Range Report Zero with Different Grain Question

[TattooBlade]

I shoot a GAP 308 with a Bartlein with 5R rifling. Both 168 and 175 grain SMKBTHP hit at the exact same spot at 100 when zeroing. I picked up a box of 150 grain and I'm curious if you think they will also hit the same spot at 100. I will get to the range to confirm at some point, but I'm sure someone here shoots multiple grains and can tell me. Where will I see the most gain or loss with a lighter round?

Thanks!

 

[TattooBlade]

Re: Zero with Different Grain Question

Whew. I don't know if I can absorb all this info.

 

[Chris K]

Re: Zero with Different Grain Question

At 100, you'll be close enough to your zero that it will make nearly no difference.

I'm assuming that you are going to hunt with 150's?

your gains will be marginal with 150's, speed will be one of them, but not by much. Your losses will be in the distance column. The 150's will not fly like your 175's. past about 600-650 the 168's fall off the edge, while 175's keep going. Your 150's will fall off sooner.

If you're talking hunting bullets in 150, and you're going to stay at the average hunting distances of 100-150yd. (under 100 in most places I hunt) you will see no significant change in POA/POI that will effect your hunt.

Hope that helps a bit.

C_K

 

[Fred_C_Dobbs]

Re: Zero with Different Grain Question

I have a .243 I use for whitetails with a medium ogive, flat base 100-gr bullet and for coyotes and such with a high ogive, boattailed 70-grainer. There's about 500 fps difference in their MVs. Using the same zero, the 100-gr bullet is dead-on @100 and almost 4" low @200. The 70-gr bullet is ~1" high @100 and ~1/4" low @200.

 

[timelinex]

Re: Zero with Different Grain Question

What do you mean when you say there is NO difference between 168 and 175. From my experience the difference is around 1 inch or so, and there SHOULD be a difference. I'm assuming then that your talking about a 'hunters zero' where anything within a couple inches is all good. If so then, the 150 should be in the same vicinity. From my exerience, my 150's I believe land 3 inches above 175's at 100 yards.

 

[TattooBlade]

Re: Zero with Different Grain Question

Nope, strange as it is, at 100 my 168 and 175 hit the same exact spot. I can shoot them both into the same group. I haven't compared them at other distances yet. Guess I'm either going to have to get to the range with the 150s prior to chasing game or either hunt with the SMKBTHP or find some 168 or 175 soft points.

 

[gstaylorg]

Re: Zero with Different Grain Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: timelinex</div><div class="ubbcode-body">What do you mean when you say there is NO difference between 168 and 175. From my experience the difference is around 1 inch or so, and there SHOULD be a difference. I'm assuming then that your talking about a 'hunters zero' where anything within a couple inches is all good. If so then, the 150 should be in the same vicinity. From my exerience, my 150's I believe land 3 inches above 175's at 100 yards. </div></div>

That is with <span style="font-style: italic">your</span> rifle/barrel. I have one that puts FGMM 168s, FGMM 175s, and Applied Ballistics 175s in the same hole at 100 yd. I have another where these three rounds are over 1" apart at 100 yd. It's all about muzzle velocity, barrel harmonics,and where things are when the projectile leaves the bore. These factors can differ widely between rifles.

 

[Sterling Shooter]

Re: Zero with Different Grain Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TattooBlade</div><div class="ubbcode-body">I shoot a GAP 308 with a Bartlein with 5R rifling. Both 168 and 175 grain SMKBTHP hit at the exact same spot at 100 when zeroing. I picked up a box of 150 grain and I'm curious if you think they will also hit the same spot at 100. I will get to the range to confirm at some point, but I'm sure someone here shoots multiple grains and can tell me. Where will I see the most gain or loss with a lighter round?

Thanks!</div></div>

I shoot 168's at mid range and save the 175's for LR. The 175's kick harder making control of the rifle more difficult than it needs to be for mid range work. For LR, the higher B.C. of the 175's assures better performance than from the 168 except in ideal conditions. Whether these bullets do or do not have the same point of impact at any distance is mostly moot.

 

[DerMeister]

Re: Zero with Different Grain Question

While I cannot answer your question exactly, I have zeroed with 150gr, and then I shot 180gr and it was about 1" lower than the 150gr.

I shot some 7.62NATO 147gr and it shot a tad higher than the 150gr. All at 100yrds.

I see the pattern, not sure if its a rule of thumb that lighter bullets will shoot a little higher than heavier bullets though.

 

[Niles Coyote]

Re: Zero with Different Grain Question

At 100y there should be a shift and FWIW I have found the heavier bullets generally hit higher than the lighter bullets at that distance. I am surprised others are seeing the opposite. The slower, heavier bullet is in the barrel longer and more effected by the beginning stages of recoil than the lighter bullet.

But either way you will only be off your 175 zero by a few inches.

 

[Chanonry]

Re: Zero with Different Grain Question

It depends.

Barrel harmonics, mv etc etc will affect the poi at 100 yds and not just in the vertical. You need to try some and see. My experience says probably different poi but its just one opinion.

I certainly do not agree with the sentiment that effective range increases with bullet weight - that is a gross oversimplification of ballistic science

 

[tobias]

Re: Zero with Different Grain Question

If everything else remains unchanged (!) (especially the muzzle velocity), the trajectory of a lighter projectile is always under the trajectory of a heavier projectile. Thus the heavier bullet hits higher than the lighter.
In practice when you change the mass of the bullet you influence other parameters as well, so it's hard to tell if the bullet hits the same spot or elsewhere.

 

[TattooBlade]

Re: Zero with Different Grain Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tob</div><div class="ubbcode-body">If everything else remains unchanged (!) (especially the muzzle velocity), the trajectory of a lighter projectile is always under the trajectory of a heavier projectile. Thus the heavier bullet hits higher than the lighter.
In practice when you change the mass of the bullet you influence other parameters as well, so it's hard to tell if the bullet hits the same spot or elsewhere. </div></div>

If that is the case, then why when comparing ballistic tables between the 150 and 175, the 150 has less drop at 500? It's more flat shooting. Shouldn't that be opposite based on what you are saying or am I reading it wrong?

 

[VKC]

Re: Zero with Different Grain Question

If you look at pure ballistics with BC, bullet weight and velocity...then the 150grs should hit slightly higher at 100 yards then the 175grs. This is because you can push a lighter bullet faster in the same caliber, which equals less drop. But a longer distances, heavier bullets with higher BC retain more velocity, even though they start slower and the results change.

However, this is not considering barrel harmonics, which varies from each rifle, and also changes the equation.

 

[TattooBlade]

Re: Zero with Different Grain Question

Yep, just finished playing with the JBM ballistics site and found the 150s should be actually .3 inches higher than the 168's base on BC, velocity, etc. Not enough to concern myself with at my estimated 100 yard hunting distances. I think I'll just feel better using a "hunting" round than a match round for chasing game and not worrry about the .3

 

[tobias]

Re: Zero with Different Grain Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TattooBlade</div><div class="ubbcode-body">}If that is the case, then why when comparing ballistic tables between the 150 and 175, the 150 has less drop at 500? It's more flat shooting. Shouldn't that be opposite based on what you are saying or am I reading it wrong? </div></div>

No, as I wrote, all other parameters have to remain unchanged. Mostly the velocity increases with a lighter bullet which comes to less drop, as vkc explained it.
I think at JBM you can change the mass independent of the other parameters. With a higher mass you should get less drop.

 

[Niles Coyote]

Re: Zero with Different Grain Question

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Finished playing with the JBM ballistics site and found the 150s should be actually .3 inches higher than the 168's base on BC, velocity, etc. </div></div>

TB, this isn’t meant to call you out, so don’t read it as such.

One must remember the ballistic computers do not experience/absorb recoil. Some will calculate barrel time and recoil energy but those alone are not the complete picture. Ever zero a scope in prone and then stand up and fire unsupported? If you triggered the shot perfectly, did the bullet hit exactly in the same location as your prone zero?

The greater the recoil energy, the greater the difference in POI from POA will be from position to position or load to load. I am not trying to argue that a 175ish grain bullet traveling at 2650ish flies flatter to a 100y target than a (insert lighter bullet with higher velocity here), as I know that is not the case. The heavier bullet is spending more time in the barrel during the beginning stages of recoil than the lighter bullet. As the body begins to absorb this the muzzle moves as well.

Don’t blindly take my word for it; the answer will present itself for you at the range or in the field.

 

[tobias]

Re: Zero with Different Grain Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tob</div><div class="ubbcode-body">I think at JBM you can change the mass independent of the other parameters. With a higher mass you should get less drop. </div></div>

Sorry for quoting myself, but I just played with JBM. I always get the same drop with different masses. I think there's something wrong...

 

[TattooBlade]

Re: Zero with Different Grain Question

Well you can all check the hunting section for the results. The 150 TTSX did their job. Hitting about an inch high at the range yesterday, dead on today when the deer stepped out.