Dope substantially off

[Megalodong]

Tikka T1x 20" in KRG Bravo
SK Long Range Match chrono'd at 1088 fps 10 shot average
50 yard zero
Actual 100 yard drop is 1.4 mils measured with scope and tape
Calculated 100 yard drop 1.7-1.9 across a few calculators


I have double checked all my info. Have accurate weather, scope over bore, velo, etc. Using .179 G1.


Not sure what to do, I can't even get to the actual drop truing BC. Adjusting velocity I have to get up to ~1200 fps to align. Have a hard time believing chrono is off by over 100 fps.

 

[DeathBeforeDismount]

What ballistics calc? Sometimes when everything is off...clear it out and start over. It's usually a setting that needs to be fixed.


We use .173 but that's not enough to account for being .3-.5 off at 100.

Make sure scope tracks with a tall target test.

After that, just dsf it out to 300 and call it good.

You are also at altitude, make sure DA is correct.

 

[b6graham]

is your zero good?

i use .132 for SK/Lapua and it dopes well to 600y

1.4 is pretty far off from about every 100y 22lr subsonic ammo. 1.7-1.9 is very very much the normal drop. 1.6 and 1.9 sometimes

 

[6.5SH]

IMO your distance for zero and or "100 yards" is incorrect. Get a cheap 300 foot reel tape measure and verify distances then make sure you are truly zeroed. No way no how is 1.4 mils @ 100 correct for that cartridge.

 

[ballisticdaddy]

Tikka T1x 20" in KRG Bravo
SK Long Range Match chrono'd at 1088 fps 10 shot average
50 yard zero
Actual 100 yard drop is 1.4 mils measured with scope and tape
Calculated 100 yard drop 1.7-1.9 across a few calculators


I have double checked all my info. Have accurate weather, scope over bore, velo, etc. Using .179 G1.


Not sure what to do, I can't even get to the actual drop truing BC. Adjusting velocity I have to get up to ~1200 fps to align. Have a hard time believing chrono is off by over 100 fps.

I am about an hour south of you and sitting at 7,400 ft above sea level and I need to dial 1.7 mils for 100 yards from a 50 yard zero. If you are using a ballistic calculator and not a kestrel then I would guess something is not entered correctly probably with atmosphere/elevation.

 

[ballisticdaddy]

is your zero good?

i use .132 for SK/Lapua and it dopes well to 600y

1.4 is pretty far off from about every 100y 22lr subsonic ammo. 1.7-1.9 is very very much the normal drop. 1.6 and 1.9 sometimes

Pretty much everybody I shoot with is using .172 for rimfire BC....see below from SK website...unless you are running flat nose???

 

[b6graham]

I am about an hour south of you and sitting at 7,400 ft above sea level and I need to dial 1.7 mils for 100 yards from a 50 yard zero. If you are using a ballistic calculator and not a kestrel then I would guess something is not entered correctly probably with atmosphere/elevation.

1.7-1.8 matches here and what i used in Boston at sea level. 1.4 makes no sense unless the 50y/100y distances are a few yards off

as far as BC. .132 worked for me with Lapua CX/Midas and SK RM from 25y to 600y at roughly sea level. 600y confirmed on paper. 3 shots. 29/2X on a normal 600y f class target.

 

[Megalodong]

Shooting indoors at a range with set distances. I have ranged the 100y spot and it's right on, I think the issue may be the 50y zero. It's more of a guess where to stop the target. I bet that is the issue, I just didn't think about that being off causing such a big deal.

1.7-1.9 calculated using AB, Strelok Pro, a couple website I just googled, and the drop charts all floating around. Putting altitude 5500', temp 65, corrected baro 24.19, and humidity 45% all in. Baro and humidity from NOAA.

This was not dialing so scope isn't the issue. Shooting a 10 round zero at 50y, backing target to 100y and shooting another 10. Measured with the scope reticle and then also measured grid on the target. 1.4 mil and 5".

Idk, I could be doing something really stupid and was off on my reticle subtens, or mis-counted grids, but they both match each other.


I'll go shoot another brick today or tomorrow and take my Sig 10ks to get a range for 50y zero and get actual environmentals. Shooting a LR match Saturday so either way I'll find out then I guess.

 

[6.5SH]

Pretty much everybody I shoot with is using .172 for rimfire BC....see below from SK website...unless you are running flat nose???

View attachment 8108671

If look at what BC actually gets measured from AB's PDM's or good LabRadar data G1's are mostly in the .13x range.
Even the tables above are mixed data, the BC is calculated at 75 (yards or meters they don't say...) but the drops are from their radar data. So the listed BC is inflated for an average.

If you use Lapua's radar data in Strelok you'll still end up with a ~1.9 Mil drop at 100 yards with 1088 fps, same for G1 of .172 or .135, the inaccuracy of it as an average starts showing up at longer distances. Trued SK LRM data for my 16.5" T1x is a 0.135 G1 out to 300 yards.

 

[B y r o n]

What elevation and temperature?

 

[b6graham]

What elevation and temperature?

OP is denver so elevation 5500-6000 assuming he was at BluCore 5800ish

he was inside so 65-75 degrees most likely

neither of which would cause a .3 mil difference unless the ventilation system is doing something SUPER goofy

 

[littlepod]

Pretty much everybody I shoot with is using .172 for rimfire BC....see below from SK website...unless you are running flat nose???

View attachment 8108671

.172 is the BC of the ammo at 50yds.

BC changes as the velocity decreases. If you're looking for an average BC out to 200-250, usually .135 or so covers it. At 300+ the BC is around .11.

 

[Megalodong]

We're all good now.

I didn't get into the exact math, but I think I had closer to a 60y zero and the furthest target stop is actually 98y. Stuff I had just called "good enough" when shooting centerfire. Obviously will have to pay closer attention with my rimfire stuff.


Thanks for the help everyone!

 

[King_beardsly]

We're all good now.

I didn't get into the exact math, but I think I had closer to a 60y zero and the furthest target stop is actually 98y. Stuff I had just called "good enough" when shooting centerfire. Obviously will have to pay closer attention with my rimfire stuff.


Thanks for the help everyone!

Rimfire is a fickle beast and a cruel mistress, it’ll definitely show you what you’re doing wrong even if it’s the tiniest thing

 

[MajorD]

Rimfire is a fickle beast and a cruel mistress, it’ll definitely show you what you’re doing wrong even if it’s the tiniest thing

Yep. I made the same fundamental mistake recently. ( you’d think after decades of various types of competition I would know better!) with my 50 yard practice target off by a few yards.

 

[DeathBeforeDismount]

Yea its always a good habit to laser the zero board to make sure you have the exact zero. I can't tell you how many are off by about 5 yards or so, which has a significant effect on your dope at Long range. There is a function in the Kestral and AB that you can set your zero to the actual range. I have had a bunch of 45-54 rimfire zeros and 96-103 yard centerfire zeros over the years when you dont have time to get a good 50/100. Its why a quality laser range finder (Leica/Terrapin) is such an important piece of shooting gear. Also get in the habit of lasering your targets, especially at rimfire matches. Being off by a few yards can be the difference between a hit and miss due to cone of fire and rimfire ammo volatility.

 

[DFOOSKING]

Many ranges are meters ranges. Not yards based ranges. Set up for things like silhouette competition. My local hometown range has been a pistol silhouette range for decades that's been semi-open to the public.

John Q. Fudd doesn't care his deer rifle is sighted in an inch high at 109 yards.

But we most certainly care it's 54 yard and 109 yard berms. Buddy of mine learned the hard way to always bring your support gear...even when zeroing.

 

[Megalodong]

Thanks again everyone, all came together and even ended up placing 1st at the match. Absolutely nothing against the other shooters, but this is certainly a friendly low stress competition, calling misses for each other etc. Still feels good though, guess I have to find a NRL22 match to get my butt kicked at now.

 

[Lightning8]

.172 is the BC of the ammo at 50yds.

BC changes as the velocity decreases. If you're looking for an average BC out to 200-250, usually .135 or so covers it. At 300+ the BC is around .11.

How do you account for the BC changing with Kestrel AB? For PRS22 - our local matches have multiple engagements 200+ and maybe one 300+

 

[b6graham]

How do you account for the BC changing with Kestrel AB? For PRS22 - our local matches have multiple engagements 200+ and maybe one 300+

drop scale factor

or AB custom curve if your bullet is there.

 

[littlepod]

How do you account for the BC changing with Kestrel AB? For PRS22 - our local matches have multiple engagements 200+ and maybe one 300+

I use the AB Custom Curve that handles all of that. They have a doppler curve for a lot of the popular ammo. I've used that curve for years at multiple sites and it's been spot on out from 25yd - 450yds. I've never touched drop scale factor.

 

[Lightning8]

I use the AB Custom Curve that handles all of that. They have a doppler curve for a lot of the popular ammo. I've used that curve for years at multiple sites and it's been spot on out from 25yd - 450yds. I've never touched drop scale factor.

It is like reloading questions and rifle cleaning questions; as a newer PRS shooter, when I ask about AB Custom Curve the responses are half emphatic no and half emphatic yes. I will try both out at range to see if I can see what works. Thanks!