Flat primers?


P5 Guy
February 5, 2008, 08:12 PM
I loaded up some 357MAG rounds and fired 24 and found that the primers are all flat and cratered. What did I do wrong?
I used the #6 Nosler reloading starting load for their 158gr JHPs. I followed everything that they recommended. Federal 357MAG brass once fired by me. Winchester's small pistol magnum primers and 15gr of H110. I trimmed the brass to 1.280 and gave a tight crimp. The COAL ran between 1.579 and 1.580.
I first thought that my scale was off, but I have checked this against another scale and they both are within a tenth of a grain. I fired these rounds in my GP100.
Any help would be appreciated.

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38 Super Auto
February 5, 2008, 08:25 PM
Flat primers are a sign of high pressure. Cratered primers are a sign of very high pressure. The next higher pressure signs are holes blown in your primers, primers blown out of cases, or something even worse.

Many things can cause higher pressure. Larger diameter bullets, hotter primers, larger propellent charge, tighter bullet crimp, smaller groove/land diameter, seating bullets deeper, etc.

I'd throttle back on your powder charge a few 1/10s of a grain. If you have access to a chrono, test your loads to see if you are getting close to the velocity reported by your load data.

Every gun and load combination is different.

February 5, 2008, 08:41 PM
many manuals recommend that you don't reduce H110 by more than 3% of maximum. Erratic pressures can occur when you reduce too much. The problem is, Hodgdon keeps jumping around with their charge recommendation. Your load may actually be too light. From mid eighties data I can tell you it's .8 grains below the recommended start charge and to the best of my knowledge there has been no change in the formulation of H110. There has been a change of mindset regarding litigation.

Others may disagree, but I believe there are better powders for the .357 Magnum. It's capacity is much lower than the case of a .44 Magnum where H110 is one of the best. AA#9 is almost ideally suited to the case capacity of the .357 Magnum and will provide the highest velocity, and it does it with some of the best accuracy you will get. There have been questions about bulk density variations with #9, so I've changed to something I hope will be even better. Ramshot Enforcer which is very close in burn rate to AA#9.;)

February 5, 2008, 08:50 PM
I have seen more flat primers from erratic pressure than over pressure. Easily cured.

P5 Guy
February 5, 2008, 09:12 PM
According to my new Nosler Reloading Manual #6 the starting load is 14.9 with the max at 15.9. I'm just 0.010 less than the published maximum COAL. My crimp is not distorting the bullet but is denting the ripples in the cannelure.
No chrono available.
Thanks for helping.

February 5, 2008, 10:30 PM
Remember also that too light a load can cause the primer to flatten. Upon being struck by the firing pin, the case is driven forward a bit, the powder begins to ignite, the case swells and grabs the chamber wall, the increasing internal pressure pushes the primer out of the pocket back against the breach face, the increasing pressure finally gets high enough to overcome the case friction and pushes the case back against the shield.....which crushes the primer flat and can even make it look like a top-hat.

As others said, low charges of H110 can be freaky. Try bumping the charge weight up to within a tenth or two of max. I'll bet your primers look fine then.

Steve C
February 6, 2008, 04:20 AM
If you can, take a picture of your primers. Your 15.0gr load is a good standard H110 load that I've used before though with CCI magnum primers rather than the Winchesters and it should be about equal to factory standard ammo. Winchester magnum primers are about the hottest primer you can find and may be the source of the higher pressure. Back off 1/2gr to 14.5 and see if your primers look right.

I found very little difference in velocity between 14.5 and 15.0grs.

The Bushmaster
February 6, 2008, 11:34 AM
FLATTENED primers are NOT a sign of over pressure. Especially with the .357 magnum. Flattened primers are the norm for .357. Now cratered primers. That is a different story...I have the Hodgdon load manual in front of me. It lists 158 grain XTP (JHP) over 16.7 grains of H110 in Winchester cases and a WSPM primer. 1591 fps at 40,700 CUP...Here is where it gets interesting...Lyman 48th lists the same 158 grain JHP and H110 starting at 16.3 grains (31,700 CUP) and topping out at 17.0 grains (38,400 CUP)...Sierra Vth second printing lists 158 grain JHC and H110 starting at 13.3 grains and topping out at 16.3 grains of H110...

I do agree with Steve C and would use the CCI-550 primer...

You can come to your own decision here, but I would increase your powder charge to at least 16 grains and try again. Continue to look for high pressure signs such as cratering, split cases and difficulty ejecting the cases from the cylinder. But not flattened primers as they are normal for .357 magnum...Please be careful...

February 6, 2008, 09:18 PM
p5 guy
what kind of brass did they use in the #6 manual it makes a difference.
secondly all my primers are flat because i use wsp, measure the case head & see how much expansion you get,none is good some is expected on upper pressure loads.
lyman 46th starts at 13.7 grs. for1087 fps 22,300cup-17.7grsfor 1387 fps 42,000cup h110 powder.
compared to factory 357 rounds ,how do they compare, stronger ,louder????


P5 Guy
February 6, 2008, 09:27 PM
I'm not able to post pictures.
I decapped the cases and they have a pretty good ridge around the outer edge and the indent from the firing pin has a slight raised ring around the dent from the firing pin.
I'm not looking to get the most velocity. I'm after good accuracy and pleasant shooting. I was thinking that the charge might be too little and was going to throw about 15.5gr. Now, from the answers here, I'm going to go to 16 and see what happens.
Thanks for all the replies.
PS, Nosler calls for Federal 357MAG and thats what I used. I have some Norma brass that is next to be loaded.

February 7, 2008, 05:47 AM
If the cases weren't hard to extract, I would say too light a load. If you put just a primed case (no powder or bullet) in your gun and fire it, you will see that the primer is about as flat as you can get.

Ol` Joe
February 7, 2008, 11:55 AM
Does factory ammo show the same flat slightly cratered primers as your handload?
I`ve seen this when the primer as suggested above is pushed a hair back before the pressures get going and the case head follows flattening them. If the pistol has a slightly large striker hole in the frame, the primer metal will at times flow back into it as it shoves the pin back when pressure rise causeing a cratered appearance. Both events can give the appearance of high pressure. If it happens with factory then I`d take the primer set back and possible large bushing hole as a likely cause.

The Bushmaster
February 7, 2008, 02:36 PM
Ol' Joe...That is exactly what happens. The hammer drives the case forward and fires the round at which point the primer backs out just a bit and the burning powder and bullet drive the case with the extended primer back against the breech face with enough force to reseat the primer and flatten it at the same time. Magnums are the most prone to this...9mm X 19 and .40 will do the same thing...

P5 Guy
February 7, 2008, 06:14 PM
I guess I'll buy a box of ammo to compare before going off to load some more.

February 7, 2008, 11:13 PM
CZ57, I agree with you that there are better propellants than H110 for the 357.

Though I have loaded .357 with H110 (125gr Hornady FP-XTP over 19 grains seem to be my most accurate), no matter what charge I experimented with I found H110 to be dirty with some powder unburnt, but without and "primer indications." Never thought I would say this, but even Unique seems to be cleaner in my GP100, and it is more economical. IMO, save the H110 for the 44 Magnum......that is where it really shines.

February 9, 2008, 03:31 AM
Ive been working up H110 loads with both 125 and 158 grain XTP's and gold dots recently.
Using 158 gr xtp's the H110 worked best just over 16.0 grains (16.2)
Loading the 125 grain xtp's I worked my way up to 21.0 grains of H110 but didnt find any real accurate loads on the way.
Now Im trying diff powders and loading down.
Im looking for soft accurate loads.

February 9, 2008, 04:01 AM
I note that you said that you are using .010 gr below the max (per your data) of 15.9 gr, meaning 15.89 gr. Others have quoted max's in the 16's, but according to your data you are so close to max that it is insignificant. I seriously doubt that your drop (or scale, for that matter) can accurately distinguish .010 gr. I'd wager that some some of your loads are 15.95+ and others 15.85--in otherwords, for all practical purposes, the max according to your data. As is well known, max in gun A is over max in gun B, but fine in gun C.

H110 is a great powder--sometimes--but always sensitive to minor variations. Actually, for quite some time I've been surprised that Hodgden keeps making it, from a liability standpoint. That said, I hope they don't quit, because when it's good, it's reeaall good!

Steve in PA
February 9, 2008, 11:36 AM
Flat primers are not always a sign of high pressure.

I load 15grs of H110 under 158gr bullets for my .357 and don't get flat primers.

I just sorted some of my other .357 brass last night.....all factory fired and some showed what some people consider '"flat" primers. These were Winchester 158gr HP factory loads fired through a S&W 686.

February 9, 2008, 12:02 PM
It has always been my experience with the .357 in Ruger Blackhawks & S&W's, is that the only reliable pressure sign is hard extraction.

If you don't have to beat them out with a stick, all is good!

Todays SAAMI .357 max pressure limit is set about 5,000 - 10,000 PSI lower then it was 40 years ago, in deference to todays much smaller guns.

Back then, even Winchester & Remington factory loads would give hard extraction in some, if not most guns.
And all of them gave flattened primers, big time!


dagger dog
February 10, 2008, 10:12 AM

i've had similar problems at times. temperature (ambient),different run of same primers,ditto on the powder,bullets etc. all and more than i can think of can cause pressure differences.

let us know what you find!

February 10, 2008, 07:31 PM
I have loaded alot of 357 Mag rounds for my S&W 686 w/ 6" barrel, and often encounter flat primers. Almost all full factory loads give me flatten primers. I have learned not to pay too much attention to them as long as the cases don't get snug and the primers do not crater (around the firing pin dimple). If I get too hot the primers will definitely crater....then I know I'm in danger zone. Take that for what it worth and be safe.

February 11, 2008, 12:02 AM
P5 Guy,
I use a Winchester Magnum primer in my .357 Magnum rounds and they all look like what you are describing. Hodgdon recommends a Min charge of 15.0gr and a Max charge of 16.7gr H110 under a 158gr Jacketed bullet. I charge 15.7gr under a 158gr bullet and they Chrono at ~1200 fps. With a charge like 15.7gr and the velocity I'm getting I highly doubt the rounds are coming anywhere neat being too high even though the primers are flat.

I wouldn't worry about it since you have double checked your scale and it's accurate. Actually, like said above, you might want to increase the charge a little. The round I mentioned is very accurate in my 4" S&W M686.

P5 Guy
February 11, 2008, 09:42 PM
I've been doing some research and have found starting loads of H110 running from 12.7grs to 16.0grs for 158gr JHP. So, I loaded up the 24 Federal cases with new WSPM primers and 13grs of H110 to try out this weekend. Wish me luck.

February 11, 2008, 10:25 PM
13 grains of H110 behind a 158 grain bullet is askin for a squib, it will also be dirty

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