Modified Ladder / OCW test 308 Win

[Deleted member 113831]

308 Winchester
175 Nosler RDF OAL 2.8"
IMR 4895 Loading from 40 grains to 42.4 grains (0.2 grain increments)
Fed 210 primer
LC brass weighing 172gr - 176.4gr
Brass is once fired, annealed, then sized, swaged, and trimmed. Not cleaned, residue in necks.

Conditions: Sunny, 1000 hrs - 1200 hrs, 50*F

Objective: Attempt to develope a load without the initial use of a chronograph at 100 yards distance.

Method: Load charges in 0.2 grain increments and look for a place where there is an apparent "flat spot" in barrel movement. This is simiar to what is done in an OCW type test, but with a single round at each charge. This is very similar to the Audette method of ladder testing, but is done at 100 yards in a horizontal orientation rather than a vertical one.

Hypothosis: The barrel will exhibit a classic sine wave pattern that will exhibit an area where the barrel movement is minimal.

 

[spife7980]

Tried to get them in one pic together for ease of viewing

 

[Deleted member 113831]

Next: Analyze pressure signs of fired brass.

Equipment: Mitotoyo micrometer capable of measuring to .0001"

Measurement of expansion ring around base of brass (Chamber size is .473"):

40.0 = .472
40.2 = .472
40.4 = .472
40.6 = .472
40.8 = .472
41.0 = .472
41.2 = .472 Clean powder burn
41.4 = .473 Full chamber diameter
41.6 = .473
41.8 = .473
42.0 = .473
42.2 = .473 Slight pressure, probably could have gone to 42.4 but stopped.

At what point did powder burn become efficient? Here we see that between 41.0 grains and 41.2 grains that the powder residue became significantly less and moved from the shoulder, to just above the shoulder / neck junction. This is indicative of reaching the optimal pressure for a clean powder burn.

Here are the next two cartridges in line. You will notice that they too exhibit less residue, and the ring has moved up from the neck / shoulder junction.

 

[Deleted member 113831]

Tried to get them in one pic together for ease of viewing
View attachment 7050083

Thanks for that, I'm not any good at the computer stuff.

 

[Deleted member 113831]

So, to summarize so far...

I have a "flat spot" that runs from 41.0 to 41.6 grains,
I have clean powder burn from 41.2 and on.
I have full brass expansion at 41.4 grains.
At 41.4 grains I have another 0.2 grains room in the "flat spot" and another 0.4 grains until the next movement in the pattern.

Working conclusion: Explore the 41.4 grain to 41.6 area and chronograph. Then move to seating depth test.

 

[spife7980]

Working conclusion: Explore the 41.4 grain to 41.6 area and chronograph. Then move to seating depth test.

I agree.

 

[Deleted member 113831]

Tried to get them in one pic together for ease of viewing
View attachment 7050083

Looking at this further, you could even break the flat spot from 41 to 41.6 down further into 2 distinct parts. The reason I draw a straight line from the POA to POI is because it makes it easier to immediately see even slight differences.

41 grains and 41.2 grains have the same vertical as 41.4 and 41.6, but have a slightly different horizontal. You see that the lines are longer for the first two.

 

[spife7980]

Looking at this further, you could even break the flat spot from 41 to 41.6 down further into 2 distinct parts. The reason I draw a straight line from the POA to POI is because it makes it easier to immediately see even slight differences.

41 grains and 41.2 grains have the same vertical as 41.4 and 41.6, but have a slightly different horizontal. You see that the lines are longer for the first two.

Yeah but that could easily just be small sample variation. With the limited data its tough to say whats what so who knows.

 

[Deleted member 113831]

Yeah but that could easily just be small sample variation. With the limited data its tough to say whats what so who knows.

I agree, this single shot method definitely has potential for identifying areas of interest very quickly and efficiently, but I don't think it has the ability to pin down a specific load. I do however think that it provideds more information for the same number of rounds than the Audette ladder, and is easier to read than the OCW.

Though to be fair, if people were able to map the group centers of the OCW in the same way and ignore group size, then you would get even more information, especially if you were using a lab radar at the same time. People just can't seem to look past group size when doing the OCW.

It is all the other clues (Powder burn, base expansion..etc) that really pin this load down to a finer point.

 

[Deleted member 113831]

I tested 41 grains thru 41.6 grains with the magnetospeed.
Temp 60*F, all else the same.

41.0 grains: 2649, 2630, 2631, 2635, 2627......Avg. 2634 fps, SD 8 fps
41.2 grains: 2644, 2650, 2655, 2647, 2651......Avg. 2649 fps, SD 4 fps
41.4 grains: 2659, 2650, 2660, 2665, 2651......Avg. 2657 fps, SD 6 fps
41.6 grains: 2647, (2675*), 2662, 2658, 2646......Avg. 2657 fps, SD 11 fps

(*) This round was the only piece of LC "07" brass. The rest were LC 11. If I substitue the 2675 fps with either the highest other speed (2662), or the lowest (2646) in that same group, I come out with a avg of 2655 fps or 2651 fps and an SD of 7 fps either way.

I think 41.4 grains of IMR4895 will be my LC brass load. My FC brass load is 41.6 grains with a 175 Nosler CC so this is right in there where I would expect it to be. So far it is definitely passing the sniff test. Next for the seating depth test.

Just some further info, 41.4 grains is 2% less than where I saw pressure at 42.2 grains.

 

[Deleted member 113831]

Seating depth test, 41.4 grains IMR 4895, annealed cases 2.800", 2.805", 2.810", 2.815"

This is a perfect example why group size and shape means absolutely nothing during and OCW test.

Interesting observation: Notice how the group center rises as the bullet is seated further out, but the center stays clocked at virtually the same angle from POA.

 

[spife7980]

 

[cornhusker86]

Seating depth test, 41.4 grains IMR 4895, annealed cases 2.800", 2.805", 2.810", 2.815"

This is a perfect example why group size means absolutely nothing during and OCW test.

Interesting observation: Notice how the group center rises as the bullet is seated further out, but the center stays clocked at virtually the same angle from POA.

View attachment 7054318View attachment 7054319

This whole thread was nicely done and informative.

 

[Deleted member 113831]

This whole thread was nicely done and informative.

Thank you. Next is to shoot 20 shots of the load at 200 yds (4 groups of 5 shots) at the same point of aim. This will be the true accuracy potential of the load (in my hands anyway). When the weather gets better, I'll do the same at 500 yds on paper.

 

[morganlamprecht]

well organized and good work

the 2.810 oal group is why im never able to trust anything done off 1 shot...assuming those shots were executed correctly, they could completely throw off any pattern if you happen to start testing with that

for the last 3-4 yrs ive ran all my load work up off 100 yd ocw, then i chrono...ive never had a problem getting single digit SDs and 20-30 ES for 10 round strings using only sized/trimmed hornady brass...no other prep and throwing powders with 2 different chargemasters

ive switched to lapua and a better scale and those numbers cut in half, i could cut the hornady numbers as well with more brass prep and sorting but it isnt worth my time to me

i have seen some bullets just flat out not shoot in a barrel regardless of the load...my current 6.5 twist 223 would not shoot 88 eld's...i tried 3 different powders and multiple seating depths from .005-.050" off...random fliers were bad...even though when i chrono'd, numbers were great...it would shoot about 70% of them inside 1/2moa, the others were out up to 1" or so in any direction...even doing charge work ups i saw some spots that looked ok, but when i went back to shoot and verify, no bueno

same barrel will hammer with 77otm, 80 vld, and 80.5 fullbores...i couldnt hold the 88s inside 1moa consistently, the worst anything else shot during workup was 3/4ish and held nice tight clusters like im used to seeing

i have also seen the similar wave patterns you mentioned, but they require a bullet to shoot well from the barrel from the get go...the 88s exhibited it slightly, but there was so much noise it was really hard to pick it out and trust it at all

 

[AMG04]

What OAL did you settle on? Something between 2.800 and 2.805 for more tolerance or did you pick 2.815 because it's the tightest group?

 

[Deleted member 113831]

well organized and good work

Thank you.

the 2.810 oal group is why im never able to trust anything done off 1 shot...assuming those shots were executed correctly, they could completely throw off any pattern if you happen to start testing with that

I agree, I have historically used OCW also. Mapping the actual mathematical center of groups in an OCW would show the same wave pattern and be more reliable to boot. It would just take 3 times the amount of shots.

However, even with single shots, broad trends are easy to see across a 0.6 or 0.8 grain spread when increments are 0.2 grains apart. For instance, in the original testing sequence the 41.8 might be lower than average or 42.0 might be higher than average. But look at the "clocking" of the angle from POA to POI....there are definite groupings that are the same. Going by the established trend, I would say that 42.0 is probably higher than average.

As far as the "clocking" I was talking about, you can see here:
40 is by itself,
40.2 & 40.4 are the same,
40.6 & 40.8 are the same,
41 & 41.2 are the same,
41.4 & 41.6 are the same,
41.8, 42, 42.2 are the same.

This is really the first time I'm paying attention to this "clocking" for lack of a better term. I think it may be a missing bit of information that gets ignored.

But if not taken in isolation and put together along with all the other clues I've mentioned, I think this can really point to a fairly small area of interest very quickly. But I don't think it is a replacement for a full out OCW.

I wonder how much it would help to dial in a seating depth with the lowest charge before proceeding with the charge progression?

 

[Deleted member 113831]

What OAL did you settle on? Something between 2.800 and 2.805 for more tolerance or did you pick 2.815 because it's the tightest group?

That is a great question. I would normally say that I would pick the 2.815" COL because I'm using micrometer adjusted Forster seating dies and they have no problem seating consistently.

However, the RDF's are infamous for being inconsistent in their base to ogive measurements, so we shall see how it works out.

 

[morganlamprecht]

I want to say I’ve tried the jump first, but it was years ago and I didn’t really see much improvement with the charge I had picked...everything was really similar and within my personal error...it would be interesting to do it again tho

 

[dirthead1]

Yes this is one of the most informative threads I've read in a long time. Excellent job!

 

[AMGtuned]

Very detailed and informative. Thank you for taking the time to perform, record, and share this. Definitely eye opening, on a procedure that has so many "personal" ways of completion.

 

[C_R_Slacker]

People just can't seem to look past group size when doing the OCW.

It really is hard to ignore, haha. But you have to stick to the method. Seeing your example's group size open up and tighten up just on a seating depth change helps to avoid that temptation.

 

[Deleted member 113831]

I did the 20 shot group today, but I did it in 2 steps. The first 15 shots were all the same LC 11 headstamp and identically prepped, to include annealing. 2.815"COL

The last 5 were mixed headstamp LC brass of identical weight as the other pieces and also annealed the same as the others.

Here is the first 15: @200 yards

The 2 shots up top are honest flyers. They felt and looked the same as the others when I broke the trigger. I made a 0.4 mil correction to the right after the first shot, so that first shot should be counted as part of the group.

 

[Deleted member 113831]

Here are all 20: @200 yards, 2.815"COL

The last 5 shots were made with LC brass that was otherwise identically weighed, prepped and annealed, but was of a different date. The shots labeled "4" and "5" are a result of that last five. The remaining three of the last five are in the group.

Shots labeled 2 and 3 were honest fliers, but not the 2nd and 3rd shots taken. I should have labeled the shots with letters instead of numbers.

So I think the load developement process went exceedingly well. There weren't any weird results to cloud the outcome. The load is a good one, probably as good as I'm gonna get out of this combination.

Despite a couple of flyers, the body of the group is sub-minute for 13 of the first 15 shots. Even with the mixed brass at the end, the load printed 16 of 20 shots in a sub-minute circular group with no stringing.

This is why I proof a load with 20 shots at 200 yards. If my first 3 or 5 shots had been in the very middle of the group somewhere, I could have come on here a bragged about my 1/4 minute 308. If my first 3 or 5 had included some of those fliers, I would have abandoned the load. This test shows me that the load is a good one, but the bullets probably aren't as consistent as I would like.....big difference!

 

[pbatesaz]

I have learned a lot from this thread. Thanks for the effort to share the info. I will be working up a load for a 6mm CM next month and plan to use this method... maybe with 3 shot groups. It will be interesting.