Effect of Seating Depth on Max Charge Weight?

[cowboyarcher]

Hi Guys,

I am curious as to how the seating depth effects when a cartridge is over pressure.

I am most curious about something in the 223 to 22-250 class. I am running a 22 PDK (22-6.8SPC, 38.5gr H20) in an AR and with mag length rounds I am unable to match the numbers the previous owner was producing. I am however using a sorter COAL than he was because of the limitations of the different magazines I use.

I just performed a mod to my mags that will allow me to seat bullets out to 2.362" rather than 2.280". I'll load my old max charges and see if the pressure signs are gone and then will work up to a new max from there. Any thoughts on what I might find?

Thanks for any input guys, God bless,

Adam

 

[ThunderDownUnder]

Difficult question but a good one to ask on this forum. Basically as you seat your bullet out further, (using the same powder charge) you increase the volume of your case and drop the pressure just a little bit. This works ok until you contact the lands, once the bullet is seated out to the lands or jammed, the pressure spikes up to approx 3000 psi more. I'm pretty sure Quickload adds about approx 3000psi for a jammed bullet seating position, but it might be a bit higher.

Short answer is that by doing what you plan to do, seating longer in your modified magazine, you will drop the pressure just a little bit which might achieve what you want and allow a larger powder charge without pressure signs.

Ian

 

[cowboyarcher]

Well I am seeing interesting results.

With my previous max loads I see perhaps just a slight speed with a 53gr Vmax that was jammed fairly heavily into the lands, and with my previous max load with a 68gr Hornady BTHP I gained approx 100 fps.

I'm running CFE223, so although it was about 8 degree warmer than when I last tested theses loads, I don't think that is affecting things.

I must be getting a slight increase in average pressure w/o an increase in peak pressure?