Primer pressure signs?

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redheadmechanic0
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Primer pressure signs?

Post by redheadmechanic0 » Tue Apr 07, 2020 9:47 am

Good morning everyone. I am shooting some handloads and want to check to see if these primers are showing signed of high pressure.

Gun :
Personal build ar15
My barrel is a mas defense 16" carbine gas 1:8 twist, Gas port is .125"

Handloads: (using Hornady bk 9th edition)
5.56 LC brass I converted with no annealing
Hornady SST 125gr seated to 2.100"
CCI #400 primer

Powder charges: (each indv. Weighed):
H110
17.0gr - 2099, 2132, 2112, 2160, 2140
17.2gr - 2148, 2147, 2170, 2157, 2145
17.4gr - 2133, 2126, 2167, 2147, 2163
Lil'Gun
18.2gr - 2208, 2219, 2265, 2213, err
18.4gr - 2193, 2207, 2239, 2186, 2242
18.6gr - 2170, 2225, 2239, 2260, 2295

Oh and this brass is the first firing after converting to 300blk so it has not been fire formed to and 300blk chamber.

These speeds are also a bit higher than what is advertised in my Hornady 9th edition: (though it lists load data for both 125, 130gr)
H110 17.7gr = 2000, 18.8gr = 2100
Lil'Gun 18.7 = 2000, 20.0 = 2100

Since i cannot post pictures the primer is showing a ridge around the dimple where the firing pin strikes but the primer is still rounded and is not flattened out

Hopefully this link works:
https://drive.google.com/folderview?id= ... jjI2JWRmh5

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dellet
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Re: Primer pressure signs?

Post by dellet » Tue Apr 07, 2020 10:58 am

The the shiny round mark at 10 o'clock is from the ejector and the sharp edge around the pin strike, early pressure signs/over gassed. Gas port is too big, load is close to max.

Confirm that with your gas port size of .125" and load being .2 grains from max listed. Could be as simple as a different lot or primer used, or that the seated depth is a bit short and probably different case capacity from what Hornady used.

Typical load work up and why you don't start at the top. Looks like you did it right and stopped at a reasonable place..

You might want to print this page and slip it in you book.
https://press.hornady.com/assets/pcthum ... 702177.pdf
300 Blackout, not just for sub-sonics.

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wildfowler
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Re: Primer pressure signs?

Post by wildfowler » Tue Apr 07, 2020 4:25 pm

I am not too concerned about the first firing and would try again using some once fired brass now that you have a few pieces. Carefully set back the shoulder for reliable feeding but not too much.

Factory ammo can make similar marks on the case heads since the brass was not originally sized to fit your chamber. (at least that’s why I think I’ve seen that happen personally, but I honestly don’t know why it can happen with factory ammo?)

I’m looking at the radius edge around the primer which makes me think you’re still within margin.

I would not personally go any higher on my powder charge, especially if you saw good accuracy. Just confirm what you previously saw With once fired brass.
driven every kind of rig that's ever been made, driven the backroads so I wouldn't get weighed. - Lowell George

redheadmechanic0
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Re: Primer pressure signs?

Post by redheadmechanic0 » Wed Apr 08, 2020 4:17 pm

dellet wrote:
Tue Apr 07, 2020 10:58 am
The the shiny round mark at 10 o'clock is from the ejector and the sharp edge around the pin strike, early pressure signs/over gassed. Gas port is too big, load is close to max.

Confirm that with your gas port size of .125" and load being .2 grains from max listed. Could be as simple as a different lot or primer used, or that the seated depth is a bit short and probably different case capacity from what Hornady used.

Typical load work up and why you don't start at the top. Looks like you did it right and stopped at a reasonable place..

You might want to print this page and slip it in you book.
https://press.hornady.com/assets/pcthum ... 702177.pdf
Thanks for the reply.
The shiny spot on the case in question is from the ejector pin based on the flat spot on my case mouth. (All my case mouths have flat spots where the case hits the inner part of the upper receiver upon extraction. I am thinking that I maybe over gassed for these supersonic loads and the gas is coming up through the bolt face and creating the ridge around the primer strike? I have an adjustable gas block (wide open at this time). I will turn the gas down and repeat this.
My gas port is indeed 0.125" and it is CARBINE length not the popular pistol length gas system.
Image
Hornady book lists winchester small pistol primer and I am using CCI #400
Hornady lists Hornday brass and a COL = 2.100" (I am seating to 2.100")
I am not 0.2gr from max my loads, see my above post for my loads. H110 is 18.8gr as MAX and Lil'Gun as 20.0gr as MAX. So i am 1.4gr+ from max.

Thanks for the errata, nothing applicable to 125gr SST's i am using, but some good info on other loads

redheadmechanic0
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Re: Primer pressure signs?

Post by redheadmechanic0 » Wed Apr 08, 2020 4:28 pm

wildfowler wrote:
Tue Apr 07, 2020 4:25 pm
I am not too concerned about the first firing and would try again using some once fired brass now that you have a few pieces. Carefully set back the shoulder for reliable feeding but not too much.

Factory ammo can make similar marks on the case heads since the brass was not originally sized to fit your chamber. (at least that’s why I think I’ve seen that happen personally, but I honestly don’t know why it can happen with factory ammo?)

I’m looking at the radius edge around the primer which makes me think you’re still within margin.

I would not personally go any higher on my powder charge, especially if you saw good accuracy. Just confirm what you previously saw With once fired brass.
I have reloaded 5 1-fired cases and will retry and also loaded 5 with CCI #41 primers for comparison. Both with H110 1.0gr.
How do you measure the shoulder? There doesn't seem to be a good location to measure shoulder and what is enough setback?
I also closed off my gas port alittle and will see if this fixes the cratering on the primer strike. I looked at some old cases that where factory loaded including Hornady ammo and also found similiar cratering. I am thinking that there is to much gas for supersonic loads.
Hornady factory loads that I shot for hunting 110gr Vmax:
Image

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wildfowler
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Re: Primer pressure signs?

Post by wildfowler » Wed Apr 08, 2020 4:53 pm

It may be oversized factory cases rather than too much gas. I don’t know what the Gasport size is supposed to be and all of that, I know the AAC blackout barrels were not designed to require an adjustable gas block but since you have it you can play around with that to see if it changes your situation any.

For set back you will need to use a setback tool or make one which is basically something that you put the case mouth into the tool and it rests upon the shoulder.

I use the hornady tool which comes with about 5 different sized adapters and a holder which clamps to the blade of your caliper.

You might be able to make one from a spent and resized 9mm pistol case. I’ve never tried to use this, but the opening of the pistol case is very similar to the shoulder diameter of the blackout case.

You then take your caliper and measure from the case head to the outside of the back of the tool and use that as a comparison.

For an AR I would try and use as little as will reliably feed, .005” should be plenty and not overly sized.

Edit: I’m not sure the 9 mm case is the exact correct size to use, but take a look at this link for the tool I was speaking of to understand how it works and you may find something else you have lying around that will work.

https://www.hornady.com/headspace-bushings#!/

Re Using a 9mm brass: take a sharpie and draw some sort of index line to use as an indexing reference point on the 9mm brass to orient it the same way in relation to your caliper jaws each time you use it.

If there is any variation in the case and you don’t orient the case in the same position every time I could see how that could give you a variation in your measurement, but it’s probably not going to be enough to matter for your purpose.

Be sure and pop the spent primer out too. I would even take the 9 mm case head and run it across an emery board or super fine grit sandpaper to smooth any burrs out until you can get a better tool to use.
driven every kind of rig that's ever been made, driven the backroads so I wouldn't get weighed. - Lowell George

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dellet
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Re: Primer pressure signs?

Post by dellet » Wed Apr 08, 2020 5:48 pm

redheadmechanic0 wrote:
Wed Apr 08, 2020 4:17 pm
dellet wrote:
Tue Apr 07, 2020 10:58 am
The the shiny round mark at 10 o'clock is from the ejector and the sharp edge around the pin strike, early pressure signs/over gassed. Gas port is too big, load is close to max.

Confirm that with your gas port size of .125" and load being .2 grains from max listed. Could be as simple as a different lot or primer used, or that the seated depth is a bit short and probably different case capacity from what Hornady used.

Typical load work up and why you don't start at the top. Looks like you did it right and stopped at a reasonable place..

You might want to print this page and slip it in you book.
https://press.hornady.com/assets/pcthum ... 702177.pdf
Thanks for the reply.
The shiny spot on the case in question is from the ejector pin based on the flat spot on my case mouth. (All my case mouths have flat spots where the case hits the inner part of the upper receiver upon extraction. I am thinking that I maybe over gassed for these supersonic loads and the gas is coming up through the bolt face and creating the ridge around the primer strike? I have an adjustable gas block (wide open at this time). I will turn the gas down and repeat this.
My gas port is indeed 0.125" and it is CARBINE length not the popular pistol length gas system.
Image
Hornady book lists winchester small pistol primer and I am using CCI #400
Hornady lists Hornday brass and a COL = 2.100" (I am seating to 2.100")
I am not 0.2gr from max my loads, see my above post for my loads. H110 is 18.8gr as MAX and Lil'Gun as 20.0gr as MAX. So i am 1.4gr+ from max.

Thanks for the errata, nothing applicable to 125gr SST's i am using, but some good info on other loads
The shiny spot on the case head is called an ejector swipe, also known as an indicator of high pressure.

The primer flowing into the hole the firing pin comes through happens from high internal case/chamber pressure. It's not supposed to do that and is an early indicator of excessive pressure.

Your Lil'gun load that is basically 1 1/2 grains lower than max and 200 fps faster indicates a hotter batch of powder or smaller case capacity. Both are due to higher pressure.

H110 and 296 are the same powder. The data in the manual reflects two different lots. Note that the 296 max is exactly where you are and you are getting the beginnings of signs of too much pressure. Maybe it's related?

Your .125" port is too big, but is not causing any of the problems you have described and pistol gas in a 16" barrel is only popular among those who do not understand the cartridge.

Pretty sure Hornady did not list a small pistol primer in the 9th edition, if they did, that mistake also would have been in the errata.

If your trim length is longer than Hornady's corrected 1.358", that will add to pressure. If you used the erroneous length of 1.390"or any thing between that and 1.368", it will definitely cause high pressure to the point of being a safety issue.

Everything you are seeing tells you to stop where you are, or proceed with caution and experience. If you had the experience, you would not have mis-interpreted the signs.

Go slow, stay safe.
300 Blackout, not just for sub-sonics.

bearcatrp
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Re: Primer pressure signs?

Post by bearcatrp » Wed Apr 08, 2020 7:35 pm

That crater ring on the primer indicates over pressure. Every barrel is unique. If commercial ammo, stop shooting it. If reloaded ammo, back off on the powder. As posted above, could be your gas port.

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wildfowler
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Re: Primer pressure signs?

Post by wildfowler » Thu Apr 09, 2020 10:25 am

Pressure is not the only cause of cratered primers. But certainly not something to scoff at!!

I would recommend ditching the CCI 400 and try something with a thicker cup.

Read this article:

https://www.accurateshooter.com/technic ... -analysis/
driven every kind of rig that's ever been made, driven the backroads so I wouldn't get weighed. - Lowell George

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Ben B.
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Re: Primer pressure signs?

Post by Ben B. » Tue Apr 14, 2020 1:46 am

I’ve spoken with 2 ballisticians at powder companies. Both indicated that “reading pressure signs” is essentially witchcraft, akin to reading chicken entrails to forecast the future. Sometimes “pressure signs” show up at low measured pressure and sometimes they never show when measured pressure is well over max. Too many variables at play to count on pressure signs. But I still check...
"rjacobs" quote removed at "rjacobs" request.

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