Pressure signs way below max load

Discussion in 'Long Range Hunting & Shooting' started by Mc Fraser, Aug 17, 2019.


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  1. amadjuster

    amadjuster Member

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    Your primers are puckered at the firing pin which can be caused by something besides pressure. I say this because the primers are not flattened and filling the pocket.
     
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  2. freddiej

    freddiej Well-Known Member

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    I have something to add to this. not one person brought this up that I have seen so I am going to. You had a gunsmith perform this barrel install. this means he did it the way I would do it, I am also a gunsmith, he probably used a reamer service that keeps reamers sharp and sharpened after about every 4th yo 6th use. this can make for a truly minimum or maybe a 0.001" under minimum chamber. this means you have a "tight" chamber. this is very good for stretching being at a minimum and other such great thing. this also means you have a closely headspaced chamber. this detracts from the area in which the case expands (minimal stretching of the case). this means your pressures are higher to start with. If you show pressure signs at a certain powder charge; consider that your danger zone and back off 1 full grain to be your maximum powder charge. This should keep you from seeing pressure signs. this is if your powder scale is not off by a certain percentage. I have three rifles like this in my own collection. all were built by me in gunsmithing college. I used 4D reamer service. all shoot very well and they save brass. an easy test is to take a fired case, measure it at the datum lines of your drawings in your reloading manuals. average is 0.003"-0.005" larger than the drawing dimensions say. if your measurements are 0.000" to 0.002" then you have a SAAMI min spec chamber and your loading data should be down loaded 1 to 2 grains depending on case volume.
     
  3. amadjuster

    amadjuster Member

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    This action is now the M7.
     
  4. Mc Fraser

    Mc Fraser Well-Known Member

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    I need to load one bullet at minimum book load, if I still get pressure signs and speeds below 2800fps I need to have a chat with my smith.
     
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  5. kiwikid

    kiwikid Well-Known Member

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    Mc Fraser can you please weigh some of you empty, unprimed cases? Norma had some production runs that weighed more than other runs. The light brass will weigh around d 215 gr and the heavy brass will be around 270 gr. In the Norma manual they give different loads for each weight brass. As an example using 200 grain Sierra MK and Norma MRP the heavy brass loads are Start 66gr & Max 68.4gr, for the light brass they are Start 70gr & Max 73.7. As you can see there is a big difference and I wonder if you may have the Heavy brass.
     
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  6. TBell

    TBell Well-Known Member

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    Confirm the bullet is not against or into the lands
     
  7. FEENIX

    FEENIX Well-Known Member LRH Team Member

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    Unless I misconstrued your previous posts, I thought you load (i.e.. #28) them and now a competition shooter friend of yours reloaded it. Which one is it? What does your competition shooter friend think the problem is?
     
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  8. Rflshootr

    Rflshootr Well-Known Member

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    I had a problem like that once that took a long time for me to figure out. After suspecting power, bullets and primers, I finally bore scoped the throat and found that the lands were smeared much more then anything else I had looked at. The reason.....the throat area on the reamer was dull. I couldn't feel much difference while cutting but after looking at the reamer, I could see it wasn't dead sharp. So to remedy this, I ran a new throating reamer in a few thou, reinstalled the barrel, got my new seating depth and the problem vanished. Not saying that what you have is the same, but if you have access to a bore scope, it's worth a look.
     
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  9. stljc2

    stljc2 Active Member

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    Did the same with my .308. My fault really. Stored IMR 4064 in the garage and haven't used it much in the last 5 or longer years...affected the powder I think..ended up tilling it into the garden. I didn't have ANY climate control in the garage. Lost faith in it so in the garden it went.
     
  10. Mc Fraser

    Mc Fraser Well-Known Member

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    Up until last night I loaded everything, #83 and #84 are loaded by a friend with my dies but everything else is his equipment. Pretty much I did that to eliminate my equipment. So far it looks like is the dies or the rifle. I don't think it's me or my equipment. He is using some very expensive equipment like the autotrickler, that induction annealing machine that costs way too much. True the powder charge and measuring devices are more accurate than mine but not to that extent.
    He's saying to go to 2-3 smiths to check the gun.

    Do you believe it's not actually pressure signs that I'm seeing and its something else? This is very interesting, can you elaborate?

    That is my next step.

    I'm not sure that I understand what you said, I believe i have to measure the chamber?
    I just don't understand ... I thought when you do a ladder test first you see the velocity flatten out and if you keep increasing the powder you start to see pressure signs, first flat speed then pressure signs, not the other way around.
    I don't think is the powder, N570, for example, I bought it a few days ago.
     
  11. CVCOBRA1

    CVCOBRA1 Well-Known Member

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    You had all those pics of the cratered primers but really did not say if that was a concern of yours. Primers like that don't always mean a sign of over pressure. It can be such a simple thing as an oversized firing pin hole. Might have your smithy check that out also. Some bolts out there needed their pin holes drilled and have bushings installed.
     
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  12. T3ninja

    T3ninja Well-Known Member

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    I’m thinking that everything is exactly the way it’s supposed to be. What I mean is, your “pressure signs”, yeah you probably have some over pressure going on with the speed you are claiming to have. I’m thinking anything north of 3k FPS in a .300 WIN with a 215 grain bullet, regardless of what any book says is “max charge weight” would be maxing out that cartridges potential.

    I have one with a 26” Bart barrel, I know I am over published max but I’m NOT seeing any pressure ( no bolt lift problems, primers are fine and no ejector ghost rings). I’m running 78.3 gr of h1000 in Gunwerks (adg?) brass, getting 2970. Accuracy, ES, and SD are all good. I’m seated .020 off lands.
     
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  13. Mc Fraser

    Mc Fraser Well-Known Member

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    2B77487A-99CE-4FE5-B486-738883ECA10B.jpeg
    That’s a good point. I guess I started with the assumption that between myself and 2 other shooters at the range that is a sign of pressure. That being said the pictures above are my concern, I suspect pressure signs.
    Here is a picture of the bolt, haven’t clean it yet.
     
  14. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    yup... you could run a semi down the firing pin hole on your rifle..
    As to pressure, welcome to my world. My 7rum has been eating book minimum or below charges and destroying match bullets all spring and summer (she's running a 8" twist brux with a rather tight chamber). I have even gone to trimming short and turning the brass for uniformity to eliminate out of round issues contributing to pressure problems.
    I finally landed on h50bmg and a 175 eld-x as a safe load that seems to shoot well..

    For your 300 win, get her close to normal working speed and accurate... then forget that the charge you run is different than max charge for most books... It is a moot point in your situation.
     
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