Large Shift in POI with .308 Ammo Change

Tungsten · Apr 1, 2018

Recently I was shooting at 200yds with Winchester 150gr Power Points. POA and POI were the same. I switched over to 168gr Federal Matchking Gold BTHP to see if I could tighten up the groups. POI changed 4 inches right and ~22 inches down.

I know that POI changes when you change ammo, but that seems extremely excessive. I checked scope, stock, etc and everything seems tight. I was having to aim off target, but I got a roughly consistent (right and very low) group (~6").

I was out of the Winchester ammo, otherwise I would have shot a few more just to confirm POI was normal for it again, but have any of you experienced that amount of change upon switching ammo? Should I be looking at chamber/head space issues?

namrelio · Apr 1, 2018

Heavier grain.

danb · Apr 1, 2018

22" seems like an awful lot. A quick calc suggests over 1000 feet per second difference. More that what is explainable simply weight and powder. Are you sure that they were not subsonic or something? If not, either a bad batch of bullets or your scope crapped out.

BradMacc82 · Apr 1, 2018

22" drop/gain at 200 is extreme. 4" to the right is also a bit much.

I'd be betting on either a horrible batch of ammo, or something mechanically crapped the bed.

BradMacc82 · Apr 1, 2018

Type of rifle, stock, and optic?

Did you check everything by hand, or by torque wrench?

Tungsten · Apr 1, 2018

Checked by hand, not torgue wrench.
Savage 11/111 Trophy Hunter XP (replaced stock after the original one split and allowed the action to be loose)
3-9x40mm Nikon® scope

I looked the rifle over when I got home, nothing seems loose. Both batches of bullets are store bought, 2017/2018 stamped.

My accuracy has not been good, 5-6" @200yd grouping typical with the Winchester. I have always assumed it was my rather poor skill level, but with this drastic shift in POI, I am now wondering if I have mechanical issues in addition to "me" issues. I shot everything from prone position off of a bipod.

Alea Jacta Est · Apr 1, 2018

Sounds mechanical to me.

danb · Apr 1, 2018

Its can be very hard to know when a scope breaks. I've had it happen. Sometimes it clear that the reticle is moving around, sometimes not.

Ponch · Apr 1, 2018

what is the twist rate of the barrel? Were you using a rest, stand bags, anything? I am a fan of 168 or 175gr out of my 308s but go with what works.

Tungsten · Apr 1, 2018

Using bipod.
The scope is the factory supplied one that came with the rifle. It seems to hold zero between range sessions up to this point.
22" 1 in 10 twist barrel

BradMacc82 · Apr 1, 2018

First inclination, I'd say ditch those rings and scope. Factory 'package deals' rarely have a optic worth keeping. It may be a Nikon, but it doesn't mean it's one of their better offerings. But I'm also really inclined to say you just shot something loose, be it the rings onto the scope base, or the scope base to the receiver.

If nothing else, strip it down and use a torque wrench - for a wood stock 40in/lbs is plenty, synthetic stock 30/35in/lbs is fine, stock/chassis with aluminum block 60in/lbs is your huckleberry. For Savages, I've had best luck torquing the front action screw, and then the rear one (the one at the trigger guard).

Scope base - 25in/lbs is sufficient, but make sure it actually lays flat/snug on the receiver. Rings, I normally use Warne's and set them at 40in/lbs. When in doubt, go with manufacturer recommendation.

If nothing else, torque everything properly, and then shoot. Run a box test with your scope - it's adjustments will only be accurate at the maximum magnification, per Nikon. If it isn't tracking properly/accurately, toss the optic and the rings.

Tungsten · Apr 1, 2018

Sounds like i have some tinkering to do. Thanks for the information on what to look for.

davsco · Apr 1, 2018

basically you're saying the same group size with both ammo's, 5-6" at 200 yds, which is nothing to write home about. but that huge of a drop between different ammo isn't right. but frankly with those large group sizes, i'd have someone else shoot some groups and see what happens with each ammo type. but yeah check over the entire gun for anything loose (scope base and rings, comp or flash hider). also, try shooting at 100yds and see what happens, maybe the 9x isn't enough for you at 200 yds. when you dry fire are the crosshairs remaining on the center of your 200yd target?

BradMacc82 · Apr 1, 2018

For what it's worth, when my buddy in VA bought his Rem 700, it was one of those package deals. Shot OK, but nothing to write home about. After going thru it, torqued everything properly and made sure the reticle was as level as humanly possible, it did shoot better, but that 3x9 'package deal' scope/ring combo was the weakest part of the equation. Once he upgraded the optics/rings, his shooting improved noticeably. Until his son dropped the rifle onto a concrete pad...

Most Savages tend to shoot, most of the time pretty well out of the box - there's always the chance there could be a manufacturing defect that slipped thru QC, but typically Savage does a pretty good job of turning out shooters instead of duds.

Tungsten · Apr 1, 2018

BradMacc82 said:
Most Savages tend to shoot, most of the time pretty well out of the box - there's always the chance there could be a manufacturing defect that slipped thru QC, but typically Savage does a pretty good job of turning out shooters instead of duds.

I'm positive that I'm the weak link in the accuracy of the rifle. My technique can use a lot of improvement, but I do think something else is going on as well.

To do list:
1. Change scope/rings
2. Shoot off a sandbag instead of bipod (I'm fighting the hop)
3. Find a lucky rando at the range and see if they can do better

Major03 · Apr 2, 2018

Just curious...did you ever switch back to your original load? If so, what were the results?

Tungsten · Apr 2, 2018

Major03 said:
Just curious...did you ever switch back to your original load? If so, what were the results?

I thought of that but had finished the box of the original ammo before switching. I still have a box of the Winchester at home, so next time I'm out I will be sure to leave a few rounds to switch back and forth and see if I still see a large difference.

I think I'm going to go ahead and get a new optic/rings regardless of any other issues I identify.

onedash · Apr 2, 2018

I have a Remington 7400 30-06 with a leupold vari x-ii variable and leupold base/rings. I have been using the 165 gr AccuTip for a long time and since they are getting almost impossible to find I tried some Federal ammo (180gr) that I picked up cheap when a gun store was going out of business. We stop at a range on our way to the hunting cabin most years and check our bzo @ 50 yards. It was dead on with the Remington ammo. I wanted to see if the federal would shoot in the same hole. It did not. I don't remember exactly but It was probably ~ 2" off in elevation (low) and windage. Still not quite as extreme as your results but some weapons have a favorite load. The box test can tell you if the scope is ok but if you and or rifle can't shoot decent groups I'm not sure if it will tell you much.

smokey · Apr 2, 2018

lazarus · Apr 2, 2018

What’s your 100 hard group look like and have you shoot several other kinds of ammo through the rifle?

My .308 Sako was having to struggle for 2” groups with match ammo and 3-4” groups with m80. That was at 100yds. After a year of struggles I swapped my other Bushnell trophy 3-9x40 on to the rifle. My groups dropped to .5” groups with PPU 155gr MHPBT (its a 12.7:1 twist, so it prefers lighter ammo). M80 was shooting a little under 2” groups.

Scope buggered (Bushnell sent me a new one).

If you have a spare scope or can swap from another rifle try that.

The POI shift doesn’t really account for scope issues though. I’d swap ammo and not see more than a 1-2” shift at 100yds and I don’t think I saw more than a 4” shift at 200yds when my scope was messed up (or now for that matter).

Large Shift in POI with .308 Ammo Change

The #1 community for Gun Owners of the Northeast

Member Benefits:

Ultimate Member

Ultimate Member

dont be a dumbass

Ultimate Member

Ultimate Member

Ultimate Member

Extinguished member

dont be a dumbass

Member

Ultimate Member

Ultimate Member

Ultimate Member

Ultimate Member

Ultimate Member

Ultimate Member

Ultimate Member

Ultimate Member

Ultimate Member

2A TEACHER

Attachments

Ultimate Member

Users who are viewing this thread

Log in

Forum statistics