OCW !!!

chambered221 · Posted: Sat Jul 10, 2010 4:25 pm Post subject: OCW !!!

I have started a new thread on this because I feel there is some discussion to be had !!!

Ive re-posted the 2 links here:
optimalchargeweight.em...space.com/
optimalchargeweight.em...4529817134

Plus I'll add this one;
www.the-long-family.co..._paper.htm
OCW came about because of this study by Chris Long.

Slimjim wrote:

I like tight groups

If done correctly and your gear is up to it OCW will consistently shoot MOA or better !!!
By going with the tightest group in initial test you stand the chance of being on the edge of what the load is capable of.
With OCW you have a built in factor of forgiveness from one day to the next.

Slim, take a load you developed by picking the tightest group, then take one that was developed in true OCW fashion. Shoot those 2 loads over time and average them over 10-15 groups or more. I'm willing to bet ya the OCW load turns in a better aggregate.

tikkat3, It's very clear to me that 49.0gr. is your load under OCW !!!
OCW is about finding a common point of impact and 48.5, 49.0 and 49.5 with out doubt have that in common. Yes a few shots are outside the common area but that can be expected.

Another thing to keep in mind, after you establish your load you can then work with bullet seating depth to fine tune the load.

moose2 · Posted: Sat Jul 10, 2010 8:25 pm Post subject: Re: OCW !!!

I've been using the OCW Method for awhile now and have been really pleased with the results. To go along with that, I find it to be a very fun method of load development. Very Happy

44marty · Posted: Sat Jul 10, 2010 8:38 pm Post subject: Re: OCW !!!

Thanks for the link, Chambered. The OCW method works great!!! It's nice to see how it was developed.

tikkat3 · Super Member Joined: Jul 30, 2006 Posts: 800

Dear Doctor Chambered
Thanks for the new thread
I have a lot of questions. But the first is........
If after the first round of developement you have a target with say, 18 holes in it(6 x lots of 3) and they are spread evenly across the target with no distinct pattern (other than shotgun type patern).
What would you do?
Try another powder? Re do the test? Try different seating depth?
This has happened a couple of times,
The last was changing from TSX to TTSX in Barnes 120grn 7mm/08

chambered221 · Posted: Sun Jul 11, 2010 11:42 am Post subject: Re: OCW !!!

Me.....a doctor.....yea right !!! No comments needed from the peanut gallery either !!!

The first thing I'd ask is about giving the barrel adequate cooling time between shots.
The method does not call for cold bore shots but you do need to give ample time for some cooling. Knowing the guns habits is an advantage here.

As far as powders go the slower for cartridge are best to work with under this method.
OCW is not about fine tuning a set of components. It's about finding where a set of components work best. As long as you follow a basic set of common rules for your caliber with the slower powders it's rare not find MOA or better if rifle and shooter are up to it.
For example, when loading for a 30-06 use the common 150, 165 or 180 grain bullets. Stay away from 125 and the 200+ weights. Use a powder like IMR4350 and a standard primer. These are very common and well known to the 30-06 !!!

Funny you mention the 7mm08 !!! I've got 120gr TTSX's loaded waiting to go to the range !!! Hopefully I'll make it before season.

Gil Martin · Posted: Sun Jul 11, 2010 1:11 pm Post subject: Re: OCW !!!

Would someone define OCW? Thank you. All the best...
Gil

slimjim · Posted: Sun Jul 11, 2010 2:03 pm Post subject: Re: OCW !!!

Gil Martin wrote:

Would someone define OCW?

Optimum Charge Weight, a process for finding the optimum powder weight that results in the most consistent point of impact (POI).

slimjim · Posted: Sun Jul 11, 2010 2:11 pm Post subject: Re: OCW !!!

tikkat3 wrote:

If after the first round of developement you have a target with say, 18 holes in it(6 x lots of 3) and they are spread evenly across the target with no distinct pattern (other than shotgun type patern).
What would you do? Try another powder? Re do the test? Try different seating depth?

this happened to me with .270 Barnes 120 BS. You need to change one of the components. I changed from Rem to Win brass and the groups changed from 1 to 2 MOA to 0.5 MOA. All my other loads did best with Rem brass. I have found changing brass has one of the biggest affects on performance for my .308 and .270 Win.

slimjim · Posted: Sun Jul 11, 2010 2:20 pm Post subject: Re: OCW !!!

chambered221 wrote:

OCW is about finding a common point of impact and 48.5, 49.0 and 49.5 with out doubt have that in common. Yes a few shots are outside the common area but that can be expected.

Picking the middle powder weight for consistent POI is a good strategy for those that use a powder thrower. If you weight each load individually, I'd go with the weight that gave the most consistent and tighter group.

chambered221 · Posted: Sun Jul 11, 2010 4:25 pm Post subject: Re: OCW !!!

I fixed the 2 links ........ Sorry for the error !!!

chambered221 · Posted: Sun Jul 11, 2010 4:37 pm Post subject: Re: OCW !!!

A true OCW load will have the forgiveness to change components such as the brass without any consequences.
I still recommend weighing each charge, This will allow for more leeway with atmospheric changes that you may encounter.

chambered221 · Posted: Sun Jul 11, 2010 4:49 pm Post subject: Re: OCW !!!

Gil, With a OCW load your bullets will exit the barrel at the same point and time in relationship to the barrels harmonics.

slimjim · Posted: Sun Jul 11, 2010 7:51 pm Post subject: Re: OCW !!!

chambered221 wrote:

A true OCW load will have the forgiveness to change components such as the brass without any consequences.

I like OCW but I haven't found it to be that resilient. I wouldn’t expect the above statement to apply to the powder that is used. I have found changing any aspect of reloading has the potential to affect the end result whether it’s a shift in POI, group size, velocity, etc. Changing brass has had the biggest affect on POI and group size for me in every rifle I reload for. I might not notice much of a change at 100 yards but, at longer ranges, it’s the norm that any change has an affect. That’s what I have experience.

Dawgdad · Posted: Tue Jul 13, 2010 11:16 am Post subject: Re: OCW !!!

Chambered,
While I share your favor for the OCW I think you may be applying a bit of Snake oil to the procedure and its results.

The optimal charge is the amount of a given powder in a load that has a plateau in the curve of velocity versus charge weight where a change in the charge weight does not give a change in velocity or presssure that is as great as the change that occurs at lower or higher charge weights. Think of a Chaise lounge lawn chair with the feet down to the left and the back up to the right. The foot of the chair is a lower charge weight the velocity increases and the plot of angles upward fairly steeply. When you reach the OCW region you are in the seat area of the chair model and the weight increase in powder charge does not give as much of a change in velocity. After you pass this point you reach the back of the chair and pressure/velocity rises again.

This is shown on paper as the three (or more) consecutive weights that give the same POI.

The group size will need to be tweaked by (Yes I am going to say it) adjusting OAL to get the bullet exiting at the right barrel vibration node. Luckily most OCW's are very forgiving and group pretty well at "standard" cartridge lengths and having to kiss the lands or some other longer length.

stovepipe · Posted: Tue Jul 13, 2010 1:23 pm Post subject: Re: OCW !!!

As soon as the weather mellows out I'm going to try some load research in earnest.

I have several scaled charges, with exactly the same components- the only variable is propellent weight, and will be looking for 2-3 that share an impact point, or closely therein. Then select the one in the middle or upper middle I feel will be the most forgiving when temps and such change.
Then- start working on seat depth/groups, if I find something promising.

It took a while to understand it but I stopped glossing over it and it finally made sense. It's not about groups but consistent POI's with diff. charges, this will let me know I'm in the ballpark for OCW. At least that's how my feeble mind grasped it, in a nut shell. Feel free to correct me if I'm missing something. Embarassed

The hardest part is the wait between sessions. I live two hours from my range and time off is a premium. Maybe I'll find something that works before I'm too old to shoot this cannon or before I wear out the barrel.