How do you use different ammo off of your current zero?

[Spearops]

I have a new gun and I am experimenting with different ammo. For now I settled on 175 gr hpbt w a .505 bc, moving at 2620fps due to cost, availability and grouping with my rifle.
I Zeroed at 100yd and my come up at 200yd is .5.
When I shoot 168gr by the same manufacturer, moving at 2680fps, w a .462 bc my 200yd come up is 0. In other words at 200yds my turret is 0.
I am going over to the 600yd range next. I have a variety of ammo left over from my experimenting. Sticking with just the 175 and 168 ammo discussed above, how would I get a good TRY number for the 168 ammo at 300,400 etc ?
If you use weaponized math my 200yd number is 0. 0x 2.48= 0.
Even if you used .1 x2.48 you get .248 which doesn’t seem right.
A broader question is if you ran out of ammo and needed to switch to a different ammo, is there a “rule of thumb” you would use to get on target without rezeroing for each ammo?

 

[37L1]

If you know the bullet speed then you can punch that into a ballistic calculator and get your come ups.

There isn't going to a lot of difference per bullet from 100 to 200 so you will be close using what you have and adjust from there as you go out further down range.

 

[UpSideDown]

Choose which ammo is your primary round and zero with it. Then any additional rounds you’ll want to shoot a group at your zero distance and determine what the elevation/Windage offset is compared to your regular zero. Any adjustments are based off of that number.

Then you can either record dope on paper or use a ballistic calculator. I use a calc. I put the bullet info and chrono velocity in for the round and it gives me numbers for ranges and wind. I then confirm those numbers at distance and change the BC of the round in the calc until everything lines up.

For any additional rounds in that gun my calculator has an Offset for each round and I can put how much that round needs to be dialed to have a correct zero (say Up .3mil/Right .4mil gives me a true aiming point zero). Then I do the same ballistic solving for that round.

 

[KZP]

I pick one as my main round then do a few shots at 100 on paper using different bullets to see the zero changes. In my Kestrel there is an option to adjust zero height offset for that bullet profile. Each profile already has calibrated velocity from those bullets going over my chrono. I let it do all the math afterwards.

 

[danatkins]

I put the zero offset in my ballistic computer on my phone. It really helps me cause my main load is a 140 eldm and then my 1 mile load is a 135 atip and hunting ammo is 140 accubond those 2 bullets aren't cheap so if I don't have to rezero all the better

 

[canezach]

If I'm understanding your question correctly, there are a couple of ways to approach this. I have a Desert Tech and AI AX, so I have multiple barrels and even multiple loads for each barrel:

First, you'll need to pick a load and zero to that ammo. My Desert Tech is zeroed for my 140 ELDM 6.5 Creedmoor load/barrel, but I also shoot 140 BTHP, 140 Hybrids, 140 Match Burners, 139 Scenars, etc. I just shoot each load and measure the offset (actually, I just shoot them on one of those mill grid targets and take a picture so I'll always have it). From there you can either write down the offset, take a picture like I did, or if you have a Kestrel, you can enter it into the zero offset and the calculator will always keep track of it.

 

[Spearops]

So if I understand it correctly,
My zero is set using my “zero ammo”
I know my 168gr shoots 0 at 200yd so I just reset my calc to show my zero distance for that ammo to 200 instead of 100. Now it shows come up to .7 at 300.
What about the third ammo that shoots a +.9 at 200yd. I am using the Hornady app and I cant seem to get the bc to match that .9 at 200yd.
Am I on the right track?

 

[canezach]

So if I understand it correctly,
My zero is set using my “zero ammo”
I know my 168gr shoots 0 at 200yd so I just reset my calc to show my zero distance for that ammo to 200 instead of 100. Now it shows come up to .7 at 300.
What about the third ammo that shoots a +.9 at 200yd. I am using the Hornady app and I cant seem to get the bc to match that .9 at 200yd.
Am I on the right track?

I use a 100 yard zero, not a 200, but the premise is the same. You zero your scope to whatever ammo you choose. Then you're going to shoot a group using different ammo and measure the distance between point of aim and point of impact. Let's say your zeroed for the 168 load and your 175 grain load impacts one full mil low. You now know you have to add 1.0 mils to any calculated solution. You can even fire a few 175 groups to ensure consistency

 

[UpSideDown]

So if I understand it correctly,
My zero is set using my “zero ammo”
I know my 168gr shoots 0 at 200yd so I just reset my calc to show my zero distance for that ammo to 200 instead of 100. Now it shows come up to .7 at 300.
What about the third ammo that shoots a +.9 at 200yd. I am using the Hornady app and I cant seem to get the bc to match that .9 at 200yd.
Am I on the right track?

Don't use 200 yards at all. Zero your "zero ammo" at whatever distance you zero at. Then shoot the 168gr at the same exact distance and measure where the rounds hit. If they're .5mil Right and .4mil Down, record that. Dial your turrets to bring that 168gr to center, then perform all of your DOPE from there.

If you use the above numbers and your calculator says that your 168gr round will drop 3.5 mils at 500yds, then to shoot 500yds you would dial 3.9mil Up and .4mil Left.

Make sense?

 

[Spearops]

That was my original thought but I wasnt sure.
My real example is the Norma 175 is .4 low at 100. The bc for this round says adjust .5 @ 200yds but my actual was .9 which makes sense. So at 400yds the bc says 2.2 but I should add the . 4 and adjust a total of 2.6.
If that works then this is not as complicated as I thought. I was thinking that the drop would be effected exponentially the further away the target is.
Thanks for the help

 

[stefan73]

I record dope for both types of ammunition between my subs and supersonic stuff.

 

[theLBC]

168gr .308 vs 175 drop comparison? For BDC

Tried searching around couldn’t find too much. My Leupold mk4 has the BDC for 168gr .308. Without shooting both 175 and 168 to compare right now, can anyone tell me the difference in drop on paper for the 2 at various distances? Trying to figure out if I can still use the BDC with 175gr Thanks

www.snipershide.com

 

[redneckbmxer24]

1. Have optic with good tree reticle.
2. Zero optic with base/main load and zero the turrets out.
3. Shoot other loads to determine POI shift and record.
4. Use that data and adjust the knobs to change zero when shooting other loads.
5. Change ballistic profiles in your kestrel and go to work holding with the tree.

Or dial your knobs and zero them out each time so that you can dial, forget to run them back and fuck up your zero. Or don’t zero and try to remember to factor in the POI difference every time you dial. Been there done that and it gets old really quick.

200y zeros are also dumb.

 

[b6graham]

if it's REPEATABLE zero change with different then just record the zero offset for each ammo at 100y and simply plug those zero offsets into ballistic app (ideally have a profile for each ammo)

or...shoot one ammo until it's gone then rezero with the case of new ammo

 

[DownhillFromHere]

OP says he is using "the Hornady app," which I take to mean Hornady 4DOF. This reply assumes he is not familiar with other apps, and I may be wrong on that.

4DOF, insofar as I can tell, does NOT support entry of zero offset. So, for everyone telling OP to enter the offset into his calculator - he doesn't have that capability (If I am wrong, please correct me, with direction on how to get to the offset entry point).

OP, below is a screen shot of one load entry (Strelok Pro) for one of my .223s. This happens to be the load - call it "Load A" - with which the rifle is zeroed, so the red-circled offsets default to zero. I use a 100-yard zero, so when I ask for a 100-yard solution the calculator gives me 0 mils elevation and 0 mils windage for that load.

Let's say that I try a different load - "Load B." I shoot five rounds of "B," and the group is .2 mils low and .5 mils right of POA. So, I enter "-.2" and "-.5" respectively in the vertical and horizontal offset fields. Now, when I ask for a 100-yard solution, the calculator shows me .2 mils "up" and .5 mils "right" for Load B. The calculator knows each bullet's BC and other characteristics, so if the 100-yard settings are carefully entered, rounds should be close to POA at distance when the offsets are correctly set.

Hope this helps.

 

[Mike Casselton]

OP says he is using "the Hornady app," which I take to mean Hornady 4DOF. This reply assumes he is not familiar with other apps, and I may be wrong on that.

4DOF, insofar as I can tell, does NOT support entry of zero offset. So, for everyone telling OP to enter the offset into his calculator - he doesn't have that capability (If I am wrong, please correct me, with direction on how to get to the offset entry point).

OP, below is a screen shot of one load entry (Strelok Pro) for one of my .223s. This happens to be the load - call it "Load A" - with which the rifle is zeroed, so the red-circled offsets default to zero. I use a 100-yard zero, so when I ask for a 100-yard solution the calculator gives me 0 mils elevation and 0 mils windage for that load.

Let's say that I try a different load - "Load B." I shoot five rounds of "B," and the group is .2 mils low and .5 mils right of POA. So, I enter "-.2" and "-.5" respectively in the vertical and horizontal offset fields. Now, when I ask for a 100-yard solution, the calculator shows me .2 mils "up" and .5 mils "right" for Load B. The calculator knows each bullet's BC and other characteristics, so if the 100-yard settings are carefully entered, rounds should be close to POA at distance when the offsets are correctly set.

Hope this helps.
View attachment 7901168

If the OP is using 4Dof, he should create a profile for each load and enter the zero range based on his verticle impact.
Windage offset can be entered by tapping the 3 dots and going to the edit function.

Go to: Set rifle info.
Here's what comes up.

Once that's done and saved, he can simply switch bullet profiles without changing anything on his scope.

 

[DownhillFromHere]

If the OP is using 4Dof, he should create a profile for each load and enter the zero range based on his verticle impact.
Windage offset can be entered by tapping the 3 dots and going to the edit function.

I can see how using zero range could provide a vertical offset, albeit not terribly intuitive - looks like a user would have to physically move a target to find the exact vertical POA/POI cross point. And that doesn't allow for windage. I poked around with various edit functions and could not see how a windage offset could be set using zero range, zero angle, or some combination.

That doesn't mean it can't be done - I just don't see it.

I'm a retired computer solutions engineer and I hated writing documentation, but I did it well - because I always asked non-SME (subject matter expert) people to perform the documented task using my instructions. If the user got hung up, it wasn't their problem - it was mine, and I fixed the doc. Many engineers treated documentation as a total afterthought - and users (and sometimes the bottom line) suffered.

Strelok's doc is no better - in fact, given the many largely undocumented capabilities of the calculator, it's worse.

 

[b6graham]

I can see how using zero range could provide a vertical offset, albeit not terribly intuitive - looks like a user would have to physically move a target to find the exact vertical POA/POI cross point. And that doesn't allow for windage. I poked around with various edit functions and could not see how a windage offset could be set using zero range, zero angle, or some combination.

That doesn't mean it can't be done - I just don't see it.

I'm a retired computer solutions engineer and I hated writing documentation, but I did it well - because I always asked non-SME (subject matter expert) people to perform the documented task using my instructions. If the user got hung up, it wasn't their problem - it was mine, and I fixed the doc. Many engineers treated documentation as a total afterthought - and users (and sometimes the bottom line) suffered.

Strelok's doc is no better - in fact, given the many largely undocumented capabilities of the calculator, it's worse.

if you're .2mil high at 100y with the new ammo, scroll yard by yard and find .2 up elevation. change zero distance to that number (with my 7SAW: 162eldm at 2840fps ballisticarc shows .2 from 160-175y so i'd set zero distance to 167/168y)

and windage offset is right there in the screenshot Mike posted

 

[GreenGO Juan]

If 175’s are .5 down @200. 168 are 0@ 200. Subtract .5 any distance past 200 off your 175 dope and you should be close for 168’s, not exact but close.

175’s 1.3 at 300, try .8 for 168’s

175 are 2.2 at 400, try 1.7 for 168’s.

175’s. 3.3 at 500 try 2.8 for 168’s

175’s are 4.4 at 600 try 3.9 for 168’s.

With out a bc calculator this should get you close.

If you have a bc calculator just change the zero to 200 and go off those #’s

 

[DownhillFromHere]

if you're .2mil high at 100y with the new ammo, scroll yard by yard and find .2 up elevation. change zero distance to that number (with my 7SAW: 162eldm at 2840fps ballisticarc shows .2 from 160-175y so i'd set zero distance to 167/168y)

and windage offset is right there in the screenshot Mike posted

Got it. Thanks for explanation. I still say the documentation could be much clearer, but y'all showed how to get it done - much appreciated. Hopefully this also helps OP.

 

[b6graham]

Got it. Thanks for explanation. I still say the documentation could be much clearer, but y'all showed how to get it done - much appreciated. Hopefully this also helps OP.

BallisticARC is much easier with offsets. and i 1000% prefer it's formatting and ease of use

but i've finally graduated to a kestrel after 8 years

 

[Mike Casselton]

if you're .2mil high at 100y with the new ammo, scroll yard by yard and find .2 up elevation. change zero distance to that number (with my 7SAW: 162eldm at 2840fps ballisticarc shows .2 from 160-175y so i'd set zero distance to 167/168y)

and windage offset is right there in the screenshot Mike posted

^^^^^
That's exactly how it's done.
I didn't write the verticle part out this morning because I made the assumption doing the verticle offset was intuitive...