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Help with velocity variance

 
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  #15  
Old 12-31-2010, 12:06 AM
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Join Date: Oct 2008
Location: Bryan, Tx
Posts: 284
Re: Help with velocity variance

+1 on the science. Haven't seen a single post listing p values, correlations, or even appropriate controls. Just gut feelings heavily defended as proof... Both types of info are helpful, but you just have to take everything with lots of interpretation. So easy to get lost in the details though. We all just love to feed those obsessive compulsive tendancies though. Want help with statistical design? Give me a shout.

Forget about 90% of these details and focus on reading the wind... you'll get more hits IMHO.
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  #16  
Old 01-01-2011, 01:01 PM
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Join Date: Mar 2006
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Re: Help with velocity variance

+ 1
The crony is too close
15 ft is. about right
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  #17  
Old 01-02-2011, 03:30 AM
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Join Date: Sep 2010
Location: So. California
Posts: 409
Re: Help with velocity variance

Another thing you may want to think about is that Most electronic scales are pure junk. Yeah, those are fighting words, but I will maintain that *MOST* of the damn things really are pure junk! You are damn lucky to get +- .2gr definition out of even "The Best". Unless of course you have a straight up laboratory grade electronic scale, and you calibrate it every time, and you let it warm up for the prerequisite length of time ... I bought an electronic scale, and very quickly found by measuring the same throws in my RCBS and my Redding balance beam scales that that electronic scale was *CRAP*. Now, I have read about some really Serious laboratory grade scales that are just about the best you can get. But those cost some serious money.

Also, I agree with the 15' from the muzzle assessment.

There are quite a few "little tricks" to getting Really GOOD match grade ammo loaded up. Once you learn them, you will quickly see your vertical spread decrease out past 500 or so. At that point, the wind starts to kick your butt horizontal!

1: Start out with good brass.
a) Measure neck thickness around the neck. What you want as an Ideal, is the exact same thickness all the way around. You will most likely have to at least lightly neck turn either the outside or the inside of the neck. I prefer the outside trim, but the inside trim has the benefit of removing "the doughnut". My forester trimmer has an attachment that allows me to outside neck turn.
2: Now, take some 91% Alcohol and measure by weight in grains the internal volume of all of your cases. The less variance here the better!! This is a step 80% of most folks never even consider.
3: The less messing around with the flash hole you do, The Better! Do Not Screw with the Flash Hole, unless there is an obvious Burr!!!!!! More people screw up perfectly good brass Right HERE, than in nearly any other step. Less truly is more. If you have a piece of brass with an off center hole, set it aside for either plinking, or for bore fouling ect.
4: I use Lee case lube. It is a white paste. I lube the inside of the neck, as well as the outside of the case. It is important that what ever lube you use, Not Contaminate your powder, create excessive bolt thrust, or mess with neck tension in a manner that lessens consistency. Even though taking a towel after my resizing operation, and cleaning off the leftover lube is a bit of a pain, it is very easy to determine when all of it is off. No White ( think about how dried car wax looks ) you are gtg. What little is left in the neck, I leave there. It does not seem to mess with ES at all. My go to loads are routinely less that 10fps, usually right around 3-5fps.
5: You should consider Neck Annealing after every 3 shots. Trust me, it matters a lot. When brass "Work Hardens" it gets springy. When that happens, it messes with neck tension big time. That destroys load consistency.
6: Neck Bumping by 1 or 2 thousandths is almost always a good idea. Also, if you run loads that are hot, or borderline hot, it is a good idea to set up your bump to partially or full length resize. What I mean is, you need to measure the web of your brass for expansion. If it is excessive, then when you go to resize the brass, instead of a pure neck size you should size farther down to bring the body / web size back down to an acceptable diameter. This too is a common misconception: "Once brass is fire formed for your chamber, it is perfect. Never full length resize again." WRONG!! Or at least, Not entirely correct! If your loads are "mild" enough to not excessively stretch your brass at the web/body area, then neck sizing is perfectly fine. But even a relatively "mild mannered" load, can become Too Hot depending on the type of powder ( it's temperature sensitivity ), and the ambient temperature / temperature of your loaded ammo at time of ignition. Suddenly, your "Good Load" has stressed your brass more than you realize. It happens. Read up on how to Shoulder Bump. They even make special dies just for that purpose if you look hard enough.

The Redding Type S dies are considered by most to be just about the best die out there. There are other things you can do if you are just Deadly Serious, but these should get you in the ball park. Personally I like H4350, H4831sc, H1000, Varget, IMR8208XBR, and RL15 powders for the biggest part of my reloading. The Varget, RL15, and IMR8208XBR overlap a lot, but I have a couple RL15 loads, and a couple Varget loads I just refuse to give up! The IMR is a "New Kid" on the block that I have recently started to play with. I have had some pretty good preliminary luck with it in light bullet 308: 135smk and 155smk. The 135smk is pretty nice for around 300-500 yards!

Good shooting,
Gary
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  #18  
Old 01-02-2011, 12:12 PM
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Join Date: Apr 2010
Location: NW Mt.
Posts: 600
Re: Help with velocity variance

Quote:
Originally Posted by cowboy View Post
Couldn't agree more with SBruce's statement. I like to place my chrony at 20'0" from the muzzle. You can easily then go to a ballistic calc. and back up to get your muzzle velocity. How sturdy is your tripod - any movement at all raises he**. Never noticed where you are from but was there any snow cover under your chrony? This at times has given me readings on a tried and true load where I was getting really poor ES etc. Solved that by laying a tarp down when we have snow.
Keep digging and when you get all the answers it'll be just in time to be able to tell them to your great great grandkids. Fun sport isn't it. Good luck.
This is an interesting bit of info. I had trouble with es the last two times out. Lot's
of snow.
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