250 A-Tip Trouble No More, BC does match *update*

[Scwalker83]

I have a 300 Norma barrel sitting in a DT A2 Chassis. Barrel is spun up by ES Tactical, 28"s 1-8 twist. Around 80 rounds on the barrel.

Decided on a load of 81.9 Retumbo in Lapua brass @ 3.6 oal w/ FG215m primer.

Chronographed w/ Magneto speed V3 @ 2860 w/ SD of 9 in virgin brass on 3 different occasions. Groups are sub half and totally sufficient for the purposes of this rifle.

Prior to that I chronographed my 6 Dasher and it reflected what I expected but I did not shoot at distance that day with the rifle. It did however shoot a match the prior weekend at the same velocity that matched expected dope.

I shoot and am consistently low at distance. So much so that I have to adjust from Hornady's published .878 G1 to .72 G1 to make it line up in JBM ballistics. I use the truing feature on my Kestrel and it changes velocity to 2785 to make it reflect reality. This is approximately an 18% decrease in BC.

I place watermarks on steel going from 500-900 yards and the 'adjusted' data is correct, it shoots the watermark every time going out.

Conditions were fairly cold. 28F, 30% humidity, 6k elevation. Strong headwind of 15 mph per Kestrel.

Berger stability calculator indicates that the bullet is plenty stabilized in the 1-8 barrel.

Does anyone know what's going on? I've double checked everything I can think of.

 

[culater]

Weather is a big factor here I believe. You might be getting wind shear effects from the head winds. Pushing the bullets downwards. I've have notice that sometimes when I go shooting with strong head winds. Wind is like water it directly effects everything when shooting. Plus shooting in colder weather can change your POI at 100 yards up to a 1/2 MOA or more from your original DOPE. So my advice is to have two DOPE cards. One for fall and winter weather and one for summer. That's why you go shoot in all conditions to find out what your load does. I have a DTA also I've got to get out and shoot in the cold this week. To find out what it does. With a DTA we have a clamp system that might shrink because it's cold outside. It will change your original DOPE. Try letting it sit outside for and hour before shooting along with the ammo. Then tighten the screws on the clamp. Then go shoot and recorded what happened and make a new DOPE cards. Just some things to think on

 

[Scwalker83]

Weather is a big factor here I believe. You might be getting wind shear effects from the head winds. Pushing the bullets downwards. I've have notice that sometimes when I go shooting with strong head winds. Wind is like water it directly effects everything when shooting. Plus shooting in colder weather can change your POI at 100 yards up to a 1/2 MOA or more from your original DOPE. So my advice is to have two DOPE cards. One for fall and winter weather and one for summer. That's why you go shoot in all conditions to find out what your load does. I have a DTA also I've got to get out and shoot in the cold this week. To find out what it does. With a DTA we have a clamp system that might shrink because it's cold outside. It will change your original DOPE. Try letting it sit outside for and hour before shooting along with the ammo. Then tighten the screws on the clamp. Then go shoot and recorded what happened and make a new DOPE cards. Just some things to think on

Sorry about the late reply. Thank you so much for your time in responding. It indeed was weather related. As soon as I went on my hunt cow elk hunt we got on a perch overlooking a meadow. Saw some elk. Ranged them, at 1106. Used my 'bad' dope from the first post, shot over the elk. The elk didn't know what happened and were milling around.

Swapped my profile on my kestrel to the original dope with velocity at 2860. Shot twice as shown on the inside of the rib cage. No exit wound. Elk moved about 15 yards between first and second shot. Didn't need second shot but I wasn't sure about my first given the bad dope on the previous one.