Where is my pressure coming from?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Tikkamike, Sep 27, 2012.

  1. Tikkamike

    Tikkamike Well-Known Member

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    I am stumped... I have a 700 in 375 ultra, I worked up a load with 270 tsx and 98 gr. of H4350 (3150 fps) It ended up being a little too hot and was stretching primer pockets after about 2-3 reloads so I backed it down a half grain, then another and so on I am not down to 96.5 grains 3030fps and the more I shoot it at 96.5 grains the harder and harder ir has been to open the bolt. I was only neck sizing but decided to FL size once and it didnt really do anything different. Still has bolt click and a couple times I have had to beat the bolt back. It does fine with an empty chamber. I bore scoped the chamber/throat to make sure there was no carbon ring or anything that looks like it may be causeing an obstruction to increase pressure. There is some copper in the bore and there is a chance I have not been getting it all out. I use wipe out and gave it the boretech test and it passed. Next time i think its clean ill borescope it to be sure. I know I can just keep backing off the powder till pressure is ok. but with it getting worse and worse each time I fire 96.5 i think there is more to it. I am about 50 fps over book max with a 2" longer barrel. Also im on the 5th firing and my primer pockets are still nice and tight. I am hoping its a copper build up and I just need to be more thourough with my cleaning but...im a little skeptical...throw me some ideas guys.
     
  2. Broz

    Broz Well-Known Member

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    Make sure you are getting the shoulders back far enough.
     

  3. Tikkamike

    Tikkamike Well-Known Member

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    Check! that was one of my first thoughts. I have the Sinclair case gauge and it measures fine, and it chambers fine
     
  4. Joe King

    Joe King Well-Known Member

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    Tight neck? Have you tried putting a bullet into a fired case? I ran into that problem with my 243, only found it when I tried making a dummy round for a new load. Or measure just ahead of the case head, could be you have excessive headspace and the cases are expanding beyond their ability to spring back.
     
  5. Tikkamike

    Tikkamike Well-Known Member

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    I wouldnt think so in a factory chamber but ill check that! very good idea thanks joe....anyone else with ideas?
     
  6. Outlaw6.0

    Outlaw6.0 Well-Known Member

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    Here a a few dumb questions.

    Any change in Powder lot? Primer lot? Bullet lot?


    Is this the new brass you just got? How does it compare in weight & capacity to the first batch you used? Have they been properly trimmed?

    Any funny looking marks on you case after extraction?

    I just can't see fouling causing pressure problems. Sure would make it shoot like crap; but excess pressure?



    A lot of redundant questions I know. :cool: Just rambling off the top of my head.


    t
     
  7. Tikkamike

    Tikkamike Well-Known Member

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    I have used the same brass as before and new brass, same bullet lott same primer lott different and same powder lott (just opened a new jug) cases are trimmed and deburred. extracted cases look fine (other than being stuck in the chamber pretty tight) I dont see fouling being the problem either but its the only thing I can think of that could possibly be getting worse as I go...
     
  8. B23

    B23 Well-Known Member

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    Mike, take this for what you want but quickload shows your 96.5gr load as over 76,000 PSI if your COAL is 3.600 if you COAL is a bit longer say 3.750 it's still pretty hot load at 70,000 PSI. Max PSI is shown at just a little over 63,000.

    Have you ever thought of using a little slower powder like H4831sc? QL shows H4831sc giving within 75 fps of your H4350 load but with less pressure.

    Sounds like everything your doing is right but your load is just a little on the hot side. Hope this helps.
     
  9. Tikkamike

    Tikkamike Well-Known Member

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    B23, my oal is 3.8, and I am considering just starting over with a new powder. I think I will probably try something like H4831sc. But I would first like to figure out what the heck is going on with this load. It is possible I suppose that the change in weather and humidity is to explain for the changes in pressure signs. I know its a very hot load. Thanks for running the number for me!
     
  10. dbhostler

    dbhostler Well-Known Member

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    See it's already been suggested.
     
  11. Broz

    Broz Well-Known Member

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    I agree that H4350 is a little fast for the case. I too would change powder. I am guessing the suspected rise in pressure is from case expansion durring previous firings and your case is now fitting the chamber tighter even though you are full sizing.

    Jeff
     
  12. B23

    B23 Well-Known Member

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    Playing with QL, RL22 and 7828ssc look like they both would get you about the same FPS but with less pressure.
     
  13. Tikkamike

    Tikkamike Well-Known Member

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    B23 how dense are the powder charges?
     
  14. B23

    B23 Well-Known Member

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    W/RL22 103.5gr is 105% fill capacity and show 64,000 PSI

    W/7828ssc 103.5gr is 103.8% fill capacity and also 64,00 PSI

    Your H4350 load of 96.5 and 3.80COAL was shown as 101.6% and 68,000 PSI