Henry Rifle Forums

Playing around with JBM ballistics calc ( https://www.jbmballistics.com/cgi-bin/j ... ft-5.1.cgi ) out of boredom so ran the numbers on the .41 mag out of my BBSC. Besides the usual inputs you need to know the bullet length (just the projectile) & barrel twist. I set it up for a 10yd zero and 10yd increments out to 200 yds. BC for the XTP bullet is .182, MV 1738, 210grn. The Spin drift result is presented as a windage, so zero out all the windage inputs to just show drift due to spin. A positive number is a drift to the right, negative number to the left of the bullet path. Also computes drift in MOA. Other inputs such as target speed are also available to calculate lead, etc.

So bottom line: This bullet will drift to the right beginning at 25yds and reaching 0.7" at 100yds. Here's the whole read out up to 120yds. Are you bored yet?

zzzzzzzzzzzzzzzzzzzz lol
Again, learned something new today
So why is the drop zeroed at only 10 yards? Is that common pistol data?

Kissmybrass wrote: ↑

Mon Aug 09, 2021 8:00 pm

zzzzzzzzzzzzzzzzzzzz lol
Again, learned something new today
So why is the drop zeroed at only 10 yards? Is that common pistol data?

I set it at that because I was interested in the total drop from the muzzle. There's no significant drop in the first 10yds in this case, but I could have set it at 0yds I suppose.

Aha I saw that at the range, not sure what this guy had but it was two identical stuctures with screens or something wired that he was shooting through.
Makes sense.

Kissmybrass wrote: ↑

Mon Aug 09, 2021 8:28 pm

Aha I saw that at the range, not sure what this guy had but it was two identical stuctures with screens or something wired that he was shooting through.
Makes sense.

I misunderstood your question and got long winded about chrono stuff. Went back and addressed your original question while you were posting a reply to my babbling about Chrono's.

Good info there! What is the rifling twist rate of the 41 Mag?

fortyshooter wrote: ↑

Tue Aug 10, 2021 10:54 pm

Good info there! What is the rifling twist rate of the 41 Mag?

1:18 according to Henry. I used 1:20 in the above example, but recalculating this morning it doesn't make a significant difference. 0.1" @100yds.

Just like any other variable, the effect of this on precision & accuracy increases with distance. The thing to keep in mind tho at ranges beyond your sight-in distance, is to recognize and compensate for spin drift just as you would for drop. Both spin drift and drop are influenced by atmospheric conditions of course, so it can get complicated.

Btw, the JBM site has a lot of information about the general topic of small arms ballistics if you want to spend some time exploring it.

https://www.jbmballistics.com/ballistic ... tors.shtml

This has to be why my cowboy loads were spraying all over the place and my 2000 fps Hornady pointy $#&@ers were dead on. Mighty interesting -
I think my middle range ammo is right at the speed or sound give or take. I think I'm gonna up the loads a tad to be sure they are around 1250.
So glad you posted this.

Kissmybrass wrote: ↑

Thu Aug 19, 2021 6:43 pm

This has to be why my cowboy loads were spraying all over the place and my 2000 fps Hornady pointy $#&@ers were dead on. Mighty interesting -
I think my middle range ammo is right at the speed or sound give or take. I think I'm gonna up the loads a tad to be sure they are around 1250.
So glad you posted this.

You're talking about the trans-sonic zone that I mentioned earlier, right? Yeah, that's a killer when it comes to bullet stability (accuracy). It also was the cause of several crashes of early supersonic aircraft back in the '50's.

Here's a good video about the problem, about 30 minutes. He's talking about very long range shooting, but the physics apply to any bullet (or aircraft, except - hopefully - an airplane doesn't spin).

https://www.youtube.com/watch?v=Ijd3cD7iQpA