CBTO Test Results

[Bigdad123]

I was recently able to acquire some Berger 140gr CH and 156 gr EOL bullets so I decided to do some load development for my Stevens 200 6.5 CM. The barrel is a Douglas 24" 8" twist I bought from Stan Taylor, RIP.

I thought I would share the results of my 200 yard CBTO test. I followed Eric Cortina's method reducing the length in .003" increments. I fired 7 3 shot groups of each CBTO variance starting with the longest (.015" off lands) first.

Observations

• I'm very happy with the barrel Stan put together, I've had several barrels on this rifle and this is the most accurate yet
• I'm not very happy with the velocity spread of 37 fps, not terrible but wish it was better. SD is in single digits, 8.92.
• CBTO results are somewhat inconclusive but I think I'll use 2.205" going forward as the next seating depth is the 3rd best group. If the group size stays in the .03's I'll be happy. Anyone have an recommendations?
• I noticed the each group is in a slightly different location on the target relative to my point of aim, I assume this is showing that the CBTO does have an impact on the grouping. Do any of you guys have any thoughts on this?
• The last group had a flier that opened it up to .69 MOA. I think the reason is the last round I loaded, I used brass that had been bumped .006" during sizing. The brass first 20 rounds were all bumped .002" When I loaded it I noted that to see if would make a difference and it looks like it did.

Here are 3-500 yard groups fired the same day. 2 were using the 156 EOL and center 1 used the 140 CH. I think I'm going to do a similar CBTO test using the 156 EOL.

 

[mikecr]

Since you're not doing full seating testing (like Berger recommended), I think you have to consider what your're doing w/resp to the powder load chosen for this, and original CBTO that you worked up the powder with. You're affecting both of these at once (departing from powder node, and the seating the node was derived at).

 

[Bigdad123]

Thanks for the feedback Mike. I did not depart from the powder node, 41.5 gr is in the original powder node I worked up to. Is the full seating testing you mentioned the one Berger suggests decreasing CBTO in .040" increments? If so I have tried that on other rifles with little success. I think by using that large of a seating change you're skipping over nodes. Have you had good success using that method?

 

[JimSC]

Nice groups. Just my opinion is the important numbers is the group sizes, not the ES/SD. Bear in mind I am the minority here.

What barrel are you running on that Stevens? I have a .223 Criterion on a Stevens 200 receiver that still gets low .4's after 3K plus rounds down it

 

[Bigdad123]

Jim, I'm running a Douglas Premium Match 8" twist on my Stevens 200. I also have a Savage 12FV with a Criterion 223 Rem 8" twist barrel. Its the most accurate rifle I own and its a lot of fun to shoot!

 

[K22]

Very impressive groups, especially at 200 yards. It also says a lot about your skill as a shooter to shoot this consistent.

I agree with JImSC, for me the performance results, i.e., group size, is what I personally would focus on.

I don't know what your shooting goals are with this rifle, i.e., competition, hunting, etc. but I would say you are well on your way to achieving it with that kind of performance.

 

[Bigdad123]

Thanks for the kind words K22. Honestly, my shooting skills aren't that great. The only way I can shoot those kind of groups consistently is to use a high end shooting rest and shoot free recoil.

My intent for this rifle is deer hunting and just have fun shooting and tinkering with it. Its just a cheap Stevens action with a decent barrel and a Boyds At-One stock that I installed pillars and bedded. I do compete occasionally but I have other rifles setup for that. They aren't any more accurate than this one though, just better suited for competition.

 

[mikecr]

I did not depart from the powder node, 41.5 gr is in the original powder node I worked up to. Is the full seating testing you mentioned the one Berger suggests decreasing CBTO in .040" increments?

You departed from your powder node the moment you changed seating and bullet grip, by changing that load density and original seating that you found the powder node with..
I'm only suggesting that you consider this.

The purpose of full seating testing is to zero in on best coarse seating. While maybe none of the 40thou increments shot well, one or two of them should have shot better than the others. You might halve one of them, and use best coarse for powder testing.
Then final tweaking of seating in it's window, with a powder node, for tightest group shaping.

Instead, you had pulled some seating out of your butt to test powder with,, right?
What was that seating?

 

[Bigdad123]

Mike, thanks for your feedback. The process I used was to work up the powder load first to get good velocity without going over pressure and still have reasonable accuracy and then fine tune the COAL.

For the powder test I decided to use 2.206 CBTO which is .020 off the lands. I loaded 5 rounds each starting at 40.3 grains working up in .3 grain increments to 41.8 grains of H4350. I never got any signs of over pressure during this test. Knowing that 41.5 was listed as the max load for H4350 and 140 grain bullets in a few of my loading guides and I got the best velocity ES and SD and smallest group at 41.5 grains I decided on that powder weight for the CBTO test.

Yes, I guess you could say I pulled 2.206 CBTO out of my butt for the powder test.

Are you suggesting that a better way is to do the CBTO test first then fine tune the powder? If so, how do you decide on the powder charge to use for the CBTO test?

 

[Bigdad123]

Thanks SPJ, do you think I should adjust the CBTO in larger increments than .003 or use .003 but more than just 7 groups for a broader range of testing?

 

[Bigdad123]

Sounds like my next course of action is to fine tune the powder to ensure I find the powder node. Would you suggest a ladder test?

 

[barefooter56]

Thanks for the feedback Mike. I did not depart from the powder node, 41.5 gr is in the original powder node I worked up to. Is the full seating testing you mentioned the one Berger suggests decreasing CBTO in .040" increments? If so I have tried that on other rifles with little success. I think by using that large of a seating change you're skipping over nodes. Have you had good success using that method?

The proper bullet seating depth testing for BERGER HYBRID ELITE HUNTER or HYBRID TARGET bullets is to test at .015, .030, .045 and .060 OFF the lands with the starting powder charge listed for the bullet/powder/cartridge combination you are loading. When you find a bullet seating depth that shows promise. Go .005 to either side of that CBTO . That will either get you where you want to be or give you a direction to go with more bullet seating depth testing.
FYI Ignore the EXTREME SPREAD and look at the STANDARD DEVIATION. Your 8. SD is below 10 and that is a good thing!
Once the bullet seating depth accuracy node is found. Work the powder charge up slowly checking for pressure signs and accuracy.

 

[mikecr]

with the starting powder charge listed for the bullet/powder/cartridge combination you are loading.

STARTING charge is the part nearly everyone misses in this.
Folks likely think this is a safety thing, and it can be as well, but this is also critical for this testing -to move you well away from a powder node.

Are you suggesting that a better way is to do the CBTO test first then fine tune the powder? If so, how do you decide on the powder charge to use for the CBTO test?

I believe I already have here.
barefooter56 answered the charge to use question (it's not 41.5gr).

You've chosen to do semi-fine tuning of seating based on a roll of the dice beginning place, and from a powder node. Well, maybe it's a powder node. You determined it at a random seating, so who knows.
But if an actual powder node, you can see clearly that your seating changes are wiggling you around from it. The seating IS affecting your powder burn -away from what you had determined was best.
So now you don't know if the grouping is because of seating change or powder burn change due to seating change. And for all you know, actual best seating could be closer to 30 or 40thou further back anyway..

Ideally for seating testing, you can see the result of seating testing.
You don't need [seating + whatever leaving a powder node does], because then you don't really know the result of seating testing.

Seating is not tuning, but prerequisite to tuning.
You can find best coarse seating following Berger's (or variant of) testing method.
At minimum charge you would hopefully be well away from any powder nodes, and big seating changes are evident in results. Ideally you're throwing up big ugly groups (like ~1moa), and big seating changes significantly open/close this. Should be very easy to see better -vs-worse.
When you get in the same zip code as best seating, well that's better to test powder with than something you pulled out of your butt. Should now be easier to see best powder load.
And this should put you in a seating window, which you can fine tune within once you find best powder load, -without taking you back out of that powder node at the same time.
That's still not tuning. It's seating adjusting for optimum.

You can setup primer striking testing with a similar method, and again see big grouping opening and closing and opening. This is not tuning either, but affects the outcome of your tuning down the road.
Like seating, primer striking responds to it's optimum.

 

[JFrank]

Wow’
That may be a fine a method .. but I really don’t subscribe to seating not being tuning etc. for us long range br guys everything is tuning including tuning equipment and one’s self.

Good luck to the OP I gotta bounce out of this thread and get on the road to a lr match.
Stay tuned
J