A jump to the lands?

JWFilips

JWFilips

Well-Known Member
I have always developed my cast bullet rifle loads based on the bullet touching the lands on bolt close! For the most part I have always been satisfied with that And as you know I'm mostly doing "Low Node" Shooting.

I would like to know what advantages there may be from loading cast bullets that jump into the lands and what scenarios dictate loading in this manor?
Just interested finding out why it would be a better system for cast bullets or maybe just for a particular style of cast bullet or a certain velocity?
My inquiring mind would like to know
Thanks
Jim
 
F

freebullet

Guest
Autoloaders.
Guns you need to retain the ability of easy unloading.
Some won't shoot good jammed.
Top 3 for me.
 
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Spindrift

Spindrift

Well-Known Member
Well, I’m no expert. But I’ll try to summarize my views.

The launch sequence is a compromise situation. It is like a highly complex equation with a lot of variables. We want the bullet to traverse the throat, and enter the barrel well centered, and with no damage. Changing one variable (pressure curve, alloy attributes, neck tension, bullet size, nose profile, bullet jump etc) can be beneficial in some ways- and deleterious in other ways.

The potential beneficial effects of bullet jump
- ease of feeding and unfeeding
- The running start to the lands makes engraving smoother, and I would excpect less «spiking» of the pressure curve- reducing the potential for base damage

The potential downside
- Bullets with limited capacity for self- centering (like bore riders) will have more «wiggle space», and would be more likely to get damaged
- The starting pressure would be lower, possible causing issues with concistency of ignition with some (slower) powders.

So; bullets with good self- centering capability have the capacity to exploit the potential benefits of a bullet jump, and may very well shoot better with a little jump. With bore riders, the «downside» effects dominate the equation- better to stuff the throat with these (PC might mitigate the situation, though)
 
Bret4207

Bret4207

At the casting bench in the sky. RIP Bret.
I was like Jim, I always tried to get the bullet into the leade. On some guns I just couldn't reach it either because of bullet style/length or mag restrictions. I never thought about really, but the ones not touching often shot as good or better than the ones with light engraving. I suppose it's habit as much as anything for me.
 
fiver

fiver

Well-Known Member
Spindrift said:
Well, I’m no expert. But I’ll try to summarize my views.

The launch sequence is a compromise situation. It is like a highly complex equation with a lot of variables. We want the bullet to traverse the throat, and enter the barrel well centered, and with no damage. Changing one variable (pressure curve, alloy attributes, neck tension, bullet size, nose profile, bullet jump etc) can be beneficial in some ways- and deleterious in other ways.

The potential beneficial effects of bullet jump
- ease of feeding and unfeeding
- The running start to the lands makes engraving smoother, and I would excpect less «spiking» of the pressure curve- reducing the potential for base damage

The potential downside
- Bullets with limited capacity for self- centering (like bore riders) will have more «wiggle space», and would be more likely to get damaged
- The starting pressure would be lower, possible causing issues with concistency of ignition with some (slower) powders.

So; bullets with good self- centering capability have the capacity to exploit the potential benefits of a bullet jump, and may very well shoot better with a little jump. With bore riders, the «downside» effects dominate the equation- better to stuff the throat with these (PC might mitigate the situation, though)
Click to expand...

your so on the right track.
okay so now split that stuff up, pair which direction you want to take.
hard/slow/jam.
hard/slow/run
hard/fast/run
hard/medium with filler/jump
medium/medium with filler/engraving
jump/hard/slow
jump/soft/fast
jam/soft/slow.

you can see there are variables to each theme.
the key is to use one of the /-/'s and then fill in the third variable to fit.
observe and move forward.
but what will happen is you'll start to see trends develop.

soft/slow/engrave,,,,,, hmm lots of win's on that one, and I still have a lot of pressure ceiling to work with.
maybe speed up the powder? or just add more to see what happens.

hard/medium/jump,,,,,, lot's of good groups here too, what if I add some pure lead [or a little more tin] to that alloy?
or if I increase the jump another .0010?
 
Spindrift

Spindrift

Well-Known Member
fiver said:
your so on the right track.
Click to expand...
Thanks, Fiver- I learned from the best :)

I do a lot of medium/medium/jump these days. Until now, I have mostly loaded cartridges to jam length (with bullet designs that needed just that). Always something new to learn. This morning, as I took my dog for a walk, I came to think about the sign you’ll typically see on train and metro stations:

Mind the gap

Now, there’s wisdom for ya.
 
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