Reading Primers for Pressure

[303Guy]

We all do it and but few admit to it as we all know it is fraught with danger. I've been caught a few times with the primer backing out thing. But I've suddenly realized that our PC monitors are marvellous microscopes. Check this out.

http://i388.photobucket.com/albums/oo327/303Guy/325gr748206grBSAM003.jpg

See the difference in pressure between the two primers?

Well it's there. Measure the primer on your screen and compare it to the flattened area. Be sure to measure each one separately as there is a camera angle difference. The trick is to get a ratio of primer diameter to flattened area diameter and there we find a difference of 82.8% to 71.8%. Both primers ignited the same charge amount but the one on the left had a 206gr boolit and the one on the right had a 194gr boolit.

So, the difference is;

94.2% boolit weight difference and 86.7% primer flattening difference. Not a linear relationship but the pressure change is probably not linear either. More significant is that the primer response to pressure difference is far from linear.

(Those were Federal primers).

[fredj338]

You are chasing your tail trying to determine pressure that way IMO. Primers vary from lot to lot in case thickness, & from brand to brand.

[stubshaft]

You're right PC's do make great microscopes. Don't see any pressure issues in the primers you posted though.

[303Guy]

You are chasing your tail trying to determine pressure that way ...Absolutely. Reading tea leaves.

However, while it is impossible to determine pressure it is possible to see the difference in pressure using the same primer lot. I've no idea what the actual pressure in those two loads were but I know one was higher than the other and I can reduce the powder charge to get more or less the same pressure with both boolit weights. The point was that by using a photograph one can actually measure difference not visible to the naked eye. And most of us do not have access to pressure measuring equipment so we are actually groping in the dark doing the best we can.

I also happened to catch one of the boolits and am able to see the effects of the pressure on the boolit base and I can see that I have reached maximum pressure for that particular alloy so I need to back down (or harden the alloy). I also happen to know from the load charts that the load I selected was below max for the gun. Max for the gun also flattens the primer a lot more. (My max is not the same as book max. Mine is a lot lower).

http://i388.photobucket.com/albums/oo327/303Guy/325gr748206grBSAM1-1.jpg

See what I mean? Those fold impressions are from the paper patch skirt. I can expect marginal accuracy from this load as there is some base edge feathering.

[uscra112]

What are you using for a camera?

[Adam10mm]

If you see pressure sign via primer reading, you're already way over pressure.

[303Guy]

It's a Finepix F5800. I used it on Super Macro which allows me to stick the lens right up the fleas bum. I originally had an old Mavica with as many pixels as a low res printer but it too could be stuck up fleas bum and produced the same results (sort of). The trick is to place the object onto something transparent so the auto-focus sees only the object. With Super Macro I can rest the edge of the lens for steadiness otherwise there is no real advantage. I crop the pictures which makes them look closer.

Recognise the record player stylus package? (Youngsters don't even know what a record is!)

http://i388.photobucket.com/albums/oo327/303Guy/325grW748206grXIXPP005.jpg

See what I mean?

http://i388.photobucket.com/albums/oo327/303Guy/325grW748206grXIXPP006.jpg

[1Shirt]

Review of primers are an indication of pressure, and only an indication. As stated there is a difference in different brands of primers and the hardness of the materials used to construct them. Regardless, IF/WHEN I have cratering indication from firing pin strike, I consider it to be to much pressure, and time to back off the load. Not scientific I realize, but it satisfies me.
1Shirt!:smile:

[Chris]

I am satisfied that wile not completely reliable, primers are a fair indicator. Combined with me other resources, it gets me by.

[williamwaco]

I agree you can't tell much about pressure from primers.

I agree that PCs make great microscopes.

Also, if you have two different loads fired in the same gun with the same primer, you ( may ) be able to tell which has the higher presure.

If you blow a hole in the primer you can pretty well guess the pressure it too high.

I really like this PC camera:

http://www.amazon.com/Celestron-Deluxe-Handheld-Digital-Microscope/dp/B004QF0A1Y/ref=sr_1_2?ie=UTF8&qid=1328658862&sr=8-2

[Bullwolf]

Recognize the record player stylus package? (Youngsters don't even know what a record is!)



Speaking of records and vinyl...I was grabbing a bite to eat at a local burger joint. While I was there, I saw a girl wearing an old 45 record insert on a chain around her neck, as if it was jewelry. It looked like it had been gold plated.

http://ecx.images-amazon.com/images/I/51h-1kg8xQL._SL500_AA300_.jpg

I suspect that she wasn't old enough to know what it was originally intended to be used for.

Just for kicks, I decided to talk with my 20 year old nephew a bit about records, and such, so I could analyze his perspective on things. He fancies himself as a young musician.

After I showed an old 45 record insert to him, and I explained what it was for. Then I also had to explain to him what a 45 rpm record was. :groner:

It was one of those signs that we are all getting up there in the years I suppose. He looked at me like I was talking about 8 track tapes or something.

Excellent photos by the way. I really need to remember that trick of placing the object onto something transparent, so the auto-focus will see only the object and not the background. Great zoom in tip.


- Bullwolf

[303Guy]

I doubt one can tell the difference in pressure from one 'identical load' to another. I did a re-measure from a different photo and got a slightly different result. Similar but probably more variance in actual measuring than in the pressure difference. Just saying it's an indication or guide and no more. One could say a dim light in the total darkness.

[Rocky Raab]

A single primer tells you no more than a single velocity reading. If you fired ten shots at each of several workup charge increments, then carefully measured and tabulated each primer for several parameters, you might be able to detect a trend.

And what it would tell you would be that more powder produces more pressure. Since we knew that to begin with, primer reading would seem to be a pointless enterprise.

[303Guy]

Perhaps, but we look at primers anyway. We look to see how much flattening there is or whether there is any cratering. Zooming in so we can measure makes things clearer. Some folks measure case head expansion to deduce pressure. If one manages to expand a 303Brit case we'd be in trouble!

I've been doing seating depth tests to see what seating below the neck might do. Trouble is I am varying the depth and the boolit weight so is the change in pressure or the fact that the boolit is seated deep? Well, measuring the primer helps me level the playing field 'cause now I can say the the lower pressure load riveted the boolit base more than the higher therefore it wasn't the pressure alone that caused it. For me in this instance it was helpful. But of course, not everyone wants to play around to that extent.

By the way, seating below the neck does sometimes cause boolit base riveting.

Here's the difference using a filler with H4227 makes. No zooming in or measuring required! But keeping it as a record for future reference is helpful. It's also helpful to see that the filler raises the pressure to above a much larger charge of rifle powder with filler.

http://i388.photobucket.com/albums/oo327/303Guy/RIVITINGDEEPSEATED1822205208WGsmall01.jpghttp://i388.photobucket.com/albums/oo327/303Guy/181gr2205Dacron208grseateddeepsmall1.jpg

[HangFireW8]

When measuring pressure with a military rifle, keep in mind that a high pressure (standard) load will inflate the primer and thrust the firing pin back, and on the rebound the firing pin re-indents the primer when the bolt spring pushes it forwards again (as pressure drops). In most cases the primer can actually assume a flat or nipple shape before being re-indented. This is a little-known (and little-discussed) dynamic among reloaders, but it has been proven by military testing using special test fixtures. For example John Garand's early designs used primer movement as an actuating mechanism.

The dynamics are a little different between commercial primers and crimped military primers. Besides inflation, commercial primers travel more in their entirety. Harder military primers inflate less than commercial ones, but they do so nonetheless.

If you think you can sort out pressures differences given all that, more power to you.

[303Guy]

Interesting. I'm not one to dismiss a new idea but neither am I one to accept without investigating what the 'experts' claim. So I'll entertain the idea but I must say that I have difficulty visualizing how firing pin spring pressure can dent a primer. The Lee Enfield firing pin rests on the primer if the bolt is locked while un-cocked. Also, a floating firing pin has no spring pressure at all. But the Lee Enfield firing pin mechanism is heavy. To move it back quickly would take quite some force. Also, I would expect to see some evidence of this phenomenon especially when developing a load from zero pressure (primer only) up to full working pressure - which I've done with shotgun powder.

I do however have one gun that produces a strange firing pin indent pattern. Perhaps that is what is occurring in that instance.

This is it.
http://i388.photobucket.com/albums/oo327/303Guy/Trailboss011.jpg

Looking closer at the photo I think not. I put down to some defect in the bolt face or firing pin. I haven't checked.

What say you all?

[runfiverun]

something is pushing in on that primer and making a cut.
the one on the right shows some wiping to the side.
whatever it is is about the same width as the firing pin indent.

[303Guy]

So I had a look under the microscope so to speak. Here's what's causing that primer damage.

http://i388.photobucket.com/albums/oo327/303Guy/Boltheadcomparison004.jpg

By the way, on the primer indent being pushed out thing, that phenomenon may not apply to the lower pressure Lee Enfield so I would not see evidence of it and can therefore not comment on it. At higher pressures where the brass has just been plasticized by the impact of the firing pin it could well push back out and in again. I don't know and cannot prove it either way.

But to ye naysayers - see, I've learned something from zooming in on my PC.
My one bolt head is damaged! :mrgreen: :drinks:

[BAGTIC]

BULLWOLF,

You had me fooled too. I that that thing was one of those contraceptive gadgets.