Erratic pressure signs on previously safe load

[Hugnot]

Whether he was firing once fired brass was never the question, you are the one who alluded to not seeing how firing new brass would result in any less pressure than with fired brass. He has changed nothing here.
Being I am willing to only provide "anecdotal stuff" that I am right, why don't you prove me wrong with science or whatever method you deem necessary. I wont be the only one waiting for this.
This is not the the op's problem.

This is the OP's problem - developing a safe reliable load in a short time. . Would the OP attempt to get new brass to get lower pressures without a good reason? What he has now don't work so good.

Did I allude? - definition being - "mention without discussing at length" It sort of appears that I questioned - "So a load that was safe on virgin brass can show pressure on 1x fired brass because it isn't using as much energy to push the case out to chamber You should be seeing velocity that's higher as well." Simply put - how can this occur?

My views are that with changes of case diameter of like .003 inches & length of .005 the .300 WSM case capacity might increase by about an estimate of 3.5 % (volume = area * length). This is just an estimate given the .300 WSM case capacity of 75 grains of H2O as seen in the Nosler manual with 150 cup & core bullets having the same approximate length as a 124 monolithic bullet. A 3.5% case volume increase would make for a 77.7 H2O capacity .300 WSM. I can't see how a case volume increase of 2.7 grains H2O would result in more pressure - just an innocent question. Assuming chambers would be same & temps would be similar between gas temps in new & 1X brass.

Anecdotal - " (of an account) not necessarily true or reliable, because based on personal accounts rather than facts or research." Like don't put good money on it.

Only trying for timeliness (limited waiting), civility & logic:

"The relationship between pressure and volume is inversely proportional. ... It is summarized in the statement now known as Boyle's law: The volume of a given amount of gas held at constant temperature is inversely proportional to the pressure under which it is measured." bold print not me, quote

P1V1 = P2V2


Old time science guys came up with this - not been shot down yet.

 

[Tidus56]

It has to do with the pressure curve, now that the powder charge isn't being used to expand the brass to the chamber the pressure curve changes and builds pressure faster. This is at least my understanding.
This is most common a problem with faster burning powder is my understanding. So Velocity will increase and pressure will increase typically not very much but if you were already close to pressure you'll see it.
There are 5+ threads on snipershide of anecdotal info showing similar experiences. Take it for what it's worth.
From my perspective just trying to help the OP. Likely barrel speed up played a larger role than anything, but there is a difference in 1 time fired brass and virgin.
I won't reply back as I have given my 2 cents and I was only hoping to help the OP.

 

[Hugnot]

Possibly this might describe what's happening:

"SAAMI pressure testing protocol uses a conformal Piezoelectric Quartz Transducer for pressure testing of centerfire pistol and revolver, centerfire rifle, and rimfire cartridges. The primary source of the conformal transducers is the US company PCB Piezotronics. The SAAMI pressure testing protocol uses test barrels that have a hole located in the chamber at a location specific to the cartridge. The SAAMI conformal transducer is fitted into a hole that penetrates the test barrel chamber in such a way that the transducer's face, precision machined to match curvature of the chamber wall at the mounting location a specific distance from the breech face, functions as part of the chamber wall. When the cartridge is fired the gas pressure causes the cartridge case to expand, contacting the chamber walls. The portion of the cartridge case in contact with the face of the conformal transducer exerts a pressure on the transducer which in turn generates a minute electronic impulse that is amplified and results in a reading in pounds per square inch (psi). The SAAMI conformal transducer has the benefit of not requiring a drilled cartridge case and the corresponding challenges of inserting and alignment required of drilled cartridge case. Instead it requires a simple pressure test of a sample case from the lot of cartridge cases being used in the test ammunition. This pressure test determines the gas pressure required to cause the case to expand and come in contact with the face of the conformal transducer upon firing. This measurement is referred to as the "offset" and makes allowance for the "loss" of that gas pressure prior to the cartridge case coming in contact with the transducer and generating the impulse. The offset is added to the pressure reading to arrive at the peak pressure reading. Other benefits of the SAAMI conformal transducer are: very adaptive to the high volume quality control testing demands of commercial and law enforcement ammunition production; protection of the transducer from direct exposure to the high temperature combustion gases and hence a comparatively long service life; 80,000 psi (551.6 MPa) maximum working pressure. Cartridges with the same chamber wall diameter at the mounting point of the transducer and which operate within specific chamber pressure limits may use the same transducer interchangeably reducing instrumentation costs"

I put the italics in this.

Me: A new case would have more expansion before contacting the transducer and would result in a pressure lag resulting in a pressure slope decrease. (brass growth - .003 diameter & .005 length) If the bullets and seating depths and all other items be the same, for both new & 1X fired brass the final/peak pressures (bullet at the leade) should be equal & the energy spent would also be equal. "The offset is added to the pressure reading to arrive at the peak pressure reading" The brass, new & 1X fired, allowing for some minor spring back should have similar dimensions after firing resulting in equal case/chamber fit. Should the 1X fired brass have more work hardening more spring back would occur making extraction easier for 1X fired brass. This assumes chamber size same. Unless the OP does not use new brass this is of no concern for the immediate problem Looks like 1X brass will be used so the new brass situation won't be an issue.

I need to see some actual pressure traces comparing new to 1X fired brass with everything else the same.

 

[Muddyboots]

How about simply too much powder? Are we over thinking the solution here? IMR4064 is pretty fast for the 300WSM even with the 124HH, so maybe just walking razor edge on pressure with fast powder that cause results like this with the slightest change in any variable?

 

[milo-2]

Hi Guys,



I don't really have time to work up a new load before leaving, so I have a two-fold question: 1) what do you think may be causing the pressure? And 2) with hammers, can I just back off a grain and more or less expect decent groups? I have time for one more trip to the range before I leave, so I'm in a bit of a tight spot.

Thanks in advance for the help.

The thread has taken a turn, you have gotten solid advice on backing off your powder charge by a couple knowledgeable guys here.
I don't know if any of us can pinpoint the pct of charge to reduce for the load to be both safe and accurate, needs to be fired.
If the rifle did speed up, and this was the source of the problem, it may be as easy as backing back down to your original velocity to retain the accuracy you had originally.
I have no history with copper solids, so no comparisons.
If the velocities you are getting are 1-200 fps faster than almost anyone else is getting, one should revisit what is going on. You made a statement you feel the barrel is fast, well, the only Free speed in firing projectiles down a barrel comes from increased barrel lengths up to a point if using the same components. All the rest of the gains come from increased pressure. You could opt for a slower powder and increase your charge, maybe even increase your velocity with a drop in overall pressure.
Good luck with this, and hope your hunt is successful. If you do not have a handle on this, grab a different rifle and tackle this upon your return.

 

[Hugnot]

My thinking is ammo reliability & safety is more important than 1% or 2% velocity increase or a small accuracy increase within a limited window.

 

[338 dude]

The crazy thing is that the previous 30 rounds had no swipes, nice round primers, no bolt lift issues….not a shred of pressure evidence. That's why I keep wondering if it has something to do with the cleaning, or maybe I left a little sizing wax on a few of the rounds, or maybe I'm crazy, who knows!

I do have a 26" barrel which seems to be on the fast side - the factory Norma 165's were flat out sizzling out of my barrel…like 100fps faster than advertised.

Any lube left on cases will increased bolt thrust and give false pressure signs

 

[338 dude]

I think you may have hit it. It is in fact a relatively new rifle…maybe 120 rounds through it.

Veteran:
I'm generally pretty good about decoppering if I'm shooting a lot of copper, but I don't usually send them this fast. I do need to buy a bore scope. Any recommendations?

Teslong for the money they cannot be beat

 

[Seabeeken]

Ran your charge in GRT but had to use a Barnes bullet as Hammer isnt in the database. There are several details I dont have but at 80 degrees your load shows 100 psi under max. Back it down. What temp was the load developed? Altitude? This is a good example to not work so close to max. IMO

 

[Hugnot]

Load data on the Barnes site with 130 Barnes TSX BT lists a max 65.4 grains of IMR4064 for 3519 fps, No pressure data was provided. The OP reports "Load clocks about 3700fps" using 1 grain less powder with a lighter bullet and different brass make.

Max pressure data on the Hodgdon site ran in the 63 K psi range with most max loads. On the Nosler site 58.5 grs. IMR 4064 provided max accuracy using 150 gr. bullets but with the warning to start low with their monolithic E Tip bullet.

The OP reported using " Norma brass, fed 215, 64.5 grains imr 4064, and a 124 hammer." All sorts of stuff may affect pressure boosting it up to the unacceptable range. Should I be in this situation I would verify the powder weight since it produces velocities about 200 fps faster than that on the Barnes site using a similar bullet. Time is running out, good results are needed. I would load 5 with 60.5 grains (Nosler's start load for 125 cup & core bullet at 3346 fps) then increase load in 1 grain increments & look for excessive pressures. I would also look for loose primer pockets in fired brass having "swipes" then check out bullet slip fit into fired brass, seating depth, brass length, and scale accuracy. The 4 grain reduction is only a 6 % reduction of powder for 5% to 10 % reduction of velocity (3519 fps - 3700 fps) and hopefully velocities some 200 fps more may be reached with good reliable ammo.

 

[Doodle]

Hi guys,

I have a crazy schedule so I have not had time to sufficiently read everything that has been posted, but I wanted to throw out a quick Thank You to everybody.

I should get a chance to read and reply in the next day or so.