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MK262 variants of 556   General Military Discussion

Started 23-Dec by smg762; 520 views.
smg762

From: smg762

23-Dec

Thanks. I was surprised that 556 reaches 450m in about 0.7secs....i thought that kind of time was reserved for the 17 rem.

Its often said that 77gr massively outranges 62, and is just generally a win win option. I wonder if this is more to do with retained energy.

I asked the original question because one of my projects is a 4.9mm (thats he actual bullet diameter) doing about 1100lbs at the muzzle.

I assumed that a 48grain would give the best time of flight, and wasnt sure if upping to 55grain would ruin things 

(Obviously downrange energy would be better)

EDIT

I just noticed that the  556 time-of-flight difference is virtually negligible at 450m.......like 0.05secs....am i reading this right?

  • Edited 23 December 2020 14:25  by  smg762
In reply toRe: msg 3
renatohm

From: renatohm

23-Dec

Yes, you are.

Such negligible differences are exactly what preclude new designs being adopted.

smg762

From: smg762

23-Dec

From those numbers it looks like the 55 would have the time-of-flight advantage to maybe 300m, and then the 77 would negate the difference.

I wonder if those principles would apply to something like the 4.85x49, if you gave it, say, a 63grain. 

In reply toRe: msg 5
Red7272

From: Red7272

23-Dec

smg762 said:

From those numbers it looks like the 55 would have the time-of-flight advantage to maybe 300m, and then the 77 would negate the difference.

Out to 400 metres all these rounds perform similarly. The M855 has a BC of about .156 and the mod 262 about .2. The current Russian round is the 7N10bis    .176 at 900 mps.  The generally low performance of the 5.56x45 is due to the lack of room for projectiles. Increasing the OAL by 5 mm or using a 40 mm case based on the 6.8 SPC are the solutions to that issue. 

renatohm

From: renatohm

25-Dec

You mean just like 224 Valkyrie?

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