Getting your SDs down.
- Thread starter Longshot
- Start date
What are SDs???
Here is a good article on brass prep:
http://www.6mmbr.com/jgcaseprep.html
After that, if SD matters (typically only at ranges past 300 yards), pick the right powder and weigh your charges. Note that short-range (<=300) benchrest shooters usually don't weigh charges.
Great read thanks, I've been hunting, shooting and reloading for many years but now want to try some real accuracy just for fun not competition.
That seems like a lot of work but I guess you have to put in the time to get the best results.
Cheers
There is a fair bit of debate about what parts of prep matter, especially when putting the round in a sloppy, possibly off-axis rough-cut factory chamber. Match chambers are a different beast. Measuring your fired brass will give you some idea of what you are working with.
Having said that, the steps are done once only (maybe the donut comes out more than once, depends on your case growth - donut removal may never be needed) and don't take that long with limited volume.
Also, the headspace thing can be done less expensively with a case gauge, e.g., http://www.sinclairintl.com/.aspx/pid=33287/Product/Wilson-Case-Gauge - drop the case in, measure distance to base with calibers, size, re-measure. The difference is the amount of "bump".
Barnes_270
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From the context I'd say standard deviations - in layman's terms, the OP is interested in reducing variation between loaded rounds to as small a value as possible.
If you really want very straight and consistent ammunition, get a set of Wilson dies and an arbor press.
If you have an off the shelf factory chamber, there can be all sorts of problems, that straigh ammunition will never cure. Most factory reamers, aren't piloted.
Get your bbl set back and a new, tight chamber recut. One that ideally you have to turn down the necks of your cases to fit.
A Palma Match chamber is about as loose as I would go.
The Wilson dies, are dead true. Less than a thousandth of an inch of perceived run out, in many cases.
This process isn't fast by any means but it's fast enough for bench rest shooters to load up 20 or so rounds between sets.
The guns I shoot all have custom barrels. I have two Bartlein's and Rock 5r. They were all cut with virgin piloted reamers.
I do weigh all charges also.I am Fl resizing so I wonder how much diff that would make. The loads I shoot are easy on brass anyways. The runout I'm getting is generally 2 thou or less and I'm happy with that.
I am not turning necks but I cant see that making THAT much difference.
Do you guys find different neck tensions helps?
My bullets are pointed and when I'm heading out to a match the meplats are also trimmed.
The powders I use are optimum for those calibers.
Just wondering if anyone has any other tricks they might share.
I do weigh all charges also.I am Fl resizing so I wonder how much diff that would make. The loads I shoot are easy on brass anyways. The runout I'm getting is generally 2 thou or less and I'm happy with that.
I am not turning necks but I cant see that making THAT much difference.
Do you guys find different neck tensions helps?
My bullets are pointed and when I'm heading out to a match the meplats are also trimmed.
The powders I use are optimum for those calibers.
Just wondering if anyone has any other tricks they might share.
1+2) try an 80% skim turn - you may see your runouts get better. Or not, but it has helped me (Lapua brass, .223, 80% skim, average .0013" and sd of .0005, measured on the beginning of the ogive).
3) yes, both in runout and SD. if you neck-turn, you can set neck tension with bushings. try .001 up and down from where you are now.
Consistency in charge weight is of course necessary. And primer selection can make a difference. However, many of the issues that cause high SDs are found in the neck area of the case.
You should be able to drop a bullet into a fired case. It should fall freely into the case. If it doesn't, where is the resistance? If it's at the mouth of the case, then you aren't removing your burrs completely. If it is at the base of the neck, you likely have donuts (yes, you can even get them in 308 Win.) or a mismatch between neck wall thickness and your chamber. Neck turning solves that. Neck turning will NOT make a significant difference in SDs if there isn't any interference when you're using quality brass like Lapua. Three is zero difference in SD between my cases with turned and un-turned necks.
Make sure than the inside of the neck is polished and completely free of carbon. I just turn a bronze brush in then a few times. If the inside of the necks on that lot of brass still look rough after that, I will put some 0000 steel wool on the brush and spin it in a drill. Several of my friends who are winning precision and F-class matches also so this.
I also swab my cases out with a bore swab. This gets out the junk that's fallen inside, including any lube. This also leaves a residual amount of lube in the necks, which also helps keep the SDs down. Interestingly, a buddy of mine in the US bought some of Bryan Lits's ammo and tooks some of the rounds down. The necks appeared to have been intentionally lubed. I know some guess that use Imperial dry neck lube.
You should be able to drop a bullet into a fired case. It should fall freely into the case. If it doesn't, where is the resistance? If it's at the mouth of the case, then you aren't removing your burrs completely. If it is at the base of the neck, you likely have donuts (yes, you can even get them in 308 Win.) or a mismatch between neck wall thickness and your chamber. Neck turning solves that. Neck turning will NOT make a significant difference in SDs if there isn't any interference when you're using quality brass like Lapua. Three is zero difference in SD between my cases with turned and un-turned necks.
Make sure than the inside of the neck is polished and completely free of carbon. I just turn a bronze brush in then a few times. If the inside of the necks on that lot of brass still look rough after that, I will put some 0000 steel wool on the brush and spin it in a drill. Several of my friends who are winning precision and F-class matches also so this.
I also swab my cases out with a bore swab. This gets out the junk that's fallen inside, including any lube. This also leaves a residual amount of lube in the necks, which also helps keep the SDs down. Interestingly, a buddy of mine in the US bought some of Bryan Lits's ammo and tooks some of the rounds down. The necks appeared to have been intentionally lubed. I know some guess that use Imperial dry neck lube.
