Primer Signs & Pressure

[SDHNTR]

OP, another thing you could do would be to get out your Dremel tool and cut a case that was fired with the max charge in half lengthwise. You will see easily if you have any worrisome case head expansion.

 

[BBob]

I surely haven’t.

Neither have I which is another reason I haven’t bothered with it (measuring cases) for a really really long time.

 

[35WhelenAI]

.0004-0006 in is considered safe maximum pressure I would not expect other pressure signs. Honestly if the load that was in the opening post of this thread showed case head expansion in that range I would consider it usable. Given there aren't any other signs.

 

[mtnbound]

Maybe I didn't make it clear, but I certainly am not chasing velocity. Rather, I am seeking to know where excessive pressure is, so that I know where a safe range of charges is to use for further load development.

It's still unknown whether I reached max pressure or not. The case expansions I measured, with an incorrect tool, of low charge weights were also an order of magnitude larger than values associated with max pressure, so those are likely nonsensical. Having a low charge weight and 400 fps less than expected max velocity is better information than a measurement with the wrong tool.

What I take from this thread is there are many possible data points to look to for pressure signs, and to use the right tool.

Stupid question time. Have you verified your charge weight?

 

[AkMtnRunner]

Stupid question time. Have you verified your charge weight?

Yep, calibrated and double checked with a balance beam scale

 

[35WhelenAI]

Lol, the dremel's like using the chainsaw when all you need is a paper clip, literally. Straighten a paperclip long enough to reach the bottom of the case . Bend a sort 90° angle on the tip. From the bottom of the case, scrape the tip on the paper clip you created up the case wall. You will easily feel incipient case head separation even before you could see a ring on the outside. If you don't feel anything you don't need to retire the brass. If you catch a groove no matter how slight, it will be OBVIOUS.

Found a picture on the internet with a cutaway view.

 

[SDHNTR]

Yes, but I’ve felt the paperclip hang up on carbon deposits too. Nothing beats a visual.

 

[35WhelenAI]

I disagree. A carbon deposit is a bump and you would feel it go up and down. A separation ring is a depression and the paperclip goes down and rises out. If I feel separation with the paper clip, I rotate the case to numerous different directions to verify.

IME, the ring felt from separation is in such a distinct spot just up from the bottom of the case wall with respect to location, it can't be confused with anything else.

 

[Bluefish]

Water isn’t compressible so it’s filling space.

Wet cases are easily a thing when hunting and it increases pressure more quickly than temperature. People are worried about temperature but never about water. You see sticky and stuck bolts at matches when it rains from loads right at the edge of pressure.

I always assumed the water acted as a lubricant, thus allowing the case to exert more force on the bolt face. That was why what we call pressure signs show up more readily. More bolt thrust, more marks on the primer and bolt face.

 

[35WhelenAI]

I've never heard of wetting a case to work up a load but it makes sense the boundary layer formed by the water would allow much more bolt thrust. I wouldn't use that as a guide with respect to hunting. If moisture doesn't get in the chamber in the first place when you put the round in to start the day, it would seem to be much the exception versus a reality. Even follow up shots would happen so fast I can't see water being an issue unless it's a downpour and that would be a rare exception to shooting game.

 

[parshal]

It's not rain to worry about it's snow. Especially if you use a detachable magazine.

 

[wind gypsy]

I've never heard of wetting a case to work up a load but it makes sense the boundary layer formed by the water would allow much more bolt thrust. I wouldn't use that as a guide with respect to hunting. If moisture doesn't get in the chamber in the first place when you put the round in to start the day, it would seem to be much the exception versus a reality. Even follow up shots would happen so fast I can't see water being an issue unless it's a downpour and that would be a rare exception to shooting game.

It's not THAT hard for rain/snow to get in an action/magazine. I've never had issues during a hunt with wet ammo/pressure but could see it happening for sure.