T97 - High mounted optic zeroing

harbl_the_cat

harbl_the_cat

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I don't recall if I've had as crazy high an optic as my T97 or if I hadn't paid much attention to how to zero such rifles at various ranges - but my setup with one of my T97's is the Clobb/SFRC carry handle mount with a cheapo Leapers compact 4x32 scope.

Just taking a rough measure, the approximate sight line difference between the barrel and the center of the scope is about 4.5 - 5" above the barrel.

When I was zeroing it, I was getting all kinds of crazy results, as I hadn't fully understood how much of a difference the ballistic trajectory was affected by the sight height - but after playing around with this website, it's all sort of starting to make sense: http://www.shooterscalculator.com/ballistic-trajectory-chart.php

I've never used a ballistic calculator before - but I think I'm going to start.

Using surplus factory Nork .223 ammo (documented shooting pretty consistently to a M193 standard) with an expectation of about 4 MOA (or less) here were some observations.

With my scope:
-A 25 yard zero resulted in a 50 yard grouping about 4" high
-A 50 yard zero resulted in a 100 yard grouping about 5.5" high
-A 100 yard zero resulted in a 200 yard grouping pretty close to zero (although I wasn't really going for accuracy at that point - just going centre of mass of an IDPA target.

Using that ballistic trajectory website, I assumed a starting velocity from the T97's 19.5" barrel to be about 3200 FPS (a future experiment will have to be to chrono it). When I entered in those figures, the chart looks to corroborate my real life findings when I was zeroing in. I have no idea what some of the variables like the ballistic coefficient or wind speed are - but I'm going for a general zero to be up to snuff of Canadian military PWT1/2 standards (that being hit a figure 11 target at 200 yards).

It's pretty interesting what the findings were. My T97 now has an rough 100 yard zero, shooting the same ammo, using that ballistic calculator, I believe my rifle should be low around 1.75" at 50 yards and low around 3" at 25 yards. I'll have to experiment with this next time I'm shooting - but this is really fascinating.
 
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Yep sounds about right. Been fiddling with high mounted optics for a while now with my cz858 and now my t97, so I'm used to getting some weird results and shaking my head then heading to the ipad for a ballistics calculator.

I find sighting in at 50 yards is ok, I don't mind my POI being a little high at 100 for .223,

I have a question, if you sight in at 50yards when's your next zero though? somewhere between 300 and 400 yards?
 
mikethebike said:
Yep sounds about right. Been fiddling with high mounted optics for a while now with my cz858 and now my t97, so I'm used to getting some weird results and shaking my head then heading to the ipad for a ballistics calculator.

I find sighting in at 50 yards is ok, I don't mind my POI being a little high at 100 for .223,

I have a question, if you sight in at 50yards when's your next zero though? somewhere between 300 and 400 yards?
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Looks like a 50 yard zero with a muzzle velocity of 3200 FPS should be around 375 - 400 yards with a 4.5 - 5" high mount.

Guess I'll be looking for a ballistic calculator for my iPhone as well.

One thing I forgot to mention was a 50 yard zero with the iron sights seemed good enough to get on paper at 200 yards. Rapid fire, 15 shots at an IDPA target, only 2 in the -3 zone, undeterminable how many in the -1 zone (old patches blew off)
 
Very interesting indeed… You mentioned in your other thread you were getting under 4" - 5 shot groups at 200yds which is 2moa. were you still getting similar groups here?
 
SQUAREHEAD1 said:
Very interesting indeed… You mentioned in your other thread you were getting under 4" - 5 shot groups at 200 m which is 2moa. were you still getting similar groups here?
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Heck no. I was doing a reliability test to test my feed ramps with my problem mags, with accuracy an afterthought. I was doing 4" at 100, but I was in a big rush to see if I could get on target to 200 yards. (First round down range at 7:57, 3 walk downs to 100 to check on 3 5 round groups, 2 walk downs to 200 to check on a 15 round mag dump at and IDPA target - last round fired at 9:15 - then a day teaching kids).

Just curious what ballistic app does anyone use for iPad/iPhone?

Edit: ah I see, I had a typo in the other thread (fixed).
 
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harbl_the_cat said:
Just taking a rough measure, the approximate sight line difference between the barrel and the center of the scope is about 4.5 - 5" above the barrel.



With my scope:
-A 25 yard zero resulted in a 50 yard grouping about 4" high
-A 50 yard zero resulted in a 100 yard grouping about 5.5" high
-A 100 yard zero resulted in a 200 yard grouping pretty close to zero (although I wasn't really going for accuracy at that point - just going centre of mass of an IDPA target.


It's pretty interesting what the findings were. My T97 now has an rough 100 yard zero, shooting the same ammo, using that ballistic calculator, I believe my rifle should be low around 1.75" at 50 yards and low around 3" at 25 yards. I'll have to experiment with this next time I'm shooting - but this is really fascinating.
Click to expand...

If your barrel is about 5" below the line of sight, trying to get it on target at a mere 25Y will mean the barrel is pointing dramatically uphill and will make the point of impact POI at 100Y REALLY high. IDK how much, but lots. Perhaps 8 or 9 inches based on your 50Y results.

Your 50Y zero was "only" 5.5" high because the bore is not as steeply inclined when set to cross at 50Y (compared to the 25Y zero)

Probably the best option is to zero for 100Y, and just keep in mind that the bullet is still rising from the very low starting point. So hold over 5" (as it is hitting low) at powderburn distance, hold over about 2 or 3 at 50Y, right on at 100Y, and further tests to confirm at 150 and 200.
 
harbl_the_cat said:
Heck no. I was doing a reliability test to test my feed ramps with my problem mags, with accuracy an afterthought. I was doing 4" at 100, but I was in a big rush to see if I could get on target to 200 yards. (First round down range at 7:57, 3 walk downs to 100 to check on 3 5 round groups, 2 walk downs to 200 to check on a 15 round mag dump at and IDPA target - last round fired at 9:15 - then a day teaching kids).

Just curious what ballistic app does anyone use for iPad/iPhone?
Click to expand...

I run the one from winchester, but it's really not that great since you have to use predefined bullet, and frankly well Winchester is biased and I can only use a sight height of 2 inches max!
That website you found is awesome, but need internet access to use it.

If someone else has any ballistic apps suggestions for Iphone/Ipad let me know.
 
mikethebike said:
I run the one from winchester, but it's really not that great since you have to use predefined bullet, and frankly well Winchester is biased and I can only use a sight height of 2 inches max!
That website you found is awesome, but need internet access to use it.

If someone else has any ballistic apps suggestions for Iphone/Ipad let me know.
Click to expand...

I think I'm going to make print outs with 1/4" increments starting from 1" with 3200, 3100 and 3000 Fps muzzle velocities for 55 gn fmj.

Won't be super precise, but should be a good ballpark for all my crazy configuration .223s.
 
tootall said:
If your barrel is about 5" below the line of sight, trying to get it on target at a mere 25Y will mean the barrel is pointing dramatically uphill and will make the point of impact POI at 100Y REALLY high. IDK how much, but lots. Perhaps 8 or 9 inches based on your 50Y results.

Your 50Y zero was "only" 5.5" high because the bore is not as steeply inclined when set to cross at 50Y (compared to the 25Y zero)

Probably the best option is to zero for 100Y, and just keep in mind that the bullet is still rising from the very low starting point. So hold over 5" (as it is hitting low) at powderburn distance, hold over about 2 or 3 at 50Y, right on at 100Y, and further tests to confirm at 150 and 200.
Click to expand...

No kidding...what a soup sandwich.
 
snipz said:
Got my VOMZ PO 3.5/20 scope and mount today from Corwin Arms...Gonna go test it out tomorrow....I think Ill zero it at 100yds.....


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You do realize that you are using a flashlight holder for scope rings right?
https://www.google.ca/search?q=flas...lashlight+rail+mount+airsoft&spell=1&tbm=isch
1-25mm-airsoft-flashlight-laser-mount-for-20mm-ris-rail.jpg
 
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