Help Reading OCW

[kaskin]

Need help reading this. Shot a day apart. Found a good node in the 38.8 powder charge. Seemed kinda low though. So loaded up some more rounds but results were disappointing, to say the least.

RAR 6.5 Creedmoor
H4350
Hornady 140 gr SST
Lapua 1x
CBTO: 2.094 = mid cannelure

Thoughts?

 

[Deleted member 113831]

You have a major POI shift just as you are coming into what should be about your optimal pressure range at 40.3gr. POI stays fairly stable till 42.1gr where there is another major POI shift just at the point where you should just be starting to pressure out. It depends on whether you want to chase a middle node or a high node.

Groups mean nothing when doing this. You are looking for POI shifts and watching velocities. Figure out which node you want to chase and start seating depth tests. For middle node chasers, 41.5gr-41.7gr is a common area to be in.

 

[kaskin]

Thanks for the reply Skookum. How does 41.2 look. Seems to be the a good middle node...
Also, do you have to seat cannelured bullets to the cannelure? These are 140 gr SST.. Loading them for my son to hunt with...

Thanks,

 

[ken4570tc in WY]

It's been my understanding from reading the various forums and published info, that when shooting for OCW, without a chronograph, you want to look for minimal vertical dispersion, not group size. I'd take the 41,2 grain load and test plus/minus .1 grain increments then, as Skookum suggested, play with seating depth to tighten the grouping of your shots. I'll be starting my own OCW work in about two weeks for my RPR .243.

 

[kaskin]

41.2 does look appealing from a dispersion standpoint. I’ll take your advice and test +-.1 and try to tighten up with seating depth.

Should I test the 6 shots and then put the magneto speed and test 42.1 and see where I’m at speed wise? Trying to Maxine my trip to the range.
Thanks guys

 

[Deleted member 113831]

It's been my understanding from reading the various forums and published info, that when shooting for OCW, without a chronograph, you want to look for minimal vertical dispersion, not group size. I'd take the 41,2 grain load and test plus/minus .1 grain increments then, as Skookum suggested, play with seating depth to tighten the grouping of your shots. I'll be starting my own OCW work in about two weeks for my RPR .243.

Good (minimal) vertical dispersion is a good place to start as long as it is within the velocity window you are looking for. But it is an accident, a fortuitous happenstance. Almost any charge within that window could be tuned for vertical with seating depth.

 

[ken4570tc in WY]

41.2 does look appealing from a dispersion standpoint. I’ll take your advice and test +-.1 and try to tighten up with seating depth.

Should I test the 6 shots and then put the magneto speed and test 42.1 and see where I’m at speed wise? Trying to Maxine my trip to the range.
Thanks guys

Since you have a magneto speed, you can re-shoot the ladder test with loads both sides of the 41.2, say 40.8, 41.0, 41.2, 41.4, 41.6. If you graph plot the average velocities for each group, you should see a flat spot where three of the loads have relatively small variation in comparison to the others. If 40.8, 41.0, 41.2 have less variation of velocity average than the other two load groups (41.0, 41.2, 41.4) (41.2, 41.4, 41.6), that would be where you would want to refine your testing in 0.1 grain increments. The theory of the system is that finding the middle of the sweet spot allows you to load ammunition that has less variation in POI based on temperature changes and other factors. I've read one article where the writer used velocities alone to do this. Another article by an old timer, claimed he could find the OCW without a chronograph by shooting a single round at each charge weight and looking for the three side by side charges that had the smallest vertical dispersion. I have to thank Skookum for his input! I read all his comments. Correct me if I'm wrong but from what I've read, I don't believe he buys into the OCW/barrel harmonics theory of accuracy reloading. I admit that I have not proven it to be gospel but I intend to test the two methods and see if they show the same results. If the results don't match up I'll confess my faults and offer Skookum a six pack of his favorite beverage.

 

[kaskin]

I have heard using the velocity method. Read and article by a couple of smart guys that find their OCW with speed alone. Looking for the plateau. I even tried it in my 308 Win. Here is the link to the thread it: https://www.snipershide.com/shooting/threads/308-varget-load-testing.6877793/ I ended up settling on 43.9 Varget with Lapua Brass 168 gr BTHP shooting bug holes with very consistent speed and low ES. Any who, that's a different story.

I will try 40.8 to 41.6 in .2 increments with magneto attached and see what kind speeds and spreads we are getting.

Sound good?

Thanks guys.

 

[supercorndogs]

Skookum laid it out perfectly. You don't need to waste more ammo running chronograph ladders. Tune with seating depth at your choice of the two charges you mentioned. Run over the chrono for MV, test at longer range. I am shooting 140 ELD and 140 a max at 41.6 in Hornady brass with CCI 250s. I think that is pretty close to their original factory ammo load.

 

[Deleted member 113831]

The reason the velocity method works for some people is that they have short throats and are already close to the lands, usually .010" or less anyway. They are already working in a very narrow window.

It just doesn't work that way for the guy working up a load with a random chamber and components.

 

[kaskin]

The reason the velocity method works for some people is that they have short throats and are already close to the lands, usually .010" or less anyway. They are already working in a very narrow window.

It just doesn't work that way for the guy working up a load with a random chamber and components.

That makes a lot of sense. My Rem 700 with factory tube has a mile long throat... Made reading the velocity method tough.

 

[kaskin]

Well... Since i don't shoot (not a place available) farther than 500 yards often, I will be trying to tune the 41.2. That should give me respectable MV in the event I would like to take it to 1k.

Thoughts?

Will post again after a trip to the range.

Thanks guys.

 

[kaskin]

Update:
Going mostly on skookum’s advice, loaded up 42 gr H-4350 and started to tune with seating depth. Results in picture. Max CBTO for this bullet (140 grn SST) is 2.194.

Thoughts?

 

[jsthntn247]

You should try 2.194, 2.189, 2.184, and 2.179

 

[lash]

Did you mean 41.2 or 42.0? Because there’s a big difference there and you OCW showed 42.0 as being right on the high edge of a node that was around 41.2-41.7. That would exactly not be the center of a node, where you want to be.

 

[honuswagner]

I'm a relative noob in the handloading world, but I'd be nowhere near where I am without the help of the folks here in the hide. So FWIW here's some of my experience.

I recently tried the velocity method to work up a load for my 6.5CM and plotted the results in Excel. Then I tested additional loads at 41.0 and 42.0. 41.0 had slightly lower standard deviation so continued with that.

This is a gas gun so my seating depth is limited by my mag. For my initial tests I seated as long as the mag would allow. After finding my nodes I shot groups, seating incrementally deeper until I found the sweet spot.

 

[kaskin]

Did you mean 41.2 or 42.0? Because there’s a big difference there and you OCW showed 42.0 as being right on the high edge of a node that was around 41.2-41.7. That would exactly not be the center of a node, where you want to be.

42.0 is what I tried. I was afraid 42.1 would not give me enough umph to go the distance. You are right. 42 is on the top end. Maybe I should try 41.7?

 

[kaskin]

You should try 2.194, 2.189, 2.184, and 2.179

I'll try seating a little closer as well. I'm not one to jam it in the lands though.

 

[lash]

42.0 is what I tried. I was afraid 42.1 would not give me enough umph to go the distance. You are right. 42 is on the top end. Maybe I should try 41.7?

Do you have any idea how fast either 41.5 or 42.0 were going? Until you know that, it’s hard to make an informed decision. Did you start with a pressure test to find out at what point you get pressure signs?

I typically start with a pressure test over a chrono. That establishes both how high is too high, how low is too low as far as desired performance, and establishes a baseline for me to make decisions from there on. It only takes one round at each load.

 

[kaskin]

I haven’t tested velocity yet. 43.4 was top end though.

 

[kaskin]

I’ll make some more 41.7 and test .030 and in. Will update with results.

 

[kaskin]

Well.. 41.7 gr testing did not meet expectations. Tested different seating depths but nothing spectacular. Maybe 42 is my charge??

Thoughts?

 

[spife7980]

Ive been avoiding stepping in but call me crazy: it seems like you are testing in the worst spot you can based on your original ocw.

I see ~38.9 gr being one node and ~40.4 as the area I would have tested further. Everything 40.9 and above seems to go random with no rhyme or reason between one group to the next that I can tell.

 

[kaskin]

Well, I’m oficially confused.

 

[jsthntn247]

Groups went to shit with more powder because he was jumping them 100k and started getting compression. I bet if he jumped them 5 or 10 and reshot 41-42.5 again it would look totally different. There is a node at 41.2 and again at 42.1-42.5. Those are 3% apart like they should be also.

 

[spife7980]

Well, I’m oficially confused.

Find a group and then see where the charge above or below it hits in the same place.

Examples
42.1: 41.8 hits way left of it and 42.4 hits way right. That tells me its not what we want.

41.2: 40.9 looks like it hits further right and 41.5 look slike it hits right and down. Not what I would want.



38.2-39.4 all seem to impact in the same area (or as close as you can get to the same in your test results) Sure there is a slight bit of shift but its way less than all of your other groups and the central part or 38.8 and 38.9 looks to be pretty consistent.

40.3 and 40.6 looks to impact in the same areas one another as well, perhaps a seating depth test will help it out a bit.


Or it could just be that youve found out why people arent setting the records books on fire with the sst bullet.

 

[kaskin]

Or it could just be that youve found out why people arent setting the records books on fire with the sst bullet.[/QUOTE]

Lol. I love it. I have some BTHP for real accuracy. These are hunting bullets that’s why the SST. However, I still want them to shoot good.

I get what you are saying. It makes sense. 40.6 and 40.9 look like a a node to me.

That’s a full grain low from what most people seem to be shooting g though. Might be a tad slow to shoot at distance...

Seems like everyone has a different view on the OCW..?

 

[spife7980]

Yeah, i know what you’re saying, every rifle should shoot good. I found Sierra game kings were the easy button for that in every barrel ever.

Those ssts have a long bearing length and as such more surface contact equals more friction so maybe those lower charges are actually making more pressure. A chronograph would help see where exactly you’re actually at, short of that though we are left reading the tea leaves as best we can. The target doesn’t lie though.

I don’t want to contradict what others are saying but the ocw only has one interpretation, some just do it wrong lol
Could be me, I’m just saying what I’m seeing.

You like 40.6-40.9: explore it! The only way to know for sure is to collect your data and it’s only a few rounds at the end of the day.

 

[kaskin]

I didn’t know that about SST’s. They are one of the few billets I can find locally (hornady). Anything else I have to order.... I may get some sierras on the next purchase I make.

Ill make some rounds and get the magneto out for them. 40.6- 40.9. Just another reason to go shoot some more. Haha.