Flattened primers with SKS... how flat is too flat?

[lexnaturalis]

I just noticed that some of the primers on my handloads are flat. I'm shooting the 7.62x39mm exclusively out of my SKS and many of the primers are quite noticeably flat.

I'm not anywhere near the maximum load, though, so I'm not sure if this is a bad thing or not.

I'm shooting 124gr FMJ w/ 26.7gr AA 1680. The max load for that powder is listed as 28gr so I shouldn't be having pressure issues.

There is still a groove between the side of the case and the primer, though, so it hasn't flowed to completely fill the primer pocket.

I just want to make sure that a flattened primer isn't inherently bad.

[Flash]

I just noticed that some of the primers on my handloads are flat. I'm shooting the 7.62x39mm exclusively out of my SKS and many of the primers are quite noticeably flat.

I'm not anywhere near the maximum load, though, so I'm not sure if this is a bad thing or not.

I'm shooting 124gr FMJ w/ 26.7gr AA 1680. The max load for that powder is listed as 28gr so I shouldn't be having pressure issues.

There is still a groove between the side of the case and the primer, though, so it hasn't flowed to completely fill the primer pocket.

I just want to make sure that a flattened primer isn't inherently bad.

Details! Details!

What brass, primer, what diameter is the bore? You have slugged it, haven't you?

You need more than an internet connection for your load tables because the Lyman 49th Edition lists 123 gr JSP .311" bullet with AA-1680 starting load at 23.0 grains and MAXIMUM AT 25.7 gr.

Are the primers beginning to flow back around the firing pin? When you get to that point, it is just about far enough, you know. You are then already in country where excitement may spring up anywhere and anytime.

Shooting through a chronograph might be a help, too.

Flash

[lexnaturalis]

Details! Details!

What brass, primer, what diameter is the bore? You have slugged it, haven't you?

The brass is a mixture of stuff, but most was brand-new IMI brass.

As far as slugging it: Uhm... no? How do I do that and what is that?

You need more than an internet connection for your load tables because the Lyman 49th Edition lists 123 gr JSP .311" bullet with AA-1680 starting load at 23.0 grains and MAXIMUM AT 25.7 gr.

Well the Speer manual #14 lists it as 26gr starting and maximum of 28gr.

Are the primers beginning to flow back around the firing pin?

What would that look like? I tried taking some pictures, but I couldn't get the camera to focus right.

[lexnaturalis]

I just checked my Sierra guide and it is in line with yours. Start at 22.2 and max at 24.6.

I wonder why the massive disparity.

[Flash]

The brass is a mixture of stuff, but most was brand-new IMI brass.

As far as slugging it: Uhm... no? How do I do that and what is that?



Well the Speer manual #14 lists it as 26gr starting and maximum of 28gr.



What would that look like? I tried taking some pictures, but I couldn't get the camera to focus right.

Slugging:

Clean the barrel, scour it until it is realy clean, and then lube it with oil, and take a leas "slug", pure lead, because it is softer, and will expad properly and conform to the bore, and still be easy enough to push through, but not stick. Take a BRASS rod of sufficient length, I generally use a 1/4" brass brazing rod, and force the bullet through the barrel, allowing it to mold itself to the inside of the rifling. When it pops out the other end, it will be a "mirror image" of your bore. You will be able to measure it with a micrometer to determine the exact inside diameter of the barrel, both the lands and grooves.

Military rifles are made in such manner as to have various different internal diameters, sometimes varying three or four thousandths from nominal, especially after being issued and shot by troops who may or may not care or be able to clean and maintain them properly.

The accuracy of the bullets you load for your rifle will significantly affected by bore measurements. There are those who think best accuracy of jacketed bullets is obtained when bullet diameter just matches groove diameter. For cast bullets, some choose one or two thousandths greater. Some choose otherwise. I find groove diameter suits me for both.

Now, on to manuals:

The sticky at the top advises reloaders to obtain two or more manuals for just such occasions as the one in which you have now immersed yourself. Having two or more manuals where the publishers have invested huge sums of money in equipment and product and labor to arrive at a provable good load, allows us to compare their data as well as their methods, granting us, the reloaders, a much greater degree of confidence in selecting and manufacturing our loads.

The reason for the disparity is that some manuals were tested in "universal recievers" with test barrels of a certain length, others were fired in a particular firearm. Different methods almost guarantee different result.

Referring to primer flow:

You state "some of the primers on my handloads are flat". You are able to see that they are not pristine as when you inserted them. Look carefully at the firing pin indentation, has any of the brass raised itself above the flat level of the fired primer, and kind of more clearly defined the point of the firing pin? Can you gently drag your fingernail over the primer and feel any of it above the level of the primer? Pierced primers are right there along with that as an indication of excess pressure.

[lexnaturalis]

Look carefully at the firing pin indentation, has any of the brass raised itself above the flat level of the fired primer, and kind of more clearly defined the point of the firing pin? Can you gently drag your fingernail over the primer and feel any of it above the level of the primer?

Yes, on a few of the primers it looks like there's a very small ridge around the firing pin indentation. The ride is slightly higher than the rest of the flattened primer. I take it that means there's pressure problems.

I'll have to find a slug of lead to find the bore measurements.

[Flash]

Yes, on a few of the primers it looks like there's a very small ridge around the firing pin indentation. The ride is slightly higher than the rest of the flattened primer. I take it that means there's pressure problems.

That's right. You are on the border uf high adventure country.

Flash

[KAL101]

[QUOTE=Flash;1127080]Slugging:
Clean the barrel, scour it until it is realy clean, and then lube it with oil, and take a leas "slug", pure lead, because it is softer, and will expad properly and conform to the bore, and still be easy enough to push through, but not stick. Take a BRASS rod of sufficient length, I generally use a 1/4" brass brazing rod, and force the bullet through the barrel, allowing it to mold itself to the inside of the rifling. When it pops out the other end, it will be a "mirror image" of your bore. You will be able to measure it with a micrometer to determine the exact inside diameter of the barrel, both the lands and grooves. QUOTE]

That is a really neat idea, I never would have thought of that. Great post!

[TimeTraveler]

Flattened primers are a sure sign of excessive pressure. Even though the max load for that powder is listed as 28gr, due to chamber variations, it may be too much for your particular rifle. You may want to back it down some until the flattened primer problem goes away. It's a safety issue. Your gun is telling you what to do before a nasty failure. TT

[Tomcat088]

Flash is 100% correct, STOP SHOOTING THOSE RELAODS!!! This is from Alliant themself, the people that actually make the powder. http://www.accuratepowder.com/data/P...0and%20285.pdf . STOP SHOOTING THOSE RELOADS!!!

I'm not trying to be a jerk, but you're already over the max published load, in a semi auto that uses an op rod. To be honest, you're lucky the rifle hasn't exploded and the rod isn't embedded in your head. Anytime you see flat primers, something is wrong or out of spec; either the reloads are too hot, chamber problems, etc. There are LOTS of other factors besides powder charge weight that can effect the pressure of a round. Cartridge overall length, and whether or not the bullets are in the lands; the length and the depth that the bullet is seated. The reloading info says you're running a compressed load, which will also increase chamber pressure.

Either way, you really need to be more careful, for your sake and the sake of anybody else that you may/may not let shoot your rifles. Just being at the range and having a rifle detonate CAN hurt, maim, or kill you or people around you at the range. So for the record, flattened primers are always a sign, and it's usually of BAD thing to come. PLEASE get help with reloading if you want to continue doing so, you MUST know when your load is too hot and what the signs are, even if they fall into the "normal" specs for that cartridge. Sometimes other problems can cause reloads to fail or not work as expected, you MUST be able to recognize this. Again, PLEASE STOP SHOOTING THOSE RELOADS.