POI Shift with Fed SMKBTHP .308

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06-18-2018, 09:41 PM
Andrew.Riehle

POI Shift with Fed SMKBTHP .308

Looking to see if anyone else has ever experienced this...

I zero'ed my new 10 FCP-SR .308 with 168gr Federal SMKBTHP about 2 months ago. This past weekend I went out to a range to get some true muzzle velocity and do a box test with my scope. I had some rounds left from the same box I used to zero with, so I decided to use the up first before I switched to the new boxes. I anticipated a slight POI shift as I zeroed at an indoor range, and now shooting at an outdoor range. There was about a 1/2 to 3/4 in POI shift. That's not the issue though, just giving some back ground. Once I used up that box and was happy with my grouping... I switched to a new box (Different lot). Moved my POA to an fresh area on the target and shot the first round and wouldn't you know it... 2" at 100 yards. I was like WTF!! Shot 2 more rounds with the same results. The group was tight, just 2" higher than my POA.

I've been shooting off and on for the past 30 years. Even dabbled in reloading for a while. I've never had that large of a POI shift when firing the same brand/grain ammo. Certainly didn't expect that from a match grade factory load. Once I dialed down 2" on my scope, the rest of the box grouped as expected (POA equaled POI).

I changed nothing on the rifle or scope between lots. I simply loaded up the new lot and fired.

My only explanation to this is different lot #'s. Anyone else experience this?
06-18-2018, 09:53 PM
lonestardiver

New lot of ammo can do it.
That is why some buy large quantities of the same lot. You especially see that in rimfire target shooters.
06-19-2018, 08:24 AM
LoneWolf

I bet if you had chrono'd both lots you'd get different results.... There is always some kind of variation between lots of powder, lots of bullets, and lots of brass. Then add in the fact that they likely were loaded on different machines and it all starts to make sense....
06-19-2018, 09:57 PM
Andrew.Riehle

I should have chrono'd the second second lot, but didn't. In all these years, I'd never guessed there'd be that much of a shift. Makes me want to get back into reloading.

Quote:

Originally Posted by LoneWolf

I bet if you had chrono'd both lots you'd get different results.... There is always some kind of variation between lots of powder, lots of bullets, and lots of brass. Then add in the fact that they likely were loaded on different machines and it all starts to make sense....
06-19-2018, 10:03 PM
lonestardiver

Even with reloading, new lots of powder or primers can change things. Sometimes different lots of bullets can have a similar effect. Change all three at the same time and the changes can be more evident.
06-20-2018, 10:17 AM
mark r

A few months ago, I purchased 60 rds of hornady 150gr sst for .300 savage. I weighed all the rounds and their was 5gr difference. The vast majority were with-in 1 1/2 grs. of each other which I use for sight-in and hunting, the others I use for fouling shots after cleaning, The point of impact between the low and high ends was 1 3/8" difference. The others I can keep with-in 7/8" group at 100yrds. Some food for thought.
06-21-2018, 12:04 PM
PaddyD

No ammunition will always shoot the same. Even ammo from the same box. Try zeroing with it in July, then go out in the middle of November and see how it groups.. Temperature has a bigger effect on pressures and velocities than some realize. The fact that you experienced dissimilar groupings and POI 2 month apart leads me to suspect temp was your culprit.
06-21-2018, 08:49 PM
Andrew.Riehle

Yeah, I zero'ed it on an indoor rage, then shot with the same lot/box outdoors. So, yes there was a POI shift, which I adjusted for and the group were great. I then switched to a new box/lot. The groups were still great... Just 2" high from where I was with the old box/lot. Like I said before... I get the fact that there would be a shift, just wasn't expecting a 2 MOA shift.

Quote:

Originally Posted by PaddyD

No ammunition will always shoot the same. Even ammo from the same box. Try zeroing with it in July, then go out in the middle of November and see how it groups.. Temperature has a bigger effect on pressures and velocities than some realize. The fact that you experienced dissimilar groupings and POI 2 month apart leads me to suspect temp was your culprit.