Hunting vs Match (1MIL left at 250 yards)

[howabouttheiris]

Seen a funny one today at the range.... unsure what to think of it.

308 Savage FTR
1-12 30" barrel
bipod / rear bag
level checked with level
wind near 0 and light fog

168g BTHP (PRVI Match) zeroed at 100, (shot 500/750/1000) planning on using this setup to hunt, so I moved to 250, put 5 into same paint chip on plate.

Switched to 165g Fusion hunting round missed plate... seen impact adjusted and found plate with next shot, shooting ~1' high and ~1' left.

Fixed POA and it consistently grouped.

I can understand some to most of the high, as it is a faster round (extrapolating, I am getting ~2850 vs ~2650 for the PRVI), but the left is boggling my mind.

Switched back to the PRVI and the old zero was on .... so my original zero was sound.

Thoughts?

 

[CatShooter]

Switching loads/bullets often moves the poi in any direction - not just up and down.

 

[howabouttheiris]

Just never seen it to this extent. Had a click or 2 in the past, but never 10.

 

[brian427cobra]

Those 168s will kill .... dead

 

[Matt Pitchon]

In my 223, I have seen a windage shift of this magnitude when switching from 55gr hunting to 75gr match. I have not seen it when switching from 75gr match to 90gr match. I don't know why. I can speculate that it has to do with the jump. My 75s and 90s are either just off the lands or jammed. The 55s are way off as they are too short.

 

[holl]

What Id want to know is after I zeroed for the new round, does the hold over/ elevation stay the same at other distances? Does it drop the same as the match round?

 

[nastynatesfish]

Barrel harmonics will play hell with you. I did the same thing. I think it's more the shape of the bullet, ya the added velocity too

 

[howabouttheiris]

I can speculate that it has to do with the jump.

I did notice a significant difference in the length. The match were on the lands (some slight bolt resistance) and the hunting round was definitely off the lands (never any bolt resistance).

I will try some heavier (possibly longer) hunting rounds to see if I can find a common windage. I would love to shoot a match / game pair that are fairly comparable during hunting season. Just hate the thought of significantly switching numbers between the range and the field.

 

[howabouttheiris]

Got a chance to work with a variety of ammo this weekend to take a second look at what I was seeing with the change in zero.

I started with the PRVI 168g match ammo again and verified my zero. Group was about 2" at 100 yards. I am pretty disappointed with this, as I was a huge fan of the price/accuracy ratio of the 69g match in my .223.

I switched to Fusion 165g hunting ammo and fired a 4 shot group (they shot a single hole cloverleaf, 0.7mil high and 0.7mil left)
I switched to Federal Premium 168g VitalShok and fired a 4 shot group (they shot about a 1.5" group, 0.2 mil high and 0.2 mil left)


I will be using the Fusion for the hunt, so I set my caps to that zero. I am really pleased with that ammo, for mid priced rounds, it shoots well.

I switched to 250 and then 500, and the rounds all followed the ballistic charts to hit steel.


It appears to be an issue with the length, as the PRVI were difficult to chamber, with the projectile definitely further out of the casing than the others.

Another slap to the head reminding me I need to start hand-loading.

 

[Lapua40X]

We often think of ballistics (trajectory) and barrel harmonics in simple terms of MV and linear barrel dynamics without giving full value to their broader implications and some of the more subtle factors involved. Barrel harmonics are not limited to the longitudinal whip action that we most commonly think about when we think of vertical spread. The barrel "whip" includes a rotational factor that can move the POI horizontally, relative to MV. We know that two identical loads will differ in how they print on the target when fired from a heavy barrel vs a lighter weight barrel (e.g. hunting rifle) and that two different loads from the same rifle will print differently, horizontally AND vertically, with a different load combination. The differences in point of impact will be more dramatic in a rifle with a light weight barrel.

 

[jcampbellsmith]

..I switched to Federal Premium 168g VitalShok and fired a 4 shot group (they shot about a 1.5" group, 0.2 mil high and 0.2 mil left)....

A small question. Am I the only one confused by your mix of metric and imperial measurements. Surely if you are using mils, cm and m follow naturally?

Regards

JCS

 

[mikecr]

I don't see radians as anymore metric than minutes.
While you could apply metric math to it, we can apply imperial, either way.

 

[howabouttheiris]

I am a Canadian living in Texas.... Just thought I was helping. :-\


So... the group was almost 0.38 decimeters. Hope that clears things up.


Like mikecr, I also don't normally associate the mil/moa option to metric/standard.... as for most I assume the choice is more based on what scope measurement you bought into.

 

[SAFEshooters]

Switching anything will most likely, inherently, change the POI. Two bullets, same weight & velocity, but with a different type of ogive will have a different POI.