Understanding Pressure



    Just finished up an article that should help people gain a better understanding of the pressure at play in their firearms. Let me know if you have any questions and I look forward to your comments!

  • Excellent article Greg, thank you.:+1:

  • Best photographic examples and writing I have ever seen on the subject.
    Thank you.
    What Camera body?

  • Well, I'm not complete done reading it yet, but I am forgetful so I decided I would take some notes or thoughts and post them.

    First of all, Clap awesome that you mention that water (And all liquids for that matter) are compressible. Having dealt with some sensitive hydraulics in my life that drove engineers mad because they were idiots and weren't factoring in both the compression of the hydraulic fluid and the expansion of rubber lines, I almost cringe when people say liquids are not compressible, I almost got fired over that deal after screaming at the engineer, of course when we found out I was right the whole thing was quickly ignored anyways.

    Second, crap I am using to much lube.

    Jeez Greg there's a hair or something on the 42 grain picture. But otherwise I never thought of using a loupe to check things, I don't know why, I have one I use for checking for burrs when sharpening knives.

    Wow that 48 grain picture is nasty, Kudos to you, I don't think I could willingly put my rifle through that.

    Excellent write up as always Greg.

  • @hypo said:

    What Camera body?

    Canon T3i

  • Here is a little trick I use for dealing with the ambient heat/sunshine heat on ammo.
    Keep the ammo in a small cooler and in the shade or cover the cooler with a towel until ready to shoot. For a small box of 50 rounds I use a soft insulated cooler and for up to 6- 50 round boxes a small hard cooler that can close.
    I also use a infrared thermometer to audit the temperature of both the chamber and the ammo.


  • Thanks Greg. As always, your dedication to helping folks out is greatly appreciated.

  • Great write up. A lot of things I didn't know. Thanks for taking the time to put it together.

  • I use WLR for my .308 mainly due to availability. They seem to flatten out irregardless of load; however, there are no other pressure signs, no cratering etc.
    The cases are either neck sized or bumped back .001-.002 with a Redding full length body die and then neck sized with a Lee collet die. The barrel is a Bartlein tite bore with a SAMMI chamber.
    The loads are middle of the road and I am very aware of temperature influence. Bullets are usually seated long for single feeding about .020 off the lands. Brass is Lapua and LC.
    So I am wondering if others have had similar experience with the WLRs or if there is something else to look at. I pretty much disregard these primers and look for the other signs of over pressure.

  • It may be the WLRs I have are "soft". 2 pierced the unsupported side on the radius to the top. The color of these primers had a more copper tone than others in this lot (13 of 22). These were loaded long, .020 off lands, with 42.0 grains of 4064 and 168SMKs. Lapua brass. The one on the left looks like an ejector mark, however using the loupe and the corresponding bolt face divot leads me to believe the outline is from the way the plasma flowed.
    All of these primers are from the same lot and same 100 piece pack. (The right side also shows cratering.)


  • These are primed cases done from the same box and 100 pack only in LC15 brass. One flattens out more than the other with the same pressure upon seating, the flatter ones are more of a copper tone than the more rounded primers.

  • 42gr is a fairly warm load in lapua brass. Couple that with a high start pressure caused by small case neck or super clean case necks... and it can certainly cause pressure.

    One easy way to tell would be to just switch primers. Clearly if you are having primers flatten out upon seating, they may be defective.

  • @orkan I shoot this exact load in LC brass as well and never had any pressure signs other than that flattened primer we spoke of previously. After experiencing these ruptures I did a web search. Turns out this is not an isolated incidence with the WLR as well as others on occasion.
    I think I will change over to Palma brass and run nothing but #41s for the .308 as well as the .223.

  • @mamalukino said:

    @orkan I shoot this exact load in LC brass as well and never had any pressure signs other than that flattened primer we spoke of previously.

    Different components = different results. Doesn't change the fact that 42gr of 4064 can be warm in some rifles with lapua brass. You can not look at two different makes of brass and say they should be identical... because they are not. Even if the volume is identical (which its not) then the properties of the brass are certainly not identical, which will lead to completely different behaviors. As I said in the pressure article... if you are getting pressure signs, then you are over-pressure. It truly is as simple as that. There's too much pressure there for the primers to handle. The solution is to back your load down, or get different primers. Switching to palma brass is probably completely unnecessary.

    You are correct in that this is not an isolated thing with winchester primers. I'd recommend switching to CCI-200's.

  • Thanks Greg, WLRs are about the only large rifle I've been able to get here in the last 7 or 8 years and I have a pretty large inventory. I am going to trade or sell what I have left for the CCI #41s and get some more Palma brass. The CCI #41s have come time and again and I have loaded up when available.
    I am liking the idea of 1 component covering both the calibers I shoot. From my understanding the #41 is identical to the 450 except for the hardness and anvil length. I have been using them in my .223 bolt gun with no problems and in the test with the .308 palma brass.

  • Everyone has their own circumstances. I get that.

    I refuse to be trapped by local considerations regarding what I buy. Were I you, I'd order primers online from Precision Reloading... and eat the hazmat once... so you can get what you want. 5000 of this 5000 of that... and you won't have to worry about it for a while. :)