Where does pressure show first?

[mao0720]

Does pressure usually show first on primers or on the case head? The reason I ask is that I have been working up a load for a 243lbc (think 6mm grendel) AR15 and I am at well below loads of what others are using, but I'm still getting light ejector marks. The primers look like they have round corners just like they came out of the box. I'm thinking the ejector marks may just be a product of shooting the AR platform, especially with a suppressor. Any thoughts?

 

[jimcasey01]

The reason I ask is that I have been working up a load for a 243lbc (think 6mm grendel) AR15 and I am at well below loads of what others are using, but I'm still getting light ejector marks.

That is why we work loads up. Many of our firearms use charge weights that are significantly lower or even higher than what others use. Custom tailor the load to your firearm, don't be too worried about what others are using.

 

[JRS]

That is why we work loads up. Many of our firearms use charge weights that are significantly lower or even higher than what others use. Custom tailor the load to your firearm, don't be too worried about what others are using.

Absolutely true, and well worded

 

[dkhunt14]

Primers area poor way to judge pressure. You need to measure case heads. Matt

 

[Paddyd]

It would depend on the softness of the case and type primer which would show signs first. Normally, it shows with the primer flattening out and completely filling the pocket edges. If you are using a copper or brass (not sure which it is made of) Winchester primer you'll normally see pressure signs there first. I'm no expert, but that's where I tend to see signs on my brass first before it starts marking up the base of the case.

 

[Lapua40X]

http://www.shootingillustrated.com/articles/2011/4/12/case-head-swipe/

 

[mao0720]

Thanks for the link and the opinions. Like I said my primers, rem br Sr primers, still have very round edges and have not flattened at all. The swipe that I am seeing is minimal and not evident on all cases I'm the same load. My thought is to remove the suppressor, which should reduce back pressure, and see if that alleviates the problem. If not, then keep working on the load.

 

[M-61]

In reply to your heading "Where do pressure show first?", my response would be (not that it is shown) but when you lift the bolt. If the bolt is stiff that would surely make me examine the case.

 

[Brians356]

In reply to your heading "Where do pressure show first?", my response would be (not that it is shown) but when you lift the bolt. If the bolt is stiff that would surely make me examine the case.

Stiff bolt lift in an AR, that's some neat trick.

 

[Hollywood]

In ar platform the bolt will rotate while still under some pressure so you can see the ejector swipe on brass. If it's just a swipe you should be safe it it is shaving brass off or leaving a dent in the brass at the end of travel you're load is probably too hot. Some brass is softer than others. My winchester brass seemed to show more than my hornady match with the same load.

 

[M-61]

Stiff bolt lift in an AR, that's some neat trick.

Thanks for pointing that out to me. I missed that entirely.

 

[ireload2]

Pressure signs that you see may vary depending on characteristics of the components, fit of the ammo in the chamber and the surface texture of the the chamber and bolt face.
A very smooth bolt face will allow a primer to spread out easier than one with circular tool marks.
A very smooth chamber will allow extraction when a rough chamber would give sticky extraction.
If the chamber back end is a close fit to the brass high pressure will not show much of a step at the solid head.
All those things are subject to some variation due to fits and finishes.

However when a primer pocket expands oversize you have a pressure sign that does not vary due to fit and finish.
When the primer pocket is ruined in one shot you can besure that you have excessive pressure.

If your primer pockets last 40 or 50 firings your pressure is ok.