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My Brain hurts....

 
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  #8  
Old 11-21-2010, 02:59 PM
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Join Date: Oct 2009
Location: Thunder Basin, WY
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Re: My Brain hurts....

Quote:
Originally Posted by ZombieHitman View Post
Ok, I've heard the term vertical stringing, but I don't understand what it means or what I am looking for to identify it.

On throat gauging, is there a basic rule of thumb I can start with?
Vertical stringing has different meanings to different types of shooters. What I mean is: A competetive benchrest shooter would probably call a 1/3 or 1/2 moa group that was mostly vertical.........vertical stringing. A long range hunter would probably call that same 1/3 or 1/2 moa group.............good to go, because 1/2 minute or less is plenty good enough for most long range hunting, especially on big game.

Guys that are trying to hit very small targets ie prarie dogs or such at distances beyond 600 yds require better than 1/2 moa to make consistant hits.

You can get an idea of how much vertical you'd see in long range groups by chronographing the loads that you're shooting at 100 or 200 yds. If there is a large amount of "extreme spread", the groups will have alot of vertical dispersion at long range.

Throat Gauging; I recommend the RCBS Precision Micrometer. They make one for most factory cartridges, they are not expensive, they will help you gauge your throat and set up your loading dies, they will give you an idea of the headspace in your gun too. Very good little tool, I've been using them for around 15 years or so on my factory guns.

I start my load development (when possible) by seating the bullets .000" to .010" back from engaging the rifleing (using the Prec Mic to get this info).
I do not seat bullets "jammed" into the rifleing. I did once upon a time, and ended up leaving a bullet in the throat when I unloaded the gun and ejected the case. Left 36 grains of H380 powder in every crack and crevice in my rifle action.....bolt wouldn't even close after that........ruined my day and took alot of time to get it cleaned out!!!!

If I change my seating depth, I only have to move it back out farther. Don't usually have to reduce powder charge because of moving bullets back, but sometimes do when moving bullets out. Another reason for starting close to the rifleing and working up with powder charges.

Good luck to ya!
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  #9  
Old 11-21-2010, 08:26 PM
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Join Date: Nov 2010
Posts: 36
Re: My Brain hurts....

Ok gang, I think I have some new concepts to apply here, in my endeavor to grow into the finest shooter and handloader I can be!

First, my thoughts for my rifle:
After rooting around for a sound starting point for my load development, I think I'll be going with, excerpted from the Sierra Load Map...
IMR 4064 - 39.7gr
F210m
168 SMK
2.800" COAL.
I have had a lot of success across the board with 165-168 grain projectiles, and use them in multiple rifles. It seems to make sense. I haven yet to decide whether or not I will lighten the load slightly, say a grain or two. I'm still pondering the pros and cons in my head. If anyone has input on this concept, I am all ears.
I'll be making up 100 rounds for the initial break in. My current break in plan is:
25 rounds - swab bore after each shot.
50 rounds - swab every 5th shot
25 rounds - swab after the fact, zero the scope, and get the full feel of the trigger.

A good cleaning and lubing job will be done once I get the bore guide.
I have a Dewey Nylon coated one piece I adore, with the brass jag & nylon bore brush. It serves me very well, and I keep it religiously clean, and in it's protective tube. I read someplace that crud gets into the coating on some of these rods, which can abrade the bore while cleaning, so I do what I can to prevent it.

I found someone who has a chrony, and once I've gotten past the break in and start really developing the loads for this rifle, we'll see about that vertical stringing thing. Hopefully I can understand it a little better by then, what causes it, how to identify it on paper, and solutions in dealing with it. I suspect it has something to do with pressure variations in each load, as that's the only thing I can conceive of that would be indicated by impacts lining up vertically.

I've ordered Lapua brass and a neck turning tool and related bushing die (backordered) Forster Hand Held Outside Neck Turner - MidwayUSA
The reviews on it are very good, and I keep hearing the Forster name. Figured it was a sound decision, even with Lapua brass being very consistent.

Ordered some Cerrosafe too, as I'd like a true method of understanding the chamber and throat, and the 3 gunsmiths I spoke with each recommended this method. I figure this will assist me greatly in getting myself dialed in as quickly and easily as I possibly can.

I also found a range nearby that has a 500 yard line...that I can drive my truck out to post targets. Happy....

More to follow....

Last edited by ZombieHitman; 11-21-2010 at 08:33 PM.
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  #10  
Old 11-22-2010, 07:07 AM
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Join Date: Feb 2008
Location: IOWA
Posts: 1,894
Re: My Brain hurts....

biggreen's post is right on. I would add that the first thing I would do is find your top end of pressure for your powder charge, then back off and work on your load developement. Need to use a chrony if you have one.
175gr SMK seems to be a popular bullet for the 308 for target., and out to 1000yards. If you are not going to shoot that far, the 168's will take you to about 800yards. I would look at shooting Nosler AB for hunting , or maybe even Barnes.
Since this is a factory barrel, I would not spend forever on barrel breakin, just shoot it and clean it and you will be fine. It wil break in on its own with some rounds down range. I would not bother with 100 rounds to do barrel breakin.
If you are going to shoot this rifle past 500yards, there might be some benefit to cleaning up the necks, or spend alittle more and buy Lapua brass for the 308.
As far as powder, I strickly use Hodgdon extreme powders as I don't want velocity changes due to temperature changes.
I use Forester dies. I would recommend a bushing die so you can partially resize the neck when reloading, leaving a small part by the neck/shoulder area unsized. This will help center your loaded round in the chamber.

There are better ways to measure your chamber length and ogive measurements than using cerrosafe on the chamber.
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