sizes change when shot without the Magnetospeed attached to the barrel?

Yes, I think it does. But I don't shoot groups with it, as Scotty said just shoot one round of each charge weight to get your velocity.I hope Dewey posts on this thread he has helped me as well.

 

[Dwh7271]

From the data you present, I would focus on the charge weights that produced groups 3 & 4. For the Creed, I'd focus on the weights that produced groups 2 & 3. Nothing wrong with that data.

As usual :grin: , I can't disagree with the Dr. Exactly where I'd have said.
Can't be a lot of help on the groups as I just shoot, sometimes into dirt sometimes into the backstop as velocity is all I'm concerned with. It does look like you have a couple fine rifles there. I would be surprised if anything from GAP didn't shoot very well though. Fine riflery on your part also.
Does the MagnetoSpeed have an impact on group or POI? Yes, absolutely. I find on mine that when using it and actually shooting a target in most instances it shifts POI high right. Every now and then it throws a curveball and impact shifts low but I assume that is due to a different change in barrel harmonics.

The interesting thing to me on the flat spot development is that it actually allows for some temperature or powder variances. I'm working on a sheet to try to see the average size of the flat spot by caliber, as it seems that each caliber has fairly specific sweet spots, if you want to call them that. My rationale on it is that if the average flat spot is say 3%, then I know that on average, a 3 % variance in burn or velocity is not going to impact me in the field or at the range. There also should be a correlation between temp sensitivity and reading the flat spot. In other words, if the average flat spot is 3% and I'm shooting the middle of it and the temp sensitivity of a given powder is .2% per 10 degrees, I have 1 1/2% either way to work with or 70 plus degrees so a 40 degree swing from where I worked up the load is no big deal and I can shoot with confidence. Clear as mud? Maybe I get a little too stuck on this stuff......

 

[truck driver]

Dewey I'm looking forward to reading your findings.

 

[SJB358]

Your .308 is delivering sterling results for you. .....
The Creedmoor is also delivering the goods for you. .....

TackDriver,

I agree with DrM, Both rifles are shooting very well to hold those grouping over
the 15 to 21 shot strings!!!

However, I'd interject that there IS NO statistical difference in those 3 shot groupings.
And would like to see the velocities of the shots if you chronoed them?
I assume those are all shot at 100 yds - Can you confirm?
My thinking is that the average velocity and the velocity variation
maybe more important at longer ranges that the differences between those groups.

Sorry, I did not include the velocities on the post. The test was used with a Oheler P35 and shot at 100 yards in about 65 degrees and overcast. I see a flat spot for the .308 on # 3 and #4, but its not a wide flat spot. There could be an indication of a false reading on #3 on 2nd shot but the velocity variation between shots isn't bad.
For the Creedmoor, I just don't see any flat spots. Seating depth is .020" off the lands and single fed. I need to seat about .050" off the lands to be magazine fed especially with those long 140 Hybrids.

I wanted to see how well it shoots with the Hybrids closer to the lands. A few weeks ago with virgin brass, it shot nicely out of the magazine and .080" jump when I did the first testing ( after break in ) and have not gone back to .080" jump yet.

I could do the seating depth test after figuring out which OCW to use as Mike mentioned.

Should I try 41.6 grains as my OCW / do the seating depth in .010" increments or narrow it down to 41.4, 41.6, 41.8 three shot groups and find a sweet spot first before going to the jump test?

.308:
1. 2705-2697-2685
2. 2716-2715-2711
3. 2740-2718-2735
4. 2740-2734-2737
5. 2766-2753-2761
6. 2772-2771-2764
7. 2791-2810-2733

6.5 Creedmoor
1. 2698-2728-2739
2. 2714-2742-2752
3. 2749-2751-2758
4. 2768-2773-2779
5. 2773-2807-2811

3&4 look pretty good on the 308 if you toss out one reading from #3

2&3 look great from your 6.5 if you toss one reading from #2.

That’d be where I would look.


On edit Mike beat me to it. Those spots look pretty good. I’d bet you’ll be in good gravy

 

[longrangehunter]

I'm with Scotty on his two posts. I always just looked for the velocity to remain the same up, or down from the charge difference vs. the long distance target test version. Then seating depth and/or minor powder charge changes which I did shoot at 300 yards..... at that distance wind usually isn't a factor and why I only go out that far, and in an area with total lack of wind, and/or wind block.

If IMR4064 doesn't hit the ball out of the park try RL-15 which the military went to after IMR4064 with the 168.

 

[Bbear]

Here's what Scotty & Ray are talking about. I 'tested' it yesterday with a known accurate load. 10 rounds (actually, 20 in case my magnetospeed 'missed' one) and my known load came out in the middle of a 'flat' spot in the velocity.

http://www.65guys.com/10-round-load-dev ... dder-test/

 

[SJB358]

Here's what Scotty & Ray are talking about. I 'tested' it yesterday with a known accurate load. 10 rounds (actually, 20 in case my magnetospeed 'missed' one) and my known load came out in the middle of a 'flat' spot in the velocity.

http://www.65guys.com/10-round-load-dev ... dder-test/

That’s pretty danged cool!

 

[6mm Remington]

Great article that described it nicely.