Theory versus reality

[tpcollins]

My last range session at the range I was 1 1/4" high at 100 yards which equated to about a 127 yard zero on the JBM trajectory, ( my Zeiss Duralyt actually converts to mills @ 100 yards) indicated I should have a 10.1" drop at 200 yards, ballistics chart said 1.4mills up.

So I fired my load that I've had since November 14th, rotated the BDC turret up 14 clicks (1.4 mils) and hit 12" low! I was shooting off my tailgate but had a Caldwell BR front rest and a Protektor rear bunny - everything was rock solid. I should have fired a verifier but I just walked down to the target expecting to see it near the bull. I had the same thing happen last year when I unloaded at the end of the season using the subtends on my 3-9 Swarovski I had on it last year.

So it's either me, my calculations, or the Barnes 250gr TMZ. I only had about a 2mph crosswind so that wasn't the issue.

 

[sabotloader]

So what powder were using and where has the rifle been stored since 11/14?

 

[long shot]

You need to shoot your rifle after your zero is done and make drop chart. then with your zero go back to range and see if the drop chart matches what your rifle is really doing . but without your initial velocity it is almost impossible. Reality ballistic charts are just starting point

 

[WTM45]

. but without your initial velocity it is almost impossible. Reality ballistic charts are just starting point

X2

 

[tpcollins]

So what powder were using and where has the rifle been stored since 11/14?

About 105gr of BH209 and it's been either outside in the garage, the bed of my truck, or on stand - never exposed to any warmth.

My muzzle velocity is only about 1850fps with that load and I've verified the crosshair does move when the turret is turned. This year I'm going to shoot the 250gr Hornady Monoflex with the black CR Harvester and hopefully I can find somewhere to shoot 200 yards after my initial range session.

 

[HoytFlinger]

Do you have a chronograph? You really need to shoot your gun through one to get close on a shooting solution with an app. I use the Shooter app by Bryan Litz for my CF rifle and it is scary accurate once you plug in actual velocity, altitude, and atmospherics. Knowing the correct BC of chosen bullet is also a must to get close.

 

[tpcollins]

[quote="HoytFlinger"]Do you have a chronograph? You really need to shoot your gun through one to get close on a shooting solution with an app. I use the Shooter app by Bryan Litz for my CF rifle and it is scary accurate once you plug in actual velocity, altitude, and atmospherics. Knowing the correct BC of chosen bullet is also a must to get close.[/quote]

- My chrono is how I know it was shooting 1850 fps with that load.

- I do input that same data into the JBM Ballistics chart, is the Shooter app by Bryan Litz really that different than the JBM?

 

[long shot]

JBM has a way to validate your velocity and correct it. I never figured how to use it. You could try Vortex Site. Up in right hand corner of page is letters LRBC click on that

 

[HoytFlinger]

[quote="HoytFlinger"]Do you have a chronograph? You really need to shoot your gun through one to get close on a shooting solution with an app. I use the Shooter app by Bryan Litz for my CF rifle and it is scary accurate once you plug in actual velocity, altitude, and atmospherics. Knowing the correct BC of chosen bullet is also a must to get close.

- My chrono is how I know it was shooting 1850 fps with that load.

- I do input that same data into the JBM Ballistics chart, is the Shooter app by Bryan Litz really that different than the JBM?[/quote]

I've never used JBM so can't rightly say, but Shooter has independently verified BCs by Bryan for the most popular rifle bullets. That is valuable as we all know manufacturers have been known to inflate advertised BCs. I would think that JBM would probably give similar solutions when the same data is entered into both. The issue you have may be due to your chosen bullet's advertised bc being off.

I think I would probably just make my own drop table for a muzzleloader if we are only talking about 200 yds or so max. Wouldn't take that long and would be true data.

 

[tpcollins]

I've never used JBM so can't rightly say, but Shooter has independently verified BCs by Bryan for the most popular rifle bullets. That is valuable as we all know manufacturers have been known to inflate advertised BCs. I would think that JBM would probably give similar solutions when the same data is entered into both. The issue you have may be due to your chosen bullet's advertised bc being off.

I think I would probably just make my own drop table for a muzzleloader if we are only talking about 200 yds or so max. Wouldn't take that long and would be true data.

The Barnes BC is listed at .210, two online BC calculators listed it higher so I don't think that's the issue. Main issue is actually finding a place to setup and shoot accurately at 200 yards.


I just did a search and found some interesting info - on the Barnes website, they list the 250gr TMZ bullet with a BC of .210, on the Hornady website they list their nearly identical 250gr Monoflex bullet at .210. I think the .210 is reasonable enough to use. What I don't understand is the G1 - G7 drag options in the calculator.

 

[ronlaughlin]

Those listed BC are G1.

 

[HoytFlinger]

G1 works best for short flat base bullets. G7 will work best with long boat tail bullets meant for long range like Berger, SMK, and Amax. That is the simple answer from Accurate Shooter.

 

[BuckDoeHunter]

Your numbers are very close to the numbers I ran. My calculator said to turn the knob up 21 clicks(1/4 inch click at 100yds). Not sure in MILS

Were u shooting at 200yds? Are u sure u rotated the knob the right way? Something is not right.

 

[Lee 9]

I had that issue with one of my loads and ended up finding out that over a long period of time and quite a bit of travel in truck and ATV the bullet sabot had moved slightly off the powder and I needed to check the seating of the bullet sabot every couple of weeks.

 

[tpcollins]

Were u shooting at 200yds? Are u sure u rotated the knob the right way? Something is not right.

Really?

G1 works best for short flat base bullets. G7 will work best with long boat tail bullets meant for long range like Berger, SMK, and Amax. That is the simple answer from Accurate Shooter.

I change the drag setting to G7 and the drop reduces to 8" with a 1.1 mill up ( 3.96"). I use a SpinJag on a special ramrod so I'm not distorting the polymer tip during the loading process. But for next year I will mark up a dowel and check for bullet movement during the season. I've always taken my ML out to the garage a few days before loading to allow it to acclimate to the temperature before loading. I'll get it figured out but it just seems odd that it drops that much. The scope is rock solid in the mounts but maybe something happened that I didn't notice.

 

[BuckDoeHunter]

Were u shooting at 200yds? Are u sure u rotated the knob the right way? Something is not right.

Really?

.

Yes, I've done it. Sometimes it just the easy stuff but apparently not in your case.

 

[tpcollins]

I had a rough idea where 200 yards was going to be based on the ruler option in Google Earth and I verified the distance by scanning the side of my pickup with a Leica CRF900 rangefinder.

Since the zero stop is set correctly, it would be pretty hard not to find 14 (1.4 Mills) on the turret dial with this Zeiss Duralyt.