screwy load... but mostly in a good way...

[Dougfirtree]

I'm still working on the load I want to hunt with out of my new Tikka. I've been refining one that seems very promising, but it's a funny one. Get this:

It's a 7mm-08 with 140 E tips at about 2725fps (Varget).

It shoots about 7/8" at 100 yards

It shoots about 7/8" at 200 yards

It drops 6.25 inches at 200 yards, from a 100 yard zero.

Doesn't that seem like a really drastic drop for that combination?!

 

[VikingsGuy]

jbm says 3.6" drop from 100y zero at sea level. I would look at the scope, as that bullet with a 100yd zero would have to be going only 2250fps to give that type of drop.

 

[Dan O]

Nosler posted the following info on their ammunition for the 7-08 140 e-tip. Velocity listed 2850 fps. Zero at 100 yards Nosler says it will drop 3.4 inches at 200 yards. It might be the difference in velocity and weather conditions and elevation of your range.
Hope this helps.
Dan

 

[Dougfirtree]

jbm says 3.6" drop from 100y zero at sea level. I would look at the scope, as that bullet with a 100yd zero would have to be going only 2250fps to give that type of drop.

What would be off about the scope that would allow it to shoot nice, consistent groups and be firmly zeroed at 100 yards, but shoot so low (but really well) at 200?

 

[VikingsGuy]

What would be off about the scope that would allow it to shoot nice, consistent groups and be firmly zeroed at 100 yards, but shoot so low (but really well) at 200?

Consistent groups are a matter of precision (did it do the same thing consistently) not of accuracy (did it hit where you pointed), so what we are looking at is likely a point of aim issue. So, what could cause you to think you were aiming correctly at 100y and 200y but in fact be 2.5" off one way or the other?

Confirming your drop expectations is a good step - if you put all the data into JBM (temp, elevation, scope height, bullet, actual velocity not box velocity, etc,) and you will get the answer required by physics. Temp, elevation, humidity, small velocity differences are all unlikely to double the drop (-6.25" drop would be consistent with 2250fps - seems like you would notice that low a velocity in your load development process) so something else has to account for the data.

The scope seems like a good place to start that inquiry. Things like parallax, cant, alignment issues, internal mechanical issues, can all cause point of aim/point of impact problems. Your data seems too big a difference at 200y for parallax or cant to be the issue. Did you dial the scope at all between the groups? Try the rounds in a second rifle if you have one, or put a different scope on the rifle and try to recreate the data.

 

[p_ham]

@VikingsGuy has good advice.
Re-shoot your 200 yd without dialing(if you were before) and aim center bullseye. Physically measure your point of impact at that range. Repeat at 300, 400, etc until you hit your max.
6" drop isn't right for your load.
If you are dialing, check to make sure your adjustments are in the unit of measure you think they are. (MOA not MRAD for instance)

 

[Brian in Montana]

I took the liberty to punch in your basic numbers to the Hornady ballistics calculator. That predicted a drop of 3.5 so I'd say yes, that is a lot of drop. Are you sure your muzzle velocity is correct? How are you using your chronograph and what type is it?

I'm not an expert, but I don't think your scope of environmental factors could account for what your seeing.

 

[huronmtns]

I'm still working on the load I want to hunt with out of my new Tikka. I've been refining one that seems very promising, but it's a funny one. Get this:

It's a 7mm-08 with 140 E tips at about 2725fps (Varget).

It shoots about 7/8" at 100 yards

It shoots about 7/8" at 200 yards

It drops 6.25 inches at 200 yards, from a 100 yard zero.

Doesn't that seem like a really drastic drop for that combination?!

Does your scope have parallax adjustment?

 

[Dougfirtree]

Does your scope have parallax adjustment?

I don't think so. It's a Leupold vx 3 2.5-8x36 Isn't parallax only an issue at 300+ yards?

 

[Dougfirtree]

Consistent groups are a matter of precision (did it do the same thing consistently) not of accuracy (did it hit where you pointed), so what we are looking at is likely a point of aim issue. So, what could cause you to think you were aiming correctly at 100y and 200y but in fact be 2.5" off one way or the other?

Confirming your drop expectations is a good step - if you put all the data into JBM (temp, elevation, scope height, bullet, actual velocity not box velocity, etc,) and you will get the answer required by physics. Temp, elevation, humidity, small velocity differences are all unlikely to double the drop (-6.25" drop would be consistent with 2250fps - seems like you would notice that low a velocity in your load development process) so something else has to account for the data.

The scope seems like a good place to start that inquiry. Things like parallax, cant, alignment issues, internal mechanical issues, can all cause point of aim/point of impact problems. Your data seems too big a difference at 200y for parallax or cant to be the issue. Did you dial the scope at all between the groups? Try the rounds in a second rifle if you have one, or put a different scope on the rifle and try to recreate the data.

Interesting. no dialing between the groups. I can probably try changing out the scope.

 

[bluespruce]

Are you using a chrono or just what would be expected from load data? If using a chrono does it match with what would be expected from load data?

And the "are you sure your cable box is plugged in" question: are you sure your 100 yards and 200 yards are actually 100 and 200 yards and not say 90 and 220?

 

[huronmtns]

I don't think so. It's a Leupold vx 3 2.5-8x36 Isn't parallax only an issue at 300+ yards?

Adjustable parallax can be an issue if it is not adjusted for the distance that you are trying to shoot. A slight head-bob up or down can cause the reticle to float a bit on target (approximately plus or minus 1.5" at 100 yards) even though the rifle is not moving at all. This can cause a perception issue of reticle position on target when you pull the trigger. I thought a slight change in your cheek weld between distances may have caused the height difference between 100 and 200 yards caused by parallax. It does not sound like your scope has parallax adjustment so my description above does not apply to your scope if it is a fixed parallax scope. That is why I asked the question. I bought a scope that had an adjustable parallax and it drove me crazy for group sizes until I figured out how to adjust it.

 

[std7mag]

It sounds to me like your barrel likes the powder charge that your using.
Bullet coming out of the muzzle at a nice consistant speed.

Problem is, your barrel is at that point on the downward side of the barrel harmonics.
Remember, the barrel moves up, down, and side to side durring a shot.

Look for a powder charge faster, or slower than what your shooting now.

An extreeme example was a 243 i had.
100gr Rem Coreloks shot great, 0.5" at 100 yards.
Did some handloads. Still 0.5" at 100 yards for group size.
Problem was my handloads were a consistent 8" higher than factory loads, at 100 yards.

 

[Dougfirtree]

It sounds to me like your barrel likes the powder charge that your using.
Bullet coming out of the muzzle at a nice consistant speed.

Problem is, your barrel is at that point on the downward side of the barrel harmonics.
Remember, the barrel moves up, down, and side to side durring a shot.

Look for a powder charge faster, or slower than what your shooting now.

An extreeme example was a 243 i had.
100gr Rem Coreloks shot great, 0.5" at 100 yards.
Did some handloads. Still 0.5" at 100 yards for group size.
Problem was my handloads were a consistent 8" higher than factory loads, at 100 yards.

That's an interesting thought... It's 40.5 grains of Varget. I could try loading up some groups with 40.3 and 40.7 and see if that makes a difference. Now I just need to find some more Varget...

 

[Dougfirtree]

I took the liberty to punch in your basic numbers to the Hornady ballistics calculator. That predicted a drop of 3.5 so I'd say yes, that is a lot of drop. Are you sure your muzzle velocity is correct? How are you using your chronograph and what type is it?

I'm not an expert, but I don't think your scope of environmental factors could account for what your seeing.

I've got one of those Competition Research ones. I'm guessing it's not hyper accurate, but it's pretty consistent and I've shot this load over several different sessions, so I trust the velocity (give or take 50fps).

 

[MThuntr]

I'm the wrong person for fully understanding harmonics but you may have some room to up your powder charge (depending on where your max is). Knowing you're shooting Etips you may not have much more room but if what std7mag is true I'd give some more juice to it.

FWIW my 7mm08 wants near max loads with Etips before things settle out so there may be another node in there somewhere.

 

[Dougfirtree]

I'm the wrong person for fully understanding harmonics but you may have some room to up your powder charge (depending on where your max is). Knowing you're shooting Etips you may not have much more room but if what std7mag is true I'd give some more juice to it.

FWIW my 7mm08 wants near max loads with Etips before things settle out so there may be another node in there somewhere.

I tested it up to 41.5 grains, but in .5 grain increments. It liked 41.5 grains at 100 yards, but less so at 200 and that feels like pushing it, pressure-wise, even though I didn't really have signs. It did not like 41 grains. Even at 40.5 it's picky about seating depth. I got good accuracy at 2.765" but it's worse at 2.75" and at 2.775".

 

[1_pointer]

I tested it up to 41.5 grains, but in .5 grain increments. It liked 41.5 grains at 100 yards, but less so at 200 and that feels like pushing it, pressure-wise, even though I didn't really have signs. It did not like 41 grains. Even at 40.5 it's picky about seating depth. I got good accuracy at 2.765" but it's worse at 2.75" and at 2.775".

I'd try going the other way. It appears that mono bullets may like a bit more jump.