Pressure signs ?

J

jetinteriorguy

New member
I started seating my bullets in my Savage 12FV out .070" further due to throat erosion, so I figured I would add powder due to the extra space in the case. I started with my original load of 38.5 gr of H4350 with Hornady 140gr ELDM's. Then I went up to 38.8,39.1and finally 39.4 gr. This is still under Hodgdons load data using a comparable bullet. The 39.4 load shot the best but I was getting some resistance on bolt lift. The primers were somewhat flattened with just a minuscule amount of cratering, but no ejector swipe imprint or swipe marks on the brass. I also had comparable results with 38.8 gr but no resistance on bolt lift. So I'm thinking I'll load ten of each, then shoot five of each over the MagnetoSpeed and five of each for grouping to decide which one to go with. Any thoughts on this process?
 
Back off the powder until the bolt opens and closes smoothly and no primer deformation at all. Start from there.
No reason that you cannot chrono and group at the same time.
What were groups like with your original loading?

Pete
 
Some primer flattening and cratering is normal. Both aren't signs of excessive pressure.

Are you full length sizing the fired cases?
 
jetinteriorguy said:
I started seating my bullets in my Savage 12FV out .070" further due to throat erosion, so I figured I would add powder due to the extra space in the case. I started with my original load of 38.5 gr of H4350 with Hornady 140gr ELDM's. Then I went up to 38.8,39.1and finally 39.4 gr. This is still under Hodgdons load data using a comparable bullet. The 39.4 load shot the best but I was getting some resistance on bolt lift. The primers were somewhat flattened with just a minuscule amount of cratering, but no ejector swipe imprint or swipe marks on the brass. I also had comparable results with 38.8 gr but no resistance on bolt lift. So I'm thinking I'll load ten of each, then shoot five of each over the MagnetoSpeed and five of each for grouping to decide which one to go with. Any thoughts on this process?
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You didn't specify but it sounds like you are testing 6.5CM ? I have a 6.5CM R700 with a McRee's Precision barrel and I have done a lot of testing and for whatever reason when I was testing the Nosler 147 ELDM and RL17 and was under 1 grain of max I definitely started to see some elevated pressure signs. I see some flattened primers, and a slight ejector swipe mark. It's been a bit frustrating for me as when I enter this area I do see an excellent accuracy node. 6.5 seems to be a caliber where you can easily observe some elevated pressure signs IME. Iv'e since backed off to the next lower accuracy node and it shoots very good, i'm not interested in flirting with high pressures and burning up a $525 precision barrel.
 
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Pressure signs on brass and primers is very unreliable. Fifteen years ago, Denton Bramwell used strain gauge pressure measurement to document the same amount of case head expansion on the same lot of 7×57 brass with the same loading history could happen on an individual case at 40,000 psi or at almost 70,000 psi. Primers are also famously variable in their response to pressure from brand to brand. Also the longer your headspace the lower the pressure at which they can mushroom because more of the primer can stick out behind the case.

Even extractor marks can vary with brass. If you use brass with a softer head, like Hornady, and you compare it to brass with a hard head, like ADG, you may see swipe marks cease and even sticky bolt lift may back off.

The bottom line with brass and primer pressure signs is you can only be sure they apply to the particular brass and primers you are working with. They may or may not apply to the gun.

One possible cross-check is to look at chronograph results. Usually, when a chamber starts to stretch (a cause of serious high-pressure-type sticky bolt lift) instead of soft brass being responsible, you will see a drop in velocity as the load increments due to the chamber volume growing near the pressure peak. It's normal for velocity to have flat spots as a load is incremented, but velocity drops mean steel is stretching. Investing in a Pressure Trace is the only further step I am aware of that a handloader can take to confirm this.

Meanwhile, try some different brass and see what happens.
 
What's the primer cup edge radius minimum that is the standard to define a flattened primer?

Is it the same for all primers regardless of cup metal properties and dimensions?

I've shot 7.62 NATO proof loads at about 81,000 psi (67,500 cup) and most people looking at the fired case heads and primers say they're a normal maximum load.
 
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If all primer pockets had the same lip radius and all primer cups were the same hardness and thickness, I suppose you could come up with a number. At the moment, all that is certain is if the primer pierces and leaks it has gone too far. Hindsight is always 20-20.

I once did some experiments with some LC 64 NM ammunition in our club Garands, tilting the muzzle down to get the powder away from the flash hole before coming level to shoot it, and tipping the muzzle up before firing to get powder over the flash hole. I got 80 fps difference in velocity and the primer went from unchanged roundness to flat. No sign of piercing, though I have noticed in the past that most old Garand bolts have a ring of gas cut pits surrounding the firing pin tunnel from rounds that have leaked. Presumably, those were mostly firing military loads which should have been tested and regulated to proper pressures about as well as factory ammo can be expected to achieve.
 
My bad, yes it's 6.5 CM. Using the MagnetoSpeed doesn't hurt accuracy other than a slight shift of POI. The brass is Starline, which in my experience is not as soft as Hornady, but not as hard as Nosler. I have worked up some loads with RE16 about a year ago and they definitely showed ejector marks accompanied by some pretty high velocity so I have an idea how that can go. Upon closer inspection of primers they all are the same right from the starting load up. My brass prep is as follows, deprime, clean primer pockets, toss in the tumbler for an hour just to make sure no crud to mess up my sizing die, then I lube and body size, followed by neck sizing with a Lee collet neck sizing die, and one final tumble with a little odorless mineral spirits and used dryer sheet. This brass has had the necks turned and runout is consistently .001" or less. I'm also using CCI large rifle primers. Originally this rifle would consistently group five rounds at 3/8" to 1/2", as the throat eroded it gradually opened up to 5/8" to 3/4". At that point I put the rifle away intending to rebarrel, then I got the urge a couple days ago to play with it some more. The 38.5 gr were just slightly over 1/2", and the 39.1 gr were just under 1/2".
 
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"...38.5 gr of H4350..." That's close to max but less than Max. You shouldn't be seeing any pressure signs. Even though it's a compressed load. Compressed loads are nothing to worry about but it starts long before you get anywhere near the Max load. The Start load is 36.0. 36.5 or 37.0 are very likely compressed.
39.4 is .6 from Max. Shouldn't be any signs there either.
"...I went up..." You should be going up by half a grain from the Start load. Not picking a load increment and hoping.
Seating longer isn't going to fix throat erosion if there actually is any.
 
I do realize seating longer doesn't 'fix' anything, it just keeps the bullet jump optimal based on my initial testing. This load wasn't compressed at all, either initially or now with the new load/seating depth. Really my only concern with all of this was feeling a little more resistance when lifting the bolt, this being the only traditional sign of possibly excess pressure when shooting this load.
 
if I have a sticky bolt lift or ejector marks I back off...period. No posting looking for opinions or trying to justify.

I don't give a darn what the experts say. It's my eyes, hands etc and if it does feel right it probably isn't right. Common sense goes a long way and a few extra FPS is not worth blowing a receiver up. A friend blew his wifes rifle up looking for that extra 25FPS. She was ok but has not fired a rifle since
 
I wouldn't call it a sticky bolt as much as it just takes a little more effort to open than the previous loads. I agree though, it's more important to be safe than sorry. I'm trying the lighter load tomorrow and if it works as good as I think I won't even bother with the heavier load. I guess the temptation to use the heavier load is due to the lack of any other real definite indicators of over pressure.
 
jetinteriorguy said:
I started seating my bullets in my Savage 12FV out .070" further due to throat erosion, so I figured I would add powder due to the extra space in the case. I started with my original load of 38.5 gr of H4350 with Hornady 140gr ELDM's. Then I went up to 38.8,39.1and finally 39.4 gr. This is still under Hodgdons load data using a comparable bullet. The 39.4 load shot the best but I was getting some resistance on bolt lift. The primers were somewhat flattened with just a minuscule amount of cratering, but no ejector swipe imprint or swipe marks on the brass. I also had comparable results with 38.8 gr but no resistance on bolt lift. So I'm thinking I'll load ten of each, then shoot five of each over the MagnetoSpeed and five of each for grouping to decide which one to go with. Any thoughts on this process?
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Despite it sounding crazy, seating closer to lands increases pressure.
 
Years ago, I ran my loads super hot in everything. One day it occurred to me, if you want to shoot 100 fps faster than a 7 Rem mag is supposed to, ream it to 7 STW. Etc. Etc.
 
Since most of my shooting takes place in an indoor 100yd range I'm not concerned over velocity, just accuracy. I don't plan on doing any shooting longer than 300yds with an occasional bout at 500 yds when available. But for me, 98% of the time I'm indoors at 100yds.
 
Pressure signs on brass and primers is very unreliable.
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I disagree. The marks are very reliable, they are there, you can see them. What is unreliable is people's conclusions about what the amount of pressure producing those marks actually is...


The bottom line with brass and primer pressure signs is you can only be sure they apply to the particular brass and primers you are working with. They may or may not apply to the gun.
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Agree with this, except for the last part. The pressure absolutely does apply to the gun. It HAPPENS IN THE GUN, for goodness sake. It applies.

Now, what doesn't apply is the belief that "excess" pressure is automatically a dangerous thing. All pressure signs are, are signs that you aren't where you ought to be. They don't reliably tell you how far beyond where you ought to be or WHY you are beyond where you ought to be, that part you need to figure out from other factors.

Whenever they show up, they are a sign you are not where you ought to be, with the specific combination of gun and ammo you are shooting.

For that, they are absolutely reliable. For anything else...not so much.

Cratered and flattened primers tell us something isn't what we want it to be. They don't tell us something is dangerous, or not, or WHICH thing it is.

I wouldn't call it a sticky bolt as much as it just takes a little more effort to open than the previous loads.
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That's the definition of a sticky bolt. "Sticky ranges from "just a little more effort" up to having to hammer the bolt to get the action open. At that point "Sticky" turns to "frozen".

By all means, chronograph those "sticky" loads. See if you get any SIGNIFICANT difference in velocity. Significant is the key here. A double handful of FPS isn't significant. A few hundred, is . See what you get and decide for yourself if the gain is worth the additional stress on your equipment (brass and the gun itself)
 
"The 39.4 load shot the best but I was getting some resistance on bolt lift.......... I also had comparable results with 38.8 gr but no resistance on bolt lift."

I'm lost as to why you would not want to stick with 38.8gr at this point. If you already have throat erosion in this barrel, why look for more with hotter loads when you have one that is "comparable?"
 
Pressure signs on brass and primers is very unreliable.


I disagree. The marks are very reliable, they are there, you can see them. What is unreliable is people's conclusions about what the amount of pressure producing those marks actually is...
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Traditional pressure signs don't show up until you are at 70,000 PSI, which is well over a max load. You could be over the max pressure allowed for the cartridge and still not get any of the traditional pressure signs.

That is unreliable.
 
I tend to think like Reynolds357; the increase in COAL moves the bullet towards the lands (obviously), but how much room is there in the chamber for the length increase? What is the current COAL? I get excellent performance with Sierra 140 MK’s using 40.3 of H4350. While I get a little primer flattening, there are no signs whatever of overpressure. In fact, the Starline brass is holding up superb, with very little stretching when full length resizing. However, if I try to increase COAL much from where I am, the bullets will be in the lands where pressure will surely increase.
 
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