Home Forums Hunting & Shooting Ask The Gunwriters Question about pressure signs when working up a new load?

Hey all,

When working up a new load, at what point do you say, "O.K, I've reached or exceeded max for my gun" and cease further shooting of that load.

I've always thought, besides flat or loose primers, that scaring on the case head from the bolt face or extractor was also a tell tale sign of excessive pressure. Today, I was told otherwise by someone I feel to be a fairly knowledgable loader. He said scaring is a sign of pressure, but not dangerous pressure. Is this true?

I've been working up loads for my 270 Wby and have experienced scaring, but the primers and pockets look fine. Is this ok, or should I consider this over max even though the primers look normal?

Thanks.

Are you chronographing as you go along? Pressure follows velocity.

I don't think the scarring is an issue ;brass flow back into the ejector slot, or hole(shows as a shiny spot on the case head)is a sure sign you have gone too far.

In a rifle with a blue printed action, a perfectly flat boltface perfectly perpendicular to the barrel, a firing pin with a perfect fit pushed by a strong spring, and a chamber with minimum headspace, when pressure signs show up, pressures will already be too high.

In rifles with lousy fits, pressure signs will start being evident before you reach maximum recommended pressures.

That is my belief.

A very reliable indicator is velocity, like BobinNH suggests, as it ain't nothing as a free lunch.

Just my two cents.

All the pressure signs really indicate is that the brass has
begun to yeild and has little strength left. Time to back off.
Good luck!

Velocity is the best indicator that us average guys have. If you ain't running them through a screen you are flying blind.

+1... Steelhead has it right! Most modern manuals are way more conservative than the older ones..I have some older Speer/Sierra/Lyman and Hornady manuals that have loads listed that I could't even come close to approaching max loads...Chronographs are relatively inexpensive today and the very best way to monitor pressures in conjunction with NEW manuals...if you do lots of reloading they are money well spent... ....FLEM

Thanks for the reply's everyone.

I am using a chronograph. The manual shows 3414fps for a 130 grain bullet with the powder weight I used. The two rounds I fired(which left ejector marks)chronoed 3459 and 3470. So just a little above book velocity. I don't consider this to be too abnormal. I have a 25-06 that often exceeds book velocity without showing signs of pressure.

Sorry for sounding like a neophyte, but how do guys use your chronograph to determine max or above max loads?

Thanks.

+ 1

There's nothing wrong with using a chronograph, but velocity isn't the last word on pressure.

I keep a close eye on the condition of the fired primers. Reading them is an inexact science, but I don't like to push a load to the point that the radius around the edge of the primer disappears.

One well known and published load for a .243 will iron the primers flat as a pancake in one of my rifles.

I have read that while working up loads ( same components as in the loading manuals, barrel length, etc. )you should not exceed book velocities to insure safe pressure. Is this true ?
What if you use a different brand of brass or type of bullet or primer ? How do you compensate for this ?
Basic questions but something to be concerned with, IMO.
Would appreciate any advice. I watch the Oheler 35, check Quick Load, and inspect the fired brass and primers. What more should I look for ?
Thanks,
Jim

IMO here, if you're getting velocities above book max I wouldn't press on...50 -75 FPS above max isn't going to help you that much anyway and then there's case integrity and other issues you may have to address...Most modern firearms will handle stout loads many of which are not the most accurate but why push the envelope..not really necessary at all...If you get the accuracy with the velocity the manuals list then it's time to stop.... ....FLEM

It depends on which book you use.

Lots of really good advice already given.... just a couple more comments.

Different rifles will give different pressures with the same load. If your MV is above the published MV for a given load, it's a good bet that you are also above the recorded pressure for that load. 50-75 FPS doesn't seem like much, but in common hunting size cartridges it indicates about an extra 2,500-3,500 PSI.

Pressure signs tend to kick in at very roughly 70,000 PSI. As stated, much too much pressure. I've not heard the comment about them showing up earlier in less precisely made firearms, but I suppose that is possible.

SAAMI pressures are supposed to be measured at 70 F. It is normal, and apparently alright, for pressure and velocity to be higher if the barrel and ammo are at a temperature higher than this.

Hope that helps. Good luck with your project.

A big plus 1...
IIRC...& that is not always the case...I don't think there is a SAAMI spec. or standard established for Weatherby cartridges as far as pressure goes...3400 fps is what the factory rounds are published at & if you're getting 3400 + along with ejector marks I'd back off at least a grain & see how it goes...wby ammo is loaded about as hot as they can safely go.

Chronographs are a great aid, but not everyone has one or can afford the luxury.

All of us curmudgeons had to get by without chronographs and pressure testing data, and most didn't even have but one loading book..

GENERALLY SPEAKING:
1. The first sign you will see is a flat primer and it may or may not be an indication but do not ignore it and proceed carefully from that point on.

2. The next sign will be an ejector mark on the case head and it will be a small square mark.

3. Next will be a burned black ring around the primer and 1 and 2 can be reversed at times.

4. Probably a sticky bolt if your lucky

5. A blown primer and enlarged primer hole

6. stuck bolt accompanied by a missing extractor perhaps depending on the make of the gun. I will add that sometimes you will hear a crack as opposed to the usual boom, that sounds different, beware of that.

7. A loud exploscion that you may or may not hear or it may be the last thing on earth that you hear!

The order of the above can be questionable and argueable and can be out of order at times, but its close and gives you a starting point and an understanding of what your dealing with..

Whatever order it occurs be prepared to back off and always keep in mind that 100 FPS makes absolutely no difference in killing power or anything else for that matter so why try and squeeze every last drop of velocity out of any cartridge, but such advise on many ocassions lands on deaf ears..

I'll just make some comments on what Ray posted, then a couple more in general:

Flattened primers can also be caused by a slight amount of headspace. The fikring pin shoves the case as far as it will go into the chamber, so the very rear of the primer isn't supported and expands more than normal. Then the case backs up over the primer, making it look VERY flat, but the problem isn't necessarily excessive pressure.

Also, some primers flatten a lot more easily.

Ray obviously only shoots 98 Mausers, pre-'64 Model 70's and others with an ejector slot. Many of those blasted push-feed rifles leave a round mark on the case head.

Also, once in a while a rifle will have a little ridge around the ejector slot/hole that leaves an imprint on the case head even with mild loads. Usually this is with a new rifle, but I've seen it on well-used rifles.

A chronograph is indeed the best pressure-indicator for handloaders. But the most accurate results by far are when using exactly the same bullet as used in the manual, since today various bullets of the same weight and diameter create widely different amonts of pressure.

I have had more than one professional ballistician tell me this in recent year, long after I had come to the same conclusion myself. In fact I wouldn't even call a chronograph a pressure indicator, I'd call it a measurement device, because the connection between pressure and velocity is so consistent.

I'd agree the chronograph is a vital tool. But the sign I use most particularly in wildcats ... when the bolt shows a touch of resistance to closing on a fired case.
Cheers...
Con

Actually it is the primer firing that pushes the case forward.
With a light load and headspace the primer stays projecting out.
At somewhere around 40 KPSI the case comes loose and backs over
the primer. If the pressure is high enough the primer will have
bulged and when it comes back it looks like a rivet.
Good Luck!

This has been posted several times by different posters, but I don't think once more will hurt anything, and might help.

When you reach any of these high pressure signs, your are already well over safe and SAAMI pressures.

The problem is, you don't know how much over.

An additional good way to measure things...using the bolt as a "feeler gauge".I do this with M70's by pulling the firing pin assembly and chambering the fired round.There is less camming power that way and you can "feel" the resistance if brass has swelled too much and failed to "bounce back".