Gents,

Went to the range yesterday, to try out a new load for the ol'416 Taylor.

I was using 73.0grs of H4895 (use at your own risk!), North Fork 370gr bullets, WW brass, and Federal 215 primers.

I fired a couple three round groups to check accuracy, which was pretty good at around 1 to 1.5 inches at 100 yards. While looking at the spent brass, I noticed the primer indentations had a slight crater effect which indicated to me that perhaps this load was a bit too hot.

Here's a picture of the primers...


You can see the crater effect. The primers were still fairly rounded at the edges though. So I broke out the old (and cheap) chronograph and fired a few more shots.

I was getting reading averaging just above 2500fps. That's really fast for this rifle! Even realizing that these bullets are 30grs lighter than the usual 400grainers I practice with, I thought that speed was a bit excessive, and decide that I had pressed my luck enough that day.

I'll be pulling the remaining bullets, and backing down a couple grains.

Just wanted to get the opinions from you guys, about the cratering, and what sort of velocities your getting from 350-370 grain bullets.

Thanks!

The load or the look of the primer doesn't bother me too bad but the velocity seems pretty rich. Any shiney spots on the case head or extraction problems? I get higher 2400 fps with 350gr bullets but am not pushing max either. I have heared that the North Forks get a "tad" more velocity because they lower preassur some, or something like that.

BW---

I see no excess pressure signs there.....only a weak firing pin spring. That's what's causing the craters.

Thanks Gents!

It's a good load, fairly accurate, and nice velocity.

Jack,

I forgot to mention that this is a M70 Classic action. I'll make sure to pull the bolt apart and clean it up. But, I guess I need to order a new firing pin spring. Probably be a good time to replace the factory extractor with a steel unit.

Any advice you have on those two procedures would be much appreciated!

AHHHH!!! i have gotten some cratering before also, thought it was from a good strike on the primer, but is from weak spring, guess I am going to have to go back and find those rifles that do it and replace the springs.

Out of curiosity, can you explain why they crater like that when the spring is weak?

I swear, I had no idea how lacking my knowledge was before coming to this group.

Red

Dago Red---

Prepare for a physics lesson---

First, the primer cup is the weakest part of the gas seal that is the cartridge case. The primer is thin and weak.

Second, the firing pin has *energy* that came from the stored energy in the firing pin spring. Energy is a product of mass and velocity. Just think of the firing pin as a bullet.

When the firing pin hits the primer it expends it's energy dimpling the primer cup.

On the other side of that primer cup is the rapidly increasing pressure from the ignition of the powder charge.

Usually the inertia of the firing pin and cocking piece keeps the firing pin all the way forward until after the pressure in the case is gone.

With a hot load, OR a weak/dirty/grease-packed spring, OR a light firing pin, the primer cup "pushes back" and forces the firing pin back through the hole. They can look like a toadstool at the extreme end of their stretch.

If the rest of the primer cup is still rounded and shows no signs of being plastered against the bolt face, but the firing pin indent is puckered outward, it means to me the firing pin's energy is at fault.

<<My mamma says, "I want to know what time it is, not how to build a clock!!">>

Last one (left) looks liek where I would be VERY comfy calling it a safe load

jeffe

Hi Brian,
To add to the great information that JBelk has forwarded there is a big difference in primers from one manufacturer to the next. I use the Fedral 215 for all my big bores and they are very consistent. If my loads showed the signs that you have and I swapped to CCI 250's they could be totally different. I think the CCI's have a harder cup than the Fedral's. As far as loadings I usually get 2500 fps with the 350 grain bullets in my 416 Taylor and reach 2400 fps with the 400's. I would think that 2500 with the 370's is pretty much the max for a 416 Taylor.
Take good care,
470 Mbogo

Thanks Jack! I am one of those people that always has to know more. Probably why my head is so full of useless information. But for all the useless I collect if I get just a little good stuff like this I am very happy. :-)

I think it was my 06ai that is doing this to the primers, I will double check and then get a new spring if necessary.

thanks again.

Red

BW.
I saw that you mentioned that this was a M70 Classic, action.
I have the same action used for a custom .338 RUM that was buildt for me, and I also thought the same as you. Me too, had cratered primers, with NO other pressure signs. And I found out just same as JBelk told you here.
The firing pin hits preatty deep too!

Thanks to all, for the helpful replies.

I received a very helpful e-mail too, and have decided that I wrong about the primer craters indicating an 'over-pressure' condition. Still, given the high'ish velocities recorded, I'm not going to be adding anymore H4895 to this combo.

As usual, I think Jack's right on this one. Had the same signs in a 25/06 which was remedied with a swapped spring from a newer bolt. FWIW I'm getting 2520+/- from 75g RL15 in a 24"A&B 350 Mag Tip but I'm not going to push things. By the way, thanks for the great site and info Brian.

One other thing that can cause "puckered" primers is either an oversized firing pin hole in the bolt or an undersized firing pin. In other words the if the pin is a sloppy fit in the hole primer flowback can and will occur.

Anything to be concerned about safety-wise when observing cratered primers due to firing pin effects (not overpressure)? I have a 99 Sav that has an oversized firing pin hole (like someone slightly chamfered the hole on the bolt face) that generates craters just about like in those pictures. Both factory and handloads behave the same. Any concerns of primer rupture? Thnx/Steve

In my opinion, the cratering shown in the pictures is not of much concern. It can occur from any of the above mentioned situations. Another cause that I have encountered, not lately though, is soft cups in the primers themselves. I shoot up to 5,000 rounds a year in various benchrest matches and have seen primers punctured many, many times. These old boys shoot hot loads more often that not and coupled with the problems mentioned, punctures can occur. I have never seen any damage other than gas cutting the firing pin and in some instances the bolt face. However it is a situation to avoid.

BW, I have gotten 2620 FPS with AA2520 powder and 350 Speer Mag tips . 25" barrel and 1-16 twist . That is where I STOPPED . I droped back to 2400 FPS and the piggies did not seem to notice .

RCHAPURA,

That is a pretty fast velocity! But, given the 25 inch barrel, and somewhat slowish twist rate, it makes more sense.

Poor lil'piggy's.