Establishing the best jump to the lands


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Andrew Leigh
February 11, 2013, 08:21 AM
Could you long range accuracy boys share some tips with me please.

I suppose this is a chicken and egg scenario. Although a reloader hunter I do like time on the range getting better groups. Currently I use the OCW method of establishing a load but I have not idea of how to tie that into the correct jump.

I shoot 180gr. Accubonds as well as 180gr. SGK's. The former off a 0.03" jump and the latter of a 0.09" jump. They both shoot about the same groups, perhaps the SGK's have the edge. I get about 0.75MOA.

So, do I get me my accuracy node from the OCW method and then play with the jump? If so do I need to drop the load as I get closer to the lands or do I simply shoot over a Chrony and check for signs of pressure.

What are the signs to check for with regarding to seating depth?

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Andrew Leigh
February 12, 2013, 01:25 AM
Should this be in the reloading section to get a response, just thought you competiton boys are more attuned to accuracy and would have a better idea?

rcmodel
February 12, 2013, 01:45 AM
How good does it shoot with factory Match loads?

They don't give a darn where the lands are.

If you can make more accurate reloads then Factory Match ammo already?

Then it's time to worry about it.

rc

Andrew Leigh
February 12, 2013, 04:10 AM
Only shot with own loads. Will buy a box of factory match ammo and see what the benchmark is, it may be that I cannot shoot well enough to exploit any accuracy improvements, perhaps the box of match ammo will prove the point.

Never thought about it that way, thanks for the advice.

savanahsdad
February 12, 2013, 04:51 AM
I run a latter test, starting low and work up a 1/2 grain at a time to find the Sweet spot for that gun , letting it cool shoot to shoot then run test again , find the smallest group in both tests, (should be the same __Gr) this is done with a jump of .020 ,I then load up a few more at that __Gr with jumps of .025 , .030, .015 , .010, if my groups stay the same then I leave it at .020, I have had better groups with less jump but had high PSI (hard bolt lift ) I then backed off the charge 1/2 gr and backed off jump .005 , how ever most of my guns get there best groups well below max,

in other words load up a bunch of ammo try this and that and keep lots of notes
alsol you might want to get "Advance Handloading Beyond the basics" on DVD it's put together by Handloader Magizne , Sierra and Redding

cacoltguy
February 12, 2013, 06:08 AM
While I'm not too familiar with the OCW method, I would do all of my load testing that revolves around powder charges first with bullets seated to magazine or factory spec OAL. Once I got this down then I would mess with the bullet seating depth to see if I could improve anything. As long as the bullets are seated off of (not touching) the lands, you shouldn't really see any pressure spikes caused by seating depth. If you are seating the bullets long and jamming them into the lands then yes, this could cause pressure spikes that need to be accounted for during load testing. Some secant-ogive bullets like Berger VLD's reportedly shoot better touching or jammed into the lands and guys will develop powder loads with this as a starting OAL. Howver, I seriously doubt there is any good reason to jam a strictly hunting, tangent-ogive bullet like a Sierra Gameking into the lands. (Never actually tried though so I guess I could be wrong) Personally I wouldn't seat any of them touching the lands in order to avoid this problem of pressure spikes and further confusing your load development. Once you get your winning powder charge just shoot groups of five starting from magazine length to .02 or so from the lands (in whatever increments you see fit) and see what you get. Of course in order to precisely know where your lands are you need a tool like a Hornady overall length gauge or something similar

Andrew Leigh
February 12, 2013, 06:42 AM
Thanks for that.

I know it is hunting rounds but one never knows where shooting will take one. I may end up punching paper seriously and therefore would like to have the disciplines correct.

I can establish if the bullets has a secant or tangent ogive?

Andrew Leigh
February 12, 2013, 09:50 AM
Google is my friend, got the info thanks.

kludge
February 12, 2013, 12:02 PM
When using a new bullet, I start with my .308 loads 0.015-0.020" off the lands. In my Savage 110FP my COL ends up at 2.900" when I'm 0.015" off the lands with the 168 SMK. Then I do a ladder test or a OCW test. After I choose a load and get that dialed in I can start messing with seating depth. Most times I don't mess with it. If I do I move in 0.005" increments (seat deeper into the case) to see if I can find an optimal seating depth - all the while keeping an eye on pressure.

The other way to do it is to start at listed COL (2.800" for the .308) and move out until you get to 0.015" off the lands and then you don't have to worry about pressure (unless you jam the bullet, then you REALLY have to worry about pressure).

In my rifle, that would take 18 different loads times 5 shots per group, that's a lot of bullets and powder and time. Hence, most of the time I don't bother.

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