Pressure signs = confusion

C

cueball

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Hi everyone, so i made up some loads for my R25
fed 1f cases
cci lr primer
44-45.5 gr H4895
Horn 150gr fmj's
So ishoot the first 5 and see slight pressure signs: slightly flat primers, slight primer extrusion around the firing pin strike, and some very slight marking from the bolt face. try the next 2 loads and signs becom slightly more noticable so i stop shooting any of the progressively hotter loads. what is confusing me is that i took the last 5 rounds of the hottest loads fired in the R25 and tried them in my tikka continental. absolutely no sign of pressure:confused:

what is up with that??
any ideas?

thanks
cueball
 
You are seeing what many of us on here have said. Rifles are all different and some will show more pressure with the same load, than will another.
 
cueball there are so many variables

a very small change in the case volume could make the difference between normal and over-pressure.

Now, assume your first rifle has the chamber bored close to the lower SAAMI diameter while the Tikka has it close to the higher diameter.

Same goes for the headspace: more headspace would increase the volume leading to lower pressure.

Throat length and shape is another factor. Heck, even the bore diameter could contribute.
 
As noted, different rifles. Starting out a .308 load with 44 grains of H4895 is rather "hot", as well, since you haven't specified a caliber and I'm making an assumption. Not only that, but semi's rarely like "hot" loads. YMMV, of course.


On a related note, I shot some load work-ups yesterday, and completely forgot that my scale was reading 0.8gr less than actual weight when I loaded my rounds.

Good news: My Savage rifle can take the maximum listed load in Hornady's Handbook for 150gr. BTSP. over 46.4gr. of IMR 4895 = good to go.

The bad news: The bolt was a tad stiff to lift with the maximum load + 0.8 grains over. :redface:
 
firemachine69 said:
...... completely forgot that my scale was reading 0.8gr less than actual weight when I loaded my rounds.
Click to expand...

What kind of scale are you using that can't be zeroed???


joe-nwt said:
If the bolt lift was stiff you are more than 0.8 over for your rifle.
Click to expand...

That's the truth!! By the time the bolt gets sticky you are a fair bit over maximum.
 
follow up

Just for some clarification, i realize that there may be different pressure in different guns using the same ammo (different chambers, throats etc), what was suprising was the extrme nature of the pressure signs. checked the loads over the chrony in both guns, when shot out of the tikka it was only about 30fps slower( based on pressure signs i thouhgt it would have been a lot slower)
c
 
'Boo said:
What kind of scale are you using that can't be zeroed???




That's the truth!! By the time the bolt gets sticky you are a fair bit over maximum.
Click to expand...



Scale was a Lee Safety Scale. I didn't notice my thumb was nicking the brass calibration nut until I started using an electronic scale, and some known weights (and the fact that it wasn't reading zero at, well, zero. :D)


And yes, all my loads were around 0.8 grains over. Keep in mind, Hornady has much higher listed maximums (about 3 grains higher) than Lee lists. I've found the Lee book fairly conservative, whereas the Hornady book seems to list closer-to-real maximums. 46.4 of IMR4895 grains for a 150gr. Hornady bullet was spot-on, worked like butter. If we were looking at the primers, they're just about picture-perfect (even for the hot loads).
 
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Most manual have a section for autoloading service rifle. They have a different pressure curve because of the gas operation.

I use Varget in my DPMS. I had the same problem with mine at the beginning and found out that I needed to load short. My guess is that your OAL is long for the S25. Make sure you load at least - .10 before the throat. You do not want that bullet sitting touching or being pushed again the throat. Check your brass - must be trimmed and full length resized. I use Redding Small Base bushing die with a bushing .335

The bushing size give you the proper tension / grip on the bullet and up to a point - the proper neck clearance.

I hope this help.
 
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I've got a Stevens 200 in 300 win mag. Even with reduced power cast loads, the primer "craters" and looks like it's in an overpressure state. Even shooting somewhat reduced hunting loads, the primers start to flatten out. This is even more pronounced with factory loads. I don't use the primers as an indication of pressure in that particular rifle.
 
It could be that the cratering around the firing pin is not caused by excessive pressure but rather an oversized firing pin hole that remington is becoming notorious for. There are other threads here that deal with that issue. Just a thought, since you mentioned the primers were slighty flattened as opposed to severely flattened. Slightly flattened is normal. How do they compare to a fired factory case?
 
cueball .......

If you work your loads up slowly, they will usually show an increasing flattening of the primers, like this:

pressure%20signs.jpg

However, as your handloads get hotter, they don't always increase as uniformly as shown here. Sometimes you'll see one or two that looks slightly hotter (with a flatter primer) than the others. Just be sure to increase your pressure slowly and when you get a few cases that look like number 4, you're at the maximum load. However, if you don't work up slowly and a round looks like number 4, it could be way too hot.

- Innovative
 
joe-nwt said:
How silly of me. Of course your load is safe, the book said so!
Click to expand...



Smartass. :p

I think the before-last load may have been a bit hot as well... Bolt opened like butter though, I'm only going by the primer. Slightly "cratered", I believe the term is, but absolutely no flattening. I've looked through Richard Lee's book, and that's all I can come up with (short of measuring the neck before-and-after, since I didn't measure beforehand). Thinking back, the recoil was noticeably "heavier" than a standard 150-grainer factory load. All others seemed fine. From what I've gathered in anecdotal evidence, best accuracy is definitely NOT at maximum loadings with my particular rifle.

I do wish I had a chronograph. Better add that to the "to buy" list.


Innovative:

HEY! The .221 Fireball. Was just reading up about the cartidge. May have to add one to the stable sometime (instead of a .223 :eek:)!
 
The way I see them is none of the four show a "maximum" load!
A factory load in the 308, 270, or magnum class of cartridges will likely flatten the primer to a greater extent.
 
The 221 Fireball cases (pictured above) are actually necked up to 30 caliber making them into 300 Whisper. The case on the far right definitely is a maximum load, and ANY rifle caliber that flat should also be considered maximum.

If you see primers flatter than case number 4 you're dealing with pressure that is beyond a "safe" maximum load. In fact, as I mentioned ...... any case that looks as flat as number 4 could be beyond maximum if it wasn't developed slowly up to that point. In other words; if you added an extra 10,000 PSI to case number 4, it would look the same.

- Innovative

[Case number 3 was actually fired in a different rifle with a smaller diameter firing pin. That small crater doesn't mean anything.]
 
Innovative said:
cueball .......

If you work your loads up slowly, they will usually show an increasing flattening of the primers, like this:

pressure%20signs.jpg

However, as your handloads get hotter, they don't always increase as uniformly as shown here. Sometimes you'll see one or two that looks slightly hotter (with a flatter primer) than the others. Just be sure to increase your pressure slowly and when you get a few cases that look like number 4, you're at the maximum load. However, if you don't work up slowly and a round looks like number 4, it could be way too hot.

- Innovative
Click to expand...

That's just about the best sequence of photos on the subject of primer-flattening that I've seen - thanks.

It would be better if it started with a weak load that showed a primer that had been pushed out a bit, and ended with a couple more that showed some further flattening and a bit of burnishing on the brass from the extractor groove, but they relay the message nicely.

I still find primer "pressure signs" very deceptive and unreliable, except for the under pressure (pushed out primer), and extreme over pressure (blown primer pocket) indicators. The in between signs are affected by too many variables such as brass and primer qualities (softness or hardness), and bolt and chamber smoothness for example.

I believe that a load book and a chronograph remain the best pressure estimators for the average reloader, short of the kind of pressure testing equipment that none of us are inclined to purchase.
 
Andy ......

I agree that the load book definitely is the best place to start, and the chronograph is a great tool for performance testing. However, primer signs (as shown) represent a typical "starting load" increasing in pressure toward a maximum load.

The hardness of primers does vary, but not nearly enough to effect the high pressure inside a fired case. Reading fired primers is the best (and most widely accepted) method for evaluating chamber pressure. For a variety of reasons, every chamber can produce a different pressures. Examining primer shape is the best way to test your particular handloads in your particular rifle. The picture is a good represenation for any rifle caliber.

[Backed out primers are a clear sign of headspace problems.]

- Innovative
 
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