Pressure increase when bullet is into lands?

[stubbicatt]

I've resisted jumping on to the thread for awhile.

Jamming the bullets is perfectly acceptable way to develop loads, provided that the handloader keeps a weather eye out for pressure signs and does common sense load development... not start with a thermonuclear load and expect things to work out right.

In fact, the uniformity of pressure curves can be improved by jamming a bullet. Not all rifles shoot well this way, but this is how I arrive at a good load, using a chronograph. Once I find the powder/primer combo, I start experimenting with seating depth. .020 in the lands, right at the lands, and then .003 increments away from the lands until the load is "tuned" to the rifle.

As all know, the issue with jammed bullets is the event of having to unload an unfired cartridge, with the resulting powder spill all over the action.

YMMV, and it would be a good idea to enlist the assistance of someone who has done this before embarking on this alone.

 

[Brian Pfleuger]

There was only around 0.002 to 0.003" headspace on the new Win brass prior to firing.

That is a bit odd, actually. A properly headspaced AI chamber is ordinarily supposed to be "crush-fit" with the parent brass. I think that's the case with all AI chamberings but I'm not positive. It certainly was true with my .243AI.

I didn't see where you mention the bullet. Ordinarily, AI fire-forming loads are at the top of the load data for the parent cartridge.

I hope you do some shooting with light bullets. I'm thinking of building a long barreled .22-250 AI and going for the 5,000 fps mark.

 

[csmsss]

I hope you do some shooting with light bullets. I'm thinking of building a long barreled .22-250 AI and going for the 5,000 fps mark.

Hahaha. I can just see the smoldering carnage that your barrel will become at the end of each shooting session with that velocity!

 

[jepp2]

A properly headspaced AI chamber is ordinarily supposed to be "crush-fit" with the parent brass

It is with new Norma brass, not with Win brass. Win sets the shoulder back further. So I just compared the shoulder differences and estimated the 2-3 assuming the Norma brass was zero. If the crush was more on the Norma, the headspace would be less. I don't currently have a 22-250 AI Go gage.

I was shooting 55 gr. bullets and near the max for the parent, but that puts it much lower down on the Improved load data due to the increased case capacity.