Pressure signs in different guns?

[leo158]

What is the cause for different pressure in same caliber guns but each their own? I am running 27.3 gr benchmark with a 35 gr berger bullet (204) and see no pressure signs and very accurate and fast. But some others have blown primers or other signs of excessive pressures that they nust back off the charge. Is it other guns metals and tolerances much better or closer to specs than others guns and say manufacturer? Just trying to figure out how a grain or two can affect one gun to another as for excessive pressure build up.. Thanks Dan.

[M.O.A.]

tolerances much better or closer to specs than others guns

that is the anwser tolerances are not the same from one to the othere

[darkker]

Yes, but a little clarification is needed.
Unless something is REALLY off, they are all "Within Spec", not "closer to spec"
The issue is that the "spec" is a range.
So your chamber may be tighter, or looser than others, the throat may be the same. Your lot of powder may be faster, or slower.

We ALL use primers as a judge, but for actual pressure they really are a fairly inaccurate judge. Cartridge brass "spec" is 85,000 PSI tensile strength. The fact they THEY are blowing primers, but you are not; is a really good indicator that you are WELL over SAAMI spec.
The second good indicator is reloading data:
THAT bullet, with THAT powder has a MAX load of 26.6gr @ 56,600 PSI according to Hodgdon.

You are WELL over pressure, you just haven't had a catasrophic case failure.

[leo158]

You are WELL over pressure, you just haven't had a catasrophic case failure.

I worked up to that charge starting at 25.5. I went to 26 then 26 4 26.6 After that I went in .1 increasements till I found the sweet spot of .5 and under groups with no pressure signs at 27.3(as I thought would be blown primers or cracked cases) Then locked it up there and stopped. Are you saying the case alone has that psi tensile strength alone? Say if was clamped shut and a fuse added to it and lit, it would take 85k in PSI to break that case? Being fire formed in the chamber,would that now increase the tensile strength since the case couldn't expand no more than already; And the wall of the barrel actually be able to add and handle a bit more pressure than the case psi strength,? All that would be left to do is actually lengthen the case from say an out of square bolt case if psi was to high?
Should I back the load down to below max then or will it be fine? I shot over 50 rnds with that load already and I check my brass each time and see no pressure signs?
I thought the max load from manufacturer of gun powder was under what really is the max load? Like sierra has a total different max load.They are very coservative I would say.
Also wouldn't smaller cases as say 204 be less prone to higher pressure and failer than larger cases as say 22-250? Like wise a 17 fb or 22 or 17 hornet. Could those build to much pressure also to cause problems?

Thanks , dan

[BoilerUP]

Powder charge isn't the only variable when it comes to pressure.

Freebore & neck diameter, OAL, headspace, etc...

[MZ5]

Velocity is a function of pressure. If your velocities are noticeably above book, then your pressures have to be, too. You can't get there from here without pressure. Now, there are a range of books with a range of velocities, which complicates things somewhat, but when people say they don't have "pressure signs" but they're running 150 feet/second (just hypothetically) above book in a 2" shorter barrel, all that really means is they don't _realize_ they're far over-pressure, but they still are.

[leo158]

Sierra and hodgdon book has 2 different load as max. Who is the correct one? Who says what the max pressure is for each load? What might be max load in your rifle might not be in mine. If they was all the same they would have one load data all being the same for every rifle. A bit confused here and some contradicting going on it seems like. Thanks,Dan

[darkker]

You REALLY need to read your loading manuals, NOT just look at the data!
Read my first post again. Powder lots change, there is NOT ONE burning rate, NOT ONE bulk density, etc.

Being "fire formed" has no real effect on tensile strength, at least in the pressures that you are operating in.

"I thought the max load from manufacturer of gun powder was under what really is the max load?"
How can you read "MAX" in your load data, and think that means anything else?

How can load data be different between manuals?
READ my first post, then READ the first two lines of this post, then MOST importantly READ your manuals!

SAAMI sets the MAX operating pressures for cartridges.
There is no contradiction going on, you need to do some studying.
As MZ5 told you, Velocity is a function of pressure.
Because of all the variables that have already been gone over, MAX in your rifle will not be the same as something that isn't the same. When you get near the same velocity as the manuals, you are very very close. If you want to be dead-on with pressure, buy yourself a Pressure Trace System. Do a Web search for them and you will find them. NIB system is about $500.
Or you can find them used, Nasaqm bought a used system from Rocky Raab a few months back.

[MZ5]

Powder lots vary, as indicated previously. I had a load a few years ago that 'showed no signs of pressure.' It was also within book-spec for the highest charge weight of that powder & bullet weight in any published reloading source (it was the max charge), but it was running a bit faster than that book's listed velocity (same-length bbl, roughly 50 - 80 feet/second faster, IIRC). It shot extremely well. Changing ANYTHING (primers, brass lot, brass headstamp, powder lot, higher temperatures... anything) pierced primers, stuck cases, cracked or separated heads, and caused all manner of havoc. Even the 'safe' load combo resulted in loose primer pockets and hard brass after 3 or occasionally 4 loads. All this simply demonstrated, though it took me a while to grasp it, that ALL of my loads were comfortably over-pressure. It just took a change in something to drive the point home.

More recently (just a couple weeks ago, actually) I was doing a load work-up in a different rifle, with a different powder and bullet. I was following the manual, but trying to be a bit cautious because some previous experience with this particular jug of this particular powder suggests that it's a fast lot, or something of the sort. Anyway, the point is that everything looked good. This particular rifle has a very tight chamber, and a very strong action. I had the chrono with me that day, too. No 'pressure signs' on the brass, not even flattened primers, as I worked up through the charges. Then, at the first shot of the max charge I'd loaded (which was also book max), a primer pierced. Now, lots of things can cause a primer pierce, and most are to do with the gun rather than the ammo. In this case, however, I had a 'heads-up' that this was pressure: the chrono. This rifle has a 20" barrel, and shots were running ~100 - 150 feet/second _above_ the book-listed velocities for a 24" bbl! Even on the case with the pierced primer, there are no other 'pressure signs.' The brass looks great, the primer shoulders are rounded, and it all looks fine. It's not fine, though. There's no way for me to push bullets that fast without being SIGNIFICANTLY over-pressure. The strength and tightness of the action and chamber simply prevented the traditional 'pressure signs' from appearing.

So, if a person is interested in staying under SAAMI-max pressures (and just to be clear: It's not of any special interest to me whether a person wants to do that or not, unless they're shooting near me or my family & friends, or are going to orphan some kids in the process. This is simply about fostering informed decision-making), a good rule of thumb is to stop adding powder when EITHER you get to book-max velocity OR book-max charges.

[leo158]

How can you read "MAX" in your load data, and think that means anything else?

Some rifles max are below books max, so wouldn't it make sense if some rifles have max loads above the books max and still be perfectly safe ?

[darkker]

Some rifles max are below books max, so wouldn't it make sense if some rifles have max loads above the books max and still be perfectly safe ?

Some Rifle REACH max prior to what you see in your manual, because of the variations that have been gone over, and are listed in YOUR MANUAL.
They aren't "Below Max"! They are AT MAX with a lower charge weight, DUE to the variables.

Obviously you don't have any pressure testing equipment, so follow your chronograph and manual; a la MZ5's post above.
MOST rifles ARE NOT as fast as the manuals. They generally don't shoot production guns, They test in universal receivers and very tightly controlled SAAMI testing barrels.

As MZ5 said, IF you want to operate above SAAMI pressures; more powder :cool:to you.

But without any testing equipment, you have no idea WHAT your pressures are; you only know that it has yet to explode on you.
CAN it be fired "Safely"? Sure.
Is it "Perfectly Safe"? No.

[kelbro]

According to QuickLoad (estimator) you are probably running close to 65.700psi and the max is 58,740. Your load is 12% over max not including powder lot variations. Looks like max is between 26 and 26.5. Yes, that 1 gr really does make a big difference. Be safe and back off.

[Blue Avenger]

http://img.photobucket.com/albums/v675/gcidso123/funny%20pic/emocons/slap.gifYOUR OVER PRESSURE, LEARN IT EASY OR HARD!

You have noticed in your book that the lighter bullets can use more powder? Anything that adds resistance to the bullet, weight or friction will increase pressure. bullets closer to the lands (rifling) copper fouling ( big problem in .204s) will raise it . burned out barrels by the flame eating them will decrease it. shooting 9 rounds and letting number 10 sit in the barrel a little longer while you bs or find your target can also do it with some powders.

are you sharing your hot handloads? BIG NO NO! You have to work up each gun!