55 gr vs. 62 gr

frogman said:

Let's take a 580 series Ranch rifle, with an 18.5", 1:9" twist rate barrel. I know that 55 gr is optimal for this configuration, but what's lost when a heavier bullet, like a 62 gr green tip is fired through it? Does accuracy suffer, and if so, at what range would that become evident?

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The M855/SS109 62 grain load for the 5.56x45 was designed to meet a Nato specification calling for the ability to defeat a Nato standard steel pot (helmet) at 600 meters, which the older 55 grain M193 load was unable to accomplish. A 1:9 twist bbl will stabilize the bullet just fine, the reason for the 1:7 twist was to adequately stabilize the M856 long trace load (64 grains IIRC and a much longer slug).

Lot of ink spilled on the M193 vs M855, but what it comes down to is that the M855 is the better long range loading. Initial velocity is lower, but the better ballistic coefficient more than makes up for this. Basically it carries better. Heavier bullets than this will work even better at long ranges but your tube has to have a fast enough twist to stabilize them.

There have been accuracy issues with some lots of M855, due to the composite construction of the bullet - it has a steel tip and lead core so if concentricity in a particular slug is imperfect the result is compromised accuracy. There have also been reported problems with the M855 due to the lower initial velocity when used with the 14.5" bbl of an M4. If the velocity drops below something like 2700fps the slug tends not to destabilize in soft tissue resulting in "through and through" wounds. At least that's my second hand understanding of the issue.

So, which is the long range load? M855. I would suggest use M193 for anything to 300 yds and after that would suggest use of the M855, which is better for cost considerations in that the M855 is significantly more pricey and less available now.

Best,
Grumpy

frogman said:

Thanks for the info Grumpy. The reason I asked is because I've run across more 62 gr Federal green tips in the last month or so, than anything else. These are the 420 rnd bulk cans too. I was wondering if I should get these when I find them, or hold out for the lighter 55 gr rounds. I didn't want to be throwing away money if they wouldn't shoot well in a late model Mini.

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Hi frogman;

You lucky dog!!

If you can get the M855 62 grain LC (Lake City Arsenal mil surp which is what is marketed under the Federal name - check the brass, it should read LC xx where xx is the year of manufacture) at a reasonable cost I'd snag 'em. They are my preferred long range loading, and the only reason I don't cycle out all of my M193 ball and replace with M855 is cost and availability. I had already cycled through all my .223AE and Prvi, upgrading with M855 and M193 when the world went crazy last December. If Sandy Hook had never happened, by now I would be on my way to having 5k of M855 and the remaining dregs of M193 on their way down range during routine practice.

The only way to know for sure how your particular mini will do is to try 'em out and see. They should be fine though if my experiences have been any guide. Careful about the M856 though - that's the "long trace" loading and it may not shoot so well out of a 1:9 bbl. I haven't tried any out of my 1:9 twist mini yet, since my range down here does not allow tracers. Usually those are marketed in a red box under the Federal name.

All the best,
Grumpy
PS Just be sure not to overpay. There is a LOT of price gouging going on now. Not sure what "fair" is, but in this neck of the woods, M193 is about 50 cents a pop. Before Sandy Hook I was paying 45 cents a pop on M855 and 40 cents a pop for M193 to put it into context.