"Newby" needing help identifying signs of pressure

[bsnedeker]

Ok, so I've been reloading for a number of years, but I've just been using off-the-shelf recipes for my 270. Living in Minnesota and never shooting beyond 100 yards I wasn't too worried about finding the best load. Last year I moved to Montana and I'm starting to get the bug to shoot long range (6-800 yards is long range to me) so I got a 300 WM and I'm trying to work up a load.

This weekend I loaded up 8 rounds to do a pressure test with Accurate Magpro shooting a 178 grain eld-x through once-fired hornady brass, remington primer. This is for my Tikka T3X so I'm loading to a COL of 3.340 due to the magazine limitation (I measure off the ogive when loading and checking, just can't remember what that number is without checking my notes)...regardless, I'm not in danger of coming close to the lands!

I checked a few reloading manuals as well as Accurate's website and found max pressure listed anywhere from 76.9 to 81.6 grains. I started at 73.4 grains and went up 2% until I maxed out a 84.9 grains. I expected to see pressure and stop shooting if I saw anything that looked dangerous. Well, I never saw anything that looked dangerous to me, but after looking at the results I think I see signs of pressure on EVERY round I fired.



Here are three rounds. The bottom two rounds are pretty obviously overpressure to my untrained eyes, and they were the two worst out of the group. On the round at the top, it's hard to see in the picture but it has a VERY faint "smiley face" under the firing pin indent. This smiley face is much more pronounced on the other two, but it's there a little bit on the top one as well. The primer is also obviously flattened in the bottom two rounds, but doesn't appear to be in the top one.

So am I looking at a full batch that were all over pressure? I don't get that smiley face when I shoot factory hornady ELD-X Hunter ammo so I'm thinking yes but I'd appreciate someone who knows what they are talking about confirm or deny that.

 

[wind gypsy]

The bottom one looks a little flatter than the others. Im not familiar with the crescent marks on the bottom two primers, usually I just see flow around the firing pin gaps in the bolt face (depending on the action) and flat edges.

The primers don’t look crazy flat though and you’d probably see some ejector marks on the case head if it was real high pressure. 84.9 grains does seem like a lot but you sure weren’t over pressure when you started. If you were over pressure at the start and proceeded to add 11.5 grains you would have been blowing primers or locking your action up.

Did it require more effort to lift the bolt after firing the highest charge weights?

Also, don’t be surprised if a 178 eldx comes apart on you at win mag velocities. They are pretty soft.

 

[Rob5589]

The primers all look a touch flat on the edges but, nothing scary from those pics.
Not familiar with MagPro but I assume there is fairly cool weather in MT currently. In warmer temps you may see more pressure signs.

 

[Rich M]

Those are what my rifle primers typically look like...

 

[bsnedeker]

Awesome info guys, thanks! Yes, on the last few shots in the group the bolt was noticeably harder to lift so I knew right away those were over pressure. I'll work my way back from that point and try to find the optimum load. I'm trying to use Dan Newberry's method for finding barrel harmonics or whatever.

Thanks for the advice on the bullet selection and temp. Obviously I chose the bullet for it's B.C. but I had heard mixed reviews on it's performance with some people saying it's a devastating killer, and other's not trusting it. I might try loading up some other bullets just to get some reference.

 

[tdot]

I'd suggest that you look at the face of your bolt. Close to the firing pin, you may see a groove or ridge that is creating that semi circular smile.

At first I thought there may be something in the bolt face that was marking the primer during extraction, similarly to a bolt swipe. But thay should only be a 90 degree swipe, not the full 180 degree that you have.

Do you have a chronograph? Pressure = velocity.
If your velocity is way higher then book, you know you're over pressure.

Personally I've usually found that max pressure is atleast a couple of grains below where I can feel it in the bolt, during extraction.

 

[bsnedeker]

I'd suggest that you look at the face of your bolt. Close to the firing pin, you may see a groove or ridge that is creating that semi circular smile.

At first I thought there may be something in the bolt face that was marking the primer during extraction, similarly to a bolt swipe. But thay should only be a 90 degree swipe, not the full 180 degree that you have.

Do you have a chronograph? Pressure = velocity.
If your velocity is way higher then book, you know you're over pressure.

Personally I've usually found that max pressure is atleast a couple of grains below where I can feel it in the bolt, during extraction.

Yeah, I do have a chrono. I didn't use it for this test but I'll use it next time. Thanks!

 

[Myronman3]

reading primers doesnt tell you what the chamber pressure is. primers could look fine, and your chamber pressure could be too high. yeah yeah, i know. like it or not, it’s true.

which is why i use book loads, and if it aint fast enough, i get a cartridge that is. with your win-mag, book loads should serve you well.

 

[ajwcotton]

One thing to add, to the mix, it looks like you are using winchester primers which are horribly soft. I get flat primers with light loads with winchester primers. CCI are pretty hard primers and federal are in the middle I just use fed match primers for everything now. They are soft enough to go off when the gun is cold and lube in the firing pin spring is gummy, but hard enough to not flatten out easily with moderate pressure loads.
Hope this helps.

 

[JeffRaines]

reading primers doesnt tell you what the chamber pressure is. primers could look fine, and your chamber pressure could be too high. yeah yeah, i know. like it or not, it’s true.

which is why i use book loads, and if it aint fast enough, i get a cartridge that is. with your win-mag, book loads should serve you well.

This is exactly why having a chronograph is important.

 

[tdot]

reading primers doesnt tell you what the chamber pressure is. primers could look fine, and your chamber pressure could be too high. yeah yeah, i know. like it or not, it’s true.

which is why i use book loads, and if it aint fast enough, i get a cartridge that is. with your win-mag, book loads should serve you well.

Totally agree that the primers aren't the final answer to looking for pressure.

But unfortunately no two chambers or barrels are the same. So while it is certainly easier to limit yourself to book. It isnt the only way. I've personally never been able to match book, within their given powder charges. I've also seen book values produce dangerously over pressure loads. So even following book values, I would personally want to know how to read pressure signs.

 

[JeffRaines]

Totally agree that the primers aren't the final answer to looking for pressure.

But unfortunately no two chambers or barrels are the same. So while it is certainly easier to limit yourself to book. It isnt the only way. I've personally never been able to match book, within their given powder charges. I've also seen book values produce dangerously over pressure loads. So even following book values, I would personally want to know how to read pressure signs.

Looking at nosler right now I’m pretty sure I’d blow a gun of mine up with some of their charges.

While velocity isn’t necessarily a be all end all when it comes to pressure signs, seems to me it’s a pretty damn good indicator even if no traditional pressure signs are present. If you’re pushing past max velocity and still not seeing pressure signs chances are you’re still over pressure you know?