Need 45-70 Trapdoor Carbine Ballistics (55gr FFg Goex, 385g RN 1:20)

[Hellgate]

I'm considering shooting my trapdoor carbine (original w/lined barrel) in a "classic battle rifle" match for any military rifle made before 1947. Most will be using milsurp rifles and likely many Garands, 1903 Springfields, and M-1 Carbines. I'd like to mix it up with my TD carbine that I use in the Plainsman side matches at Cowboy Action shoots. I have the rifle sighted in to hit 2" high at 50 yards which is perfect for the typical Plainsman match where there is rarely a target over 75 yards and more commonly under 50 yards. In the Practical Rifle classic battle rifle match I am supposing there will be targets out to maybe 300 yards maximum with most between 50-200yds. I'd like to know what the holdover would be at 100-200 yards. I'm shooting 55grs of FFg Goex under two thin beeswax discs under a Lyman 457124 385gr cast bullet of approximately 1:20 tin/lead sized to .459 with 50/50 beeswax/deer tallow BP lube. This load groups nicely at 50 yards and the gun has gone 40 rounds straight without fouling out. I do not expect much of a score due to my aging eyes and the iron sights are fixed (the sight ramp used to gravitate upward under recoil so I seized it up with a dab of fingernail polish to keep it in place). I do not know the velocity nor the ballistic coefficient of the bullet or else I would go to the Hornady ballistics calculator to get my answer to holdover.
Thanks in advance. Even simple data points like "on zero at 50 yards puts you X inches low at 100yds, X+@150, and X++@200) will do.

[Hickory]

Without doing calculation, I would just shoot it at the yardages you listed.
That would give you true performance of your load/gun.

[bigted]

Please do report your findings. I also have a trapdoor carbine and love shooting that exact load. How thin are your beewax disc's?

[Hellgate]

Big Ted
The BW discs are merely sheets of medium brood core (MBC) punched out over the mouths of the charged cases. MBC is that thin beeswax sheets sold in hobby shops for rolling into candles. It has about 1/8” diameter hexagonal indentations in it for bees to start their honeycomb on it. If you send me your address by PM I can put a half sheet in a manila envelope and mail it to you. The hobby shop stuff is more expensive and often comes in various colors. I get it from a beekeeper supplier.

[Tom Myers]

I'm considering shooting my trapdoor carbine (original w/lined barrel) in a "classic battle rifle" match for any military rifle made before 1947. Most will be using milsurp rifles and likely many Garands, 1903 Springfields, and M-1 Carbines. I'd like to mix it up with my TD carbine that I use in the Plainsman side matches at Cowboy Action shoots. I have the rifle sighted in to hit 2" high at 50 yards which is perfect for the typical Plainsman match where there is rarely a target over 75 yards and more commonly under 50 yards. In the Practical Rifle classic battle rifle match I am supposing there will be targets out to maybe 300 yards maximum with most between 50-200yds. I'd like to know what the holdover would be at 100-200 yards. I'm shooting 55grs of FFg Goex under two thin beeswax discs under a Lyman 457124 385gr cast bullet of approximately 1:20 tin/lead sized to .459 with 50/50 beeswax/deer tallow BP lube. This load groups nicely at 50 yards and the gun has gone 40 rounds straight without fouling out. I do not expect much of a score due to my aging eyes and the iron sights are fixed (the sight ramp used to gravitate upward under recoil so I seized it up with a dab of fingernail polish to keep it in place). I do not know the velocity nor the ballistic coefficient of the bullet or else I would go to the Hornady ballistics calculator to get my answer to holdover.
Thanks in advance. Even simple data points like "on zero at 50 yards puts you X inches low at 100yds, X+@150, and X++@200) will do.

Hellgate,

I am going to make some assumptions concerning your barrel and sight configuration, such as
Barrel length of 30"
Front sight height of 1"
Sight radius of 24"
These values should get you in the ball park, considering the precision level of open sights.

I located a Lyman image of the 457124 Bullet:



I then used the Precision Cast Bullet Design software to create a file for the scaled dimensions of of the Lyman 457124 bullet:



The Design software calculates an estimated Ballistic Coefficient for the design of 0.2431

The design dimension values were then exported to the Precision Precision Load Records and the Precision Ballistics and Trajectory
software applications:

The Load Records application contains a very good Black Powder velocity calculator (estimator) which was used to calculate the approximate muzzle velocity of 1211 fps for the Lyman bullet from a 30" barrel using 56 grains of Goex FFG powder.



This information was then exported to the Precision Ballistics and Trajectory application where the ballistics and trajectory values were calculated:



The Calculated chart shows, among other critical information, the bullet drop at various ranges if your rifle is zeroed at 50 yards.
If your point of aim is 2 inches high at 50 yards then you would need to add 3 inches of drop at 75 yards, 4 inches at 100 yards and 8 inches at 200 yards.

Of course, all this is estimations based upon assumptions of your barrel and sight configurations but should be close enough to the precision of open barrel sights.



If you were to add a set of precision peep or vernier sights to the firearm, the software could (Based upon real and unassumed data from your firearm and load.) calculate quite accurate ballistics data and precise sight adjustment values at any and all desired ranges.

Hope this helps.

[Hellgate]

Tom,
I am overwhelmed by the detail in your calculations. Thank you so much. Now, I must apologize for not providing proper data to be entered. I just pulled the rifle out from the back of the safe and did some measurements (which I should have done in the first place before posting, for which I am sorry):
The distance above the center of the bore for the front and rear sights is .75". The rifle is a cavalry carbine with a 22" barrel (from breechblock face to the muzzle). I do not know the twist of the barrel as I had it relined due to a slight barrel bulge and rusted bore. It consistently shoots 1" groups 2" high at 50 yards with the fixed sights. The velocity will likely be less with the shorter barrel measurement. The point of aim is "0" with the POI 2" high@50yds.

[Larry Gibson]

"Fixed" sights? What kind of rear sights does the carbine have? Is it an actual TD carbine rear sight? If so which one? A picture of the rear sight would help. If it's an original rear sight (M1873, M1879 or M1884) it is adjustable for the longer ranges.

[Hellgate]

Larry,
I use the rifle 3 or 4 times a year for Cowboy Action Plainsman side matches and the sights as they are set work perfectly for those matches. It has the original ramp sight with the yard designations but because the ladder (?) was loose was loose it would work its way up the ramp under recoil and change the POI with each shot so I glued it in place to hit 2" high@50 yds. I don't want to unglue it. The "battle rifle " match referenced in my first post is only held once a year.

[Larry Gibson]

Hellgate

Sounds like you got a M1879 rear sight on the Carbine. There should be a "C" on the left side. "Ladder" is a common designation for the part that flips up for longer ranges but it's actually called a "leaf". The "sight" on it that is slipping up under recoil is called the "slide". The slide has a buckhorn shaped eye piece attached to the top of it. There should be a tension leaf inside the slide that prevents it from movement under recoil yet allows it to be readily adjustable. Yours is/was apparently broke or missing. The parts are still available or you could even replace the entire leaf assembly as it's held on the base with just a pin.

Being able to adjust the sights for the range, especially longer range such as you want, is much more accurate than using hold over which with a low velocity level carbine load can be discouraging if not frustrating........been there, done that. However, if you want to try 100 and 200 yards with your sights fixed and with your load hitting 2" high at 50 yards. then the bullet will be about 3 - 5" low at 100 yards and close to 38 - 40" low at 200 yards.

[Hellgate]

Larry, You are correct. It is the 1879 sight. I fished the rifle out again, disassembled the sight and found the spring (flat curved) under the slide. I took it out and gave it a tweak to put more curvature to it and put it back. Now the sliding sight doesn't move near as easily as before. I will take the gun out and shoot it to see if the sight still migrates up the ramp. Thanks for all the suggestions everybody.