Interesting zeroing experience today

[Nico9283]

was attempting the 50/200 yard zero today. Rifle being used had a 11.5” Ballistic Advantage barrel 1:7 chambered in 556, Larue MBT 2 stage trigger, a Primary Arms 1x MicroPrism with an Sig Juliet 3x magnifier, and was using Black Hills 77g TMK.

I began at the 25 yard range just to make sure I’m on paper. Then went over to the 50yd range and got it zeroed. I wasn’t super impressed with the grouping size.. probably 2” groups at 50 yards isn’t what I was expecting, especially with such good quality ammo. I’m not a sharpshooter but I know I’ve got decent mechanics so maybe I was just having an off day or was cold since the range is outside.

I was about to call it a day but went over to the 200 yard range to confirm my zero. What happened there was pretty interesting to me. Right off the bat, all my shots were hitting damn near 12” high. According to every ballistic calculator I have ever used, I should’ve only been about 0.5” high but even 3-4 inches high would be acceptable considering I was either having an off day or this barrel is only shooting 2-3MOA. But 12 inches high was alarming. So, I adjusted the elevation on my optic to re-zero for 200 yards and after a few minutes was able to get it to the point of putting 6 out of 8 shots into a ~6” group (headshots on the silhouette target I was using). Still was hoping for better accuracy out of this barrel but 3moa at 200 yards is acceptable to me for a non-precision rifle.

HERES the part I found most interesting…. I went back to the 50 yard range and was still pretty much dead-on at 50yds. I cannot figure out how to explain this other than perhaps I wasn’t as dead-on at the 50 yard range as I thought I was the first time around, and that slight off-zero was highly exaggerated at the further distance.

Anyone else ever find that their longer zeros don’t match the theoretical expectations?


Ps.. I’m Open to critique if you think there’s a reason other than the barrel f that I had poor groupings.

 

[240Geezer]

IDK if 77grn is good for that twist rate. I take it that you didn't try just a standard 55 grn.
Other than that, operator error?
Off the bench? Offhand?

 

[Mountain]

If you were on paper at 200 and able to adjust to center from that, I'd call that initial 50 yard zero a 'win'.

Also 3 MOA from what is essentially a SBR is decent shooting. Probably you can tighten that up a bit with technique. Were you shooting via support with sandbags or something else?

 

[Mountain]

IDK if 77grn is good for that twist rate. I take it that you didn't try just a standard 55 grn.
Other than that, operator error?
Off the bench? Offhand?

77's in a 1/7 twist rate is in the optimal zone. 55's are too light and too fast for top accuracy via that twist rate.

 

[Nico9283]

If you were on paper at 200 and able to adjust to center from that, I'd call that initial 50 yard zero a 'win'.

Also 3 MOA from what is essentially a SBR is decent shooting. Probably you can tighten that up a bit with technique. Were you shooting via support with sandbags or something else?

I suppose you’re right. I think I had it in my head that I’d be expecting 3” groups at that distance but A.) I think I’d need a better quality barrel for that like a Daniel/Noveske/Criterion, and B.) without a higher power optic, I don’t know if I’d be able to detect minute movement of the dot, which would make it near impossible to see if my point of aim just shifted an inch at the target distance.

I have a 4-12x scope lying around, I’m Thinking I should throw that on there just to see how much better I can do with that before blaming the barrel.

And I was sitting with the handguard on a bench rest. No sandbags.

 

[Broc]

I wasn’t super impressed with the grouping size.. probably 2” groups at 50 yards ...

I was about to call it a day but went over to the 200 yard range to confirm my zero...all my shots were hitting damn near 12” high.

I was either having an off day or this barrel is only shooting 2-3MOA.

2" groups at 50 is not a 2-3 MOA. You are looking at 4 MOA, and my guess is if you are estimating they were probably 3" (or bigger) groups, so 6 MOA which means 12" at 200.

 

[Nico9283]

2" groups at 50 is not a 2-3 MOA. You are looking at 4 MOA, and my guess is if you are estimating they were probably 3" (or bigger) groups, so 6 MOA which means 12" at 200.

But that’s the thing, the groups at 200 weren’t 12” , they were 6”… but the groupings were 12 inches higher than they theoretically should’ve been. If I’m almost center at 50 yards, I should be about 2 inches high at 100 and right about zero again at 200. Obviously the math on that has some variables that might equate to the second zero being more like 180 or 220 depending on bullet speed… but i wasn’t expecting the bullet arc to be THAT off. That would put me at a second zero close to 300 instead of 200

 

[fencer]

I always say the same thing when people have wonky stuff happen when sighting in any firearm.
Strap that sucker into a Lead Sled. Eliminate the possibility of the rifle moving.

 

[VTski4x4]

Could be wrong, but I've read many places that 77gr is not even close to optimum for an 11.5" barrel, regardless of twist.

 

[Nico9283]

Could be wrong, but I've read many places that 77gr is not even close to optimum for an 11.5" barrel, regardless of twist.

I’m not 100% positive but I’m fairly sure the reason behind 77grain not being optimum for an sbr has nothing to do with accuracy (1:7 twist makes it suitable) but has to do with the bullet not reaching a high enough speed in a short barrel, since it’s a heavier bullet to push, to reliably expand/fragment at distances greater than 150-200 yards..

TMK rounds solve that issue.

 

[BTSDOG]

im going with barrel too short. bullet not getting enough rotation. Try it with a 16 0r longer barrel......

 

[KMM696]

I had what sounds similar to your problem once, zeroing a new ACOG in the cold. Put the ACOG on a solid 2MOA upper I'd had for a couple years, and went out to zero outdoors on a nice 15 degree day. Had a terrible time of it, scope didn't seem to be responding properly or predictably. After wasting far too much ammo, which included putting the old LPVO back on to shoot a couple decent groups (without rezeroing) just to prove to myself the upper still worked, I figured out that the windage and elevation adjustments were lagging in one direction. If I turned windage or elevation in, they worked normally. Turning them out the adjustment screws are being backed off with the spring on the other side pushing the internal tube to follow the screw. My theory was that in the cold the internal lube was causing zero adjustments to lag in one direction, and then gradually move to where they should be over the next couple shots.

I did get a successful zero eventually, if after making an adjustment moving the screws out I fired 4-5 into the berm before going back on target. I don't know if this is an all scopes can do that, ACOGs can do that, or that ACOG had that issue - sample size of one. I've zeroed conventional scopes in similar weather without issues, but after the ACOG session you'll also see me rapping on the scope every time I make an adjustment, which is not really a habit I can back up with facts.

To sum up, weird shit happens when mechanical objects get cold. Something to keep in mind.

 

[1903Collector]

Isn't that 50/200 zero based on the 55gr/193 loading and a 20" or 16" barrel?

 

[Ron Jablonski]

Isn't that 50/200 zero based on the 55gr/193 loading and a 20" or 16" barrel?

I was wondering the same thing.

 

[Nico9283]

Isn't that 50/200 zero based on the 55gr/193 loading and a 20" or 16" barrel?

I was wondering the same thing.

The math checks out for Tmk out of an 11.5. It’s more like a 50/185 but is within a half inch in 200. Theoretically at least.

 

[mac1911]

was attempting the 50/200 yard zero today. Rifle being used had a 11.5” Ballistic Advantage barrel 1:7 chambered in 556, Larue MBT 2 stage trigger, a Primary Arms 1x MicroPrism with an Sig Juliet 3x magnifier, and was using Black Hills 77g TMK.

I began at the 25 yard range just to make sure I’m on paper. Then went over to the 50yd range and got it zeroed. I wasn’t super impressed with the grouping size.. probably 2” groups at 50 yards isn’t what I was expecting, especially with such good quality ammo. I’m not a sharpshooter but I know I’ve got decent mechanics so maybe I was just having an off day or was cold since the range is outside.

I was about to call it a day but went over to the 200 yard range to confirm my zero. What happened there was pretty interesting to me. Right off the bat, all my shots were hitting damn near 12” high. According to every ballistic calculator I have ever used, I should’ve only been about 0.5” high but even 3-4 inches high would be acceptable considering I was either having an off day or this barrel is only shooting 2-3MOA. But 12 inches high was alarming. So, I adjusted the elevation on my optic to re-zero for 200 yards and after a few minutes was able to get it to the point of putting 6 out of 8 shots into a ~6” group (headshots on the silhouette target I was using). Still was hoping for better accuracy out of this barrel but 3moa at 200 yards is acceptable to me for a non-precision rifle.

HERES the part I found most interesting…. I went back to the 50 yard range and was still pretty much dead-on at 50yds. I cannot figure out how to explain this other than perhaps I wasn’t as dead-on at the 50 yard range as I thought I was the first time around, and that slight off-zero was highly exaggerated at the further distance.

Anyone else ever find that their longer zeros don’t match the theoretical expectations?


Ps.. I’m Open to critique if you think there’s a reason other than the barrel f that I had poor groupings.

Was your 2” group all around your point of aim at 50 or was it high/low

 

[alx]

Right off the bat, all my shots were hitting damn near 12” high.

…. I went back to the 50 yard range and was still pretty much dead-on at 50yds.

Assuming you shot in the 40ties outdoor temp or below ... if you had a chrono you would found out that the 200 and the 50 thereafter were about 50-75 fps slower than the initial 50 yard shots...

Your barrel got hot(ter) and expanded.. rounds went slower (less psi behind the bullet). In addition ammo got colder so the bullets shrunk amplifying the barrel expansion... I will let you do the math yourself... this scenario is common. Once you corrected for the temp change of hardware dimensions you were on point.

I would venture to say that your barrel quality leaves a bit to be desired. Oh, and in cold weather keep your ammo at constant temp during zeroing.

My 2 cents...

 

[mac1911]

Could be wrong, but I've read many places that 77gr is not even close to optimum for an 11.5" barrel, regardless of twist.

Nothing 224 is optimal in a 11.5” barrel. Lol

 

[mac1911]

Assuming you shot in the 40ties outdoor temp or below ... if you had a chrono you would found out that the 200 and the 50 thereafter were about 50-75 fps slower than the initial 50 yard shots...

Your barrel got hot(ter) and expanded.. rounds went slower (less psi behind the bullet). In addition ammo got colder so the bullets shrunk amplifying the barrel expansion... I will let you do the math yourself... this scenario is common. Once you corrected for the temp change of hardware dimensions you were on point.

I would venture to say that your barrel quality leaves a bit to be desired. Oh, and in cold weather keep your ammo at constant temp during zeroing.

My 2 cents...

So now when everything is room temp again your off again , lol.

 

[mac1911]

was attempting the 50/200 yard zero today. Rifle being used had a 11.5” Ballistic Advantage barrel 1:7 chambered in 556, Larue MBT 2 stage trigger, a Primary Arms 1x MicroPrism with an Sig Juliet 3x magnifier, and was using Black Hills 77g TMK.

I began at the 25 yard range just to make sure I’m on paper. Then went over to the 50yd range and got it zeroed. I wasn’t super impressed with the grouping size.. probably 2” groups at 50 yards isn’t what I was expecting, especially with such good quality ammo. I’m not a sharpshooter but I know I’ve got decent mechanics so maybe I was just having an off day or was cold since the range is outside.

I was about to call it a day but went over to the 200 yard range to confirm my zero. What happened there was pretty interesting to me. Right off the bat, all my shots were hitting damn near 12” high. According to every ballistic calculator I have ever used, I should’ve only been about 0.5” high but even 3-4 inches high would be acceptable considering I was either having an off day or this barrel is only shooting 2-3MOA. But 12 inches high was alarming. So, I adjusted the elevation on my optic to re-zero for 200 yards and after a few minutes was able to get it to the point of putting 6 out of 8 shots into a ~6” group (headshots on the silhouette target I was using). Still was hoping for better accuracy out of this barrel but 3moa at 200 yards is acceptable to me for a non-precision rifle.

HERES the part I found most interesting…. I went back to the 50 yard range and was still pretty much dead-on at 50yds. I cannot figure out how to explain this other than perhaps I wasn’t as dead-on at the 50 yard range as I thought I was the first time around, and that slight off-zero was highly exaggerated at the further distance.

Anyone else ever find that their longer zeros don’t match the theoretical expectations?


Ps.. I’m Open to critique if you think there’s a reason other than the barrel f that I had poor groupings.

Keep in mind the 50/200 yard zero is a “close enough good enough” zero. Its also highly dependent on you,platform and ammo all coming together and being in sync.
I can zero my AR, Garand ,M1a at 50 yards using a 3” aiming black and at 200 yards I will be 2 moa ish high/low.

Whst type of velocity loss from the 11” barrel. IIRC BH 2750 20” barrel

Did you use/not use the magnifier for each yard line.
What type of reticle and wher you using the same target for each yard line.