Is this approximated calculated ballistic coefficient reasonable?

[JimGnitecki]

I am running a 357 Mag 158g hard cast RNFP Wolf bullet in both my Cowboy Action Shooting lever rifle and revolvers, that is coming out at a muzzle velocity of about 910 fps from the revolvers and about 1320 fps from the rifle, and is delivering pretty good statistics:

But I was curious about what the ballistic coefficient of this bullet is, because I wonder how far a lever action rifle shooting such a Cowboy Action handload can actually practically shoot in the real world. I wonder: Can it practically be used in moderate range "CAS side matches" if i put a tang aperture sight on it?

Sellier & Bellot published a simplified way to determine the G ballistic coefficient, that does not account for differences in altitude unfortunately (it assumes about 400 meters = about 1300 feet, which is apparently the average elevation for all of Slovakia). But for what it’s worth, that simplified formula is;

G = .0052834 x distance in meters / (square root Vo - Square root Vdistance)

They specify “meters” for the distance, but were silent on the units for velocity, so I had to assume “meters per second” (“m/s” since that is what they use on their ammunition spec webpages), and converted fps to m/s.

The Labradar recorded yesterday’s Vo from the rifle as 1129fps and the V at 50 yards = 45.7 meters as 1053 fps

Plugging in the variables, using m/s versus fps for the velocities (1 fps = .305 m/s), I get:

G = .0052834 x 50*.9144 / (sqrt of 1129*.305 - sort of 1053*.305) = 0.381

This sounds high to me for a flat nosed cast .358” diameter bullet. But I suppose our 3000 foot elevation here around Lethbridge, Alberta, Canada does reduce air resistance versus S&B’s 1300 feet). And I suppose the BC does vary with bullet velocity ranges, and this IS at a pretty slow bullet velocity.

IF this BC is actually reasonable, I could use it to generate a trajectory table.

Does it look reasonable to you, or ?

Jim G

 

[fxvr5]

First, Disclaimer: I know nothing about BC, how it's calculated and so forth.

But, I looked at the BCs on Hornady's website for their handgun bullets. You could check their numbers for their 38 caliber bullets and see what you think.

https://www.hornady.com/bullets/handgun/#!/

 

[CQB45ACP]

Lots of big words…ask ChatGPT

 

[mdi]

Ohhh, my head hurts. Haven't seen that much math since my electronics classes...

 

[Walkalong]

You're way over thinking it.

 

[GeoDudeFlorida]

Holes in paper matter.

 

[JimGnitecki]

Holes in paper matter.

Yeah, but it's nice if we can get them on the paper at least for distances we have not shot before with that firearm and that handload. This light CAS load is slow for even a modern handgun, and has a flat point, so when your target paper is letter size, it would be nice to have a clue about the potential drop. In a timed CAS side match, with timed sighter shot plus 5 or 10 score shots, knowing the trajectory is helpful.

Jim G

 

[AJC1]

Yeah, but it's nice if we can get them on the paper at least for distances we have not shot before with that firearm and that handload. This light CAS load is slow for even a modern handgun, and has a flat point, so when your target paper is letter size, it would be nice to have a clue about the potential drop. In a timed CAS side match, with timed sighter shot plus 5 or 10 score shots, knowing the trajectory is helpful.

Jim G

There are numbers for bc in the Lyman manual, I'd use the closest shape I could find and call it good. Subsonic is way different than supers and then the math gets real fuzzy in transonic. In the situation you describe I load the rcbs 358-180-sil

 

[fxvr5]

Jim, what distance will you be shooting in the side matches?

 

[JimGnitecki]

There are numbers for bc in the Lyman manual, I'd use the closest shape I could find and call it good. Subsonic is way different than supers and then the math gets real fuzzy in transonic. In the situation you describe I load the rcbs 358-180-sil

Is that the Lyman loading manual or the Lyman Cast bullet manual? I'm asking because I already have the cast bullet manual on order (delivery this next mid-week), but not the loading manual.

Jim G

 

[GeoDudeFlorida]

Yeah, but it's nice if we can get them on the paper at least for distances we have not shot before with that firearm and that handload. This light CAS load is slow for even a modern handgun, and has a flat point, so when your target paper is letter size, it would be nice to have a clue about the potential drop. In a timed CAS side match, with timed sighter shot plus 5 or 10 score shots, knowing the trajectory is helpful.

Jim G

You misunderstand. The point is, it doesn’t seem likely you have enough data points yet for speculation. I’m saying you need to use a steady rest and see if a locked down rifle - human error removed - can put holes in paper sufficient to justify a peep sight.
Also, you are considering a sighting system which was superseded quickly by other systems; specifically, the receiver sight and ladder sight. Tang sights died out before receiver sights and for very good reasons. The tang sight has a number of points of flex which make it delicate. The best versions are very expensive - close to the price of a rifle.
Unless Canadian rules dictate the use of a tang sight for side matches, which as I understand it are not strictly enforced according to SASS rules, I would consider a period Twin-Zero receiver sight. I have a few Alf. Parker receiver sights from the late 1800’s for Mauser bolts and Remington rolling block rifles.

 

[higgite]

But I was curious about what the ballistic coefficient of this bullet is, because I wonder how far a lever action rifle shooting such a Cowboy Action handload can actually practically shoot in the real world. I wonder: Can it practically be used in moderate range "CAS side matches" if i put a tang aperture sight on it?

Shoot it and find out?

 

[JimGnitecki]

Jim, what distance will you be shooting in the side matches?

The ranges are undecided yet, as the relatively new club has apparently never yet had an actual side match. For the LEVER rifle side matches, I think the guys will favour using the 200 yard range, because all of them have lever action rifles in a pistol caliber, and many of them have .45-70 lever action rifles. Hence my question about the BC for the main match handload.

But there are also several guys with single shot Sharps, Rolling block, etc rifles in .45-70 or stronger calibers (including me) who would like to see 300 to 600 yard matches (Our facility has the ranges to enable that), and the man who is our leader has a fullsize steel buffalo profile target, a huge John Deere tractor that easily picks it up and moves it, and lives only 11 km = 7 miles from the club facility, driving on a sparsely driven road, and he brings the tractor to the club regularly. The longer ranges and the buffalo target itself, would both be strong draws to get more participants and club members. So, I suspect very strongly that we are going to be having 300 to 600 yard matches!

I can only find up to 405g cast bullets commercially for sale here in Canada, and the legality of importing them via shipping versus personal transport is questionably legal for some obscure reasons. But the same man who has the buffalo target and the John Deere also casts his own 500g POINTED bullets, and has given me a few to "try" in my .45-70 Pedersoli Sharps. He has also indicated a willingness to help equip me for casting my own. So, as I consider the near future, I see me shooting 500g bullets, and you don't waste those on 200 yards.

Jim G

 

[JimGnitecki]

Shoot it and find out?

How vertically large a target am I likely to need at say 200 yards? WITH a wind (we are famous here for wind gusts that hit 60 mph or more. Second windiest place in Canada). And what shape and size of aiming point would work well at that distance without the benefit of optics?

One buddy has suggested I cut a 2 foot by 3 foot cardboard sheet to use as the backer, as a letter-size target sheet won't be much help in even getting on paper! He thinks a large black or white cross on the cardboard might work, but has no idea how thick its cross-arms should be for me to see them clearly enough and yet not so large as to make "pinpoint" accuracy impossible. He shoots F-class, so uses strong optics where the target aimpoint can still be very small, and I think he thinks i'm nuts to try to shoot several hundred yards without a scope.

Jim G

 

[higgite]

He shoots F-class, so uses strong optics where the target aimpoint can still be very small, and I think he thinks i'm nuts to try to shoot several hundred yards without a scope.

He could be right, you know.

 

[GeoDudeFlorida]

He could be right, you know.

Nah. A good set of iron sights on an accurate rifle is fine for 300yds on deer-sized game. I use mostly receiver sights on Mauser actions and a couple of Enfields. But you have to know the gun and the way it responds to a variety of conditions. Just sending a couple boxes down range at 50yds then trying to extrapolate the drop and stability out to 300 is an exercise in frustration.
I don’t think it’s crazy at all, I just think it’s a bad idea taking shortcuts and trying to extrapolate with a tiny dataset.

 

[JimGnitecki]

First, Disclaimer: I know nothing about BC, how it's calculated and so forth.

But, I looked at the BCs on Hornady's website for their handgun bullets. You could check their numbers for their 38 caliber bullets and see what you think.

https://www.hornady.com/bullets/handgun/#!/

I just looked at those myself, and they are discouraging! For .38 caliber lead cast bullets, they show BCs from only 0.047 (semi-wadcutter) to 0.135 (SWC) to 0.159 (lead round nose). My RN FLAT point bullets would then be likely to actually be well under 0.159 ! So, I guess I did the math somehow wrong, or the S&B simplified formula is not quite applicable. It looks like for side matches, I might need a significantly hotter .357 Mag lever rifle load to avoid a "rainbow arc" even at 200 yards.

Jim G

 

[JimGnitecki]

Nah. A good set of iron sights on an accurate rifle is fine for 300yds on deer-sized game. I use mostly receiver sights on Mauser actions and a couple of Enfields. But you have to know the gun and the way it responds to a variety of conditions. Just sending a couple boxes down range at 50yds then trying to extrapolate the drop and stability out to 300 is an exercise in frustration.
I don’t think it’s crazy at all, I just think it’s a bad idea taking shortcuts and trying to extrapolate with a tiny dataset.

I did not intend to "extrapolate" at all. I had just gotten the impression that if you know the approximate BC, obtained from a velocity differential at 2 different points in a shot's tarjectory, you can then at least figure out a rough trajectory - good enough to get on paper at 200 yards, and then tune the sights from there. To see where the bullets are actually grouping, I need a paper or carboard target, and I can't just put up a really giant one to start with because our winds around here will simply pick it up and send it to the next county! And no, there is no mount to enable mounting a scope temporarily as a help either.

Jim G

 

[Varminterror]

.381 G1 for a RNFP 158grn .357” is WAY, WAY too high. Not a chance in hell that number is correct. I’d be surprised if the actual G1 is even 0.-ONE-81. Not many .357/8” pistol bullets even break 0.2G1, a LOT are in the .15G1 ballpark, I shoot die drawn Speer HotCor 180grn .358” RIFLE bullets with a long ogive in .357/44 B&D and they only have .245G1 BC, and they’re WAY longer and more aerodynamic than an RNFP.

You are not shooting these far enough to be worried about excessive target size to catch bullets. Given a good chrony speed, I would personally punch in a .15 G1 and then correct for that drop at 200, and that will be close enough on paper to catch with a decent, reasonably sized target backer. I’ve shot my 357/44 out to beyond 300, and shoot 22LR out as far as 500, so what you’re doing is very, very attainable, you just need to go into your calculator with PROVEN math, not backdoor science. All you need to do is estimate your BC, punch in good chrony data, and send it. CAS side match targets are huge anyway, and truing your BC before the match will be super easy. There’s only ~3.5moa difference at 200yrds between a .12G1 and a .18G1 at 1129fps, out of ~35moa compensation at 200 from a 50yrd zero… So I’d dial/adjust sights by 35moa with a ~30” target (more than twice my expected error above and below the aiming point), and I’d be highly confident that I’d land my bullets on that page.

Group size and visibility with naked eye will likely be bigger problems than the drop compensation. If you’re shooting 4moa at 200yrds, that’s a pretty big target, and you’ll need a pretty big target just to be able to see it.

Doing this with irons first would be a mistake, in my opinion. I’d put a scope on at least until I had the data I needed.

Given iron sights, in general, most front sight beads are around 1/8”, which at the end of a 20” rifle barrel, let’s say 30” from the face, where 1moa would be 0.008725”, so the front sight blade is ~14.25 MOA wide. So to paint targets, at 200yrds, your front sight will cover ~28.5” of target… if you have a finer bead, you can scale linearly. I generally need 1moa of high contrast aiming point to see targets at all with a naked eye and prefer 2moa or larger, so I’d want at LEAST 2” aiming point, but generally would want additional aiming reference as wide as my front sight, so I would be looking EITHER at a 30” circle aiming black, with a 2-4” orange dot in the center OR with buckhorns, a larger + or X with broad 6” lines which terminate in a ~60-90 degree point, touching the 2-4” aiming center. If you have an aperture rear, circle favored over the +/x. Of note, this is just for your home range testing —> it has been a lot of years now, but every LR side stage I ever shot in CAS/SASS was just black or white steel, with no aiming points. So with irons, I’d up my target size from 30” a little to give myself more aiming reference.

I’d do the math on my sight radius as well to determine how far my adjustment hashes would be moving my downrange angle.

But if possible, again, I’d mount a scope to determine all of my DOPE, then translate that back to the irons.

But again - I am absolutely certain 2 things are true here: 1) there’s no way in hell your bullet has a .381 G1, and 2) you’re not shooting far enough that a slight error between .12 and .18G1 estimate will be terribly far off.

 

[AJC1]

Is that the Lyman loading manual or the Lyman Cast bullet manual? I'm asking because I already have the cast bullet manual on order (delivery this next mid-week), but not the loading manual.

Jim G

They are in the cast manual. You can also cruise the noe sight for the same data they provide for their molds.

 

[mdi]

I'm a simple guy, so I figger the truth is in the shootin'. I started my 308 at about 50 yards, easy to keep on a 8 1/"x11" piece of paper after bore sighting. Move out to 100 yards, try again and record results. I like reloading, ain't in no hurry, so trying several different distances, or loads is just more fun. I can hardly see a school bus at 200 yards, but I try that distance any way (I don't hunt any more so rarely shoot at anything over 100 yards)...

 

[GeoDudeFlorida]

I did not intend to "extrapolate" at all. I had just gotten the impression that if you know the approximate BC, obtained from a velocity differential at 2 different points in a shot's tarjectory, you can then at least figure out a rough trajectory - good enough to get on paper at 200 yards, and then tune the sights from there. To see where the bullets are actually grouping, I need a paper or carboard target, and I can't just put up a really giant one to start with because our winds around here will simply pick it up and send it to the next county! And no, there is no mount to enable mounting a scope temporarily as a help either.

Jim G

Sounds like you got it all figured out before you asked the question. Again. And it also sounds like any opinion but yours is just an excuse for an argument. Again. Even when someone agrees, if they aren’t patting your back, you get your hackles up. Kinda strange way to act, you ask me.
Glad you got it nailed down. Have fun.

 

[JimGnitecki]

.381 G1 for a RNFP 158grn .357” is WAY, WAY too high. Not a chance in hell that number is correct. I’d be surprised if the actual G1 is even 0.-ONE-81. Not many .357/8” pistol bullets even break 0.2G1, a LOT are in the .15G1 ballpark, I shoot die drawn Speer HotCor 180grn .358” RIFLE bullets with a long ogive in .357/44 B&D and they only have .245G1 BC, and they’re WAY longer and more aerodynamic than an RNFP.

You are not shooting these far enough to be worried about excessive target size to catch bullets. Given a good chrony speed, I would personally punch in a .15 G1 and then correct for that drop at 200, and that will be close enough on paper to catch with a decent, reasonably sized target backer. I’ve shot my 357/44 out to beyond 300, and shoot 22LR out as far as 500, so what you’re doing is very, very attainable, you just need to go into your calculator with PROVEN math, not backdoor science. All you need to do is estimate your BC, punch in good chrony data, and send it. CAS side match targets are huge anyway, and truing your BC before the match will be super easy. There’s only ~3.5moa difference at 200yrds between a .12G1 and a .18G1 at 1129fps, out of ~35moa compensation at 200 from a 50yrd zero… So I’d dial/adjust sights by 35moa with a ~30” target (more than twice my expected error above and below the aiming point), and I’d be highly confident that I’d land my bullets on that page.

Group size and visibility with naked eye will likely be bigger problems than the drop compensation. If you’re shooting 4moa at 200yrds, that’s a pretty big target, and you’ll need a pretty big target just to be able to see it.

Doing this with irons first would be a mistake, in my opinion. I’d put a scope on at least until I had the data I needed.

Given iron sights, in general, most front sight beads are around 1/8”, which at the end of a 20” rifle barrel, let’s say 30” from the face, where 1moa would be 0.008725”, so the front sight blade is ~14.25 MOA wide. So to paint targets, at 200yrds, your front sight will cover ~28.5” of target… if you have a finer bead, you can scale linearly. I generally need 1moa of high contrast aiming point to see targets at all with a naked eye and prefer 2moa or larger, so I’d want at LEAST 2” aiming point, but generally would want additional aiming reference as wide as my front sight, so I would be looking EITHER at a 30” circle aiming black, with a 2-4” orange dot in the center OR with buckhorns, a larger + or X with broad 6” lines which terminate in a ~60-90 degree point, touching the 2-4” aiming center. If you have an aperture rear, circle favored over the +/x. Of note, this is just for your home range testing —> it has been a lot of years now, but every LR side stage I ever shot in CAS/SASS was just black or white steel, with no aiming points. So with irons, I’d up my target size from 30” a little to give myself more aiming reference.

I’d do the math on my sight radius as well to determine how far my adjustment hashes would be moving my downrange angle.

But if possible, again, I’d mount a scope to determine all of my DOPE, then translate that back to the irons.

But again - I am absolutely 2 things are true here: 1) there’s no way in hell your bullet has a .381 G1, and 2) you’re not shooting far enough that a slight error between .12 and .18G1 estimate will be terribly far off.

Varminterror; THANK-YOU! Your very detailed reply did a great job of answering my questions and concerns. Now I know how to properly address this. I cannot mount a scope on this rifle - it's a lever action "Old West replica" that needs to stay looking "original", and it also ejects its fired cases right out the top of the receiver, so I am stuck with non-optical tools and procedures. Your description of a suitable target was particularly helpful, as I have never done this before.

The 28.5" target cover was a real wakeup call! Mine will actually be larger, because I had my original front sight replaced because it was too small (about .090" gold bead) for fast sight acquisition in the regular CAS stages with my 72 year old eyes. The new .150" gold bead front sight made me MUCH quicker in sight acquisition, but at 200 yards = 7200 inches it will cover .150/30 x 7200 inches = 36 inches!

So, for a "center-hold" sight picture, I would need a larger target and target stand than exists at the range! However, I can maybe use a 6-o'clock hold on an aimpoint shaped as " _|_ " and place the top of the bead right under the bottom end of the vertical line. To see the aimpoint clearly enough at 200 yards, the width of its lines will likely indeed need to be 6" wide as you suggested. So, perhaps overall, I need a cardboard target sheet maybe 36" square, with the aimpoint centered on it.

I'll use a couple of BCs of maybe .130 and .140 in a trajectory calculator, and see how much sight height travel I might need. I don't think my barrel-mounted elevator ramp sight is going to work at all for this because with the higher than OEM height of the top of the bead, I'm using up almost all my elevator height just to shoot at 75 years. So, a fold up/down tang peep sight will likely be required, and really makes the most sense at long ranges because it takes away the need to pay any attention to the rear sight during sight alignment. Such a sight simply folds down for a regular CAS stage, and gets popped up for long range shots, so that would be workable.

I know this sounds stupid, especially since I have never tried using a pistol caliber rifle at any meaningfully long range, but it could be really FUN!

Thanks for all your help!

Jim G

 

[AJC1]

Varminterror; THANK-YOU! Your very detailed reply did a great job of answering my questions and concerns. Now I know how to properly address this. I cannot mount a scope on this rifle - it's a lever action "Old West replica" that needs to stay looking "original", and it also ejects its fired cases right out the top of the receiver, so I am stuck with non-optical tools and procedures. Your description of a suitable target was particularly helpful, as I have never done this before.

The 28.5" target cover was a real wakeup call! Mine will actually be larger, because I had my original front sight replaced because it was too small (about .090" gold bead) for fast sight acquisition in the regular CAS stages with my 72 year old eyes. The new .150" gold bead front sight made me MUCH quicker in sight acquisition, but at 200 yards = 7200 inches it will cover .150/30 x 7200 inches = 36 inches!

So, for a "center-hold" sight picture, I would need a larger target and target stand than exists at the range! However, I can maybe use a 6-o'clock hold on an aimpoint shaped as " _|_ " and place the top of the bead right under the bottom end of the vertical line. To see the aimpoint clearly enough at 200 yards, the width of its lines will likely indeed need to be 6" wide as you suggested. So, perhaps overall, I need a cardboard target sheet maybe 36" square, with the aimpoint centered on it.

I'll use a couple of BCs of maybe .130 and .140 in a trajectory calculator, and see how much sight height travel I might need. I don't think my barrel-mounted elevator ramp sight is going to work at all for this because with the higher than OEM height of the top of the bead, I'm using up almost all my elevator height just to shoot at 75 years. So, a fold up/down tang peep sight will likely be required, and really makes the most sense at long ranges because it takes away the need to pay any attention to the rear sight during sight alignment. Such a sight simply folds down for a regular CAS stage, and gets popped up for long range shots, so that would be workable.

I know this sounds stupid, especially since I have never tried using a pistol caliber rifle at any meaningfully long range, but it could be really FUN!

Thanks for all your help!

Jim G

I really like Williams peep sights. Lyman also makes a decent version. If your using up all of your elevation at short range, then a shorter front post will really help you out. Based on a much larger appiture length than my little carbine it probably won't take very much. I really enjoy Lyman front globes with the inserts. You may find that an insert with a hole "double appiture" reduces your need for such a large target. They have a bunch of diopter options with color lenses depending on what is allowed.... I dont use diopters so I cannot advise on those...

https://www.lymanproducts.com/brands/lyman/sights/target-front-sights

https://www.lymanproducts.com/brands/lyman/sights

https://shop.williamsgunsight.com/e...-336-firesight-set-wramped-front-sight-070282

https://shop.williamsgunsight.com/e...sight-with-inserts-less-attaching-base-047478

https://shop.williamsgunsight.com/ecommerce/p/globe-sight-attaching-base-047620

 

[AJC1]

https://www.meritcorporation.com/
Adjustable peep