I e-mailed Federal to ask about the minimum expansion velocity for the 62 grain Fusion load. This was their response:
[i]Greetings,
Minimum velocity to produce reliable expansion with our 223 Fusion
bullets is around 1350fps, this is an estimated not proven number with
our ballistic data.
Thank you[/i]
Quite frankly I’m skeptical of of the number but I figured that I would pass it along to anyone else who was interested.
So at what range can you count on this round to reliably expand?
Probably close to 550yds/500m.
http://www.fusionammo.com/ballistics/rifle.aspx?id=803
I doubt you’d get more than simple JSP bullet deformation at that range/velocity.
eta: remember that those specs are cooked out of 24" bolt action test platforms. Your 14.5 midlength will not produce that same velocity figure (or range).
At best, it is acting like a 9 mm JSP at that velocity, but they are still working darn well at 2100 fps…
9mm JSP at 500m? I’ll take it.
Really?
Dr. Roberts,
I, and certainly others, would be very interested to learn about any low-velocity terminal effectiveness testing you have done.
In particular what projectiles have shown good unobstructed performance at low velocities(~2000 fps). This would give some insight into the effective range of the commonly available defensive loads.
62 Grain Federal Tactical Bonded out of a 10" barrel, after auto glass.
15.7” Penetration, 65% Weight Retention, 0.36 inch Expansion.
With more and more advanced bullets like the barrier blind loads recently developed, this Fusion load I suppose, etc - in the 62 grains and under range - might we see the 1:7 twist become less desirable? Or maybe not quite optimal?
The search for the “optimal” twist among AR fans amuses me.
Once it is fast enough to stabilize the bullet, there are so many other factors that have FAR more influence on accuracy that trying to optimize twist is as useful as trying to count angels dancing on the head of a pin.
And contrary to popular belief, there is no such thing as too fast a rifling. Highpower rifle competitors long ago stopped bothering with special uppers with 1 12 twist for short range matches. Why? Because 1 in 7 and 1 in 8 uppers drove the 52 Sierras into little knots at 100 and 200 yards and still worked the 80 VLDs at 600.
Slow twist ARs (even 1/9) are a waste of time, money, and capability.
I like that. A few years back SME’s more often than not declared 1:9 pretty stupid. 
A few better choices within it’s range though now I guess.
I’ve not noticed poor accuracy from our 1:7s on lighter bullets at 100 yds either. Although one “old” high power shooter told me my N4 barrel might spin 52 grainer to dust before they reached 100 yds.
We have seen new 1/7 twist barrels with sharp rifling cause lightweight, fragile .224 projectiles like the Federal 40 gr Blitz disintegrate in mid-air a few yards after leaving the barrel when launched at higher velocities…
Other than that, there are no disadvantages to running a faster twist 5.56 mm/.223 and there are some advantages, particularly with SBR’s, to ensure sufficient rotational velocity for adequate upset with some projectiles. The 1/7’s have offered superb accuracy and terminal performance in our testing using bullet weights from 45 to 100 gr.