Zero Range for 10.5 inch upper

Ajax

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I need the bullet data on the M855, with a 10.5in upper(Colt and Bushmaster), with a EOTECH on it. Trying to find out what the zero range needs to be.

Fellas, this is a request from a peer in DoS. Quick response is appreciated.
 

Centermass

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One of my buds is an armorer with DSS. He's a walking bible when it comes to specs. Give me a few and I'll see what I can come up with if he's available.
 

Diamondback 2/2

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I would go with a 50 yard zero, giving him range with out hold off at 200 yards. The bullet drop will stay the same for the most part, but the ability of the bullet to penetrate is going to be greatly reduced due to the short barrel, but the ballistics of the bullet drop is pretty well the same out to 350-400 yards.

With out getting into twist ratio and type of irons he would be running as backups, the 50 yard zero is the way to go. Especially with an EoTech!

Zero at 50 yards, point of aim point of impact.

At 200 yards he should be around 2-2.5 inch low, at 300 he is looking at 9 to 12 inch low, meaning he would hold crown of the head for a center mass (body) shot. If he can confirm the data on an actual distance range, he will have more of a for sure data of his hold off.

Just like any other weapon, take a few index cards after you zero and and test your hold off and record it down. Then tuck in your kit as a reminder ;)


Hope this helps!
 

AssadUSMC

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Definitely 50m. That's the whole point of a sight like the EO-Tech. If you're doing 100m+, then put an ACOG on it. If it's DSS, then it's all gonna be close up and personal or else there's plenty of room to get off the X.
 
A

arizonaguide

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Skeeter Skelton. :) (not exactly was he a Combat Shooter like Cooper..but good "down to earth" (Border Patrol)type gun stories).
skeeter.jpg

Not meaning to hijack the thread...just had to throw that name in there. Not too many remember it.
:cool:
 

Etype

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The bullet drop will stay the same for the most part, but the ability of the bullet to penetrate is going to be greatly reduced due to the short barrel, but the ballistics of the bullet drop is pretty well the same out to 350-400 yards.

How is bullet drop going to remain the same but penetration is going to be reduced? Both are a function of velocity. From what I know, M885 has 'optimum' penetration around 250-300m, this is where it attains it's most stable velocity. Inside and outside of this range, you get the good yawing and corkscrewing effects that we look for, but also limit penetration in liquids (or mostly liquid humans).

Just like any other weapon, take a few index cards after you zero and and test your hold off and record it down. Then tuck in your kit as a reminder ;)

Memorize it, brother. 5.56 and 7.62 mil holds are about the same out to 600m, commit them to memory if you're shooting a 110 or SPR. As for using your EOTECH- Listen to JAB and go with the 50/200m zero, a 300m zero will have you missing heads high at about 200m. Be realistic, train for headshots out to 200m, with a free float CQBR type upper and a good barricade supported position that shouldn't be too hard- point of aim will give you headshots from 200 and in. After that, it's torsos- hold neck at 300, 400 and out you're going to be holding over his head but it's not that bad out to about 500m. For 500m, I take the distance from the crotch to the top of the head, and hold that height over center of mass, or half that height over the head (or sometimes I dial, I shoot a Trijicon Accupoint on my work gun).
 

Diamondback 2/2

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How is bullet drop going to remain the same but penetration is going to be reduced? Both are a function of velocity. From what I know, M885 has 'optimum' penetration around 250-300m, this is where it attains it's most stable velocity. Inside and outside of this range, you get the good yawing and corkscrewing effects that we look for, but also limit penetration in liquids (or mostly liquid humans).

LOL good point. I was not talking about penetrating humans, more so vehicles and cover positions (brush, glass, wood ect).

The only real input I can give on it is that the accuracy that M855 gives in the SBR’s is basically minute of bad guy at 300yards (roughly 3+ MOA) making the hold offs seem to be the same, but the inconsistency in performance made it very difficult to measure. M855 in the SBR’s penetrated well at 50-300 yards, but not as well as in the M16A4 (20inch barrel) this is due to the bleed off of the velocity of in the SBR’s. Past 300 yards the M855 did not penetrate ¼inch cold rolled steel plate, that is was penetrating at the shorter ranges, however when fired from the M16A4 in continued to penetrate the steel out to 500 yards.

The M855A1 was designed due to the massive amounts of data and research on how the M855 did not penetrate well (in the M4) and to give increased accuracy in the SBR M4.

I think it boils down to the same issue of the M193, most will say that it penetrates better then M855 at closer range b/c of the velocity being about 300fps faster. However, they do not take into account the steel core penetrator in the M855 giving it the ability to penetrate better than M193. IDK some things are just beyond explanation and some are easily explained.

If I was running the SBR and it was the perfect world we would all love to live in, I would use:
55gr Soft Point for CQB.
M855 (M855A1 if I could get it) for general purpose.
MK262 for longer range shooting.
 

Etype

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Going off topic a bit but staying with the bullet talk-
It's sad when we are going to war with bullets that fish and wildlife doesn't trust to kill a deer (M855), but we expect to kill something that shoots back. Sierra Match Kings (Mk262) are nice, but lets get some real man killers like some Trophy Bonded Bear Claws, Barnes TSX, maybe Hornandy A-Max?

It wouldn't be hard, and I'm sure many bullet companies would go far in depth to do it- lets get two bullets with near identical BCs and identical weights, one is a low cost training round, and the other is a man killer shipped taken with you to X country of choice.
 
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