Scope zero question

[SHYGUY5150]

I just put a used (like new)Millet TRS1 on an ss bull barrel platform 20" 1-8 twist..
Question is... I zeroed my AR using 55gr LC at 50 yds my grouping was ten rounds that I cover with a half dollar coin.. I was happy so I moved out to 100 yds and the pattern got wider 4" or so and couldn't bring the shots together.

Factors:
zeroed @ 50 yds @10 power
zeroed @100 yds @10-14 power
Bench shooting using bipod, little to no wind..

Thanks for any feed back..john

[Glockrocks]

I would practice more, if your reticle is covering the bulls eye dial in a couple of mils left or right so your bulls eye is not blown out from your hits.

[schills]

Its not the scope or its settings. If the scope adjustment was off, you would be missing the bullseye, but all the rounds would end up in the same place right on top of each other, even at 50 yards. Its the gun, shooter, or the ammunition. . . unless the scope or something in it is loose. Its not hard to imagine a 1/2" spread at 50 yards expanding to 4 inches at 100 yards. Make a peace sign with your fingers. Look how close your fingers are at the bottom of the V and how far apart they are at the top. The spread increases pretty quickly over distance.

[JMP]

If you are shooting with magnification and dials, the cannonical zero is at 100 yards as that's the common distance most easily to set on US target ranges. This range provides enough distance where your projectile has leveled off. Because the scope sits above the bore of the rifle, you must point it down slightly in relation to your muzzle as the bullet travels straight and starts dropping with gravity. After 100 yards, most cartridges will continue to drop, and this is why you zero at 100 yards as you now only need to worry about dialing up for elevation as you have just one point of intersection. If you zero at 25 yards or 50 yards, this makes it awkward because the trajectory of the bullet is pointed upward in relation to the bore of the scope. Thus, the paths will intersect and cross at 25 or 50, then you will find that they once again intersect at 200 or 300ish. That means you need to dial up and dial down after your zero, which gets confusing.

This is common to do for AR A2 iron sights as that is part of the system. You zero at 25, 36, 50, etc. to set a zero, then you have another zero around, say 300, which you also know. This keeps for less overall adjustment within your most common range (0-300), then you only need to dial up for subsequent shooting beyond the second intersection point, commonly at 300 yards.

This is why there is quite a large difference between using a magnified scope optic that dials vs. standard iron sights. However, it all boils down to preference and what you want to use your rifle/optic for.

[TKM]

Sandbags are your friend.

I can watch my reticle bounce at high magnification if I'm trying to shoot and pump blood at the same time. The same thing is happening with irons or low power scopes but it isn't as obvious.

[schills]

If you are shooting with magnification and dials, the cannonical zero is at 100 yards as that's the common distance most easily to set on US target ranges. This range provides enough distance where your projectile has leveled off. Because the scope sits above the bore of the rifle, you must point it down slightly in relation to your muzzle as the bullet travels straight and starts dropping with gravity. After 100 yards, most cartridges will continue to drop, and this is why you zero at 100 yards as you now only need to worry about dialing up for elevation as you have just one point of intersection. If you zero at 25 yards or 50 yards, this makes it awkward because the trajectory of the bullet is pointed upward in relation to the bore of the scope. Thus, the paths will intersect and cross at 25 or 50, then you will find that they once again intersect at 200 or 300ish. That means you need to dial up and dial down after your zero, which gets confusing.

This is common to do for AR A2 iron sights as that is part of the system. You zero at 25, 36, 50, etc. to set a zero, then you have another zero around, say 300, which you also know. This keeps for less overall adjustment within your most common range (0-300), then you only need to dial up for subsequent shooting beyond the second intersection point, commonly at 300 yards.

This is why there is quite a large difference between using a magnified scope optic that dials vs. standard iron sights. However, it all boils down to preference and what you want to use your rifle/optic for.

Everything you said explains why he might be missing the bullseye, or the target completely, but not why he has a spread of over 4". None of what you mentioned is the root cause of his problem.

[Jarhead]

Match Ammo would help

[lump]

Groups moving from ~1.5" at 50 yds to 4" at 100 yds seems pretty reasonable to me. It should be a little more than double. Also, variation happens...in the greater scheme of things a sample size of 10 is not definitive. Did you try repeating back and forth a few times? Also, maybe parallax impacting you more at 100?

[Cody]

Match Ammo would help

^ This. If you're using 55gr FMJ then don't expect 1 MOA groups.

[bohoki]

when you mount the scope you have to make sure the vertical crosshair cuts dead center with your bore that way most inconsistacies will lead to stringing instead of spread

unfortunatly sometimes when you allign your scope that way it looks canted since most mounting systems have a bias

[SHYGUY5150]

First of all thanks all for the feedback, I knew 55 was light for the twist but it would still shoot.
I'm going to try sand bags, and if that doesn't help its back to square one.
john

[Cody]

First of all thanks all for the feedback, I knew 55 was light for the twist but it would still shoot.
I'm going to try sand bags, and if that doesn't help its back to square one.
john

It's not the bullet weight that's the issue but more likely the bullet type. A 1:8 twist can shoot anything from 40gr to 77gr accurately depending on the ammo quality.

[RobertMW]

More likely, just the shooter.

You might try grouping off of a more precise aiming point, instead of a blob of a bullseye try the corner of a diamond, your reticule will cover less, and you will have a more precise aiming point, that should cut some human error out of the problem. If that cuts your group size significantly, its just practice practice practice time.

[Sig Marine]

More likely, just the shooter.

The four major components of shooting a rifle accurately are: the rifle, optic, ammunition and shooter. The system will only be as accurate as the weakest link. If the rifle is capable, the scope, including its base/rings, are mounted correctly and adjusted properly and you are using quality ammunition, then the shooter is the most probable cause.

You didn't give us your experience level and capabilities. If you have the fundamentals down and are capable of shooting 1 MOA or better at 100 yards, then more evaluation of your system (rifle, scope (including base and rings) and ammunition) is in order. However, if you are just starting out, like we all did at one time or another, then have a competent shooter take the rifle out to 100 yards and evaluate from there.

[avcrew]

One thing to add is barrel harmonics. Does OP have a free floated handguard? Or standard drop in handguard? Using a bipod?

If using a bipod attached to a drop in handguard, instead try using sandbangs near the rear base of the handguard. Hold and position rifle consistently for subsequent shots.

I also agree, good quality higher grain ammo helps a lot.