I down loaded some 257 Roberts ammo for my 8 year old. I took the info off of Hogdon's site. 35grs of H4895. Velocity was 2670 fps and accuracy was good. Then I noticed all the primers were protruding from the primer pocket a bit. Only slightly, however the full loads of 4064 were not doing this.

Any thing to worry about???

Cause?

Perry

I have seen this happen with low power loads. I believe what happens is that the case is shoved forward somewhat by the firing pin and upon ignition the primer is pushed out of the pocket a little as the case is gripped by the chamber wall. It never caused a problem for me, maybe some of the experts can shed more light on this.

Steve E.............

too low pressure casues this,,,

I am basically a rookie, so I may be the last person to give advice, but I will take a stab at this one. Actually, a couple of ideas come to mind.
High pressure pushing the primers out. Were they flattened excessively? Any other signs of high pressures? No?
Could the primer pockets be ever so slightly over size? Could they be out of round or otherwise mis-shapened or incorrectly sized? Not that either?
Is it possible that the primers themselves are a bit too small? Are you certain that they were seated in the pockets to the correct depth to begin with? Still not it?
Likely some one will come along behind me and say "oh yeah, primers popping out of the 257. Happens all the time." or they will write "well it is obviously clear that the cause of these primers coming out is....."
But my only guesses (and they are just that, guesses)have to do with something being out of spec, or otherwise, a pressure issue. That is about all I can think of, off the cuff, as it were.
As I said, I'm no expert. If this don't help, you will have to wait for that other fellow to come along and say "sure, I know what that is....."

Perry Steve and jeffeosso are correct about about the low pressure. I would suggest you are also pushing the shoulder back a little too much when you are re-sizing the case. What is happening is when you pull the trigger the firing pin pushes the case forward until the case shoulder comes into contact with the chamber shoulder. This now creates a space (headspace)between the bolt face and the head of the case. The primer is now unsupported except for the firing pin. As the powder starts to burn the neck of the case expands and seals the gas, bullet starts moving forward and the primer backs out until it touchs the bolt face. Under normal pressures the case then stretchs until the case head contacts the bolt face. With normal pressures this would reseat the primer but it would have a very flattened apprearance. Since this is a reduced load there is not enough pressure to stretch the case so the primer remains backed out of the primer pocket slightly. If you adjust your size die so you don't push the shoulder back quite as much your cases will last a lot longer. If the case is sized properly there is minimal headspace and the primer is supported by the boltface and it cannot back out. Hope that helps

Thanks guys for the answers, it is all correct. I appreciate yall taking the time to answer.

Snowman
The cases used were sized for a short chambered 257, it is currently at the smiths having the chamber re-cut. That fits your scenario perfectly. Future cases will not be sized as severely.

Perry

quote:

Perry Steve and jeffeosso are correct about about the low pressure. I would suggest you are also pushing the shoulder back a little too much when you are re-sizing the case.

+1

quote:

Originally posted by Steve E.:
I have seen this happen with low power loads. I believe what happens is that the case is shoved forward somewhat by the firing pin and upon ignition the primer is pushed out of the pocket a little as the case is gripped by the chamber wall. It never caused a problem for me, maybe some of the experts can shed more light on this.

Steve E.............

Steve & Jeffe are right on.

You can measure a once fired case w/case mic, then insert the unsized empty case in your rifle and dry fire. Re-measure the cse and you will find it to be a few thousandths shorter than it was before dry firing. The reduced pressure load will not stretch case back to fit chamber and excessive headspace lets pressure push primer out.

Regards,
hm

So....are low pressures a problem, too low???

Perry

quote:

So....are low pressures a problem, too low???

If the pressure gets too low or the fill capacity gets too low it can cause problems. In your case I don't see this as the issue. You have some brass that has a little extra headspace. Your load is down in the 40,000 range and when you fire the case goes forward and the pressure pushs the primer back. You simply don't have enough pressure to stretch the brass back to push the head agains the bolt.

If a little set back is your only issue shoot them and have fun. 4895 responds well in lower pressure loads.

Thanks.

Perry

I'd agree with the others on low pressure but what's your bullet weight? Didn't see it listed anywhere.
Bear in Fairbansk

quote:

Originally posted by Bear in Fairbanks:
I'd agree with the others on low pressure but what's your bullet weight? Didn't see it listed anywhere.
Bear in Fairbansk

100gr Sierra SBT

Perry:
Just for fun I ran your numbers thru my copy of Quickload. QL predicts a velocity of 2670 fps and a max. pressure of 34784 psi. Pmax. for the .257 Rob. is listed as 51488 psi but QL recommends not loading to more than 90% of that (46339 psi.)
I'd say your working pressure is too low. Understnd tho that QL is only a guide as to what you can expect.
Good luck.
Bear in Fairbanks

quote:

Originally posted by Bear in Fairbanks:
Perry:
Just for fun I ran your numbers thru my copy of Quickload. QL predicts a velocity of 2670 fps and a max. pressure of 34784 psi. Pmax. for the .257 Rob. is listed as 51488 psi but QL recommends not loading to more than 90% of that (46339 psi.)
I'd say your working pressure is too low. Understnd tho that QL is only a guide as to what you can expect.
Good luck.
Bear in Fairbanks

What are the dangers associated with "too low" of pressures? I have never loaded down before

Perry When you shoot a normal pressure cartridge you are relying on the pressure inside the case to be high enoungh to expand the soft neck area and form a gas seal between the brass case and the neck area of the barrel. If you are playing with very low pressure loads you will reach a point where you will see some soot like discolouration on the neck of the case. This should tell you that you no longer have enough pressure to properly seal the case to the barrel. The next thing that will happen is more of that gas will leak past the neck and actually collapse part of the case in the shoulder area.You may also "feel" a shot of gas in your face depending on how well your action handles escaping gas. Worst case senario here is it could cost you an eye.A picture of a collapsed shoulder can be seen on page 59 of the Speer # 10 loading manual.The Speer manual talks about too slow a powder in rifles with a lot of freebore causing the collapse. Too slow a powder with a lot of freebore cause very low pressures which causes the leaking gas and the shoulder collapse. Very low pressure rounds were made with very thin and soft brass cases so they would expand enough to form an effective seal. Modern cases are designed to handle a lot more pressure (50-60,000 psi). If you have a need for some low pressure rds such as starting a youngster out will low recoiling rds make sure you use a fast burning powder like 4895. Other wise I would suggest you get the pressures back up in the area they should be. Also when a case is new the neck area is quite soft and forms this seal quite easily. Each time you fire that case then resize it you harden that brass a little and it will take more pressure to expand the neck and form a seal. The necks eventually get hard enough that they start to discolour (sooty apprearance). This is also when you start to see some case necks start the split. This is where you should either anneal the necks (if primer pockets are still tight) or throw the brass away and start with new.

Thanks Snowman.

Perry

On top of all that, my experience with low pressures is that you will also have a pretty broad deviation in velocity, which usually makes accuracy go to pieces, especially at say (pulling number out of thin air here...) ranges over 50 yards.