Help with interpreting an OCW & Seating depth test

[ReaperDriver]

Hi All, I'm struggling a bit to settle on a final load so I can just go shoot the rifle at distance and put all this load development behind me and concentrate on practicing skills for upcoming comps.

After many rounds of chasing my tail with loads that were too hot and blowing out new brass..... I settled on a couple of loads to then do a seating test to tweak it and be done. But now I'm a bit more confused than ever on where to go.

Rifle is a JP barreled .260 Rem. I used two different bullets 130 Berger AR Hybrids / 123 Scenars and IMR 4451 for the powder. Neck turned Lapua cases, F210 Primers.

Here is the load dev for the 130 Bergers:

And then the seating test for the 130's using the 41.0 (target #9 above)

Below is the same test sequence with the 123 Scenars:

and below is the seating test for the 123s at 41.6 gr of IMR4451.

Did I choose the correct OCW node for the seating test? Any advice or suggestions to get this finalized? TIA.

Not sure if it matters, but the Chrono is a Lab Radar. The ES/SD for the initial OCWs were pretty good (but only 3-shot groups). However the final ES/SDs were horrible for all of the Seating depth options I tried.

 

[AllenOne1]

I think you are picking the correct loads for the groups you have but none of them look real good and I can see why you are questioning it. At this point I would load up some of the 130 Bergers at 41 grains with a seating depth of 2.775 from target 3 and go have some fun with it. You can always come back to load development at a later date if you don't feel like it is shooting as good as you can shoot.

Trade the Lapuas for some Hornady BTHP and see how they run for you.

 

[918v]

Your seating depth test should be done in .005” increments if your 2.840” coal produced a .2” group. Go plus minus .005” from 2.840” to see how wide the node is.

 

[Doom]

I think your first set powder charge is between 40.7 and 41gr. I would put the second set at 41.5gr. You are stating seating depth based COAL, no CBTO. If the bullts are not seated to uniform CBTO, then this may explain some of you scatter

 

[nn8734]

@ReaperDriver: what was your CBTO measurement for your initial OCW for the 130 Bergers? Also, did you incorporate a group with that same seating depth in any of your seating depth tests for the 130Bs?

I’d be tempted to load up ~20 rounds with that 41.0g load at whatever CBTO you initially used, zero the rifle then fire groups over LabRadar at steel 600-800m away. See how it does. If it groups nicely both at 100 and at those further distances, I’d say it’s prob GTG. Then you simply fill out your dope card and take more data either when changing powder lots, in winter or whenever you travel to places with different elevations/atmospherics to compete.

 

[Precision Underground]

Did you shoot these round robin? How confident are you that the movement on the target isn’t induced by you? IOW are you 100% sure these were all good trigger pulls that you could call? The results don’t look to show anything concrete. Yes there are a couple of good groups but that’s not really the point of an OCW. Without a pattern it’s not really doing you any good IMO.

 

[nn8734]

Did you shoot these round robin? How confident are you that the movement on the target isn’t induced by you? IOW are you 100% sure these were all good trigger pulls that you could call? The results don’t look to show anything concrete. Yes there are a couple of good groups but that’s not really the point of an OCW. Without a pattern it’s not really doing you any good IMO.

Good points, it may be worth it for him to reshoot 40.7-41.3 round robin to see if there really is a harmonic node in that charge weight range before doing anything else.

 

[308sako]

I think I would stay at 41 with 130's and maybe 41.7 with 123's.

Can't see them both at virtually the same powder charge, coincidental nodes.

Once you add the can to the mix what will your apparent pressures look like. Dwell time might not be favorable to the hottest nodes.

 

[nksmfamjp]

I’m confused by your method. It seems like you are selecting charge wt with one 3 shot group and seating depth with one 5 shot group? Your final groups are ok, but not amazing. I would suggest you didn’t find the right charge wt. as the reason your 5 shot groups are larger. Still not bad.

I would shoot 5 shot groups with my labradar. Develop that until I got about 5 sd. Then shoot 10-25 to confirm the sd.

Then shoot a seating depth text from -0.010(or +0.010 in a field rifle), max mag length, or some other reasonable max length to about 0.1” shorter. Some go 0.15” shorter. The Houston warehouse folks basically found near 0.000” was best. The PRS blog talks about something like +0.050” being idea. Berger suggests out to 0.120”. Personally, I don’t care. I just know from experience that +0.015 to +0.030 is where all my sweet spots have been, but for field guns I have to be out of the lands.

Finally shoot 25....yep 5 groups of 5 as one chrono group. This will give you your best explanation of how that load will shoot. This is where things get hairy....often times great development can lead to 0.75” average group size and 7-8sd. That is pretty good for most folks.

I think that will narrow things in a little better for you.

 

[ReaperDriver]

I think your first set powder charge is between 40.7 and 41gr. I would put the second set at 41.5gr. You are stating seating depth based COAL, no CBTO. If the bullts are not seated to uniform CBTO, then this may explain some of you scatter

Yeah, sorry - I am measuring primarily using CBTO with the Hornady device. I just didn't list it, as not everyone uses the Hornady or does CBTO at all - so it didn't seem like a valid yardstick for everyone in this discussion unless everyone uses the same CBTO gauge.

Original CBTO for the OCW for the 130 bergers was 2.214 and then for the seating depth test I started again at that same CBTO and then went down in .02" increments. The starting one is just about about mag length so I went down from there. I probably have a little bit of room to go longer, but due to inconsistency in meplats, sometimes the longer ones drag on the inside of the mag's front wall.

The 123 Scenar's starting CBTO was 2.270 and then went down in .02 increments. That starting point is about .01 off the lands, given the ogive of the Scenars is so much further forward up the bullet than the bergers.

I'm using a Redding micrometer seating die, so in either event regardless of how I'm measuring them, they are being seated to a consistent depth in each string, even if what I measure might not be perfect. I've noticed that even the high quality bullets like Bergers and Lapua still have some inconsistency ogive to base and the Lapua seems to be ever so slightly more consistent than the Bergers.

 

[ReaperDriver]

@ReaperDriver: what was your CBTO measurement for your initial OCW for the 130 Bergers? Also, did you incorporate a group with that same seating depth in any of your seating depth tests for the 130Bs?

Yes, the first groups in the seating depth test for both bullets were using the same CBTO as the OCW powder tests.

 

[ReaperDriver]

Did you shoot these round robin? How confident are you that the movement on the target isn’t induced by you? IOW are you 100% sure these were all good trigger pulls that you could call? The results don’t look to show anything concrete. Yes there are a couple of good groups but that’s not really the point of an OCW. Without a pattern it’s not really doing you any good IMO.

No, I didn't do a round robin. I've tried it before, and I just seem to have a mental block about shooting that way, I guess I should just get over it and do the RR. You don't do a RR for the final seating test though, do you?

And I'm fairly confident that most of the trigger pulls were decent, but I never ever discount that a scatter could be self-induced. So I'm definitely not 100% sure that these were partly me shooting poorly. I know the rifle shoots really really well, as I've already gone through a load development series that consistently shot in the .4s and under. But they were way too hot and were destroying my new Lapua brass within 2-3 loads. Lots of over pressure signs. So that's why I'm doing this new test to find a lower node(s).

One thing to add, the day started off pretty calm, but by the end of the Berger ladder and through most of the 123's ladder - the wind picked up and was pretty gusty. It was mostly all pure headwind, but I could tell I was working harder to keep the xhairs from moving. So those later horizontal groups could easily be wind induced. <shrug> Dunno.

 

[ReaperDriver]

I’m confused by your method. It seems like you are selecting charge wt with one 3 shot group and seating depth with one 5 shot group? Your final groups are ok, but not amazing. I would suggest you didn’t find the right charge wt. as the reason your 5 shot groups are larger. Still not bad.

I would shoot 5 shot groups with my labradar. Develop that until I got about 5 sd. Then shoot 10-25 to confirm the sd.

Then shoot a seating depth text from -0.010(or +0.010 in a field rifle), max mag length, or some other reasonable max length to about 0.1” shorter. Some go 0.15” shorter. The Houston warehouse folks basically found near 0.000” was best. The PRS blog talks about something like +0.050” being idea. Berger suggests out to 0.120”. Personally, I don’t care. I just know from experience that +0.015 to +0.030 is where all my sweet spots have been, but for field guns I have to be out of the lands.

Finally shoot 25....yep 5 groups of 5 as one chrono group. This will give you your best explanation of how that load will shoot. This is where things get hairy....often times great development can lead to 0.75” average group size and 7-8sd. That is pretty good for most folks.

I think that will narrow things in a little better for you.

Don't worry.... I'm almost 500 rounds into this new barrel and I'm as confused by my own method too and feel I'm no closer to being done with development than when I started. I started off trying to conserve barrel life by following Dan Newberrys (OCW guy's) advice of "don't waste ammo by starting too low". That plus my .260 Rem AI-AT bolt rifle shoots like a laser well beyond a 1K with much hotter loads (high 2800 and low 2900s) with zero pressure signs. So I just couldn't convince myself to start that low with the gas gun. So the unfortunate end result of that initial development resulted in having to throw away a brand new box of Lapua brass away after 3-4 loads and a lot of barrel life sacrificed for no gain.

 

[nn8734]

Yeah, sorry - I am measuring primarily using CBTO with the Hornady device. I just didn't list it, as not everyone uses the Hornady or does CBTO at all - so it didn't seem like a valid yardstick for everyone in this discussion unless everyone uses the same CBTO gauge.

What everyone else uses is largely irrelevant when it comes to measuring your rounds’ dimensions as long as you’re using the same tool each time. The numbers are valid for you provided you’re performing the procedures correctly and the measurement tools themselves are in good working order. I have the same Hornady tool as you but if we measured one of your loaded round’s CBTO with both yours and my Hornady tool and got slightly different results, it wouldn’t mean anything for you as your tool is the measuring tool that counts in that scenario. Just wanted to clarify that so you don’t think sharing such info is problematic.

The 130 Bs are pretty easy to get shooting, they aren’t fussy about seating depth. I got them to group in my 6.5 CMoor at both .040” and .075” off the lands using a few different primer/brass combos (used H4350 as the powder in both cases).

Id re-run your OCW on a calm day with the same load to see if you actually have a pattern of stability anywhere on the charge weight curve you’re working with because the existing one doesn’t show any discernible repeatability in POI (except maybe not re-shoot it this upcoming week, given the likely temps we will see here). Once you have a pattern established and group sizes aren’t to your liking, I’d play with seating depth.

 

[Precision Underground]

No, I didn't do a round robin. I've tried it before, and I just seem to have a mental block about shooting that way, I guess I should just get over it and do the RR. You don't do a RR for the final seating test though, do you?

And I'm fairly confident that most of the trigger pulls were decent, but I never ever discount that a scatter could be self-induced. So I'm definitely not 100% sure that these were partly me shooting poorly. I know the rifle shoots really really well, as I've already gone through a load development series that consistently shot in the .4s and under. But they were way too hot and were destroying my new Lapua brass within 2-3 loads. Lots of over pressure signs. So that's why I'm doing this new test to find a lower node(s).

One thing to add, the day started off pretty calm, but by the end of the Berger ladder and through most of the 123's ladder - the wind picked up and was pretty gusty. It was mostly all pure headwind, but I could tell I was working harder to keep the xhairs from moving. So those later horizontal groups could easily be wind induced. <shrug> Dunno.

Most people skip the RR aspect of the test and it can be a huge mistake. Sometimes it may not matter but it definitely can matter. It’s just a way to spread out any variables, mainly in the shooter IMO, to let you know what you’re seeing across the target is as controlled as possible.

A successful OCW test will usually show you a pattern. A bunch of randoms with a good group here and there says shooter to me. That’s not a knock on you I just understand how difficult it can be to shoot a series of groups without inducing movement on target. What RR can really do is keep you from fooling yourself by getting a good, focused position on one group and then thinking that’s the load. When in reality most of the movement on target was all you.

Again, not a knock on you. I consider myself an excellent shooter and can call pretty much every shot. But I still stick to RR because I know all it takes is .001 movement at the stock to move you over an inch on target. Not to mention recoil management and how any inconsistency can lead to big moves on target. An OCW looks to identify movement between charge weights, not good groups. When you shoot RR you aren’t shooting groups. You’re basically shooting dot drills. So that helps eliminate the “group” mentality from it and gives you a much cleaner result IMO.

I’d load the 130s at 41, 41.2, 41.4, 41.6 and shoot them RR. Use whatever seating depth seemed to be best on that test. My guess is those low shots were shooter induced and most of those charges will be good so you can settle at 41.3ish.

 

[ReaperDriver]

What everyone else uses is largely irrelevant when it comes to measuring your rounds’ dimensions as long as you’re using the same tool each time. The numbers are valid for you provided you’re performing the procedures correctly and the measurement tools themselves are in good working order. I have the same Hornady tool as you but if we measured one of your loaded round’s CBTO with both yours and my Hornady tool and got slightly different results, it wouldn’t mean anything for you as your tool is the measuring tool that counts in that scenario. Just wanted to clarify that so you don’t think sharing such info is problematic.

The 130 Bs are pretty easy to get shooting, they aren’t fussy about seating depth. I got them to group in my 6.5 CMoor at both .040” and .075” off the lands using a few different primer/brass combos (used H4350 as the powder in both cases).

Id re-run your OCW on a calm day with the same load to see if you actually have a pattern of stability anywhere on the charge weight curve you’re working with because the existing one doesn’t show any discernible repeatability in POI (except maybe not re-shoot it this upcoming week, given the likely temps we will see here). Once you have a pattern established and group sizes aren’t to your liking, I’d play with seating depth.

Yeah, thanks - I'm well aware that as long as the measurement is with the same tool each time, that's all that matters. I was simply trying to translate that into a common language for discussion here as everyone understands COAL. But yes, as long as I am measuring it the same each time, that's all that counts.

I'm probably going to just sit on this for a week and then re-run the OCW in a RR format this time.

 

[ReaperDriver]

Most people skip the RR aspect of the test and it can be a huge mistake. Sometimes it may not matter but it definitely can matter. It’s just a way to spread out any variables, mainly in the shooter IMO, to let you know what you’re seeing across the target is as controlled as possible.

A successful OCW test will usually show you a pattern. A bunch of randoms with a good group here and there says shooter to me. That’s not a knock on you I just understand how difficult it can be to shoot a series of groups without inducing movement on target. What RR can really do is keep you from fooling yourself by getting a good, focused position on one group and then thinking that’s the load. When in reality most of the movement on target was all you.

Again, not a knock on you. I consider myself an excellent shooter and can call pretty much every shot. But I still stick to RR because I know all it takes is .001 movement at the stock to move you over an inch on target. Not to mention recoil management and how any inconsistency can lead to big moves on target. An OCW looks to identify movement between charge weights, not good groups. When you shoot RR you aren’t shooting groups. You’re basically shooting dot drills. So that helps eliminate the “group” mentality from it and gives you a much cleaner result IMO.

I’d load the 130s at 41, 41.2, 41.4, 41.6 and shoot them RR. Use whatever seating depth seemed to be best on that test. My guess is those low shots were shooter induced and most of those charges will be good so you can settle at 41.3ish.

Agree, I'll probably do exactly this ^. Thanks. And I like the concept of thinking of it as a dot drill rather than shooting groups. I find shooting RR to be tedious, but I understand the rationale behind it.

And I consider myself to be an above average shooter, But am fully aware that most of my rifles shoot far better than I do and most of the errors are usually the nut behind the trigger.

One last question for the group....... given this is a gas gun, I presume that you are still shooting single shot/manual load for each of the RR loads and are not loading the mag with the different RR loads, correct?

 

[nn8734]

Yeah, thanks - I'm well aware that as long as the measurement is with the same tool each time, that's all that matters. I was simply trying to translate that into a common language for discussion here as everyone understands COAL. But yes, as long as I am measuring it the same each time, that's all that counts.

I'm probably going to just sit on this for a week and then re-run the OCW in a RR format this time.

Got it. Figured you did but your post seemed to indicate otherwise.

When I do RR, I Ioad the mag up vs single feed as I don’t like to break cheek weld loading another round as I don’t want that to have an impact on my POI.

Good luck with it. I’m sure you will get a load dialed in pretty quickly.

 

[ReaperDriver]

Thanks all for the great advice!

 

[Precision Underground]

Agree, I'll probably do exactly this ^. Thanks. And I like the concept of thinking of it as a dot drill rather than shooting groups. I find shooting RR to be tedious, but I understand the rationale behind it.

And I consider myself to be an above average shooter, But am fully aware that most of my rifles shoot far better than I do and most of the errors are usually the nut behind the trigger.

One last question for the group....... given this is a gas gun, I presume that you are still shooting single shot/manual load for each of the RR loads and are not loading the mag with the different RR loads, correct?

Yes load the mag hottest charge first amd shoot in order. You don’t want to have to break position on every shot. It also helps to have your targets all lines up horizontally on the same level, as close together as possible. That way you aren’t adjusting a lot between rounds. Just make sure you’re deliberate with your position and make it repeatable.

 

[ReaperDriver]

Yes load the mag hottest charge first amd shoot in order. You don’t want to have to break position on every shot. It also helps to have your targets all lines up horizontally on the same level, as close together as possible. That way you aren’t adjusting a lot between rounds. Just make sure you’re deliberate with your position and make it repeatable.

Interesting - I would have thought that's counter-intuitive to not wanting to heat up the barrel or letting rounds cook in the chamber while you're lining up your next shot. I could see it for a Bolt gun, because you don't have to chamber the round until you're ready. But no such luxury in a gas gun.

 

[Precision Underground]

Interesting - I would have thought that's counter-intuitive to not wanting to heat up the barrel or letting rounds cook in the chamber while you're lining up your next shot. I could see it for a Bolt gun, because you don't have to chamber the round until you're ready. But no such luxury in a gas gun.

If you’ve comfortable with your fundamentals and your targets are lined up nicely you shouldn’t have to cook rounds. Shoot, shift and resettle, shoot, repeat. I’ve never timed it but I’d guess I have 6-8 seconds between shots.