POI shift due to different weight projectiles

AR-15 » Ammunition

AR Sponsor:

Site Notices

2024's Favorite CCW? | PSA Micro Dagger

[ARCHIVED THREAD] - POI shift due to different weight projectiles

Posted: 10/15/2018 12:03:02 AM EDT

I noticed that with 6.8 spc 130 grain Sierras at 2250 fps I get a different POI than 110 grain with Hornady V-max that are going closer to 2500 fps and have a POI that's higher.

How much deviation in POI is normal when going from 130 grain projectiles to 110 grain ones? The trajectory remains similar but the POI shifts 2.5" inches at 100 yards.
Is that enough to re-zero it or just leave it alone?

Posted: 10/15/2018 12:40:28 AM EDT

[#1]

Are you ok with it being 2.5” off? Zero it to the kid you use most.

Posted: 10/15/2018 7:07:20 AM EDT

[#2]

I would say there is no normal. I shoot 3 different loads of the same bullet in my 308, they all have a different POI.

In my Grendel my 140cc load is different than my 140hyb load by an inch, my 147 load is 2.5" from my 140hyb load.

My thinner profile AR barrels SEEM to have more poi shift load to load than my very heavy profile barreled .308.
I'm not sure barrel stiffness really has an effect, maybe it just seemes that way, don't care enough to look into it.

Rezeroing is up to your needs. For my precision rifles that I shoot long range, I get one load close and that is it I never rezero the scope for that load or any other load.
I use the zero offsets in my ballistic calculator and it acoounts for where my bullet is at 100yds in relation to the poa.

For shorter range rifles I zero for my most used load or most important load(hunting load is more important than a plnking load).

Posted: 10/15/2018 11:33:27 AM EDT

[#3]

I zero with what I shoot most, or if it’s a hunting/HD rifle I zero with what it’ll be loaded with. It’s never been more than maybe 1” POI shift at 100 for me, but obviously you’ll want to verify for yourself.

Posted: 10/15/2018 2:41:50 PM EDT

[#4]

Quote History

Quoted:

My thinner profile AR barrels SEEM to have more poi shift load to load than my very heavy profile barreled .308.
I'm not sure barrel stiffness really has an effect, maybe it just seemes that way, don't care enough to look into it.

View Quote

Barrel harmonics definitely play a significant role. Heavy bull barrels will almost always have less POI shift between different loads than a lighter profile barrel.

Posted: 10/16/2018 4:13:43 PM EDT

[#5]

It is an interesting point you make.

Posted: 10/16/2018 4:16:26 PM EDT

[#6]

They already mentioned it... i was going to ask what profile is your barrel?

Posted: 10/16/2018 9:11:21 PM EDT

[#7]

It's kind of a medium profile. Neither pencil barrel nor the heavy target type.

Posted: 10/18/2018 8:45:21 PM EDT

[#8]

Barrels do what barrels do.

Set your sights and shoot, it's common with all kinds of ammo.

Posted: 10/19/2018 9:30:43 PM EDT

[#9]

Quoted:

I noticed that with 6.8 spc 130 grain Sierras at 2250 fps I get a different POI than 110 grain with Hornady V-max that are going closer to 2500 fps and have a POI that's higher.

How much deviation in POI is normal when going from 130 grain projectiles to 110 grain ones? The trajectory remains similar but the POI shifts 2.5" inches at 100 yards.
Is that enough to re-zero it or just leave it alone?

View Quote

Absolutely normal in any caliber.

-Stooxie

Posted: 10/23/2018 9:37:10 PM EDT

[#10]

Makes sense.

Posted: 10/27/2018 3:38:17 PM EDT

[#11]

I'm not sure about 6.8 SPC, but let me tell you what I've found on some other guns.

I have a Mauser 98 in 7.92x57mm with a 29" barrel. Using Turkish surplus ammo with a 157 gr bullet, my POI is 0.5" high at 50 yards. Using Romanian surplus with a 170 gr bullet, my POI is 4.0" high at 50 yards. I think the velocity is way higher on the Turkish ammo. There is no difference in windage.

In two different M1 Garands US, Korean, and Greek .30-06 150 gr FMJs shot exactly the same. They had the same bullet weight and profile.

Generally I've noticed that heavier bullets hit higher. You don't tend to see a windage shift, but in some cases you do if it's a different bullet type (like FMJ vs. SP).

Posted: 10/27/2018 9:26:40 PM EDT

[#12]

Quote History

Quoted:
I'm not sure about 6.8 SPC, but let me tell you what I've found on some other guns.

I have a Mauser 98 in 7.92x57mm with a 29" barrel. Using Turkish surplus ammo with a 157 gr bullet, my POI is 0.5" high at 50 yards. Using Romanian surplus with a 170 gr bullet, my POI is 4.0" high at 50 yards. I think the velocity is way higher on the Turkish ammo. There is no difference in windage.

In two different M1 Garands US, Korean, and Greek .30-06 150 gr FMJs shot exactly the same. They had the same bullet weight and profile.

Generally I've noticed that heavier bullets hit higher. You don't tend to see a windage shift, but in some cases you do if it's a different bullet type (like FMJ vs. SP).

View Quote

I have seen windage shift's many times, even with ammo of the same weight.

Maybe not as much as vertical, but plenty.

I shoot a lot , on my own place in the middle of nowhere, when switching loads such as bullets even the same weight, or a change of powder,

And when I want it settled in and sighted in I pick a quiet day, and I see up's and downs and side to sides shifts with just about every change.

Not at close range, 50yds I don't think you'd see much.

Posted: 10/29/2018 11:41:18 PM EDT

[#13]

I was under the impression that lighter, faster projectiles hit higher than slower, heavier ones. However my sample size is very small.

Posted: 10/31/2018 6:55:02 PM EDT

[#14]

Quote History

Quoted:

I was under the impression that lighter, faster projectiles hit higher than slower, heavier ones. However my sample size is very small.

View Quote

I think all things being equal that would probably happen, but that oftentimes that difference is less than the difference made by barrel harmonics with each round. It’s usually enough of a difference, and individual enough, that no one can say anything definitive about POI shift other than ‘dunno, you’ll have to see for yourself on yours.’

I always zero for a particular round, but I’ve never really seen much more than 1 MOA shift @100 either so it’s mostly me being particular.

Posted: 10/31/2018 10:54:33 PM EDT

[#15]

Quote History

Quoted:

I was under the impression that lighter, faster projectiles hit higher than slower, heavier ones. However my sample size is very small.

View Quote

Sometimes yes , sometimes no. Many times if you load up some screaming lightweight ammo they will shoot lower.

Posted: 10/31/2018 11:15:53 PM EDT

[#16]

Ballistic coefficient also comes into play. Longer bullets usually have a higher BC and fly better so they can hit a little higher

Posted: 11/1/2018 10:08:10 PM EDT

[#17]

You have to pick the load you intend to shoot and zero it. When changing ammunition you have to re-zero. Differences between ammo types are expected and are routine.

[ARCHIVED THREAD] - POI shift due to different weight projectiles

AR-15 » Ammunition

AR Sponsor:

Win a FREE Membership!

Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!

You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.

Warning

Confirm Action

About AR15.COM

Stay Connected

Newsletter

Contact Us