Flat primers warning

[Ozark mike]

I know this has been covered before but I keep hearing people say i havent seen flat primers when referencing to cartridges like 44 spl and 45 colt. Im going to put this out there for all the fellers getting into reloading. THIS IS BAD ADVICE DO NOT USE PRIMERS AS A TOOL FOR MEASURING PRESSURE. as ya get a little experience you will see primers like win lrp flattening with higher pressure rounds up above 40000 cup and get flatter the higher ya go. The primer materials and thickness will also play a role in this . A lot of pistols will detonate long before ya get to this point period. So all im saying is please dont rely on primers to develop loads thats what pressure transducers are for

[littlejack]

Plus one on that subject Mike. I started reloading when I was 15 young years old. That was 55 years ago. I learned years ago, that flattened primers are not a true indicator of high pressures. I have seen flattened primers on range pick up cases of factory ammunition. You are correct in that the cup hardness and thickness will give false information. Expierience IS a great teacher. Starting reloaders, and newer inexpierienced reloaders will learn a lot by asking questions of seasoned reloaders. One thing for sure! If a person fires a reload that flattens the primer all the way across the primer pocket, you definitely have high pressure. But, you will also most likely have sticky case extraction, as well as hard bolt opening.

[megasupermagnum]

The flattest primers I've seen have come from excess headspace, not pressure. There's definitely an art to reading pressure signs, and primers are one of the least reliable indicators.

[dtknowles]

Yes, and no.

The first gun I reloaded for was a Win M94 30-30. I was young (15 years old), unsupervised and invincible. I loaded it to max and then some. All the handbook loads did not flatten primers but I kept going until the primers flattened. The increased recoil was obvious. I did not shoot many of those loads but I am sure if I kept it up the gun would have gotten loose.

Flattened primers can be a sign of higher pressure. They can happen at normal pressure or they could be because of headspace or other issues.

It takes experience to tell what is why.

Tim

[Norske]

It can, but it isn't consistent enough to rely on. It's better to reference even QuickLoad's estimate, best is following reloading manual recipes. They aren't predictive, they have been tested in a ballistic lab. The only measurement most of us have that is proportional to pressure is chronographed velocity. There is no such thing as a "fast" barrel.

[megasupermagnum]

It can, but it isn't consistent enough to rely on. It's better to reference even QuickLoad's estimate, best is following reloading manual recipes. They aren't predictive, they have been tested in a ballistic lab. The only measurement most of us have that is proportional to pressure is chronographed velocity. There is no such thing as a "fast" barrel.

Sure there is such a thing as a fast barrel. A revolver in particular can vary between nearly identical guns more than anything. It's not unusual, although not common, for a 4" barrel revolver to shoot faster than a 6" barrel revolver of identical model.

[Ozark mike]

Well i still stand by my previous post you cannot tell the difference in small enough pressure diffrences only big ones. Yes i can see that primers flatten when i go up in pressure but that doesn't tell me what the pressure is it only tells me that it is going higher. I imagine that a ssa would go poof before any perceptible diffrence could be perceived

[shooting on a shoestring]

My tight GP100 in 327 flattens primers because I run enough pressure to get 115 grain boolits to 1550 fps from the 4.2” barrel.

My 32 S&W Lemon Squeezer from 1889 flattens primers because of end shake. Not using enough pressure to crack 600 fps with a round ball.

Flattened primers are never something I strive for. But in the above two instances they are something I live with.

The sanctioned SAAMI MAP for 327 is 45k PSI. In the GP100 with that small cartridge diameter I’m comfortable playing around in that neighborhood. But with a big bore like 45 Colt or 44 Special in a Colt SAA...NOooo!

Correcting the end shake in my top break Lemon Squeezer, futile. But I doubt I’ll fire more than a couple dozen rounds through it in as many years.

I always have a glance at primers as a matter of habit. There is information there. But it’s always a matter of interpretation. I agree it is not a direct and accurate read of pressure. Reading primers as a pressure gauge can mislead you into over pressure. A good tightly head spaced gun with tough primers can look great when the pressure is actually way high. Over pressure in a big bore is much more dangerous than in a small bore. Pressure is pounds per square inch. Big bores have more square inches for those pounds to push on.

[Ozark mike]

Over pressure in a big bore is much more dangerous than in a small bore. Pressure is pounds per square inch. Big bores have more square inches for those pounds to push on.

Hydraulics at its finest and another good point

[dtknowles]

Hydraulics at its finest and another good point

Not to quibble but Pneumatics not Hydraulics. Difference between gases and liquids. You could use the term Fluidics.

[M-Tecs]

Pressure is pounds per square inch. Big bores have more square inches for those pounds to push on.

That is true for bolt thrust but not so much for case or barrel failures.

[Potsy]

Back around '03 or '04, I was playing with my bisley and W-296. Hadn't been reloading long and was still trying to find the hottest thing out there for everything.

Found some data somewhere for 340grn. LBT's that sounded pretty sporty. I had bought some 340grn. Flat Points (not LBT's) that undoubtedly seated deeper in the case. Waltzed out on a 95 degree day to try them out. I was expecting 11-1200fps, I got 1450. Primers were fine. Cases (Starline) fell out of the chambers. It handled a dozen of them like a champ. But I knew I was well north of where I wanted to be (likely around 50KPSI+).

On the flip side, I've got a Browning .25-06 that'll put a nice ejector mark on federal factory loaded brass.

I ladder tested some .223's the other day. I flattened some primers at below max loads (but at the upper end of my ladder), but the chronograph told me I was getting very warm. Stuck the cases in the de-capping die when I got home, primers fell out with no resistance. Yep.

I just chronograph everything any more. It is the ONLY way for the average reloader to KNOW where they are at in terms of pressure, and even then, there is a degree of guesswork.

[MT Gianni]

Reading primers is a very useful tool for bottleneck rifle cartridges and a poor one for handgun pressures. Extraction is equally poor.

[Norske]

Lane Simpson's loads for his wildcat rifle cartridges based on the 8mm Rem Mag case were found to run around 70,000 psi peak pressure by Remington when they were working on factory ammo for them. Lane had no obvious/traditional signs of high pressure because his guns were custom and very tightly machined. Factory rifles would have had problems.