Bullet Pressure Ring Question

[Dos XX]

What is meant by a pressure ring on a bullet? Is it a slightly larger diameter at or near the boat tail / bearing surface junction?

I measured some Berger .30 caliber 185 juggs and 200 hybrids. They seem to be slightly bigger in diameter at that point on the bullet. I measured some 6.5 mm bullets, three different brands, and they all seem to be the same diameter at the boat tail / bearing surface junction as they are on the bearing surface itself. I'm talking .0001 or .0002 larger on the .30 cal. Is that what is called a pressure ring?

The reason for the question is that it seems to take a lot more seating force to seat 6.5mm bullets in new or fired Lapua brass than it does .30 caliber bullets in Lapua brass. In both instances the brass was expanded with a PMA neck turning mandrel for appropriate caliber, so it is probably .001 to maybe .002 under caliber diameter.

I am wondering if the absence of the larger diameter portion means you are pushing more surface area into the neck on the 6.5mm bullets. In other words, is it possible that the .308 "pressure ring" is leading the way and expanding the brass whereas you don't have that with a 6.5mm?

 

[JRS]

Pressure rings are found on flat base bullets. It's the nature of bullet making dies. Some boat tail and VLD bullets exhibit a larger diameter at the junction of the bearing surface point. The bullet makers have to rely on the custom die makers to produce the dies to the tightest dimensions humanly possible.

 

[X-Caveman]

I think it's just the luck of the draw. I recently measured several lots of Berger 130gr & 140gr 6.5mm bullets (VLDs and Hybrids). They all exhibited some taper on the bearing surface. The lot that concerned me/ seemed extreme had .0007" taper (fattest by the boat tail). Others had .0002-.0003" taper. I called Berger tech line and was assured that they were in spec and should shoot fine and that the taper was a design feature of the bullet. I've only loaded and shot 5 of them, but I think the he was correct.

 

[Dos XX]

Every bullet mentioned in my post shoots great. My question is concerning the greater seating force on the 6.5 mm bullets versus the .30 cal, and if the .30 cal bullets being larger in diameter at the boat tail could make them easier to seat than a 6.5 mm bullet that is the same diameter at the boat tail as the bearing surface.

Might just be the nature of the brass. The necks are the same thickness but they are obviously smaller in diameter on the 6.5 mm. It could just take more force to move the metal.

 

[dkhunt14]

I think it may have to do with the hardness of the brass. My 6mm bullets seem to seat easier then 30. A 30 has more bearing
surface area so you would think it would take more pressure to seat. Matt