OCW shows its teeth with my CZ550

[Pond, James Pond]

I went out again today, having prepared my 3 cartridge sets as suggested earlier. Same set up. 100m, same rifle same prone position, similar weather, but colder. Still above freezing though.

First of all, I must say I am a bit annoyed with myself. I didn't rush, I concentrated on my breathing and yet I could feel my shooting just didn't come together the way it had for the first lot. Perhaps it was the fact that I had had to rush to the range, having a full day ahead of me, or perhaps I was a bit cold. Anyway, some groups opened up a bit and I can't help feeling this was down to my fudging a shot here and there.

For group 6 (41.3gr) I had to change POA as the first shot was almost off the top of the target. Anyway, here are the results from that shoot with a picture to follow later:

All measurements are in millimeters from POA
39.8 grs
Shot 1: 70.4mm above, 16mm left
Shot 2: 64mm above, 9mm left
Shot 3: 34mm above, 10.2mm right

40.1 grs
Shot 1: 78.8mm above, 16.5mm left
Shot 2: 62.9mm above, 4.5mm left
Shot 3: 67.5mm above, 10.1mm right

40.4 grs
Shot 1: 90.8mm above, 10.3mm left
Shot 2: 68.7mm above, 10.3mm right
Shot 3: 55.6mm above, 1mm right

40.7 grs
Shot 1: 96.1mm above, 25.1mm left
Shot 2: 79.3mm above, 13.9mm left
Shot 3: 61.9mm above, 11.3 left

41.0 grs
Shot 1: 77.7mm above, 11.6mm left
Shot 2: 71.1mm above, 6.6mm left
Shot 3: 89mm above, 2 right

41.3 grs
Shot 1: 110.3mm above, 17.2mm left
Shot 2: 124.9mm above, 12.4mm left
Shot 3: 85.8mm above, 7.4mm left

41.6 grs
Shot 1: 131.6mm above, 14.5mm left
Shot 2: 119.8mm above, 18.4mm left
Shot 3: 113.3mm above, 8mm right

41.9 grs
Shot 1: 117.2mm above, 4mm left
Shot 2: 107.2mm above, 6mm left
Shot 3: 114.4mm above, 8.8mm right

As seen in the picture, the tighest groups were 41gr, 41.6gr and 42gr (the tightest). 41.3 was all over the place...

The results from last time suggested that the 40.7, 41 and 41.3 loads would be the tightest, but that does not appear to be the case.
I had hoped this would confirm prior findings, rather than throwing them into doubt. I hope that is not what has happened. Only the black art of statistics can reveal the truth now!!

[Jimro]

James,

This is going to sound weird, but the goal of OCW isn't to get the exact tightest most perfect groups.

The goal is to develop a load that is "charge weight tolerant" with your powder so that when you get a slightly heavier or lighter case, or a your charge is off by 0.2 grains, that you can't tell on paper as your load has some wiggle room for those sorts of variances.

You are in an Estonian January. Do you think that chosing the load that gives you the absolute tightest groups now will be the same load that gives you the absolute tightest groups in an Estonian August?

What you are looking for is the LEAST amount of shift between charge weights. Looking at your target your 3,4,5 groups are all about 6 squares above your point of aim. This represents small shift. Your 6 group is about 10 squares, your 7 group 9.5 squares, and your 8 group is about 8.5 squares. This means these loads are not very "shift tolerant" as a small change in powder charge produces significant vertical shift at 100 yards.

I'm guessing each square is about a quarter inch, or around 6 mm. When a 0.3 grain charge difference is throwing you off a quarter minute at 100, it will get bigger the further downrange you go. That being said, the bulk of your shot groups are sub MOA, with the 2-5 groups clustered in the same 0.75 MOA area. I consider this very promising.

Anyways, I still recommend concentrating on 40.9 grains of powder and experiment with seating depth to develop a charge tolerant load that shoots tight in your rifle. You could definitely shoot more to get more complete statistical data, but I think you have enough to go on for now.

Jimro

[Pond, James Pond]

Thanks for the evaluation.

I understand the principle of the OCW method, but I loose sight of that when looking at my shooting results: I have difficulty equating what I'm trying to achieve, what I've shot and how to interpret and match those two aspects, so thanks for getting my thinking back on track.

As I'm hoping to improve my shooting skills, I am instantly drawn to group size, first and foremost.

Your point on charge weight is noted and indeed the 41gr group seemed to be the one I had to work least hard on to shoot well, if that makes sense.

I think I have loaded enough charge sets for now, as you point out, and will move on to seating depth options.

I am nonetheless curious to see what Unclenick's stats will show up.

Your point about the weather is quite accurate although we have been blessed with an uncharacteristically mild winter so far: much kinder on the heating bills and the fingers, and the nose and the belly as I lie prone on a concrete floor!!

PS: yes those are 1" squares. They are a Hoppe's #9 100yd sighting target. I like them because I can put together several groups on one sheet, and the orange makes it easier for me to see any hits in the solid areas, compared to black.

[tobnpr]

When group sizes and distance from POA are very close, I go with the one with least vertical dispersion. More consistent velocity.

Of course, the guy that developed OCW is often on the forum, so maybe Dan will chime in here...

[Pond, James Pond]

Jimro's point about making a "charge weight tolerant" load got me thinking.

Given the cost of brass over here, I have shamelessly pounced on any .308 brass I have found at the range. I have some by Norma, of course, and now PRVI too. But I have also found or given peened-primer cases by CBC and R1M1 ( Who?!) as well as Swiss Munitions cases.

I have quite a few of these, but they are not my go to cases, IYKWIM. I'd rather not go through the same rigmarole of OCW testing to find a load for those cases. If I have to, I may just bin them all.

If the primer and bullet are the same, isn't the point of the OCW system that I can then use that same load (especially as it is likely to be a full grain below max charges) in other cases with little effect on performance?

Could case brand to case brand variation in volume be so great as to affect my charge weight beyond the OCW tolerance range?

[RC20]

James,

I took a look at your rifle choice and I believe its a good one in that the 550 Varmint is a heavy barrel.

I also do not see what powder you are using? Primer, brass listed but not the powder. There are some known good powders that tend to work across a wide range of guns, and then there are some ones that are not. They might work well in one gun and not at all in another. Tell us what powder you are using. A lot of powders out there, some are fine for hunting but not target shooting.

I have one that some days I get great resutls and others its all over the map (I use a control gun and its all over the map with that gun as well). Will see if I can get it consistent.

As noted by Eppie, unless you have a good baseline round to start with in known accurate loads or rounds) then all sorts of factors can cause things to shift.

The shooter is certainly one a big part of it. Some days you shoot well and some days not so good.

Once of the best tecnuqiues I know of is to shoot 5 round groups and use a bse target, pull the top taget each time and putting a new target over the top each time.

That way you can see the true scatter of many 5 shot groups and still see ow they did on their own.

The reality is there will be a lot bigger group than any of us would like but thats also the true combo.

Bench rest on a sand bag is another method that puts consistent bearing spot on the stock (bi-pods have lever out front and can distort the stock action relationship)

It also gets into checking the stock and see if the gun is free floated or touching as well as weather and humidity on wood stocks (ergo the move to synthetic stocks).

It takes a lot of time and patience to work through all of that

[Pond, James Pond]

The powder is VihtaVuori N135.

I would have added to the OP, but my edit option has expired...

Happily I can say that the barrel is free-floating as I sanded away some of the stock inner surface that was touching near the fore-end until I could pass paper between the two, unhindered.

The next stage for me is some OAL variations, but I am waiting for the delivery of a bullet comparator kit to get accurate ogive to lands measurements.

[RC20]

James,

The powder should help the others who shoot it to assess it. Not one I deal with unfortunately so no idea how it does in 308

James: Here are a couple of my shoots with a 1903 30-06 Sporter (my dads with a new barrel) that shoots 5/8 to 1 1/4 typcialy (or maybe me and the ammo shoot that as I suspect it can do 5/8 with the right shooter and ammo.

No attempt to optimize to the lands as same rounds get shot in ohter guns.
This one was at 75 yds, 6 shots acualy but as noted 5 at 3/8 inch group. Where the flyer came from, not a clue. That would be aboutr 1/2 inch group at 100 yds (and you get a bit of a bonus as 100 meters is yard so have a fraction off the size!)



Why I shot a group that good under not so good condtions (15 degeF) and windy I don't know. I tend not to be able to.

HS 5 Shot 3-8 11-23-13.JPG

This one was a 10 shot group with a flyer that I wold not have called, so again why I don't know (gun is bedded). So its a 2.5 inch group, throw out the flyer and its 1 3/4 but you can see that 3 hit in one spot making a ragged hole with 3 other making a 1 inch 6 shot group but as fun as it is to cherry pick its at best a 1 3/4 and really 2.5 inch.

HS 10 Shot 1-3-13.JPG

Reality is if I was shooting for score its a 2.5 inch group though obviously on a good day the gun and or right reloads can shoot far better.

Its certainly a challenge and I have been at it for 2 years pretty much weekly now. My brother who is generality a better shot has bad days he can;t group worth a hoot and next week does well.

[Pond, James Pond]

I hope to be able to produce groups like those once this load is finalised and I am more comfortable with it. Some of my groups last time seemed to be entirely populated by flyers!!

The other powder that I had thought to use was N140. It is just below Varget on charts of burn rate, whereas N135 is just a tad faster burning than Varget.

[RC20]

James,

I did a quick read on the 135 and it is a 308 listed load though none in my books under bolt action. It was in the Semi Auto though that may be a cycling issue as those are sensitive to powder types (not sure when it came out and how dated I am, my newest ones are several years old now)

155 gr was at the top its listed range though that may or may not mean anything.

The 140 seems to be more main stream for 308 in bolt. What twist does the CZ have?

You are doing very well so don't be discouraged. I have been shooting all my life (some target, some hunting and now back to target). I have no qualms on my ability to take a Caribou or a Moose as they say, minute of game is good enough! Good consistent target shooting is a whole different story. I could take a Moose out to 400 yds with my groups and miss a target with those flyers!

Target shooting is a real challenge and so many variables. Back to getting a load that shoots well and then playing with a single variable (bullet seating depth).

I am not going to get into the super serious nuance of eccentric of cases, weigh bullets etc. A lot of that stuff is whats needed to go from say 5/8 (which is my ultimate goal) down to 1/4 (maybe when I retire!)

You have inspired me to think of a 308 though. No one makes a heavy barrel 30-06 and a good off the shelf 308 would be the next choice as there is a wide range of them out there in various mfgs.

[Pond, James Pond]

You have inspired me to think of a 308 though.

Just doing my bit for the sport!!

Well, I like the looks of the dedicated long range rifles a la Sig SSG3000 just not the price tags. Apparently the Varmint action (1:12 twist, BTW) is based on the CZ 750 Sniper rifle. I liked it as soon as I'd laid eyes on it but at €900 I couldn't afford it. When a barely used one came up for €500 because the owner was a leftie and the rifle was for right-handers, I jumped on it.

Ideally, I would have bought the laminated stock version, but that would have cost €1100 new and I don't expect to see one of those for sale.

Anyway, aesthetically it is pretty much want I wanted: I like the old-school target shooter look. Real-world performance it is clearly accurate ad should do me for as much distance as I can handle. The only downside is the weight if shouldered, but recoil-wise it helps a lot.

[RC20]

James,

I think you found a good choice at at least a decent price.

Yea I keep looking at what I might want vs what I can afford and.....

[mattL46]

Ok I'm very intrigued...I have a sako L46 pre vixen in 222 Remington which is regarded as one of the most accurate combinations in firearms history (note I said one of them) and this OCW stuff is really peaking my interest. I haven't had much time to work on load development and I don't shoot it a whole lot but plan to do some accuracy work with it. (Seating depths, charge weights, components etc etc) So could someone fill me in as to what the hell is going on here? What is OCW? Ive gathered it has something to do with charge weight?

[Jimro]

James,

Dan, the guy who created the OCW system of load development, has a sub-MOA shot group from 3 different brands of 308 brass on his homepage.

It can be done. It isn't a pretty group, but it is sub MOA at 600 yards.

I would still sort your brass into lots for best accuracy, but you should end up with a charge weight that will work decent in all of them.

Jimro

[Unclenick]

Matt,

The OCW web page is here.


James,

I should get new plots up tomorrow. The higher resolution data has already uncovered a new puzzle for us to solve. I'll explain then.

[mattL46]

Thanks unclenick. I took it upon myself to research. Very interesting stuff. Which will make my load development that much more obsessive.

[Pond, James Pond]

The higher resolution data has already uncovered a new puzzle for us to solve. I'll explain then.

Oh cruel world! Why?!

At this point, if this puzzle can be put down to the "user factor". I think we've probably found the answer!!

Seriously though, I'll be very interested to see what you've found out!

I would still sort your brass into lots for best accuracy, but you should end up with a charge weight that will work decent in all of them.

Sorting cases would not be a problem, but being able to use the same charge in all my .308 cases with the AMAX would make no end of difference to my time. Developing a load is interesting and educational, but if I had to do it for each brass brand I found, I'd just ditch all non Norma brass!!

To think I will have to go through all this again with my Scenar and Lockbase bullets!!

[John C]

Before you ditch all of your non-Norma brass, work up a load in the Normas. Once you have that worked out, try some of your final loads in your other brass. If it works well enough, keep them. If not, recycle them.

Using the OCW, and changing that one variable, you should see adequate results. That's the whole point of OCW; to find an accuracy node that is tolerant of minor variations.

[Pond, James Pond]

Using the OCW, and changing that one variable, you should see adequate results. That's the whole point of OCW; to find an accuracy node that is tolerant of minor variations.

That is pretty much what I wanted to confirm. That is one thing that makes the OCW system so handy for the real-world shooter. By real-world, I mean having normal levels of equipment, money, time and expertise.

Yes, the dedicated long-range, bench-rest shooter may be able to turn out an even more accurate round, perfectly attuned to the rifle, but most of us don't have the resources needed to achieve this, nor the need for such accuracy. Instead flexibility whilst maintaining a respectable degree of accuracy is a more appreciated outcome.

If I can do that with the OCW and get sub-MOA accuracy at 100m, then that means I stand a chance of being able to shoot out to ranges of 600-, 800- or even 1000m, provided I can start to read wind speed etc...

In the meantime, it also means that I can get more trigger time using the resources I have than blowing 10 hrs of range time on another 100 brass cases.