Where are the pressure signs????!! [Archive]

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boombotz401

11-14-15, 19:06

Hey everyone please save my sanity lol

I worked up an ar comp load with the intention of going until I saw pressure signs and I'm clearly not seeing something. I did notice 2 of the 25.6 primers were cut up a bit so I do know the limit there but I'm thinking 25.0 is my comfort level

http://images.tapatalk-cdn.com/15/11/14/385347790eb5518788e1093067cd768a.jpghttp://images.tapatalk-cdn.com/15/11/14/a36f9e38d37227fc22404fa4056f94fa.jpghttp://images.tapatalk-cdn.com/15/11/14/b1171b0ed69b3a03d73b8ba851fd08fb.jpghttp://images.tapatalk-cdn.com/15/11/14/4ed00b1e5261f16dc95de2f71e9d7417.jpghttp://images.tapatalk-cdn.com/15/11/14/3e6c71c25a6ed65b6c3ac41899562c11.jpg (no I didn't start @ 24.5 that was my regular load I was just curious what AR COMP was capable of)

They list 25.6 as max and I find that way to high but I was curious and averaged 3100fps from a 16" BCM 5.56 AR, how is that not over pressure?

In the photo

24.5 ----one case up for reference
25.0
25.3
25.6

I'm not seeing overly flat primers..velocity was still steady climbing with a good SD no split or cracked necks

Where am I hitting over pressure?

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markm

11-14-15, 19:13

They list 25.6 as max and I find that way to high but I was curious and averaged 3100fps from a 16" BCM 5.56 AR, how is that not over pressure?

3100 is just a stout load. Published max pressures are generally somewhat conservative. XM193, for example has hit over 3300 out of our 20" barrels. So 3100 from a 16 is just a stout, but probably safe load.

Where am I hitting over pressure?

Hard to say. Some powders turn on you quick. XBR will show no signs of pressure, and then all of the sudden I'm blowing primers a about a 5% rate. I'm not familiar with AR comp, or its burn rate. But there are many factors that contribute to pressure signs.

I'd watch this load in warmer seasons. I think AR comp is supposed to be Reloader's (relatively) temp stabile powder, but their other powders are so bad at temp swings, I'd still be cautious.

boombotz401

11-14-15, 19:31

This was just for testing purposes I was comparing to h335 as I'm trying to decide on a primary powder between the 2

I won't be loading 25.6 again and certainly not in the blazing summer!

Quick load calculates 25.6 @ 64329psi

Fiocchi 55gr averaged 2875 earlier today for a factory comparison

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anachronism

11-14-15, 21:08

It is impossible to estimate chamber pressures by primer condition. There is no direct correlation between primer manufacturers, some use harder and/or thicker cups in manufacturing. Primer compounds also vary from manufacturer to manufacturer. The same with case conditions. You could use case head expansion to gauge pressures somewhat, but you can't use that as a tool if you don't have new brass from the same lot to develop your handloads with.

wilson1911

11-14-15, 23:24

I do see a small amount of ejector swipe on the cases, which show it to be a hot load. Flat primers come next.

markm

11-15-15, 09:29

Yes. On second look, there are a number of swiped on those heads. Whether they were from a prior firing or not may be unclear.

I'd only pick H335 if i were blasting FMJs and didn't care about the high flash from that powder. I keep a pound of it on hand for my beater upper that has a large chamber comp. It flashes like artillery.

boombotz401

11-15-15, 11:03

I did notice those ecjector marks though I see those also on factory American eagle 55 @ 2875

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sinister

11-15-15, 11:16

Frankly I don't see any excessive pressure signs. I see a few flattened primers but the majority still have radiused primer cups. Some have raised craters about the firing pin impact point, but that shows a large firing pin hole or an undersized firing pin nose.

3100 is pretty fast for a 55 out of a 16-incher.

rjacobs

11-15-15, 11:22

I dont mind H335, but only for 55g FMJBT's. 25g is the go to load IMO and a bunch of other peoples(probably the most hits when I searched for a load years ago). 3031 is also a decent powder for plinking and its close enough to H335 you can almost use the same load.

And when you are checking loads for pressure signs you HAVE to use all the same headstamp brass. You have mixed brass in there. You cant read mixed brass. Some is smaller volume, some is larger, 556 vs. 223(556 case bases/webs are supposedly stronger than 223 case bases/webs), etc... Impossible to read IMO.

markm

11-15-15, 13:47

I did notice those ecjector marks though I see those also on factory American eagle 55 @ 2875

That brass is pretty weak in the web. So mild pressure will still show those swipes sometimes.

And when you are checking loads for pressure signs you HAVE to use all the same headstamp brass. You have mixed brass in there. You cant read mixed brass. Some is smaller volume, some is larger, 556 vs. 223(556 case bases/webs are supposedly stronger than 223 case bases/webs), etc... Impossible to read IMO.

Although there's probably a good point there, in that not all case heads are the same hardness... I mix almost all kinds of brass together for .223, and get great results. PMP and a specific variant of PMC have noteworthy internal volume variances, but most of the rest are too close to give a second thought.

And 5.56 brass webs are no stronger in my experience. Maybe a little, depending on how work hardened the head is. But some 5.56 is actual weaker.

rjacobs

11-15-15, 13:55

Although there's probably a good point there, in that not all case heads are the same hardness... I mix almost all kinds of brass together for .223, and get great results. PMP and a specific variant of PMC have noteworthy internal volume variances, but most of the rest are too close to give a second thought.

And 5.56 brass webs are no stronger in my experience. Maybe a little, depending on how work hardened the head is. But some 5.56 is actual weaker.

I mix all brass for plinking loads too with good success. I was simply talking about reading pressure signs. If 1 headstamp of brass has something like a grain or two smaller(or larger) internal volume, you might either get(or not get) pressure signs on 1 piece of brass while at the same time at the exact same powder charger on a different head stamp might(or again, might not) show pressure signs. Same goes for different loads. You might not see pressure on 26g on one type of brass, but you might see pressure on a 24g load on a different piece. That was my only point in the OP asking about reading pressure signs on mixed brass. Its a crap shoot. In practical terms, you are shooting a 55g FMJBT which is a 1.5-3moa bullet on average so a little pressure change due to brass internal dimensions isnt going to cause much outside of what the bullet is already capable of. On precision stuff, it does matter though in my experience(and im sure you share that).

556 webs should be a little stronger due to how they are made from what I understand. 556 spec calls for the brass to be struck twice in the forming die, again from what I understand, this should, in theory, make them a little stronger due to them possibly being a little denser from this double strike. NOW there MAY be a lot of "223" brass that is also struck 2x, simply because its run on the same line as 556 brass, I dont know.

boombotz401

11-15-15, 14:35

Thanks,

I have used 3031 noticing it's always on the shelf when components are scarce and had very good results but getting hung up in 223 necks wasn't worth it to me as a high volume shooter.

I was going to use new brass but my thought was I'm usually reloading mixed brass so a "real world" test may be best.

What I'm noticing is there's no clear answer to where "this is your limit" is.

My goal for this test was to find one powder for mainly 55gr that I could download for plinking and run higher velocity if need be

the occasional 68-75gr with a relatively low flash, since I also have an 11.5 barrel AR in the works.

I just found it odd that @3100 fps from a 16" I really wasn't seeing any solid defined signs on 3 of five cases

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markm

11-16-15, 12:01

556 webs should be a little stronger due to how they are made from what I understand. 556 spec calls for the brass to be struck twice in the forming die, again from what I understand, this should, in theory, make them a little stronger due to them possibly being a little denser from this double strike. NOW there MAY be a lot of "223" brass that is also struck 2x, simply because its run on the same line as 556 brass, I dont know.

Yeah. I've had 5.56 brass that's much harder than commercial brass, and 5.56 brass that's much softer/weaker. Some of the "L C 1 0" (with no NATO cross) has been very weak, for example. I've read that the more dimples (I forget their real name) on the head, the more work hardened that head will be. The simple head stamp in the LC10 brass I mentioned seems to lend some support to that notion.

bigedp51

11-16-15, 22:51

Any time you see the brass start to flow into the ejector it means you have exceeded the elastic limits of the brass and are way over pressure for that make/type of brass.

Below from AccurateShooter.com many of the thousand yard shooters said they kept increasing the load until they had brass flow into the ejector. Then these shooters reached this point they backed off 1 or 2 grains of powder, this is a visual indication. Depending on the brass hardness the brass flow starts when you are 5,000 psi over the maximum rated pressure of 55,000 psi for the 5.56 NATO cartridge.

http://i122.photobucket.com/albums/o254/bigedp51/marks_zps63d0459a.jpg

The second more accurate method is to measure how much the case head has expanded in diameter just above the extractor groove.

Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads

"Using a blade micrometer that measures in ten thousandths (.0001"), new, unfired cases can be gauged before and after firing to determine reasonably accurate maximum loads. Micrometers measuring in thousandths (.001") are insufficiently accurate to perform these measurements, and should not be used. Previously fired cases cannot be used accurately due to various levels of brass hardening. Measurement is taken just ahead of the extractor groove on the case head and must be taken at the same place on the case before and after firing. By placing a small mark on the case head – entering the cartridge in the chamber with mark at 12 o’clock – a consistently accurate measurement can be taken with each firing.

Lower pressure rounds, like the .30-30 Winchester, usually yield maximum pressures at .0003"-.0004" expansion. Modern cartridges, like the .223 Remington, will show maximum pressure at .0004"-.0005", while .308 Winchester, .270 Winchester, etc., typically yield .0005"-.0006" expansion at max pressure. Magnums, like the .300 Winchester Magnum, show maximums at .0006”-.0007” expansion, and should be measured on the belt."

The old thumb rule was anything over .001 case head expansion was a sign off excessive chamber pressure.

Below the Rockwell hardness of military Lake City cases and .223 cases. So brass flow will start earlier with the softer .223 cases.

LC 2008 = 96
Lapua 223 Match = 86
Winchester 223 = 69
Remington "R-P" = 49
(Federal brass is even softer than Remington)

So remember your "case swipes" and chamber pressure will vary with brass hardness.

http://i122.photobucket.com/albums/o254/bigedp51/556hard-a_zps7570e6b0.jpg

http://i122.photobucket.com/albums/o254/bigedp51/hardness-a_zps8d54ad66.jpg

The reason Lake City and all commercial contract 5.56 ammunition is made of harder brass dates back to the Congressional hearings on the early jamming problems with the M16 rifle.

http://i122.photobucket.com/albums/o254/bigedp51/Casehardness-a_zps14dbe0fd.jpg

Below is a Quickload chart for my practice AR15 ammunition at approximately 50,000 psi to make the brass last longer. The load is 25.0 grains of H335 with a Hornady 55 grain fmj and Lake City brass and 5,000 psi below the max rated pressure.
(paper targets always die no matter what the bullet velocity is) :lol:

http://i122.photobucket.com/albums/o254/bigedp51/288_zps26698a67.jpg

Airhasz

11-16-15, 23:27

Good post, Biged.

bigedp51

11-17-15, 00:40