Range Report Data Question

[KeithR41]

Shot my two new rifles today after a 6 year hiatus from shooting, anyway, here’s my question. Zero’d the .260 at 100 yds. Input date into Ballistic AE. First rnd hit on a 10 inch steel plate at 800. (Probably worth mentioning I was using a .260 load with several thousand rounds of data on it so it was reliable.)

Zero’d the .300wm at 100 yds. Shooting Barnes 220gr match OTM. Input data (same atmospherics) in to Ballistic AE and crossed referenced with the ballistic data from Barnes. They were .10 mil off. 5.6 and 5.7 mils respectively.

Anyway, I’m 1.5 mils high on the same 800 yard target with 5.6 mils dialed. Dialed down to 4.2 mils and dead on. I would expect a little variation especially shooting a brand new load but this seemed out of the ordinary.

Played with Ballistic AE a little and had to raise velocity to 2925 from 2775 ( from Barnes) for the data to work.

Any ideas regarding this large of a discrepancy? Especially after my .260 was perfect.

Thanks, K41

 

[tnichols]

Double check your data entry for the 300. With a new undocumented load, you have many more variables. I agree that 1.5 mils is a bunch. However, if your data is good, play with MV and BC and see if things line up you. If that doesn’t solve the problem, report back.

 

[Matches Malone]

Shot my two new rifles today after a 6 year hiatus from shooting, anyway, here’s my question. Zero’d the .260 at 100 yds. Input date into Ballistic AE. First rnd hit on a 10 inch steel plate at 800. (Probably worth mentioning I was using a .260 load with several thousand rounds of data on it so it was reliable.)

Zero’d the .300wm at 100 yds. Shooting Barnes 220gr match OTM. Input data (same atmospherics) in to Ballistic AE and crossed referenced with the ballistic data from Barnes. They were .10 mil off. 5.6 and 5.7 mils respectively.

Anyway, I’m 1.5 mils high on the same 800 yard target with 5.6 mils dialed. Dialed down to 4.2 mils and dead on. I would expect a little variation especially shooting a brand new load but this seemed out of the ordinary.

Played with Ballistic AE a little and had to raise velocity to 2925 from 2775 ( from Barnes) for the data to work.

Any ideas regarding this large of a discrepancy? Especially after my .260 was perfect.

Thanks, K41

2775 MV is fake news brah. I looked at ballistic ae and Barnes 220 otm was not a preloaded profile.
I found the information you used from the box info on midwayusa.

Even if it was on AE, they use the box information, and is up to the user to get the correct MV, usually via chrono initially, or as you did, through truing.

These numbers are based on “standard conditions” and a 24 inch test barrel. If you have a 26 inch barrel and you are at 2500ft you’re going to have a faster MV, before getting into any barrel differences. As to why your .260 rem was gtg using the same method, luck. I have a ruger American as the lady’s hunting rifle. Coincidentally, the load it uses matches perfectly with box info MV, chrono’d and verified, and the temp chrono’d was 85 degrees in the mountains, but uses a 22 inch barrel. Its the only gun I own that does this, and I have a few to say the least.

Also with only 800y data I wouldn’t go ham on the BC tweaking yet.

 

[Powder_Burns]

The box data is trued to the factory’s test barrel. A mv variance is common even in barrels from the same batch from the same mfg in the same profile. Some barrels shoot faster than others, and some shoot slower. BC’s are a general number for drag constant for a given bullet’s average performance, and are velocity dependent. Higher speeds mean more drag, but can also mean less drop compared to the same bullet flying slower with less drag force acting on it.
Ultimately a software modeled drag curve is just a prediction and not a fact. You still need to verify your dope at distance, and then correct the software model to match your real world results.
Sometimes things line up perfect like your .260 load, but that is the exception and not the rule in my experience.