New accurate at 100 yards, wildly inaccurate at 200 yards

[joeb33050]

NEW ACCURATE AT 100 YARDS, WILDLY INACCURATE AT 200 YARDS
The Savage Striker pistol in 308 Winchester with Simmons 2-6 scope shoots averages of 5 5-shot groups at 100 yards of less than 2”.
The load is: 314299 bullet ~200 grains sized .312”, Lyman Super Moly lube, IMR4227, Rem. 2 1/2 LP primers, 2.790” OAL.
The Lyman 48th Reloading Handbook with 311299, an almost identical bullet, gives 21 grains of IMR4227 as a starting load and 29 grains as the maximum load. This is with a 24” barrel.
With 16 grains of IMR4227 the Striker shoots fine at 100 yards, and this was my favorite load.
I wanted a 200 yard zero, there’s no 200-yard range near home in FL, and so I brought the pistol and some reloading stuff up to Massachusetts. At Old Colony, at 200 yards, I didn’t hit a ~2’ X2’ target once in 20 shots at 200 yards. I had a pal watch as I shot at a rock, and the bullets were hitting all over the place. We guessed that it was shooting into maybe six feet.
On 8/11/09, 18 and 20-grain loads of IMR4227 were shot. Both shot reasonably good 200-yard groups, and will also shoot less than 2” at 100 yards.
18/IMR4227 shoots ~ 18.5” low at 200 yards.
20/IMR4227 shoots ~ 14.75” low at 200 yards.
I’ve read and thought that the bullet RPMs diminish only slightly over the bullet’s travel. If this is true, then the wild 200-yard shooting must be because velocity falls to below some critical velocity, or because the bullets go below the speed of sound between 100 and 200 yards.
When I got back to Florida I tested lower loads of IMR4227 at 100 yards, to see if I could make the bullets fly wildly inaccurately at this shorter range.
No scope elevation changes were made after 8/11/09 in Massachusetts.
Here are the results of the testing:
Quickload MV data thanks to John Bischoff

Elevation fps Group”
21 +1.375” 1468 1.95
20 0 1410 2.35
19 0 1350 2.45
18 1290 2.176
17 1229 2.019
16 -1.4” 1167 1.96
15 -1.625 1104 1.8
14 -1.5 1041 2.3
13 -.75 978 2.03
12 -1.375” 914 1.825
11 -.75” 850 2.6
10 -1.5” 787 2.7
9 -3.5” 724 2.1
8 -7” 662 2.35
7 -11.75” 602 2.7
6 -16” 544 4.3


“Elevation” is the location of the group center with respect to the target center.
“Group” “ is the average of all groups shot, minimum of 2.
All group size measurements with a plastic 1/10” graduated plastic scale, readable in .025” increments.
Conclusions:
Reasonable group sizes result with velocities unreasonably low.
This 10” twist barrel provides sufficient rpm to stabilize 1.2” long bullets at unreasonably low velocities. No key holing or greatly elongated holes were found down to 544 fps. Velocity has little effect on stability in this region.
The Creighton Audette Ladder Testing effect was noted as velocities increased from 544 to 724 fps. Above 724 fps to 1468 fps groups stayed +/- 1.5” elevation.

I can't make the groups wild at 100 yards with any load or figure out what's happening between 100 and 200 yards with 16/IMR4227.

joe b.

[JSnover]

My guess is the same as yours. As the boolits fall into the transonic range they destabilize. Notice from 1350 to 1468 fps the groups start to shrink. Try a little more speed to keep them supersonic at the 200 yard line.

[44man]

I don't think the boolit is spinning fast enough to stay stable. Outside influences at range are effecting it too much. I think you would do better with either a lighter or faster boolit.

[Lloyd Smale]

no doubt thats your problem. The strikers short barrel isnt going to give you enough velocity to keep that bullet stable.

[joeb33050]

At 16 grains, 1167 fps MV, I'm guessing that the bullet is below the speed of sound before 100 yards.

18 and 20 grains of IMR4227, MV of 1290 and 1410, shoot fine at 200 yards.

MV down to 544 fps has bullets NOT making big groups, and going through the paper straight. Stability has NOTHING to do with MV,
down to 544 fps, through 100 yards.

Somewhere between 15 grains 1104 fps MV and 18 grains 1290 fps MV the bullets should go through the speed of sound before 100 yards and get wild. Didn't happen. Maybe the speed of sound business is a myth.

It ain't stability and it ain't the speed of sound, near as I can figure.
What's going on?
joe b.

[Ricochet]

Perhaps an initial instability problem that worsens over distance? Muzzle crown problem or some such?

[runfiverun]

speed of sound stability issues are a myth.......
maybe your lube is just finally coming off at 120 yds.

[snowtigger]

I've got a weird one myself. Put a new scope on my Rem660 350 Rem mag just before moose season.
I bore-sighted it and went to the range to try it out. I don't especially trust bore-sighting, so I started at twenty-five yards to see what I had. I could not get two bullets on paper, much less get a group.
Finally, out of frustration, I picked out a rock out at the far end of this range, about 135 yards. It disentigrated!! I shot at a couple more rocks and they did the same.
I set a target and put three in 1 1/2" , good enough for moose.
I still don't know what happened, don't really care. The moose is in the freezer.
The Barnes 225's performed just like the pictures.