Calculation of Bullet Drop/ Various Models

[HappyHellfire]

Do you currently have Strelok? Curious how you "checked it out" if not...

Good question. You can infer the type of solver by looking at the inputs and outputs. For example, if it asks for line of fire, it has Coriolis included. If it asks for barrel twist it isn't a flat fire solver or simple 2 or 3 DOF.

Of course I don't have access to the code but it's still pretty obvious. Kind of likes mechanic looking at cars

 

[Dave M.]

John,
When exactly would my bullet order by shipping out to me and what advice do you have for powder type, powder charge and seating depth to achieve the accuracy you are speaking of? Also, any help in adjusting the scope for the slower velocity to get the bullets on target as quickly as possible? I only have 10 bullets and I’d like to shoot two groups of 4 shots, which means I need to get it on paper at 100 yards in two shots. I doesn’t really matter where on the paper because I plan to hold the same point of aim for all shots, so if the group forms 6” under the POA that’s just fine; but I do imagine I’ll need to add some elevation to get it in the neighborhood as my current 6.5CM competition gun (Kelby Panda action, Bartlein 4 groove cut rifled barrel, shooting Hornady 140g ELD-M bullets, I will be shooting from a 21st century hybrid X front rest, and a Protektor DR rear bag, all shooting to be done prone and using wind flags and Garmin chronograph).
Dave

 

[RabbitSlayer]

I have been a Strelok Pro user for a very long time. It is good. Any ballistic solver suffers from garbage in, garbage out. Aside from BC variations from published, the next biggest problems I see users having is 1) scope height as this directly affects predicted adjustments (higher looks flatter on paper) and 2) zero offset. Shooting 1" high to preserve aiming point but not putting an offset in your zero distance will have you scratching your head if you go from 100y zero to 1000y as it will likely be close to 1.5moa off.

You mean like 1 inch high at 100 to get MPBR? I just play with the zero distance until it is the same as my 1" or 1.5" high at 100. I also play with it to figure out MPBR and zero that high at 100. For myself, any gun zeroed for MPBR is not used for long range. If I zero for MPBR I rarely shoot it beyond MPBR. Anything for long range is a 100 yard zero. I never have understood the zero offset in strelok....

 

[RabbitSlayer]

One thing in a Hornady podcast was how bullet makers have got BC in the past. They have setup 2 or 3 chronographs in a tunnel at 100, 200, 300, and calculated BC based on the velocity change. They didn't lie about BC, thats just what they had to measure it. Now we know BC changes with velocity etc so the BC from a 22250 is not the same as the BC from a .222. The BC at 300 is not the same as at 2000.

 

[Fast14riot]

You mean like 1 inch high at 100 to get MPBR? I just play with the zero distance until it is the same as my 1" or 1.5" high at 100. I also play with it to figure out MPBR and zero that high at 100. For myself, any gun zeroed for MPBR is not used for long range. If I zero for MPBR I rarely shoot it beyond MPBR. Anything for long range is a 100 yard zero. I never have understood the zero offset in strelok....

No, zero offset. I zero my turret at 100y with impact not on the point of aim. In the picture below, my turret is at zero. The offset is the distance from POA to POI. Zero offset subtracts this from total elevation needed to be on POA at distance. Think of it like positive compensation, but in the turrets of your scope.

MPBR adjusts your zero distance to achieve a set height above and below line of sight without compensating with scope corrections.

 

[Fast14riot]

To help visualize it, here is my calculated dope to shoot POA/POI, for 100y, because I have a +1" zero offset it tells me to dial DOWN 0.9moa to shoot dead on at 100.

 

[357Mag]

All -

Howdy !

It recently occurred to me:

I've never read anything about the impact use of an ( example ) 20moa scope base has on the amount of scope clicks needed to adjust elevation for the desired zero.

When using such a base, scope' centerline is a certain height @ one end of the scope; and a different height @ the other end. In such instances... what scope height input would / should be made to a external ballistics calculator ?

Is there some sort of compensating equation, or special algorithm et al that needs to be applied in such cases ?

It strikes me that one might apply too many clicks of elevation when using an ( example )
20moa scope base; across certain distances....if / when applying calculated amount of elevation based on use of a constant scope centerline-derived data ?


I think my mind just threw up !


With regards,
357Mag

 

[Fast14riot]

No difference in calculated dope. All an angled scope base does is afford you more travel in one direction to keep the erector tube where it has the most windage travel. I measure scope height to the turrets location of the scope tube.

 

[RabbitSlayer]

To help visualize it, here is my calculated dope to shoot POA/POI, for 100y, because I have a +1" zero offset it tells me to dial DOWN 0.9moa to shoot dead on at 100.
View attachment 1566412

Oh, so its the same thing but for a different, and as far as I know, an unknown reason. I don't understand why your zero would not be dead on at 100 if it wasn't for MPBR.

 

[Fast14riot]

Oh, so its the same thing but for a different, and as far as I know, an unknown reason. I don't understand why your zero would not be dead on at 100 if it wasn't for MPBR.

Think of it as not changing your scope zero for two different loads. Load one has an offset of 0.25" but load two has an offset of 1". Thats where it is useful. In my case, I have fire forming loads, light bullet and heavy bullet loads for the same gun. If I had to re-zero my scope turret for each load, I would have to shoot confirmation rounds before every match and adjust my scope for every load. MPBR moves your zero distance, not your POI.

 

[Thauglor]

Well I just ordered some bullets from his site to put this to the test and end all debates. Let’s see if I ever receive any product. For the record, I was order #00004 on his site. No advice on what powder charge to use or how much I’ll need to come up at the 100 yard mark to have the same (or approximately same) zero as my current 6.5CM rifle. I only order a 10 pack of bullets so before I shoot them I will look for the best manner to do so from the entire team of n this site.
Dave M.

Damn Dave, very nice of you to try out the bullets

 

[dusterdave173]

I have found that JBM when you use correct inputs is close enough for me
The last load I did --I got a dead nuts 100 yd zero with correct speed--used the published G7 info from Berger and per the dope it spit out dialed to 600 yards and busted a 4 in clay on the first pop--calm wind day
From rookie standpoint it just works

 

[HappyHellfire]

I used the Lieske model for the several deck guns and it worked pretty well for direct fire but it tended to diverge for really long range lob fire (>10 miles). The yaw of repose approximation is good but not great. You have to estimate a term for spin drift.

I'll go calculate Coriolis and spin drift for a standard 6.5 at 600 yards and see how they compare.

 

[HappyHellfire]

Quick side question. I've had several people ask about a 5.56 aerospike. I have designs for one but I need a 1:7 bolt action to test it. I've had serval mishaps with AR style and it is just safer to develop prototypes with a bolt action. The only one I can find is a Savage precision for like $2,500. Does anyone else make a 1:7 bolt action or single shot 5.56/.223 for cheaper?

I didn't know that people even reloaded them.

 

[HappyHellfire]

John,
When exactly would my bullet order by shipping out to me and what advice do you have for powder type, powder charge and seating depth to achieve the accuracy you are speaking of? Also, any help in adjusting the scope for the slower velocity to get the bullets on target as quickly as possible? I only have 10 bullets and I’d like to shoot two groups of 4 shots, which means I need to get it on paper at 100 yards in two shots. I doesn’t really matter where on the paper because I plan to hold the same point of aim for all shots, so if the group forms 6” under the POA that’s just fine; but I do imagine I’ll need to add some elevation to get it in the neighborhood as my current 6.5CM competition gun (Kelby Panda action, Bartlein 4 groove cut rifled barrel, shooting Hornady 140g ELD-M bullets, I will be shooting from a 21st century hybrid X front rest, and a Protektor DR rear bag, all shooting to be done prone and using wind flags and Garmin chronograph).
Dave

I'll get them in the mail today. Did you download the data sheet for the bullet? It has my loading data as well as the full drag profile and a sample drop table in it.

I'll throw in an extra pack to help out.

 

[Dave M.]

Damn Dave, very nice of you to try out the bullets

I can’t wait until they show up. I’ll attach pictures, measurements, mass, etc. I have also asked Dr. John for the best starting load and seating depth because I can’t fully develop a load for radically new bullet shape when I only have 10 bullets.
Just a thought, but if the “spike” on the back of the bullet has been redesigned and truncated, perhaps “Aerospike” isn’t the best name for this new bullet??
Dave

 

[Dave M.]

I used the Lieske model for the several deck guns and it worked pretty well for direct fire but it tended to diverge for really long range lob fire (>10 miles). The yaw of repose approximation is good but not great. You have to estimate a term for spin drift.

I'll go calculate Coriolis and spin drift for a standard 6.5 at 600 yards and see how they compare.

At 600 yards, spin drift for a typical 6.5CM 129g SST round will be between 1.4-1.75”

 

[Dave M.]

I used the Lieske model for the several deck guns and it worked pretty well for direct fire but it tended to diverge for really long range lob fire (>10 miles). The yaw of repose approximation is good but not great. You have to estimate a term for spin drift.

I'll go calculate Coriolis and spin drift for a standard 6.5 at 600 yards and see how they compare.

Coriolis effect will depend on direction of fire and your position on Earth.

 

[Dave M.]

I'll get them in the mail today. Did you download the data sheet for the bullet? It has my loading data as well as the full drag profile and a sample drop table in it.

I'll throw in an extra pack to help out.

Is this chart on your data sheet for your load??

 

[Dave M.]

I'll get them in the mail today. Did you download the data sheet for the bullet? It has my loading data as well as the full drag profile and a sample drop table in it.

I'll throw in an extra pack to help out.

I have plenty of H4895, but I don’t have any IMR4895; I know they are not the same but the are very close on the burn chart. Also, the two powders you selected are quite far apart on the burn chart (IMR4895 and Win 760), there are lots of more common long range powders between those two that you may want to explore (RL15, 15.5, Varget, 203B, N140, N150, and H380).
Dave