Range Report Help with 308 load question

[Turk10mm]

I'm using a Shooting Chrony Beta that shows my average to be about 2660 at 10ft. I'm shooting berger 175 hvld from a 20" barrel. 44.7gr Varget 2.005 OAL which is .007 jammed. Lapua brass, CCI BR2 primer.

JBM shows my 200 and 300 drops to be 1.8" and 4.5" respectively. But when I shot today I was dead on at 200 with 1.75 dialed in. But at 300 I doped 4.5 and was over 2" high.

If I play with the velocity and up it to 2700 in jbm then I get 1.7" which is still what i shot with today at 200, but my 300 goes to 4.25 which is what my real dope was after changing my dope from 4.5.

Can I really be running 2700 and my chrony is wrong?

I need to go out to the 600 yard range and vet out my dope, but I don't have time before I go LR hunting.

 

[azimutha]

Re: Help with 308 load question

The short answer is you really need to make that time to dope out to 600 if you're going to ethically hunt LR...unless we're talking pigs or 'yotes. But even then, wouldn't you want to be proud of every shot?

More info would help...like all the settings you're entering in JBM (you can copy/paste that from the results page). Also, it's a bit confusing. Were you shooting .308 Win (assuming the 2.005 OAL was meant to be 2.805???). Assuming a 100 yard zero, how are you getting numbers like 1.8" @ 200 and 4.5" @ 300? I shoot 175 gr. OTMs with a lower BC but at higher altitude @ 2795 FPS and my drops are 3.2" @ 200 and 12" @ 300.

Provide those JBM details first and maybe there will be some clue there on what to correct. Also, confirm what cartridge you're shooting.

 

[Turk10mm]

Re: Help with 308 load question

Thanks for your assistance, 2.005 ogive sorry, not OAL.

Input Data
Ballistic Coefficient: 0.498 G1 Caliber: 0.308 in
Bullet Weight: 175.0 gr

Muzzle Velocity: 2660.0 ft/s Distance to Chronograph: 10.0 ft

Sight Height: 1.80 in Sight Offset: 0.00 in
Zero Height: 0.00 in Zero Offset: 0.00 in
Windage: 0.000 MOA Elevation: 0.000 MOA
Line Of Sight Angle: 0.0 deg Cant Angle: 0.0 deg

Wind Speed: 10.0 mph Wind Angle: 90.0 deg
Target Speed: 10.0 mph Target Angle: 90.0 deg
Target Height: 12.0 in

Temperature: 75.0 °F Pressure: 30.09 in Hg
Humidity: 77 % Altitude: 26.0 ft

Vital Zone Radius: 5.0 in

Std. Atmosphere at Altitude: No Pressure is Corrected: Yes
Zero at Max. Point Blank Range: No Target Relative Drops: Yes
Mark Sound Barrier Crossing: Yes Include Extra Rows: No
Column 1 Units: 1.00 in Column 2 Units: 1.00 MOA
Round Output to Whole Numbers: No
Output Data
Elevation: 4.162 MOA Windage: 0.000 MOA

Atmospheric Density: 0.07389 lb/ft³ Speed of Sound: 1133.6 ft/s

Maximum PBR: 329 yd Maximum PBR Zero: 280 yd
Range of Maximum Height: 155 yd Energy at Maximum PBR: 1736.0 ft•lbs

Sectional Density: 0.264 lb/in²
Calculated Table
Range Danger Space Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
0 *** -1.8 *** 0.0 *** 2666.0 2.352 2761.3 0.000 0.0 ***
20 0-256 -1.0 -4.9 0.0 0.1 2630.3 2.320 2688.0 0.023 4.0 19.0
40 0-245 -0.5 -1.1 0.1 0.3 2595.0 2.289 2616.2 0.046 8.0 19.2
60 0-237 -0.1 -0.1 0.2 0.4 2559.9 2.258 2546.0 0.069 12.1 19.3
80 0-233 0.1 0.1 0.4 0.5 2525.1 2.228 2477.2 0.093 16.3 19.4
100 0-232 -0.0 -0.0 0.7 0.7 2490.6 2.197 2409.9 0.116 20.5 19.6
120 0-234 -0.3 -0.2 1.0 0.8 2456.3 2.167 2344.1 0.141 24.8 19.7
140 0-238 -0.8 -0.6 1.4 0.9 2422.3 2.137 2279.7 0.165 29.1 19.8
160 0-246 -1.6 -0.9 1.8 1.1 2388.6 2.107 2216.6 0.190 33.5 20.0
180 0-255 -2.6 -1.4 2.3 1.2 2355.1 2.078 2154.9 0.216 37.9 20.1
200 0-266 -3.8 -1.8 2.8 1.4 2321.9 2.048 2094.6 0.241 42.4 20.3
220 0-279 -5.3 -2.3 3.5 1.5 2288.9 2.019 2035.5 0.267 47.0 20.4
240 144-293 -7.1 -2.8 4.1 1.6 2256.2 1.990 1977.8 0.294 51.7 20.6
260 189-308 -9.1 -3.4 4.9 1.8 2223.8 1.962 1921.3 0.320 56.4 20.7
280 221-323 -11.5 -3.9 5.7 2.0 2191.6 1.933 1866.1 0.348 61.2 20.9
300 250-339 -14.1 -4.5 6.6 2.1 2159.7 1.905 1812.1 0.375 66.0 21.0
320 276-356 -17.0 -5.1 7.6 2.3 2128.0 1.877 1759.4 0.403 71.0 21.2
340 301-373 -20.2 -5.7 8.6 2.4 2096.6 1.850 1707.8 0.432 76.0 21.3
360 325-390 -23.8 -6.3 9.7 2.6 2065.5 1.822 1657.5 0.460 81.0 21.5
380 348-408 -27.6 -6.9 10.9 2.7 2034.7 1.795 1608.4 0.490 86.2 21.7
400 371-426 -31.8 -7.6 12.2 2.9 2004.1 1.768 1560.4 0.519 91.4 21.8
420 393-444 -36.4 -8.3 13.5 3.1 1973.8 1.741 1513.6 0.550 96.7 22.0
440 415-463 -41.3 -9.0 15.0 3.2 1943.8 1.715 1467.9 0.580 102.1 22.2
460 437-481 -46.5 -9.7 16.5 3.4 1914.1 1.689 1423.4 0.611 107.6 22.3
480 459-500 -52.2 -10.4 18.1 3.6 1884.7 1.663 1380.0 0.643 113.1 22.5
500 480-519 -58.2 -11.1 19.8 3.8 1855.6 1.637 1337.7 0.675 118.8 22.7

 

[Turk10mm]

Re: Help with 308 load question

Sorry, what i meant was 1.75 and 4.5 at 100, what i doped into the scope.

 

[Turk10mm]

Re: Help with 308 load question

one other thing to note, the 200 yard target was actually 208 and the 300 was 301 lazed. The only reason I mention that is it supports the fact that i was dead on at 200 if my velocity was indeed 2700. I was dialed in 1.75 and jbm says 200 is 1.7 at 2700fps.

 

[azimutha]

Re: Help with 308 load question

Okay, I gotcha ya. Looks like you're running the numbers right in JBM. Sometimes altitude can get messed up, but being where you are that's not an issue! So looking at what might be going on, you may well have an actual MV that is higher. Or your scope may not be precisely calibrated.

I've spent some time around Houston so I realize getting to a 600 yard range may be hard to do, but still it would be really good to get that number. Then you could interpolate the 400/500 yard numbers. Where are you going hunting? In terms of approx. elevation and temperatures?

 

[Turk10mm]

Re: Help with 308 load question

Junction, 2200 feet few degrees cooler than houston. I never thought about checking my scope. I guess I could run up 4.5 at 100 and verify that I'm not geting more than that pretty easily.

Its a nightforce 3.5x15 so I hope the scope is good.

I will try to make it out to American this weekend and shoot 600.

Thanks for your help.

 

[azimutha]

Re: Help with 308 load question

Chances are the scope is good. I've never had a problem with a NF. So it may well boil down to the chrony under-reading the MV. As far as the bullet is concerned, Berger's numbers are ones I trust since they're calculated by Bryan Litz.

If you can get a reliable dope @ 600 you can use that along with tinkering with the MV in JBM to get a decent drop table between 200-600. Interesting that weather reports there seem to only report corrected pressure (http://forecast.weather.gov/MapClic...l&smap=1&searchresult=Junction, TX 76849, USA). The reason I looked is in case you don't have a barometer (in a GPS or wind meter) to get station pressure. Fact is, if you're within 10 degrees and around 2000 ft. the drop @ 600 would only vary about 3".

 

[Turk10mm]

Re: Help with 308 load question

Thanks for the help. I'll get down to American and shoot their 600 and see what's up.

 

[Turk10mm]

Re: Help with 308 load question

Azimutha, thanks for your help. I shot 100, 300, 600 and 615 yesterday. Turns out, my zero at 100 was shooting almost 1/2" high. I zero'd the rifle to absolute zero, shot 300 with 4.5 dialed in per jbm and hit center bull at 300. Went out to 600 and 615 and had 15 and 15.25 dialed in and hit poa per jbm.

So the culprit was 1/2" high on my 100 zero.

 

[George63]

Re: Help with 308 load question

for the best MV off jbm, I like to get a 25 yd come up (measured from target to scope turret, not muzzle), then another accurately measured distance, as far as possible - as long as all the other parameters entered are good it will be better than about any chrony

 

[azimutha]

Re: Help with 308 load question

Turk, good to hear...sounds like you got it worked out great.

George63, that sounds like a method I'd like to combine with chronograph-measured MVs. I'd want all other variables, particularly the BC (I only trust Berger/Litz numbers), correct. Also, if using carefully prepared handloads or match ammo, MV (SD) shouldn't vary much. It seems to me that even at my most convenient range, which only goes out to 300, this could be a good confirmation technique.