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EXCESSIVE PRESSURE

RosieRosie Member Posts: 14,525 ✭✭✭
edited July 2007 in Ask the Experts
Bought a 91/30 with matching numbers some time ago. Ordered a couple of tins of the Bulgarian 762x54R which I believe has around 187 grain bullets. The fired cases look great after firing but the primers show a little oozing back into the firing pin hole. Not much but noticeable which tells me excessive pressure. Any Ideas why? This gun looks like it was never issued and the rifle grooves looks great.

Comments

  • sandwarriorsandwarrior Member Posts: 5,453 ✭✭✭
    edited November -1
    Rosie,

    I can't say what they are doing without a picture, but recently firing of my 91/30 shows a very large primer hole which may give the impression you speak of. High pressure will generally be shown on the primer as a double dimple and sometimes a shiny crest on the edge(s) of the dimple. You can see high pressures as well on the cases just like reloading. A shiny head, a matting-like pattern very low down from the shoulder on the base of the case. And, of course, hard to remove from the chamber. If not hard to remove from the chamber it might just be your rifle or those particular bullets that are giving an impression of high pressure. You may need to chrono the loads to see what they are doing or just wait until it gets cooler to shoot them. Hope that helps if any.
  • glabrayglabray Member Posts: 679 ✭✭✭✭
    edited November -1
    Primer cratering can be used as an indication of higher pressure in a rifle you have some firing history on but it is pretty unreliable for a gun that is new to you such as this. As mentioned, an oversized firing pin hole can cause cratering of primers for loads that are well below the danger zone. A better indicator some times is to compare the radius of the edge of the primer of a fired round with that of an unfired one. If the radius of the fired round's primer is a lot less, or if there is no radius left (totally flattened) that could be a borderline load. Another good check is to mike the diameter of the case head of a round before and after firing.
  • JKJK Member Posts: 223 ✭✭✭
    edited November -1
    All of the above +1 but don't forget to notice the head stampings. If the stampings start to "flatten" compared to a normal head after firing this is a asure sign that pressures are building. If they are flattened out even more, it's reasonable to assume that you're in over 60,000 PSI, which could mean trouble. Make sure the chambers of ANY HI power pistol and rifle are FREE of any oil in the chambers before firing. Oil will produce needless pressure on the bolt face/lug/ or what have you. Rifle/pistol chambers are designed to grip the chamber wall. If the walls cannot accept this constriction then the bolt face/cartridge head gets it all that the walls can't take. .005 to the inch is a standard taper but mostly used for easy extraction as long as the locking angle of the case does not exceed 6 degrees. This is also directly dependent upon the caliber and power of the cartrige itself as in some low powered cartridges there is no case taper
  • v35v35 Member Posts: 12,710 ✭✭✭
    edited November -1
    Try some Russian Wolf ammo and compare. There has been some complaint about Bulgarian 7,62x25 being over pressure but that may not be your case.
    As to case taper; 7,62x54, .348 Win, .33 Win, 8mm Lebel and some other
    mostly older cartridges have very steep case tapers on the order of .015"/" for easy extraction. For that reason cases and chamber need to be dry of oil to minimize unnecessary thrust on the bolt face.
    The Moisin Nagants are very strong rifles.
  • RosieRosie Member Posts: 14,525 ✭✭✭
    edited November -1
    Thanks guys. I will check a little more.
  • vicg1vicg1 Member Posts: 1,033 ✭✭✭✭✭
    edited November -1
    check your firing pin protrusion too...
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