Good thread on Bullet Seating Depth

[Darkhorse]

http://forum.snipershide.com/snipers-hi ... uracy.html

I just found this thread today and coincidentally "Tripwire's" methods are almost identical to my own. I had never heard about OCW etc. before, but after working with a Browning BOSS extensively I was searching for a way to apply those principles to a regular barrel.
The barrel in question is a stock M700 7mag. and my load test targets all show what "Tripwire" describes. I'm sold on this method and sticking to it.
Just read the thread and I trust he explains it all better than I could.
Keep in mind I'm talking about the final tweaking to find the accuracy node. Any powder choice, charge weight, pressure tests etc. have already been done prior to this point and in no way am I touching on those subjects with this post.

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[FOTIS]

Not an issue. Can you explain the OWC method to me? I mean how it is done not how it works.


Is each group the same powder charge???? I guess I do not understand the round robin part of it.....


http://optimalchargeweight.embarqspace. ... 4529817134

 

[Darkhorse]

Today was the first time I ever read of heard of the term. But, I'm pretty sure it means "Optimum Charge Weight". The way I did it was shoot a series of targets with different charge weights while leaving the seat depth the same. The load that showed the most promise was the one I picked to work with the seating depths. I think they go into it much deeper than I did.
http://practicalrifler.fr.yuku.com/foru ... AOcBPldXmb

In group 1, I shot a series with the same seat depth but 3 different charge weights. Target A at 60. grs. was tighter but Target B at 61. had a better shape. So I decided to try 60.5 and vary the depth to see what would happen. I just got lucky by only needing to shoot 3 charge weights.

 

[Darkhorse]

But I really wanted to shoot 63. grs so basically I loaded several sets with 63. but kept increasing the seating depth on the theory that I would eventually walk my way into the node. A seating depth of .045 off the lands has given a more than adequate group. But I've decided to load another set at .047 off the lands just to see what happens. This is just a method that doesn't depend of finding the Optimum Charge Weight, and resembles the effects adjusting a BOSS has on finding the node. Now it depends on the shooter to manage 3 good shots.

 

[Darkhorse]

I just looked at that link you posted. It seems that the definition of OCW is that charge weight that gives the best groups with no seating depth change. Obviously that's NOT what I'm doing. I'm going to read that link more in depth.
Maybe that just shows there's more than one way to skin an armadillo.

Before I started shooting these series for results I spent a good bit of time refining my loading process until I was satisfied my rounds were as concentric as possible. I had also glass bedded the receiver and floated the barrel. Along with taking the trigger apart and doing a trigger job. I was pretty satisfied the actual loads themselves were the main variable I was working with.

 

[FOTIS]

1. Decide on the bullet you want to use.

2. Choose a powder. This is probably the most important step in the whole process. As a rule, you should choose the slowest burning powder practical. There seem to be plenty of exceptions here, so if you have it on good authority that a slightly faster powder works well with the bullet/cartridge combo you're using, feel free to choose that powder. A couple of examples would be IMR 4350 in the 30-06 and IMR 3031 in the .243 Winchester. An aside: When in doubt, consult the Nosler manual for their "most accurate powder tested." That powder nearly always gives good results in the application listed.

3. Consult at least three load data sources for maximum charge weight for the powder you've selected. Powder manufacturers are the most reliable source. You must then decide on what your maximum charge will be.

4. Back away from the maximum charge by 7 to 10 percent, and load one test round with this charge. Add 2% to the charge weight, and load another cartridge with that charge. Load a third test cartridge with the next 2% graduation. You will use these three cartridges for sighters, and more importantly to determine pressure tolerance in your individual rifle.

5. Add another 2% or so to the charge level used in cartridge #3 of step 4, and load three rounds with this charge weight. Add .7% to 1% to this charge, and load three more. Add that same graduation again, and load three more. Continue adding the chosen graduation until you have moved ONE increment above your chosen maximum powder charge.

6. The seating depth for all test loads should of course be the same. I normally seat the bullet a caliber's depth into the case, or to magazine length--whichever is shorter. I don't believe loading to approach the lands is necessary, or even desirable in most situations. So long as the bullets are seated straight, with as little runout as possible, the advantages of loading close to the lands are largely over-stated. This said, be certain that the seating depth you choose does not cram the bullet into the lands. Stay at least .020" or so off the lands for these excercises.

7. The primer brand you choose is entirely up to you. Use magnum primers only with magnum chamberings, as their added pressure may distort the OCW conclusions on standard chamberings. One exeption here would be with low density loads, as I believe that magnum primers improve ignition consistency in loads where the powder only fills 85 percent or less of the case.

8. At the range, you should set up 5 to 7 targets at 100 yards. The number of targets you use will depend on how many "sets" of cartridges you loaded. Be sure the targets are identical, and level. I like to use a simple black square, drawn on a white background with a large felt tip marker. I draw the square about 3/4" (interior dimension) for my 9 power scope setting. This allows a "tight fit" of the crosshairs in the square, and thus a repeatable sight picture. For higher power scopes, draw the square smaller, and vice versa.

9. You can also put up one "sighter" target, and use the initial reduced rounds to get the POI on paper, as close to the bullseye as possible.

10. Your barrel should of course be clean before starting. Depending on the number of rounds you will fire, you may decide that it is necessary to clean half way through the string, fire a couple foulers, and allow a couple of minutes to cool before continuing. With custom barrels, you may be able to fire 25 shots or more before fouling begins spoiling group sizes. With factory barrels, I wouldn't fire more than 15 to 18 shots before cleaning... This is all relative, of course.

11. After you have fired the sighters and confirmed that there are no pressure signs (hard bolt lift, flattened primers, etc.) you allow the barrel to cool for an adequate amount of time (use common sense--the hotter it is outside, the longer it will need to cool) you will then fire your first shot from the first group of the graduated charges. You fire this shot at target number 1.

12. Allow the barrel to cool, then fire a shot from the second graduation at target number 2. Wait for cooling of the barrel, then fire a shot from the third graduation at target number 3. Continue this "round robin" sequence until you have been through all of the targets three times. At this point you will have a three shot group on each of the targets.

13. It is assumed that you are an experienced reloader, and that you know to watch for pressure signs on each of the increasing charges. Fire the subsequent charge only if there are no pressure signs on the previous charge. You can safely fire the heaviest charge you loaded so long as the next charge under it showed no pressure signs. This "heaviest charge" should be about 1% over your selected maximum charge, but will be safe so long as the next lowest graduation showed no pressure signs.

14. Triangulate the groups. This means to connect all three shots in a triangular form, and determine the center of the group, and plot that point on the target. Measure this point's distance and direction from the bullseye, and record the information somewhere on the target. Do this for all of the targets. If you have a called flyer, you should discount that shot, or replace it in the group if you have an additional round loaded with that charge.

15. You will now look for the three groups which come the closest to hitting the same POI (point of impact) on the targets. The trend of the groups should be obvious, normally going from low and favoring one side, to high and favoring the other side. But along the progression, there should be a string of at least three groups that all hit the target in the same relative point.

16. After you have carefully measured group sizes and distances and directions from the bullseye, you will know which three groups come the closest to hitting the target in the same POI. You now choose the powder charge which represents the center of this string. For example, if 34.7, 35.0, and 35.3 grains all grouped about 1.5 inches high, and about 3/4 of an inch right of the bullseye, you would choose the 35.0 grain charge as your OCW (optimal charge weight). This charge will allow 34.7 and 35.3 grain charges to group right with it. This will be a very "pressure tolerant" or "resilient" load.

17. Remember, don't get "bowled over" by a tiny group which falls outside the OCW zone. You can tune any of the groups to be tiny with bullet seating depth changes. After you have determined the OCW, you may want to try seating the bullets deeper or longer in .010" increments to see where your particular rifle does its best. I have often found that OCW recipes are so reliable that seating depth alterations--especially for hunting cartridges--often don't seem necessary.

18. Your next step would be to confirm your load recipe at the maximum range you will expect to use it. Load one round about 1% below, and another round about 1% above the OCW charge, and fire a three shot group with these two charges plus the standard charge at the maximum range you will require the load to be accurate at. You should note MOA, or very close to MOA grouping...

19. The OCW load development plan works best with rifles and shooters that are actually capable of MOA accuracy. If your rifle has not shown a propensity for reasonable accuracy, you may want to have it corrected before wasting time and material with additional load developement. If you are not confident that you are at a level where you can shoot consistent MOA groups, you may want to hold off on intricate load development until your skills are better honed. Lots of practice with a scoped .22 LR is invaluable...

20. I would sincerely recommend using shooting glasses during the firing sequences of ANY load testing. You can never be too careful here... And please know that anytime you embark on load development, you're basically on your own. Just like any provider of load data or development instructions, I must mention that I accept no responsibility whatsoever for any occurrences which are outside the realm of your expectations...

 

[Darkhorse]

I got distracted by "OCW". I actually paid little attention to that initially and my original post really had little to do with that.
What I was really referring to is the very good explanation of how small changes in bullet seating depths can make big differences in group size due to approaching and finding the "Node". Simply because many hand loaders don't have a good understanding of this aspect and I thought the explanation given was a good one.
The only reason I searched for an accurate powder charge in the first place was because I was unsure of the condition or accuracy of my barrel as I had shot it extensively in the past. I was planning on a new barrel if this one did not shoot to my satisfaction. It did with the right loads so it stays.
Now on to the next objective, as this is a hunting rifle I wanted to develop a accurate load at 63. gr. IMR 4350, the max. load according to Nosler with the 150 gr. 7mm BT.
I'm getting there.
If I was a target or varmint shooter then finding the OCW may have value, but for my purposes I can't imagine any, and I don't intend to dwell on it. For my purposes I want to choose or work up a load via pressure testing, then by adjusting the seating depth fine tune it for optimal accuracy.

 

[truck driver]

Thanks for posting this. It answers a lot of questions. I never got too deep on the tech end of reloading just read a lot and tried different things to find something that worked with out really knowing why it did.
Don't remember where I read this but I have always used a powder that best filled the case, gave maximum printed velocity and allowed me to seat the bullet at caliber depth. I would play with the powder charge at near max until I found a charge that would give the most consistent accuracy.
It may have been in one off the old spiral ring Lyman manuals from the 1960's or a powder guide that the manufactures put out that were free in all the gun shops that sold reloading supplies.
Been reloading since I was 12 and now at 65 I'm just understanding what I have been doing all these years with out blowing my head off. :lol:

 

[joelkdouglas]

I'm torn between adjusting powders, powder charge, seating depth, primer type, brass, etc. and just picking a good powder for the charge weight, work up to a near max charge, put the bullet 0.03 off the lands, and go shoot. I'm not saying OCW doesn't work, but I've had several instances I've abandoned working up a load and taken up approach #2 with better results.

 

[barthowes]

my method is to load all cartridge's to 0.010 off the lands and vary powder charges. I take the max charge and load it and five loads below it with charge increments of 0.5g. I Always shoot the lowest charged load and work up. I see which load give me the best accuracy and adjust the seating depth to tune it IF I'm not happy with the results.. generally I don't have to as i have not had a load not be 0.5" - 0.75".. I found my savage 110 and RL-17 will shoot the exact same charge in both a barnes 168 TTSX and Nosler 168 BT into the same POI.. Different seating depth's as barnes like a 0.035 jump and BT are .010"..