Is the accuracy of your rifles this sensitive to charge?


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Crazy Fingers
September 9, 2008, 11:24 PM
Sunday I was testing my .22-250, an RWS Model 89 (a Howa 1500). I have had some problems with factory ammunition in this rifle, none of it would shoot tighter than 2" at 100 yards, so it was time to start reloading.

I was shooting various charges of IMR 4895. Bullets were at 50 gr Hornaday V-Max. Most of the bullets were just barely touching the rifling.

All groups were shot at 50 yards (the longer ranges were flooded out), they were the longest distance between the center of any two shots of a five shot group. They were shot with a Lead Sled to attempt to get me out of the equation as much as possible.

35.7 gr = .903"
35.9 gr = .868"
36.1 gr = .181"
36.3 gr = 1.295"
36.5 gr = .868"

I just can't believe that it tightens up that much... does this happen frequently or is my rifle just super picky?

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Grumulkin
September 10, 2008, 07:26 AM
If you were to use EXACTLY the same powder charge, you would likely have a distribution of group sizes such as you got. The 0.181 in. group doesn't mean that the powder charge used was fantastic; only that you were lucky.

Increasing powder charges by 0.2 grain increments is a noble endeavor in a 22-250 but unnecessary. I would be starting with 1 grain increments and, when approaching a maximum load, by 0.5 grain increments (in a smaller case, smaller increments should be used). I would shoot 3 shot groups and said loads would give me an idea of the load range that would give the best accuracy.

Once I had zeroed in on the load range to use, I would load up a series of cartridges 0.5 grains apart in powder charge and test the load more extensively. Once I had determined where the best accuracy was to be obtained, I would shoot several groups with that load to make sure my results were real rather than luck.

I once shot a 0.5 inch 3 shot group at 100 yards with an M1 Garand with iron sites. I've never done that since and probably never will. It was luck and luck can happen to anyone.

Walkalong
September 10, 2008, 08:05 AM
Agreed. Now, if it does it again, and again, you really have something, but usually a .2 Gr difference is not that dramatic.

Dave P
September 10, 2008, 08:15 AM
but usually a .2 Gr difference is not that dramatic.


Which is why it is often silly to get carried away with expensive powder dispensers and digital scales accurate to .oooo2 grains!


I don't think 50 yards is giving you worthwhile feedback. Try 200-300 if you can. I would step at .5 grains to start with. And maybe 10 shot groups.

Walkalong
September 10, 2008, 01:49 PM
.2 grain difference, not variance. ;)

jwr747
September 10, 2008, 03:51 PM
I've talked to benchrest shooters about how picky they were on powder charges,and most say 2 tenths variation in charge weight is a "non-issue". jwr

ranger335v
September 10, 2008, 07:57 PM
"36.1 gr = .181" "I just can't believe that it tightens up that much... does this happen frequently or is my rifle just super picky?"

Don't believe it. And your rifle isn't all that picky, the group's a fluke. There is no way a .2 gr. charge difference can produce such a dramatic but valid decrease in group size.

We all get an occasional wallet group like your's that's much smaller than the norm. It's fun to see but it's a statistical anomaly, without meaning. On occasion, a small group of anything, even a 2 moa load can hit in a much smaller cluster, but if it cannot be consistantly repeated it's not valid.

NCsmitty
September 10, 2008, 08:12 PM
Were these single 5 shot groups of each or did you shoot several 5 shot groups of each loading? If it's single 5 shot groups, then that data and conclusion is nearly meaningless. A proper test would begin with 10, 5 shot groups of each and an average taken for comparison. That would be far more telling.

NCsmitty

dirtman
September 10, 2008, 11:46 PM
repeat - repeat- repeat...

or that group don't mean nothing...

Tarvis
September 11, 2008, 12:21 AM
repeat - repeat- repeat... or that group don't mean nothing...
There it is. Next topic ;). Longer ranges is a good idea as well.

Theoretically: If you figure that a given rifle will shoot, say 1 moa with certain ammo, it will shoot at most a 1 inch group at 100 yards. Now, if you shoot a 3 shot group and all 3 shots happen to be on the left side of that 1 inch "circle of accuracy" you have a fluke group of, say .3 which is not repeatable with any regularity.

30Cal
September 11, 2008, 01:15 PM
I think you need more data. On a side note, I would reject any load that was extremely sensitive to charge weight.

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