FPS vs. bullet drop

[Thunder head]

The scope on my Coyote gun has a BDC reticle for a specific load. I have been trying to reproduce this load by hand.
Load: .223 with 55 grain bullets 3240 fps at the muzzle
Powder: Hogdon varget

Using the starting and max load data. I determined the ratio of FPS per grain of powder. This tells me i need somwhere in the niebhorhood of 26.1 to 26.3 grain of powder. I tried 26.1 first. Its on at 100 yards but 4" low at 200. I then tried 26.2. Its on (maybe slightly high) at 100 but its 5" high at 200.
Should there 9" of difference in drop at 200 yards with .1 grain of powder difference?

 

[enysse]

No there shouldn't be that much difference. Varget is a excellent powder, but it isn't working quite right for what you are trying to do. If you liked the load with a regular scope, and it produced good accuracy...that's great, but you'll have to try a different powder with the BDC reticle.

 

[sestoppelman]

I would suggest that the problem of a nine inch difference in elevation has nothing to do with .1 grain of powder, any powder. The difference in velocity is essentially nil. Varget is good stuff and quite consistent and one of the best in the .223. My own best AR load is 26 grains of the stuff behind the Hornady 60 gr V-Max.

 

[enysse]

I think sesstoppelman may be on to something I missed. A gun inspection to check that the scope is tight and level. And have someone else shoot the gun...that's my last clue that something is wrong...if someone else is shooting it excellent...then I'm doing something wrong.

 

[Thunder head]

Thats what i thought. I am beggining to think i screwed up the 26.1 loads somehow. I loaded the 26.2 again yesterday and got the same results as last weekend. Ill have to work on it somemore.

 

[Calhoun]

1 tenth of a grain will not make that much difference in bullet drop. The only way you will really know if you are even getting close to achieving that fps of that load is to shoot the bullets over a chronograph. Every gun does not produce the same speeds as the shooting manual says. When I reload & develop loads I always jump .3 -.5 grains per next test batch until I get close to maximum. Trying every tenth won't gain you much except more reloading & shooting time and it will drain your wallet!