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Brass pressure signs...

F

FootSoldier

Sergeant
Full Member
Minuteman
Feb 29, 2008
128
0
Phoenix, Arizona
I have read some very good info on this subject and think I am "reading" my brass better now. But I need some confirmation.

.308 Win
43.7 grs Varget
155 Scenar
Lapua brass
BR-2 primers
2.805" OAL (.020" off the lands)
1800' ASL, 65*F
2848 fps (Shooting Chrony)
3 groups, 5 shots each; .362", .381" and .377" c-t-c.

I love this load, but my M2008 GAP has a short throat and my (un-nameable) computer program says I am 2% compressed with this load.

I read the primers as slightly flatened, but no appreciable cratering.

What do you think? Any reason to back off the load?

IMG_1953.jpg

IMG_1958.jpg

IMG_1944.jpg
 
Re: Brass pressure signs...

Those look fine.

When they are flat, they are smooth (or darn near smooth) where the primer meets the primer pocket.
 
Re: Brass pressure signs...

Wow, those are REALLY flat. Should have stopped long before that.
 
Re: Brass pressure signs...

Wow! That's flat!

OK, I think I'm good.

I guess the computer program saying I was at compressed load and the sound of Varget granules crunching was getting in my head a little.

The load just works so well. Tight groups, low Es/Sd, and good velocity. I'm 8.5 mils at 1000 yards.

Thanks MontanaMarine.
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">Wow, those are REALLY flat. Should have stopped long before that. </div></div>

Not mine. I googled up the image.
 
Re: Brass pressure signs...

I am suspicious of the chrono as well. I have had 10 shot strings chrono at an average of 2829, 2848 and 2852 fps. All this from a Bartlein 24", 11.25 5R barrel, at least that's what my Shooting Chrony is saying.

I measure every powder charge individually on a Dillon digital scale. Calibrate, then confirm with check weights, and trickle and weigh every one.

It's slow, but I think it is accurate. Quickload says I should be 100 fps slower, but I only know what I can measure with the gear I have.

I cross check to Seirra and my come-ups seem right on at 1000 yards. I had some small deviation at lesser distances, but not much.
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MontanaMarine</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">Wow, those are REALLY flat. Should have stopped long before that. </div></div>

Not mine. I googled up the image. </div></div>

Of course, sir. I have seen your shooting and I wouldn't expect that out of you.

M193 does look like that from the factory, though.
 
Re: Brass pressure signs...

Fired rounds look good. Strange combination for drop and load weight compared to what I have had/seen.

I think I was 45gr Varget in a Bartlein 24", 2840 fps.
 
Re: Brass pressure signs...

I've heard of a lot of folks that are getting the velocity from drop data, and using the chrono's to get ES and SD data and not really believing the velocity data they get from them. I don't have the money to buy the super high end chrono's that everyone recommends, so i'm stuck with the cheaper ones for now.

I think that mind has been fairly truthful to me, Getting my drop data from it has been fairly dead on out to 800 yards so far.

Branden
 
Re: Brass pressure signs...

Concure with the chrono error. I run 47gr Varget with a 168gr amax and lapua brass with no pressure signs. No flattend primers at all. I dont have a chrono but a quickload out of a 20" barrel is runnin about 2725fps.
 
Re: Brass pressure signs...

dscf0032bulletpinch308brass243chambercroppedtwice.jpg


The real limit to pressure is brass life.
These pieces of LC 308 brass have expanded primer pockets, and so are at end of life.
 
Re: Brass pressure signs...

tight bore coupled with a short throat could yield said velocities easily. If you are indeed .020 off the lands at 2.805 then I suspect your chrono could very well be accurate.
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body">
dscf0032bulletpinch308brass243chambercroppedtwice.jpg


The real limit to pressure is brass life.
These pieces of LC 308 brass have expanded primer pockets, and so are at end of life. </div></div>

Hart sells a tool for tightening up primer pockets. These pieces of brass may have a few firings left in them
grin.gif
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">

Hart sells a tool for tightening up primer pockets. These pieces of brass may have a few firings left in them
grin.gif
</div></div>

I have some fireformed 257 Roberts Ackley Improved brass I would like to resurrect from the bone pile.

Gotta link to the Hart product?
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 308sako</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FootSoldier</div><div class="ubbcode-body">I am suspicious of the chrono as well. I have had 10 shot strings chrono at an average of 2829, 2848 and 2852 fps. All this from a Bartlein 24", 11.25 5R barrel, at least that's what my Shooting Chrony is saying.

I measure every powder charge individually on a Dillon digital scale. Calibrate, then confirm with check weights, and trickle and weigh every one.

It's slow, but I think it is accurate. Quickload says I should be 100 fps slower, but I only know what I can measure with the gear I have.

I cross check to Seirra and my come-ups seem right on at 1000 yards. I had some small deviation at lesser distances, but not much. </div></div>


If your Bartlein is a "tight bore" then you may well be getting accurate readings of muzzle velocity. One of our group shoots a 22" Bartlein tb and his 175's scream. </div></div>

No, not a tight bore. The throat is short and Quickload says I am 3.9% compressed. I can hear some granules crunch when I seat bullets.

I am going to try to find another chronograph to get a reading from.
 
Re: Brass pressure signs...

I'd say you're at least 100 fps lower than you think. I envy that short chamber, though. My rifle's magazine might be useful for something if my chamber was that short.
 
Re: Brass pressure signs...

EddieP,

Footsoldier has an 1889 Mauser case head with large Boxer primer pocket.

You are showing a 1950 Remington case head with small primer pocket, like these:

PrimersFallingOut223tiny.jpg
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MontanaMarine</div><div class="ubbcode-body">Flattened primers:
image001.jpg
</div></div>

Ironically, that was actually caused by having too low of a pressure...
 
Re: Brass pressure signs...

243 is large primer.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body">EddieP,

Footsoldier has an 1889 Mauser case head with large Boxer primer pocket.

You are showing a 1950 Remington case head with small primer pocket, like these:

PrimersFallingOut223tiny.jpg
</div></div>
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: EddieP</div><div class="ubbcode-body">243 is large primer.


</div></div>

I was so full of sh*t.

I saw the ejector mark on the case head, and I thought it came out of and AR15.
 
Re: Brass pressure signs...

Reading primers is at best hit n miss

Look for ejector wipe, forget primers

If ya see ejector wipe back it down

Ideally you want to identify max load in your rifle, not doing so leaves a window of performance untapped.

Example
you current load 43.5 shoots good so ya stopped there, but wot if you loaded to 46.5 before you had ejector wipe

Thats a big window to tune with more fps available, i always look for a max load with any combo then work back until i get accuracy needed
 
Re: Brass pressure signs...

Thanks Jedi. I am loading some FL sized brass to be sure I don't have two issues to work and then I will step up from the 43.7 and see what I get?

I had a load in my FNH that made slight ejector wipe marks on the brass so I backed off. I haven't gotten anywhere near that with my new rifle.
 
What does extractor wipe have to do with max load?

1) In strong rifles, I load up until I can measure the threshold of extractor groove growth with dial calipers, by rotating the case and maintaining jaw contact.
This is a better indicator of primer pocket growth than:
a) pin gauge measurement of the primer pocket
b) primer decapping force
c) primer insertion force
d) the primer falling out

The reasons extractor groove growth is better:
a) Primer pocket growth is not symmetrical, and may not be detected with a round pin gauge.
b) Primers, like hanging chads, are very inconsistent in what it takes to make them fall off.
c) Extractor growth can be measured right before and after firing at the range, and does not require reloading at the range.

This determines the real max load. This is more accurate than some max load from a load book.

2) Then I back off on the powder charge by a safety margin.

This determines my practical max load.

3) The exception is 6mmBR [and other 1889 Mauser case heads with small Boxer primer pockets], in which the threshold of primer piercing, not the primer pocket growth, determines the real max load.
 
Re: What does extractor wipe have to do with max load?

Clark, thanks! You know a lot more about this than I do and I really appreciate the info. I'll try measuring the extractor groove on 8-10 pieces of brass before and after shooting for load development.

This whole discussion is helping me look at the forces at work on a piece of brass when being fired, from a far more detailed point of view.

I really want to understand the different cause and effects related to sending a bullet downrange accurately and then being able to repeat that process over and over.

Thanks again.

Steve
 
Re: What does extractor wipe have to do with max load?

How would you work this high end loading for a gas gun? It seems in determining the abosolute max pressure in an auto, you'd be one step from destruction.
 
Re: Brass pressure signs...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: EddieP</div><div class="ubbcode-body">Wanna see pressure????

pressure.jpg
</div></div>

It really saves on decapping pin wear.

209r4mg.jpg
 
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