HAS ANYBODY EXPERIENCED THIS?

[budlight]

When choosing a load to test, keep in mind that seating depths can make a HUGE difference in pressure. Remember that seating bullets into the lands can raise pressures but moving 0.020″ or more AWAY from the lands can also raise pressures, because you are reducing the effective case capacity.

I came across this while trying to figure out why I was popping some primers in my 308 loads even when I was 5 grains under the listed max and I thought that by making a longer jump to the rifling would be a way to decrease the pressure over pulling the bullets and reloading at an even lower level of powder.

Load length of 2.740 so they will fit in clips with a max of 2.760. I made them 2.700

 

[cape cove]

What are the details of the load that pops the primers. I would think that at 5 grs under max you would be safe regardless of the OAL. Maybe something else at play here...

 

[BallisticsGuy]

I've had all kinds of surprises in almost 30 years of hand loading. I had a 6.5 Grendel that would expand primer pockets at 4 grains under max. Never did find the issue. Replaced the barrel and it was fine.

 

[budlight]

I was using LC brass that has a smaller case capacity than commercial brass like Win or RP. 24 inch stainless barrel. They tell you to go down 2 grains for mil spec 7.62X51mm

I also did Saami spec inside and outside neck turning. Because I thought that maybe I was having tight chamber problems.

This was three different rifles though.

 

[Tiny Tim]

tagging in

 

[cohunt]

With lc brass in my 308, I hit max pressure at 1 to 1.5 gr under book max with lead core bullets. But with mono bullets im about 4 grains under due to the longer bullet and longer bearing length.

 

[PowellSixO]

I personally believe that people make the biggest mistake in reloading, by working their brass too much. When you resize the brass too much, it does weird things. Primer issues, signs of over pressure, split necks, and more. Size you brass just enough to fit your chamber without too much resistance when closing the bolt, if you're loading for a bolt gun. A little bit more, if reloading for a semi auto. You mess with the head spacing if you work your brass too much. The firing pin comes forward, strikes the primer pushing the case forward in the chamber, the primer ignites, the powder ignites, and the case comes slamming back into the bolt face, while also expanding to the chamber. This is a huge no no.

 

[budlight]

What are the details of the load that pops the primers. I would think that at 5 grs under max you would be safe regardless of the OAL. Maybe something else at play here...

TAC 150 HDY BT-FMJ 42.4 2,715 47.1 2,957 61,478 2.735

I was clear down at the 42.1 grains with cci 200 large rifle. weather about 80 and we kept the bullets in the shade. I was different date mil spec one shot brass. Very random and maybe once every 30 rounds Dillon 550 Using prepped brass that gets tumble wet polished before using.

Like I said after a popped primer and heavy extractor ding. I pulled the whole lot of bullets and weighted the charges. So I seated the bullets deeper thinking that it would also lower pressure. If anything the number of popped primer went up to maybe 1 in 20.

I ended up pulling them all and just saying to not use mil spec brass anymore. I bought a five hundred commercial one shot brass to replace them. big difference in case capacity.

51 grains of Big Game fill a mil spec level with the top of the case. Where win and R&P are 1/2 inch down in the case

 

[budlight]

I did some more looking at my military brass 7.62X51, lake City, GFI, and some unknown manufactures. 51 grains of Ramshot Big game fills them to the top. On the commercial side sierra and lapua fill to the base of the neck and the biggest case volumes are winchester followed by R&P and Hornaday. I'm going to look online for some 308 case volumes. I'm just not going to use military brass. It takes a lot of prep work. I had to swage every case to get a primer in and then inside and outside neck turning after full length resizing. Maybe people with the lower powered service rifles like them.

51 grains of big game is about the slowest powder practical for 308 and commercial cases. It's the top end load for 165 gr and only goes down a few grains clear up through 180's With low pressure and great velocity.

 

[Bob Wright]

Sounds like water volume comparison is in order. If your load data is based on another brass mfr., it begs the question how far out of volume are these brass components vs. RP/Win/Federal or what is specified in the manual.

 

[budlight]

This was online. But you can see how much less volume a Lake City has

 

[budlight]

https://loaddata.com/articles/PDF/BenchTopics%2087.pdf

 

[wildbillb02]

Maybe a bad swage?

 

[budlight]

Maybe a bad swage?

How can you bad swage? I have a Dillon swager arm type press. The pressure was so high that the now ruined case also has a shiny ding in the from the extractor.

The original problem was occasional blown primer. Which appeared to get worse when trying to seat the bullets deeper. It appears to decrease the case volume even more instead of the typical getting away from the lands and jumping the bullet where you get less pressure.

The 308 was new animal for me to reload.