An interesting OCW related result with a new chamber in an "old" barrel.


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1858
September 9, 2009, 06:12 AM
I just got my .308 back from the gunsmith last week. I had welded a new handle onto a new PT&G bolt (O.D. of 0.700") and the headspacing was too short so it went to the gunsmith. He removed about 1" from the chamber end of the barrel and cut a new match chamber. He also installed a BO recoil lug. I managed to paint the barrel and bolt with GUN-KOTE (light desert tan, base color for camo pattern), installed a new BO 20MOA base and then reinstalled the scope.

This past weekend I decided to use up 23 loads that I had left over from a match back in June. That particular load shot very well at 600 yards and I considered it to be the OCW load for the original Krieger barrel and chamber. The OCW load consisted of 43.2gr of Reloder 15, a Nosler 168gr HPBT CC bullet, Lapua brass once fired and neck-sized, a CCI 200 primer and an OAL of 2.845". MV was right around 2,700 fps.

The first thing I discovered is that the new chamber is shorter than the original chamber so I had to seat the bullet 0.044" deeper to maintain 0.020" of clearance off the lands. Those cases were fired once in the original Krieger chamber and were neck-sized only so they wouldn't chamber in the new match chamber. I ran all 23 loads through a body die to bump the shoulder back to SAAMI specs. Given the required changes to the OCW load, I wasn't expecting much. After sighting in the scope, I shot one 5-shot group before the rain came and ended the day. Here it is ... 0.662" shot at 100 yards prone with a bipod. To be honest, I wasn't expecting such a good result but now I'm even more convinced of the validity of the OCW method. This weekend I'll make up 42.9gr, 43,2gr and 43.5gr to see if 43.2gr is still the OCW load for this rifle. It'll be interesting to see if the velocity increased a little with the bullet sitting 0.044" deeper in the case.

http://128.171.62.162/hawthorn-engineering/thr/rem700_308win/range_targets/ocw_new_1.jpg


Here's the rifle ...

http://128.171.62.162/hawthorn-engineering/thr/rem700_308win/photos/rem_700_308win_3.jpg

My thinking/understanding/interpretation re the OCW method is that the primer and powder ignition result in a shock wave that moves from the chamber to the muzzle and back again at some frequency (many times before the bullet leaves the barrel). The vibration that results is a function of the amount of powder, the energy of the primer and the mass and stiffness of the barrel and chamber. The position of the muzzle is a function of the frequency of the vibration of the barrel. The fact that the barrel and chamber are now both shorter has a minimal effect on the resonant frequency of the barrel/chamber so the OCW doesn't change even though the bullet is now seated 0.044" deeper. Case sizing, bullet seating depth, neck tension, case neck thickness, neck runout, bullet runout etc. all play a part in the group size, but it's my opinion that those variables don't affect the OCW load much at all. They simply fine tune it from good to better to best. I'm open to any thoughts on this so fire away.

:)

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USSR
September 9, 2009, 01:47 PM
1858,

I used to kid Dan Newberry years ago, when he would post on the Hide about his OCW's and other acronyms, that my load development involved finding SFG loads and avoiding SLS loads.;)

Don

1858
September 9, 2009, 03:14 PM
my load development involved finding SFG loads and avoiding SLS loads.

Don,
I know you're not a fan of the OCW method and you obviously have your reasons. I've found it to be very useful and it makes a lot of sense from a scientific standpoint. It's been validated for me empirically many times so it's the system that I prefer. I've never used the ladder method but it shares more similarities than differences with the OCW method. Whether directly or indirectly, all load development is about finding the nodes where the barrel is most stable. Once a node has been found, it's up to the individual to decide if they want to find the next higher node in order to attain a specific velocity range.

:)

something vague
September 9, 2009, 05:09 PM
I just kind of feel as if this OCW method is starting the load development at too high of a charge to begin with. I haven't actually performed this method myself but the reason was due to this fact. According to the directions it seems as if you are always real close to the max listed data for a particular load. I don't debate it's validatity but have always experienced in my load development that my most accurate loads are not quit that high up in the data. But then again I'm also not shooting to attain such high velocities, I'm going for the best shooting load. And I'm also not shooting customized benchrest rifles with extremely tight match chambers. To each his own. One of these days I am going to make a point to try this method out though.

WNTFW
September 9, 2009, 05:53 PM
1858,
I have used the OCW method a grand total of 2 times. Both were with the same .308.
My first effort was not impressive - at first. I was trying to get a load quickly and decided OCW would be my method with Varget & 168s. I shot poorly. None of my groups looked real good. I felt they were almost inconclusive. I don't know what my problem was. Almost a waste of 23 rounds, outdoors at 100yds.
I ended up taking the best group (by OCW definition) and using that load. I had to go with the results I had on paper. It was all I had. Maybe it was the bullets? I figured I would leave the load stable and just keep shooting it until I got better or the 500 bullet got used up. Saturday I shot a 1/4" group @ 100 yds with no changes to the load. It was only a 3 shot group but still my best 3 shot group ever. In between testing & the best group I shot at other distances under 1/2 MOA, just no groups at 100.
My next OCW test came from using up the Varget. I finally was up against the wall failing to get more Varget and decided to start using Reloder15. I could either go to a 50yd indoor range or not test. I loaded up 35 rounds and shot some 3 shot groups twice, again it was done by OCW definition. I wasn't sure if I could tell at 50 and I ended up glad I shot the groups twice. I had a bit of a time deciding between two of them.
I haven't been able to shoot it and say how good it is, but I did get a load that I feal condfident in.
I loaded a ladder for .308 and have never been able to test it. It is always something. The disadvantages of it are valid even though I think the concept makes sense.
I think the OCW method is pretty good. I am a definite believer in it.
I recommend that reloaders should at least read up on it. I feel there are points of interest to it even if you don't use the method. I am just very impressed with the results I got from shooting only 23 test rounds and rather poorly at that.

WNTFW
September 9, 2009, 06:10 PM
Something Vague
I had to get past the way the method blows past the low end of the scale. It does test some low end loads just for safety and doesn't really give it too much of a chance. You could always fill in the gap at the low end if you wanted. My best Varget load was the OCW starting load. Not the low single loads but the lowest 3 shot load. My next 'chore' is to shoot some more groups @ 100 with 5 & 10 shots to see what I get.

Now that I am shooting better I can go back & refine or retest to find something better.

I don't have a chronograph, It is on my wants list.

I personally would like like to have less powder and have a more accurate round. Less cost, less recoil and all that. But I am learning what I think is not what ends up being the most accurate.

Walkalong
September 9, 2009, 06:55 PM
OCW mo CW. Try a couple of loads and see if they shoot. If one shoots well enough, your done. For the most critical accuracy needs, bump it up until you find the sweet spots. Pick the highest velocity sweet spot within safe limits. Then just shoot it and don't blame "fliers" on the load. :D

USSR
September 9, 2009, 08:41 PM
I personally would like like to have less powder and have a more accurate round. Less cost, less recoil and all that.

WNTFW,

Here you go:

Hornady Match brass
168gr HPBT bullet
Russian primer
37.2gr IMR4895

Have won several local 200 yard F Class matches with this. It's a SFG load, and not a OCW load.

Don

Walkalong
September 9, 2009, 08:45 PM
I'm writin' that one down Don. My nephew just bought an FN .308 bolt gun and will soon be looking to load for it. :)

ranger335v
September 9, 2009, 09:03 PM
"I'm also not shooting to attain such high velocities, I'm going for the best shooting load. "

Like all "rules of thumb", loading down a bit for accuracy is wrong as often as not, in my experience anyway.

I often find my best loads at or close to absolute max charges. I've guessed it has something to powder burning more consistantly at its design pressure range, not below it.

essayons21
September 9, 2009, 09:07 PM
What type of target is that?

WNTFW
September 9, 2009, 10:19 PM
USSR,
Thanks. I am going to develop some loads for other powders in my .308.
4895 is one of my choices of powders.

I would like to get some F Class advice from you. I'll PM you. I shot a 534-6x at 600 with my .308, winner was a 572-?x. I just shot a 559-8x with a different rifle someone offered up to me at the last minute. It was a really nice .223! All my 600 yd experience has been in F class matches. 264 rounds so far.

Thanks,
WNTFW

USSR
September 9, 2009, 10:25 PM
loading down a bit for accuracy is wrong as often as not, in my experience anyway.

I often find my best loads at or close to absolute max charges. I've guessed it has something to powder burning more consistantly at its design pressure range, not below it.

True. And I believe the primary factor in whether you can find an accurate reduced load is the powder. In regards to the .308 with a 168gr bullet, while I could find an accurate reduced load with IMR4895, the same could not be said of either Varget or RL15. They both seem to like high pressure loads.

Don

kelbro
September 9, 2009, 11:15 PM
I have used the OCW method to develop loads for several rifles. Seven or eight successes, one failure. Pretty good results from my point of view.

1858
September 9, 2009, 11:18 PM
I just kind of feel as if this OCW method is starting the load development at too high of a charge to begin with.

Load development starts where you want it to start. If you take a look at the load data from Sierra below, there's no reason why you can't start with 38.8gr of Reloder 15. There are a number of nodes between 38.8gr and 45.0gr so it's up to you to decide which node you're interested in. I regularly shoot at 600 yards so I want a velocity close to or greater than 2,700 fps.

http://128.171.62.162/hawthorn-engineering/thr/reloading/load_data/308_168gr_data.jpg

:)

1858
September 9, 2009, 11:39 PM
I think the OCW method is pretty good. I am a definite believer in it. I recommend that reloaders should at least read up on it. I feel there are points of interest to it even if you don't use the method. I am just very impressed with the results I got from shooting only 23 test rounds and rather poorly at that.

I agree 100% with you. I'd be interested to see what everyone's favorite load does with +/- 0.3gr of powder. I'm not trying to imply that the OCW method is the best method, but the theory behind the method does explain how Federal Match ammunition performs so well in so many different rifles. Some think that this shows that the OCW method is BS, I think it shows the opposite.

What type of target is that?

It's a target that I designed for load development. The first three shots missed the target completely :o . I decided to bore sight the scope at that point and used shots #4 through #8 to get on target.

http://128.171.62.162/hawthorn-engineering/thr/rem700_308win/range_targets/09-06-09_3.jpg

:)

WNTFW
September 10, 2009, 12:48 AM
1858
Permission to R&D your target design.

I just find OCW effective in that it puts you in the right place to look. If nothing else it is a system that takes into account that there are variables affecting your results that are averaged over time hence the round robin approach.

One particular point of interest is this: (quote from: http://optimalchargeweight.embarqspace.com/#/ocw-vs-ladder/4529811360 )
"But the real reason I wanted to discuss the scatter group is this: Please note that in each of the scatter groups shown above, ONE shot lands right on the same POI (or within 3/8 MOA or so) as the groups preceeding and proceeding it. This means that in at least one of three instances, during a conventional Ladder Test, the target would indicate a wide "sweet spot" where it should not. The OCW round-robin testing easily identifies the problem with this charge weight level, but in (at least) one of three instances, the Ladder Test will miss it--which may lead a shooter to an incorrect conclusion as to the center of the true accuracy node."

This coupled with group size and group location (POI relative to POA) gave me some insight in how to interpret my data into information. I would have just thought best group size wins and rezero as needed.

So is a flyer a flyer or a just scatter node. Whenever I shoot a rifle I own everything. If I claim the X's I claim the misses. I don't ignore flyers. I figure if I am getting flyers with 1 load and not another the no flyer load is better. It is what it is.

The two biggest drawbacks of the ladder seem to be sample size and range required, which OCW combats.

I have suggested OCW to many people that will not give it a look. I read the instructions a good 3 times before considering doing any loading.

WNTFW
September 10, 2009, 01:07 AM
1858,
What is BO? I just thought it out: Badger Ordinance
I knew you weren't referring to the way we smell after a day at the range.

One day I spent 2 550 bulk packs on range trip. I had at last 2k of AK rounds shot by friends on the left and another bulk pack on my right. All day long there was a constant wind directly in our faces. I took a shower soon after getting home. Afterwards my daughter came get me because she thought she smelled something burning in the bathroom.

That is a nice rifle.

1858
September 10, 2009, 01:21 AM
1858, Permission to R&D your target design.

No problem ... in fact, here are a couple of versions of the target I designed. One is a 100 yard zero target and the other is a 200 yard zero target (for .300 Win Mag).

100 yard zero target. (http://128.171.62.162/hawthorn-engineering/thr/targets/100y_zero_x3.pdf)

200 yard zero target. (http://128.171.62.162/hawthorn-engineering/thr/targets/200y_zero_x3.pdf)

If you print the targets with Page Scaling set to NONE, the targets will print correctly i.e. 1/4" grid measures 1/4".

So is a flyer a flyer or a just scatter node.

This comes down to calling your shots correctly. Usually I know if I screwed up a shot, so if it felt good but was out of the group it's a scatter node. If it felt bad and it's out of the group it's most likely a flyer/flier :confused: . If a shot felt bad but it landed in the group, it's still a flier Also, I mark every shot on a card (9 reduced targets per 8-1/2" x 11" sheet) so that I know where each shot went over a 30 or 35 shot session.

That is a nice rifle.

Thanks ... it's almost done ... just need to install the TUBB firing pin and spring this week and then finish painting the barrel ... and possibly change the scope to a NXS.

:)

WNTFW
September 10, 2009, 01:29 AM
I'm not that good at calling shots or seeing bullet traces for that matter.
I need to get my eyes checked. It has been a while.

I did shoot with a night forces scope once. quite nice.

Thank for the targets.

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