Standard Deviation Problems.... Help!

[ducks-and-bucks]

I'm having problems keeping a tight, close standard deviation. Last chrono shoot I had six different loads, lowest SD being 25 fps, and highest SD being 70 fps. I cant understand what I am doing wrong or not doing at all... each piece of brass is ran through the re-sizer, then I measured them with a case gauge to make sure the case specifications are correct.... each load of powder is the same amount, same bullets, same primers....

I have weighed my brass and all vary within a grain and a half of each other. Many that are within .1 or .2 of a grain from each other.... I've weighed bullets, each usually weighs the same.

Problems I can foresee:

I CAN feel different neck tensions in cases when seating bullets, some are tighter than others when the bullets is seated, others seem to go in with more ease, and then I have the happy medium between them all. Then the other thing I had in mind was when I ream the case mouths to get a little the angle on it, that it's very possible I take off a pinch more or a pinch less when running the brass over the case prep center. Though I only ream the neck to get the angle once on each piece of brass because it usually holds up after that... (until I have to trim the neck mouths, then I would ream them again...) Other factor can be a tad of case resizing lube getting in the mouth of different cases when resizing, that would allow the bullet to be seated with more ease.. I have notice powder sticking in the neck sometimes.. Anyone follow? What do I need to do to get tighter Standard Deviations?

 

[BigDMT]

It's your neck tension or a dirty barrel. If getting varying neck tension, It's definitely time to anneal your cases.

Might have some copper fouling too. Have you bore scoped your barrel?

I'd bet it's one of those two things....

If it ain't one of those, you'll just have to try different loads. But remember, LOW SD's DO NOT ALWAYS EQUAL TOP NOTCH CONSISTENT ACCURACY. Sometimes it makes a load better, sometimes a big SD doesn't seem to effect accuracy at all. So don't get too bent out of shape over SD's if the load is consistently accurate at the range you are shooting. Consistent accuracy is what really matters

 

[mac86951]

Its also possible that you are out of an accuracy node for your rifle. Have you done testing +/- 1-2% to see how the deviation performs? Also possible its flash-hole/primer pocket uniformity, try another primer?

I've seen SD change drastically by the following:
Ladder testing
Flash Hole Uniforming (my reference is .223 remington)
Federal/Remington Primers (different lots)
Case Lube (I now use Hornady one-shot spray as I have a decent method for application)
Case Cleaning (do you run a brass brush into case after deburring/chamfering?)
Primer Seating (goes with primer pocket uniforming).

The list above is in relative sequence for what I found was the most drastic changes. Example: 23.7gr of Varget was SD of 70fps for me, however, with ladder testing 23.2-23.6 were very close, so using 23.5gr my SD jumped from 70fps, to 13fps with no other intentional changes (always important to look for unintentional changes too). Velocity, this was a change from average 2690 to 2660 (IE not much).

-Mac

 

[Immike]

The paper is a better judge than the machine. Mike

 

[timeout]

There are a lot of unknowns here. I am wondering for example how and with what are you weighing the charges. I am guessing that your case prep in the neck area especially, is not conducive to consistent neck tension. I am no expert, but I would believe that your handloading practices are about where mine were a year ago. I agree that the holes on the target are what counts. The best thing would be for you to find a mentor in your area and have them go through their loading routine with you. There is a discussion about neck tension here: http://forum.accurateshooter.com/index.php?topic=3801711.0

 

[BigDMT]

I'm still developing loads for this rifle, but I mean even a tighter group that isnt horrible has a big SD. I mean if its shooting groups, I dont care about the SD, but in a perfect world I'd like to have every load pretty close to the same fps.

Wait, wait, wait, wait!!!!....Before we get too far here fellas, lets back up a bit and ask the most important question first.

Is this a custom rifle with a custom hand lapped premium barrel? Or is this a factory rifle with a factory barrel?

If it's a factory rifle with unlapped "hack saw" cut or hammer forged rifling, you can pretty much forget about tight SD's.

If it is a custom rifle with a premium hand lapped barrel, ie; Krieger, Brux Obermeyer, Bartlein, Lilja, Pac-Nor. McGowen, etc... Did you conduct a proper barrel break in? If it is a custom and had a proper break-in, then lets continue

 

[savagedasher]

Try different primers. SD doesn't mean much at 300 yd or less. 75fps at 1000 yd the game changes.If your using more then 45 grains of powder and in cold weather try hotter primers.
Good Shooting Larry

 

[Terry]

How about more to go on.

Gun/Barrel/etc.

Cartridge/Powder/etc.

 

[savageshooter86]

maybe need to anneal the cases to get more consistent neck tension and shoulder bump?

 

[bozo699]

Ducks,
There are to many varibles here and the guy's have answered most of them but what no one has touched on is your chronograph and how are you using it and what are the weather conditions? Is it partly cloudy out? is it real sunny out? was it one way one day and another the next day? was it exactly the same distance from the muzzle, is your cases all from the same head stamp" you definitely have neck tension issues, if you know some of them have lube in them why haven't you wiped them out,..Brandon mentioned copper fouling, that can make a difference but not nearly as much over the Chronograph as carbon fouling in the throat, have you checked for carbon? is it a factory barrel? and what kind of powder scale are you using? what kind of powder/primer combo are you using? I can ask about 300 more questions that could have something to do with SD but answer these first please.
Wayne.

 

[XTR]

If it's a good barrel I'd bet on neck tension. If it's brass with more than 2 or 3 firings on it start thinking about annealing

The other neck tension variables you can eliminate by either turning and using bushing dies or for those that don't need .1s you can use a Lee Collet sizer, they are great.

One other thing, if you are shooting to 1000 yards then 25 FPS means 8 to 10 inches on the target, at 500 yards it's about an inch, so depending on your application does it really matter?

 

[bozo699]

Changing up primers to see what happens sounds like a good step. By no means am I a pro at reloading, I've been doing it for only 2.5 years now, still learn every day. I tried CCI 450 primers from the CCI BR4 to have a little bit hotter primer due to the small dense case capacity of the grendel brass. But, I can not tell much of a difference.

Okay well there isn't much difference in those to primers component wise also Besides what Tom told you about what to do you already admitted to having neck tention problems so you need to take care of that first by replacing, annealing or at least sorting them by force needed to seat the bullets, I think if you do this and do what Tom suggested you will see a difference right away then play with primer/powder combo's and you will dial it in, again on the Chronograph you have to set it up the same and if it is partly sunny and partly cloudy and tha clouds are moving your chrono readings will be all over the place, they work by bending light so I need to say no more about that,.,.right?...best of luck to you.
Wayne.

 

[BoydAllen]

Sort by the amount of force that it takes to seat bullets, and chronograph each group. Let us know what you get.

 

[bozo699]

Ducks,
If you take advice from anyone Tom and Boyd Allen are the two to get it from, both great guy's and both extremely knowledgeable.
Wayne.

 

[bozo699]

Ducks,
When Boyd speaks it's from experience,... he has never steered me wrong, we have had hour after hour phone calls. As far as your other post I do not believe in neck sizing that is a old school short range br idea and most of those guy's fl size now, however you can make very good ammo with a redding body die and the lee neck collet die, I learned that trick from Boyd
Wayne.

P.S I forgot about it being a ar platform,..well in that case you HAVE!! to f/l resize everytime! so it will feed reliably.

 

[BoydAllen]

Standard, one piece FL dies over size the neck, and then the pull that the expander ball being pulled back through the neck is so great that the case gives a little at the shoulder...unevenly, cocking the neck. I do not load for an AR, but I do know that they require more room all around the case to function reliably with loads of normal pressure.

A friend has a Grendel, and he has had his share of trouble trying to get the accuracy that he expected out of it, in spite of it having a match grade barrel and having been built by Alexander Arms. It seems to me that this case is a bit small to be a good choice for 1,000 yard work, despite the published numbers. Long range shooters have found that annealing helps their ES and SD, but with a semiautomatic, I would think that you would have to be careful not to soften the cases too much. I would be touchy, and there is a lot of bad annealing advice on the internet. My friend has learned how to do a good job of annealing, and the result has been much more consistent seating force and accuracy, but he has only tried it on his bolt guns.

 

[300 RUM]

I shot an AR-10 (Armalite)Custom barrel chambered myself. The rifle will stack them on top of them selves at 200 yards less then 1/4 MOA if I do my part. Most experienced shooters know there are many causes for "bad groups" but one lesson I learned over the years is how important neck tension is, flash hole uniformity and bullet seating depth. With new brass regardless of make one must due their part in brass prep. So when I have done my part I see a SD between 7-12, when the brass starts to go bad I can see it rise fast, a load that starts off at 7-12 that goes to 20-30 means it's time to anneal and then it goes back to 7-12 for SD. When starting off with a high SD look at every thing especially seating depth and the flash hole, make sure the barrel is completely clean and free of copper build up and so on.

An AR can have problems that a bolt gun will not have, one thing I would check is head space, your single loading but it is still an AR so shoulder bump should be somewhere around .0015-.002. Shoulder bump that is excessive .0025-.005 or more will cause a high SD in an AR also. It took a lot of learning by trail and error to figure the AR out, but today I can build them to shoot less then a 1/4 MOA. The ammo you feed your AR needs to be twice the ammo you feed a bolt gun.

 

[BoydAllen]

Seldom do I read such high quality advice. I will read it twice, and pass it on to my friend.

 

[brian427cobra]

Get yourself a super accurate scale, I'm not talking a Chargemaster, something that will consistently weigh charges to the kernel, I use a Gen 2 Prometheus, my SD/ES is less than 10fps, I don't weigh brass, I don't weigh bullets, I only use Winchester brass that I skim the necks to .0135, uniform the pockets, debur the flash holes, and anneal every 2-3 firings, when I switched from my Chargemaster to the Gen 2 my vertical at 1000 cut in half, it has since gotten even smaller.

 

[jo191145]

If you see powder sticking to the necks you still have lube inside. Some will be lubed more than others. Chances of finding accuracy or low SD under those conditions are slim to none.
If your die requires an expander ball switch to Imperial Graphite dry lube for the neck I'ds.
Its a PIA but its the best method for consistent seating pressures.

Basically you need to lube the neck interior with graphite. Clean off the outside with rag.
Do about 50 then use whatever lube you normally use for FL sizing making sure to get none in the neck.
Clean off lube from outside and they're ready to go. No need to clean the dry lube from inside.

As I said a real PIA. Especially for a semi which uses lots of ammo ;D
You would need to clean that expander ball and die real good before trying.
Bushing dies are the best. No interior lube required.