Quite a spread in FPS in my 45-70 (Trapdoor) loads.

[Bang]

Got a surprise today. Shooting the Springfield Trapdoor. Checked windage at 50 yards, good to go. Fired at steel at 200 yards, resounding clang. Fired again. Missed. Missed again. Understand, this was a near impossible job. Could not see the sights, could barely see the steel in a bunker which is deeply shaded. Had to align front and open rear sight where I could see them, then swing the rifle a little, trying to maintain the alignment, then trying to judge where the front sight is in relation to the steel, while allowing for a strike which should be 18 above line of sight. Meaning aim lower than the target.

Went to 100 yard paper. Windage remained pretty good, elevations were inconsistent but a few rounds grouped. Another shooter on the range was shooting through a chronograph. I asked to use it. (Theoretically, my loads should be near 1250, which would be the fps needed to agree with the sights). Firing three rounds, it registered 1339, 1258 1316 for an average of 1301 fps. I was disappointed in that spread from 1258 to 1339. The loads are weighed on an Ohaus balance scale that remains accurate. The bore is .463 (slugged) and so are the flat based bullets, so they are marginal for ability to seal. I guess all that's needed is a slight difference in bullet-bore relationship to upset the applecart. Still, that seems a spread that maybe caused by something else. Thought of it. Forgot to hold the cartridges bullet up to assure the powder was back by the flash hole. Also, weather was a bit chilly. Maybe the powder s better in warm weather. The powder is IMR 4759, no longer available.

[dkf]

If there is a lot of empty space in the case maybe you want to try a filler. Some powders are pretty temperature sensitive but I would think all the rounds you were shooting were probably close in temp to each other.

[Bang]

I use a swatch of Dacron. Should hold the powder back, but I lost track of how I've been storing and handling them. Good catch on all the same temp. Just wondered if low temp could induce erratic burn. Thanks.

[Tim Ault]

Try a different primer or even try large pistol primer, I know with some of my light to medium cast loads in rifle calibers switching to a LP primer really helped , do you tamp your Dacron down onto the powder or fluff it up so it fills the case ?

[knight0334]

Always use magnum primers in large cases. If you are having misfires due to light hammer strikes, switch to a softer primer. CCI's are notoriously hard, Winchester and Remington primers tend to be softer.

One tip when shooting those old blackpowder cases loaded with smokeless - keep the cartridge bullet up. Then when loading, raise the muzzle of the gun, slowly tilt the cartridge to chamber it so that the powder sits against the primer. Then slowly bring the rifle down to aim.

This can be avoided by using a powder that fills the case more per unit of volume versus weight. Or by using a wad, however wads can have the drawbacks of increasing pressure - which is an exceptionally BAD thing with older guns, notably the Trapdoor models.

[knight0334]

While I don't use it personally, a lot of fellow 45-70, 45-90, and longer cartridge shooters use Trail Boss due to its case filling ability.

[cephas]

just to throw another idea in the mix how about neck tension? Lightly applying a circular crimp utilizing the Lee factory rifle crimp die has had a positive effect on my loads.

[daschnoz]

Bang, what is the load you're using? What you are seeing is a symptom of inconsistent ignition and it looks like you've been lucky so far - but don't push it.

As others have mentioned, tip the gun back (muzzle up) and slowly lower it before firing.


Shrink yourself down and put yourself into the case with the powder.
Here's what is going on:

When the powder is spread out all over the floor, the flame (primer blast) that comes out of the wall showers across the room and ignites the powder that is on the floor - all granules at the same time. This results in a very sudden spike in chamber pressure - a pressure that could ka-boom the works.

By tipping the muzzle up, you're piling the powder on the wall. When the flame shoots out of the wall, it hits the powder that is right in front of the hole and the powder burns outward from that spot. The chamber pressure rises more slowly. The pressure increase from further powder burn is offset by the increasing room volume as the bullet travels down the bore. Once all the powder is consumed, pressure will only decrease until the bullet leaves the muzzle.

The big difference is WHEN the powder is burned - all at once or slowly** over time.


**slowly being relative. We're talking fractions of a second that look like 0.000 before you get to any non-zero digit, but with the pressures that we're playing with, it makes a HUGE difference.



When I'm playing with loads that are this light, I stay with fast powders - Unique, Red Dot.

OR

Trail Boss - which isn't super fast on the burn charts, but it was purpose designed for exactly what you're doing - low power load in a high volume case. It is ridiculously bulky (8gr of Trail Boss will fill a 223 case).

[knight0334]

just to throw another idea in the mix how about neck tension? Lightly applying a circular crimp utilizing the Lee factory rifle crimp die has had a positive effect on my loads.

Yep, crimps help keep pressures/velocities closer.

[Bang]

21.5 grains, 405 gr bullet. Goal is 1250 fps, which is what the Buffington sight and standard front blade is designed for. I am not that far off, and the load is a tried and true amount in use for decades.

I don't see the advantage to crimping. It's single shot, no magazine involved, the bullets are relatively soft lead and I do not want to disturb the bands. The exterior of the shells are coming out clean so the chamber seal is very good.

I think my biggest problem is bullet to bore. I paper-wrapped some .458s and they printed a much better pattern.

I'll try the Trail Boss and magnum primers. Heading for Oaks. Thanks all.