Problems Loading for Trapdoor Springfield

[Pawpaw40]

I loaded up some 450 grain powder coated cast lead bullets for my 45-70 Trapdoor Springfield and took them to the range. They were at the starting load out of the Lyman Cast Bullet book, using Varget. Shot them through the chronograph, and they were averaging 1800 fps, the book said that they should be 1227 fps. No signs of excess pressure, no difficulty extracting, no flattened primers. I went back to the book, and I found where I had the COAL wrong. I had made them 2.545" (2.550 was the COAL for 405 gr. bullet) rather than the 2.850 the 450 gr. bullet required. Pulled the bullets, made one the 2.850 length and tried to chamber it. It will not chamber at that length. I had to take a cleaning rod and knock it out from the muzzle. The bullet had hit the lands and grooves. The bullet is 20 to 1 lead/tin ratio, pretty soft. The bore slugged .458, the bullets measure .4575, I wanted the softer bullet, so they would obdurate to fit the bore. There was no evidence of keyholing. No leading of the bore. It was the Lee #457-450-F mold and the recommended alloy was 10-1



I am confident that the chronograph was reading correctly, I had shot some subsonic 300 BO the same session, and they were as quiet as normal, and velocities were all fairly consistent, for both calibers. I know that powder coating will usually produce higher velocities than hard cast lubed bullets, but not 50% higher, at least not in my experience. In 300 BO it will produce on average about 100 fps, just enough to get it over the speed of sound. I was thinking that the shorter COAL might have raised pressures enough to get the velocities up, and that may still be true, but I have to get it about that length to chamber.



I was thinking about reducing the charge of Varget by 5 grains (below recommended starting load), shooting it over the chronograph, and working the velocities up to around 1400 fps, which is about the middle of the range for that bullet/powder combination, or when the gun groups best, whichever occurs first. And holding to the 2.545 COAL, which I know will chamber. What do you all think?

[Targa]

Deleted

[trails4u]

It sounds like your approach is solid, using velocity as your guide. I personally believe the chronograph to be our most useful tool in load development, as I believe velocity / pressure correlations are pretty hard to argue with.

[rockrat]

You might move your chronograph about 10ft farther from the muzzle and try again. I have had some readings that were not believeable in velocity, but once I moved the chrony a bit farther from the muzzle, readings were in the range of where they should have been.

[Electrod47]

You might move your chronograph about 10ft farther from the muzzle and try again. I have had some readings that were not believeable in velocity, but once I moved the chrony a bit farther from the muzzle, readings were in the range of where they should have been.

Yeah, the concussion from a 45/70 could be shaking the whole thing.

[warren5421]

I load for a 1884 Trapdoor Rifle and load with the bullet touching the lands and grooves. Take a shell place the lead bullet in the shell not crimped leave the bullet long shove it in the chamber shut the door, open and remove. Mic the length of that shell take .001"-.002" from that length and that is the max length (OAL) you want your shells. You may need to use a filler with some powders to keep them next to the primer. I like using black powder in the trapdoor. There are several good books out there to help you load the .45-70 Government.

[NSB]

Your chrono reading must be off because it’s too close. First off, you didn’t get too much pressure by seating the bullet “short”. That is far less a problem than seating it to where it’s on the lands when it’s chambered. You need to be off the lands one or two thousandths to allow pressure not to spike too high. If you actually are getting 1800fps with a starting load of Varget, your scale is way off. You’re not actually using a “starting” load. I’m guessing you’re a new reloader? I’m glad you’re posting this and that’s how you avoid mistakes in the future. The other responders jumped in with some good comments. If you are new to reloading, please read the introduction in your loading manuals where it explains the basic knowledge needed to make good, safe ammunition. What manuals are you currently using? If you don’t have a Lyman Reloading Manual, I strongly suggest you get that one right away.

[TCLouis]

Drop a boolit down into the chamber.
Measure from the back of the chamber to the base of the boolit.
That measurement PLUS the length of the boolit is the MAXIMUM OAL of a loaded round.
Take a little off of that length as your max loaded OAL and you will have backed off the lands.

[Pawpaw40]

I've been reloading for only about 40 years. I weighed every charge, twice. I have a Lyman Auto scale, and then I checked it on a digital scale. The chronograph was 15 feet away from the muzzle, which is the recommended distance. I stated in my OP that I was using the Lyman Cast Bullet manual. I ordered a Hornady overall length gauge modified case, to get a measurement for the correct COAL.
I found some IMR 3031, I'm going to try it, and moving the chrono farther away.

[Tar Heel]

Isn't shooting smokeless in a Trapdoor illegal?

[Larry Gibson]

What was the charge of Varget? Judging from the #4 BH that should have been 43.2 gr? Are you sure that was the charge? Are you sure you loaded it with Varget?

Also keep in mind the longer barrel of the TD will give higher velocities than the 24" Lyman test barrel but a 600 +/- increase is still a bit much.