Reading Groups

[Drewbis1]

I've been reloading for a few years for range plinking ammo for both handgun and semi-auto rifles. I've dove into the realm of precision shooting and I'm developing a 6.5 Creedmoor load for my Bergara HMR. Components are Starline brass, Winchester WLR primers, H4350, and I've tried both Hornady ELD-M 140 and Sierra Match King 142 projectiles. For ES/SD my barrel loves both the Sierra and Hornady, but for accuracy, the Sierra's are all over the place.

I'm following the Erik Cortina method of reloading. Steps I've used are as follows:
1) Started with prepped brass, I found my jam point in my rifles chamber with said components. I used (3) and took the shortest measurement as Jam. Measured with a comparator, I backed off Jam .020" and used this as my testing depth for velocity.

2) Loaded (3) shot groups in .2gr increments at stated seating depth .020" off Jam point from middle of the road powder charges in published data, to just over max and shot over Magneto Speed V3 looking for a flat spot in velocity where it doesn't increase much between powder charges. I found one near 40.5gr and another near 41.2. Since this rifles intended use is out to 1000 yards, I wanted the increased velocity so I used the 41.2 grain charge around 2700 fps. Using only (3) shot groups, I know I don't get the most conclusive data here, but my ES/SD were both single digit at this powder charge.

3) Using 41.2 gr charge, I adjusted seating depth looking for accuracy. I loaded (3) shot groups starting at .020" off my jam point and seated deeper in .003" increments. All were seated with a Forster Micrometer Bench Rest Die. The Sierra 142's were all over the place. I've concluded my barrel just doesn't like them. The Hornady were much tighter, but I'm needing advice reading the group shapes. Cortina's theory is to find (2) small groups in a row and load to the longest seating depth -.001". This allows the throat of the barrel to erode as you shoot more and still be within your accuracy node.

My shots were starting with my longest seating depth on top left and decreasing in depth as I go right. 2nd row down, same thing. The depths are listed next to each target. All shots off of bags at 100 yards. My question is: I have (2) separate strings that have consecutive small groups. First is at 2.256 followed by 2.253. Next is 2.244 followed by 2.241. Which would you choose? A common pattern is vertical groups and the upside down triangle group. Is one more desirable for longer range?

Any advice is appreciated. I'm still learning about the fine details of precision reloading, but I welcome all your knowledge, criticisms, critique, and advice.

 

[918v]

I would take the 2.256” one and load 41.1 and 41.3 grains using that seating depth to see if the group stays tight and in the same spot. And if it does I would try 41.0 and 41.4 grains to see how wide the node is. Then I would take the middle charge and increase and decrease the seating depth to map out that aspect.

What is the overall coal of the 2.256” load and is this 6.5CM?

 

[Drewbis1]

I would take the 2.256” one and load 41.1 and 41.3 grains using that seating depth to see if the group stays tight and in the same spot. And if it does I would try 41.0 and 41.4 grains to see how wide the node is. Then I would take the middle charge and increase and decrease the seating depth to map out that aspect.

What is the overall coal of the 2.256” load and is this 6.5CM?

Thanks, I'll give that a try.

I didn't measure COAL of all seating depths, just my chamber max (jam point). COAL was about .615" longer than BTO. So in theory BTO of 2.256" would be in the ballpark of 2.871" COAL if the polymer tips are pretty consistent.

And yes, this is 6.5 CM. I don't think these will fit into my Bergara magazine, but maybe into a Magpul AICS. Either way, magazine feeding isn't a priority for me. I've been single feeding and learning patience, lettings the barrel cool between shots/strings.

 

[918v]

Thanks, I'll give that a try.

I didn't measure COAL of all seating depths, just my chamber max (jam point). COAL was about .615" longer than BTO. So in theory BTO of 2.256" would be in the ballpark of 2.871" COAL if the polymer tips are pretty consistent.

And yes, this is 6.5 CM. I don't think these will fit into my Bergara magazine, but maybe into a Magpul AICS. Either way, magazine feeding isn't a priority for me. I've been single feeding and learning patience, lettings the barrel cool between shots/strings.

Try seating them shorter to 2.850” or so. That seems to be the magic seating depth for ELD-M in the 6.5CM.

 

[MarkyMark007]

brian lytz is loading at (max-1.5/2gr) and than he is using his seating depth to close the group.
and he prove the group with more than 3 shots.

 

[acudaowner]

how I read your target from top left to right row by row .
I read it as you jerked the trigger for the first one giving you that flyer , and either your dialing it in or still not trying hard enough for the second group , the third you decided to use the force it did not work or it worked depending on how you feel about it , now the forth you took your head out of the clouds and really tried to group em and while not perfect it's pretty good for 50 ft oh shit you were at 100 yards you yea I guess it's ok (you shot good there ) i guess little white lies are OK from time to time , the fifth and sixth groups you blew either slacked off or forgot what you went to the range for , and the seventh you forgot to use the rear bag . Now the eighth group you woke up used the bag and were ready to do some shooting . and the ninth and tenth you fell back to sleep or were so drunk at that point you called it a day and passed out almost in your car on the ground while bugs took you for a dead think crawling in your nose mmm protein . not trying to offend just making a joke .

 

[Drewbis1]

how I read your target from top left to right row by row .
I read it as you jerked the trigger for the first one giving you that flyer , and either your dialing it in or still not trying hard enough for the second group , the third you decided to use the force it did not work or it worked depending on how you feel about it , now the forth you took your head out of the clouds and really tried to group em and while not perfect it's pretty good for 50 ft oh shit you were at 100 yards you yea I guess it's ok (you shot good there ) i guess little white lies are OK from time to time , the fifth and sixth groups you blew either slacked off or forgot what you went to the range for , and the seventh you forgot to use the rear bag . Now the eighth group you woke up used the bag and were ready to do some shooting . and the ninth and tenth you fell back to sleep or were so drunk at that point you called it a day and passed out almost in your car on the ground while bugs took you for a dead think crawling in your nose mmm protein . not trying to offend just making a joke .

Ha! You hit a few of those remarks on the head. I did realize I have a lot of practice ahead of me. I've only been shooting for about a year and am realizing all my mistakes when developing precision loads.

Touche, good sir. Touche.

 

[NBPRP]

And here I though we would be talking about Shakespeare, Hawthorn or Camus. Guess I'm in the wrong reading group.

 

[Ruff 364]

I have the same rifle, left hand in 6.5 CM stock with the exception of a Hellfire brake.

I did the same workup using EC guides. Ended up with 40.8 of R17 w Hornady 140 ELDM at 2.133" BTO in Starline brass. Amazing shooter for a factory rifle.

 

[TCreedmoor]

You did an excellent job of documenting your situation. If you just want the executive summary of this long message: I recommend you continue investigating 2.256, 2.250 and 2.244 with additional 5-shot groups.

I'm new to this, but I'm willing to share a few items I learned as I went through this same process and found my rifle's ideal seating depth(s). I was lucky enough to find a mentor that has helped me tremendously. I'm going to use a numbered list to enhance readability and future reference. These should not be taken as priority or relative importance.

1. I think 3-shot groups are too small for us non-F class shooters to draw conclusions.
   1. Your 2.256" group looks like the smallest MOA. However your 2.250" and 2.244" could have been starting out as a tight group with one flyer. I believe those warrant additional testing.
   2. In many of my 5-shot groups, there is one round that is significantly off from the other four. With only three shots, it is difficult to see if a consistent pattern is developing.
   3. As an example, attached are two recent seating depth targets with 5-shot groups at 100 yards with H4350 and 140 gr ELD-M. (The squares are 0.25" and the blue circle is 1" in diameter.) Yes, even the COAL of 2.821" has a total of 5 rounds.
      1. On the 40.5 grain sheet, the 2.821" 'flyer' was the first round after the range's shooting break.
      2. On the 41.0 grain sheet, the 2.821" 'flyer' that hit the bullseye was actually the 5th round. I blame myself for choking after seeing my best 4-shot group ever.
2. You didn't mention these in your post, so I'm going to ask some diagnostic questions. Forgive me if any of these seem basic.
   1. You mention shooting off of bags. Does that include a rear bag to support/stabilize the buttstock? We're trying to remove as much of 'you' (the human factor) from the shooting process to see what the rifle likes.
   2. Please confirm the front bag is supporting for foregrip and not the barrel itself.
   3. Was a MagnetoSpeed attached to the barrel while you were shooting these groups?
   4. Anything touching/hanging/supporting the barrel will definitely affect your accuracy. (front bags, rests, and MagnetoSpeeds)
3. Are there any differences in your brass?
   1. When resizing my brass, any piece that is too short for my case trimmer's fixed position (1.917") gets set aside. For now I have enough brass that allows me to only reload the cases where the trimmer actually took something off the neck. (i.e. all my reloads have a case trimmed to 1.917") Eventually I'll dial my trimmer down 1.915" and incorporate the brass that was previously set aside.
   2. My mentor is big on neck tension, seating force and annealing. Those are beyond my scope at this time.
   3. As a side note, I started reloading with the old brass I accumulated since I first purchased the rifle. Early on, 6.5 Creedmoor ammo was hard to find and I'd buy whatever I could find in the stores. In June I segregated the non-Hornady brass and reloaded the cases by headstamp and shot several 5-shot groups at the optimal seating depth for the IMR 4350 I had at the time. There was definitely a group size difference between S&B, *USA*, and the Hornady cases.

Please let us know how things go with your load development and seating depth testing.

If you made it this far, thank you. I hope you found something helpful in this port. I apologize if I rambled or if I asked a question or stated something that is obvious to others.


Sincerely,

TCreedmoor