Trying to get my head around this one ...
I worked up a new load with 168gr SMKs over IMR4895 last week and when testing I found my elevation zero had to be brought up .9 mils. Running thru the dope tables it was within .2 mils of the previous load (IMR4064) all the way to 400 yards. I figured ... "New load, new POI so I need to change my zero. i get it."
But when I fired some of the 4064 loads I changed my zero elevation back to what I had used to prove the dope tables withit previously, and it was about .8 low. I had to use the new zero elevation for the old load also. Almost a full mil. Both loads still shot within .1 or .2 mils of the dope table - 50 yard increments to 400 yards - and only the zero changed.
The JBM calcs doesn't reflect this great of a change given the temp, humidity and pressure difference. In fact, there was almost no change at all indicated in JBM. The difference in temp was only 4 degrees F from the last time I zeroed and shot thru the dope. I checked every nut and bolt and fastener and nothing was loose. In fact, the new OCW load and the old load with now-separated brass are both shooting 1/2MOA to 400 if I'm having a good day. My best groups ever.
Anyone have an idea why the POI changed so drastically on the zero for both loads? I mean ... this is almost a full mil POI change on the zero, while the dope stayed the same, essentially. I must be missing soemthing?
I worked up a new load with 168gr SMKs over IMR4895 last week and when testing I found my elevation zero had to be brought up .9 mils. Running thru the dope tables it was within .2 mils of the previous load (IMR4064) all the way to 400 yards. I figured ... "New load, new POI so I need to change my zero. i get it."
But when I fired some of the 4064 loads I changed my zero elevation back to what I had used to prove the dope tables withit previously, and it was about .8 low. I had to use the new zero elevation for the old load also. Almost a full mil. Both loads still shot within .1 or .2 mils of the dope table - 50 yard increments to 400 yards - and only the zero changed.
The JBM calcs doesn't reflect this great of a change given the temp, humidity and pressure difference. In fact, there was almost no change at all indicated in JBM. The difference in temp was only 4 degrees F from the last time I zeroed and shot thru the dope. I checked every nut and bolt and fastener and nothing was loose. In fact, the new OCW load and the old load with now-separated brass are both shooting 1/2MOA to 400 if I'm having a good day. My best groups ever.
Anyone have an idea why the POI changed so drastically on the zero for both loads? I mean ... this is almost a full mil POI change on the zero, while the dope stayed the same, essentially. I must be missing soemthing?
