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Old July 26, 2020, 06:01 PM   #1
armednfree
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finally really working with the 284

17 years ago I had a Winchester 22-250 Coyote, laminate stock, rebarreled in 284 Winchester. I had a 28 inch Douglas heavy barrel put on. I first tried to load 145 grain Speer match bullets but quickly went to 168 Matchking's when 145's were neither very accurate nor carried well beyond 800 yards. I tried several powders but ended up with H4831sc. I could not go beyond 56grains, max book is 58, in the Winchester brass. The Winchester brass would expand it's primer pockets at 56.5 grains and beyond. The Winchester brass was not really good requiring heavy sorting. Weights ran as much as 3 grains difference and neck walls were all over the place. I moved on to other rifles for long range and the 284 mostly sat in the safe.

I got other brass, Peterson, which is very consistent. I got it in my head to try and push that 168 to 3000fps using R17. At first I used the Winchester brass in case there was some sacrifice. I did hit 3024fps average but accuracy was dismal running in the 1.2" to 1.7" range. A switch to the Peterson brass brought that down to 1"-1.3", still not good. I abandoned the R17 pursuit.

Back to H4831sc. 56 grains in the Peterson brass far outclassed the same in the Winchester brass running groups of .7 to .9. Then I decided to bump it up to 56.5. The brass took it with no issue, pockets still tight. Groups shrank to .5-.6 and velocity averaged 2874fps. ES was only 57 fps with an SD of 17 on a 10 shot string (I forgot to reset the chronograph).

This next set, more 56.5 grains of H4831sc and then 57 grains IMR7828scc.

I'm not making 3000 fps with any accuracy but I'm only 125 or so FPS short of that. The 1-10 twist is marginal according to Berger's program. They want 1.5 and mine is 1.48. Close enough I'd say.
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Old July 27, 2020, 09:43 AM   #2
Unclenick
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It's close enough, especially in the summer conditions when the heat and humidity make the air less dense. The Miller estimator on the JBM site lets you enter those to see what difference it makes.

Long ago, a Sierra technician told me they use a stability factor of 1.3 to 3.0 for "hunting accuracy" and 1.4 to 1.7 for match accuracy. Authorities have disagreed about what is optimal. Don Miller, who worked under Robert L. McCoy of U.S. Army Ballistics Research Laboratory fame, thinks 1.5 is optimal. Robert Vaughn, who was a distinguished and published scientist and head aeroballistician at Sandia National Laboratories thought 1.4 was best. Another authority, whose name refuses to pop back into my mind, thought 1.7 was best. I am sure that is what the Sierra range comes from.

Note that the bullet design matters. I've found the Don Miller estimator on the JB Ballistics site can underestimate stability factor in .22's and saw a post on accurateshooter.com suggesting the .243 can do the same thing. What causes this is a false assumption that is more significant in the smaller bullet diameters and that is that bullet material density is distributed uniformly throughout the bullet's length. Hollowpoint match bullets have an air space behind the hollow tip that makes the tip less dense and that moves the center of gravity back and lowers the overturning moment of inertia that spinning has to correct for. Plastic tipped bullets are similar. Miller felt you can compensate closely enough for plastic tips by just omitting the length of the visible portion from the total bullet length entry.

Finding the equivalent length for hollow points is more bother. I just see how far a thin wire drops into the nose before it stops. I know the lead will have a slightly raised area in the center under there, so I subtract that depth from the bullet length as an approximation, with the assumption the space around the lead stub would compensate for the volume of jacket in the length I am omitting. It's not a very scientific method, but I think it gets closer to reality in the small bullets. I don't really trust the result very far. I can get closer with my CAD software which finds CG and moments of inertia, but the new result and the number you get from using the full length of the bullet in the calculation gives you some idea of what range the real GS is likely to be in.
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Old July 27, 2020, 10:34 AM   #3
std7mag
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My first question would be "Why try to push the 168gr bullet to 3,000 fps out of a non competition built 284 Win"?

Bench match shooters, and F-Open shooters trying to do so are using custom competition actions and reamers. Everything is done with precise tolerances and on the tight side dimensionally. Allowing them to load upwards of 70,000 psi, and getting them to those velocities.

Granted your going to get about 100 fps faster than my 24" barrel in theory.
But i feel your chasing velocity THEN accuracy.
I'd invert that.
ES in the 50s, and double digit SD are not your friend at long distance.
In comparison i was getting ES of 6 fps and SD of 2 fps with my 7mm-08AI over 10 round string.

I've lately been playing with the 160gr Tipped MatchKing and Alliant Power Pro 4000, with really good accuracy. I haven't had a chance to chrono yet.

Start low, work up & let the gun tell you what it likes. Then do seating depth to let the bullet tell you what it likes.
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Old July 27, 2020, 03:47 PM   #4
armednfree
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Actually I already did that. 56 Grains H4831sc in the Winchester brass and 56.5 in the Peterson brass. The Peterson brass load runs faster, but only by about 50fps. It is much more consistent, being over all better brass.

Why, well, just to see if I could. Simple curiosity. Not that I believe the 125 fps, or 180 fps in the case of the Winchester brass, would make a difference. The bullet is still going trans sonic around 1200 yards more or less.

I never shot paper at those long ranges, only ringing steel. Either on a static firing like or a "Sniper Walk". On some days when the environmental gods smile I do 1200 pretty well. But when they give the heavy air 1100 is even a bit of a challenge.

If I was to build that rifle today it is likely I'd stay with the 284. But it would have an 8 twist 28" barrel and would center on Berger 180 grain VLD bullets.
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