Pictures: 2353 ·
Views: 331627 ·
| OCW ( Optimal Charge Weight )
:D I would like to give all credit for the following information to
" Dan Newberry " this article was posted by him on the
( www.savageshooters.com ) website along with links to his website at (www.clik.to/optimalchargeweight )
This information is something that I wish that had been available years ago, it would have saved me tons on powder, primers & bullets finding a good load for all of my rifles. Give it a look over, I hopw that you get as much from it as I have. Best Wishes & Safe Shooting. Flint54
Do you have a need for a decent long range rifle load? It really doesn't require as much work as one might suppose--in fact, you can actually develop and be shooting the load for your rifle in as little as 30 shots or so. Don't believe it? Read on...
Most of us get tripped up by loading WAY too many shells of each powder graduation. We decide to try too many bullet types, and often too many powders. All the while, you're spending money on this end that could be saved to purchase more of the right bullets and the right powder after you've identified the final load which you will be using.
Here's the shortcut to putting together an accurate and successful load for your LR rifle.
Choose a bullet. That sounds easy, but it's getting harder and harder all the time. There are many--almost too many--choices out there. My recommendation would be to take a look at what the successful shooters in the long range competitions are using, and narrow your choices down that way. As a rule, you'll *****t to go with the highest BC (ballistic coefficient) that your rifle's twist will stabilize. Of course if you're shooting a chambering that won't get the required velocity from a very high BC bullet, you may *****t to step down a bit in bullet weight so you can step up in velocity. Again, see what folks who "know what they're doing" are shooting and that'll get you some good ideas.
We've all heard folks say (and have perhaps said it ourselves) that "my rifle doesn't 'like' Varget, IMR 4895, BL-C(2)," or whatever. Keeping in mind that this is an opinion, allow me to say that I'm not inclined to believe that a particular rifle really dislikes a particular powder. Barrels aren't all that different. Likely, when we came to the conclusion that our rifle didn't "like" IMR 4064 (and folks, I remember concluding that once, way back when ) we were shooting with a bad scope, bad bullets, incorrect powder charge range, bad powder or bullet lot, poor or underdeveloped bench technique--or any number of other things. I've since proven that that old rifle which I thought hated IMR 4064 actually likes it after all. And it likes it very, very much...
I mention the above because powder choice is very important when you set out to develop a load. And the overwhelming liklihood is that your barrel will indeed "like" a standard powder used by many other shooters using the same chambering.
So, let's say you're working with a Remington 700 in .308, and you *****t to ring the 1K gongs. That rifle will have a 1:12 twist, and it'll handle bullets up to 180 grains pretty easily. Maybe a little heavier--but let's keep them at 180 and under so we can get plenty of speed from them. Let's say that after reviewing all of your options, you've decided to stay pretty standard and go with the Sierra 175 grain Matchking. (good choice, by the way). Now all you've got to decide is what to push it with.
If you'll poll most .308 win long range shooters, you're going to find these powders rule: (in no particular order) IMR 4064, IMR 4895, Varget, H4895, BL-C(2), Reloder 15, and the old stand-by W748. Wow. Which to choose...
Here's the truth. You can put together a pretty decent long range load with any of those powders. The idea that your barrel won't "like" one of those is extremely remote--again, my studied opinion. You can make any good powder in the proper burn range work for you.
So you've chosen a powder. For the sake of discussion, let's say that your buddy gave you a good deal on a couple pounds of W748 he had left over from an eight pound jug.
Next you gotta have some brass. Again, check around. You're going to be told that Lake City Match, Lapua, Winchester, Norma, and IMI are some of the better choices. Since Lake City isn't always available and Norma is too expensive for what you get, that leaves Lapua, Winchester, and IMI. IMI is a military brass case, and in the match form it's quite good. It's on the heavy side, so reduce listed maximums accordingly. Lapua is great brass, and can be had at a decent price. I like Winchester because it's cheap and good. Lapua is a little more than twice the price of Winchester, but it is better brass as far as uniformity and case life goes. But since I've shot some of the best groups of my shooting career with Winchester cases, and since you asked me you've bought a couple hundred Winchester brass cases.
Do I need to de-burr the flash holes and uniform the primer pockets? In my opinion (in this opinion piece, remember?) you shouldn't bother. I've not seen any compelling evidence that match prepping cases really helps practical accuracy at all (except in the instances where a shooter is working with a non-optimal powder charge--which of course he shouldn't be -- see "walking the tightrope to accuracy" referenced later in this post). John Barsness used a Remington 40X with a custom barrel a few years ago to test the benefits of 1000 shots of prepped .223 brass versus 1000 shots of unprepped, straight from the bag Winchester brass. Guess what? The average group size favored the unprepped brass by a slim margin! So don't waste your time.
Gotta have primers, right? Right. And here again, don't lose sleep over which primer to use. Some powders do indeed seem to have a "favorite" primer, likely because of how hard (or easy) they are to light uniformly. Since you went with W748 I think I'd stick with the Winchester primers. W748 is a ball powder, and it will pack into the flash hole inside the case (and possibly even find its way into the primer cup). WLR primers are on the hot side, and will breath good fire right on through if you end up with some rounds with impacted flash holes and others with unobstructed flash holes. Ball powder really isn't harder to light than extruded (stick) powder--but over the years knowledgeable folks have come to believe that ball powder shows an affinity for hotter primers. (Speer actually uses magnum primers with W748 and other ball powders). I wouldn't go that far, but I do think WLR's are great with the W748.
But you couldn't find WLR's. Sold out. Losing sleep...
Get the Federal 210's and let's get some stuff loaded up.
You're going to be pushing a 175 grain bullet with the W748. Let's see... what do the loading manuals say? An average of three sources I looked at says that 45.0 grains is max with 180 grain bullets. Why did I look at the 180's? Because I couldn't find (and you likely won't either) much data for W748 and the 175 grain Sierra Matchkings.
For an OAL you will begin at about a caliber's depth of bullet into the case. Don't count the boattail, by the way--you *****t a caliber's depth of bearing surface for good neck tension. For a thirty caliber bullet, that'll of course be about .30" or so. You can "depth tune" the finished product later on, by testing seating depth changes in .005" increments. Generally, a properly developed OCW load will not be really particular about the seating depth--but you can "fine tune" the accuracy by slight seating depth changes if you wish. An aside: If you find that a caliber's depth of bullet bearing surface still leaves the cartridge too long to magazine feed, just seat the bullet to near the max length the magazine will tolerate. This is a Remington 700 we're talking about here so just go on ahead and seat the bullet to an OAL of 2.810", tip to case head. That way it should mag feed easily...
Using the OCW instructions you'll find at my website ( www.clik.to/optimalchargeweight ) you put together ONE cartridge using 41.5 grains of W748, then another with 42.0 grains, and a third with 42.5 grains, and a fourth with 43.0 grains. These are the pressure test shots. Now you're ready to load three each of the following charges: 43.4 grains, 43.8 grains, 44.2 grains, 44.6 grains, and finally 45.0 grains. You're moving up in approximate 1% increments.
(An aside: If reliable sources indicate that you can go slightly above 45.0 grains with the W748, then go ahead and load three cartridges with 45.4 grains. Fire these in the round robin test mentioned next if and only if there are no pressure signs at the 45.0 grain level. In the event that 45.0 grains would be the OCW, you'll need the 45.4 grain charge to prove that. For the purposes of this discussion, we'll stick with the five graduations already mentioned).
You fire the three test shots in increasing charge weight order to check for pressure signs, and set your zero as close as possible to the bullseye at 100 yards with shot number 3. Now, you'll have five targets set up at 100 yards. Keep the bullseyes as close to each other as practical to minimize light and angle differences between them. I just put five squares on the same white piece of paper, about three to four inches from each other.
Beginning with the 43.4 grain charge, fire one shot at target 1. Then go to the 43.8 grain charge and fire one shot of that at target two, move to target three, and fire one shot of the 44.2 grain charge at that target, and so on. Go through all five targets three times each in this "round robin" fashion. Watch for pressure signs along the way, and stop if you encounter such. When you're done with all fifteen test shots, you'll have a three shot group of each charge weight represented on its own target.
(A tip: For your individual targets, use 5 x 7 index cards with black squares drawn in the center with a Sharpie marker, each square in the identical location on each card. Use one card for each target. That way, when you're done, you can see which powder charge graduations hit the same POI by stacking the cards).
Now you're almost done. Look at the groups and determine which three groups all appear to be hitting the same point of impact on the 100 yard target spots. Let's say that 44.2, 44.6, and 45.0 grains all seem to hit in the 2 o'clock area, about an inch from center of the bull. Since all three of these groups hit the same spot (for the most part) then your choice for your long range load is going to be 44.6 grains.
At this time you've fired eighteen times, and spent eighteen bullets, eighteen charges of powder, eighteen primers, and you've diminished your barrel life by only eighteen rounds.
Yeah, but who's gonna really believe that 44.6 grains of W748 (in this example, remember) is going to shoot tight at long range? Folks, in all of the OCW tests I've done I've yet to find a recipe developed in this manner which wouldn't shoot well "way out there." You see, by virtue of the fact that you've chosen a powder charge weight from the center of a three shot string of graduations which impact the 100 yards target in the same location--you're choosing a pressure tolerant load, in the "sweet spot," if you will.
But let's shoot three bracket groups to be sure that 44.6 grains is indeed the Optimal Charge Weight. (Remember, this is an example--I'm not contending that 44.6 grains of W748 is an OCW load). For your bracket groups, you'll simply shoot one shot of 44.2, one of 44.6, and a third of 45.0 grains into the SAME GROUP at 100 to 300 yards (the longer the better here, but since some folks don't have immediate access to ranges longer than 100 yards that range would be fine). All three shots--even though they are of three different charge weights, should print together on the target. By "together" I'm speaking of MOA from rifles capable of such. Here is an example of an OCW bracket group fired for the .243 win at 100 yards:
If you shoot three bracket groups you've now shot a total of only 27 rounds. And if those groups land tight at 200 to 300 yards, you know you're in the OCW zone, and you can be all but certain that the 44.6 grain charge will perform very well for you at longer ranges.
So at this point, with less than 30 rounds invested, you very likely have a load recipe that's going to serve you well at the longer ranges.
What about velocity?
Notice, however, that I didn't mention anything about a chronograph just yet. For my part I don't get curious about the velocity of a load until I find an accurate load. Many folks "shoot for" a particular velocity when developing a load, but the truth is if you *****t a pressure tolerant load (or by definition an Optimal Charge Weight load) you cannot let the chronograph tell you where to take the recipe. There will normally be two distinct OCW zones with any given powder and bullet. The low zone is fine for close work, but it'll generally have a larger extreme spread (velicity differences from slowest to fastest shot) than the high node OCW will. And for a long range load, you'll *****t as much velocity as you can safely get. Generally, the OCW will exhibit tight velocity spreads from the get go, but you shouldn't simply shoot a bunch of shots across a chronograph and look for a tight velocity spread--that can lead you astray because some non-optimal powder charges may indeed show tight numbers so long as you're within .1 to .2 grains or so. That's not good enough, as you'll be "walking the tight rope to accuracy," and having to do meticulous case prep, weigh powder charges to the tenth of a grain, weigh cases and such--just to stay on that tight rope. Step slightly to either side and accuracy "falls off" noticeably.
So by shooting the round robin sequence through the higher charge levels (right up to the maximum) you will almost certainly find the high OCW zone. Once you've identifed the high OCW zone (by finding the three consecutive groups which have a common POI) you choose the center charge weight, and live with that velocity. If possible, you should chronograph the final product (44.6 grains of powder in this example) so that you'll have a rough idea of trajectory, and also the velocity at 1000 yards. You could shoot several strings across the chronograph just to see what the ES would be, but why not just shoot the recipe at long range and see what the vertical spread looks like? The target is the final arbiter anyway--regardless of what the chronograph says or doesn't say.
A 2600 fps 175 grain (30 cal) Sierra Matchking with it's ~.500 BC will make it very nicely to 1000 yards. And with a 24 to 26 inch barrel, you should have no trouble getting close to or a little above 2600 fps from the 175's with the high OCW of W748.
A final note: Could I have used IMR 4064 or another type of primer and gotten an even tighter shooting load? Very possibly, yes. Perhaps not. But the degree to which a load is more or less accurate is far less important than simply learning all about the load you have. A 3/4 MOA load made with W748 and Federal primers, and practiced with religiously is a far more formidable system than a 1/4 MOA load in the hands of a "fair weather shooter" would ever be.
Don't develop "a" load. Develop the load. www.clik.to/optimalchargeweight
Posted by Flint54 on Friday, May 13, 2005 (14:54:30) (21486 reads) [ Administration ]
Average Score: 4.82
Please take a second and vote for this article: