264wm Posted August 30, 2011 Report Share Posted August 30, 2011 I will try and explain this best I can. Load 1. 139gn Lapua,68gn retumbo, fed210, 3187 avg fps, ES of 36fps Load 2. 130gn Accubond,68gn retumbo,fed210, 3100 avg fps,ES of 26fps The accubond's wouldn't shoot at all, or should I say that they woudln't in my rifle, the Lapua's have always been consistent, and when I say consistent I mean sub 1/2. I pulled several cases with the accubond's and loaded Lapua bullets,when I put them through the chrony they were consistently 100fps slower.I would presume that neck tension had been altered with me pulling them, and in turn had affected the overall performance.I can only presume that retumbo works best under pressure. What I can't get my head around is that the heavier bullet is faster with the same load! Anyone any theories? regards Griff Link to comment Share on other sites More sharing options...
1967spud Posted August 30, 2011 Report Share Posted August 30, 2011 Wl come to the forum . What calibre? Link to comment Share on other sites More sharing options...
264wm Posted August 30, 2011 Author Report Share Posted August 30, 2011 Wl come to the forum . What calibre? Hi Spud. 264 winmag regards Griff Link to comment Share on other sites More sharing options...
Snowz Posted August 30, 2011 Report Share Posted August 30, 2011 Wonder how you chose your user name lol Welcome there's plenty of knowledgable shooters on here that will help you out Atb Richard Link to comment Share on other sites More sharing options...
264wm Posted August 30, 2011 Author Report Share Posted August 30, 2011 Wonder how you chose your user name lol Welcome there's plenty of knowledgable shooters on here that will help you out Atb Richard Thanks Richard, username, it just came to me in a flash of inspiration. regards Griff Link to comment Share on other sites More sharing options...
1967spud Posted August 30, 2011 Report Share Posted August 30, 2011 i did wonder but didnt want to presumputous Link to comment Share on other sites More sharing options...
1967spud Posted August 30, 2011 Report Share Posted August 30, 2011 were both load shot in the same conditions or was one shot on a hotter day and the other on a colder day if so this would result in greater pressures resulting ion more fps if not ..im stumped as well Link to comment Share on other sites More sharing options...
pat Posted August 30, 2011 Report Share Posted August 30, 2011 Griff, you don't mention how long the barrel is. Retumbo is a slow powder and your choice of primer is mild, so you aren't exactly giving it a kick up the backside to get it going. It is entirely feasible that the end of combustion is after the bullet exits the muzzle and therefore the heavier bullet is showing a greater area under the pressure curve / ballistic efficiency because the powder can do more work before the bullet disappears off down range. Peak pressure would be higher with the greater mass. Cheers, Pat. Link to comment Share on other sites More sharing options...
264wm Posted August 30, 2011 Author Report Share Posted August 30, 2011 Both shot this evening about 30 mins apart Barrell length 25.5", according to QL it is a 100% burn but only showing 3000fps. regards G Link to comment Share on other sites More sharing options...
6.5shooter Posted August 31, 2011 Report Share Posted August 31, 2011 Scenars are known for being marginally thinner in diameter. This could be why as they dont create the same resistance in the barrel to keep the pressure up. Garry Link to comment Share on other sites More sharing options...
6.5shooter Posted August 31, 2011 Report Share Posted August 31, 2011 Scenars are known for being marginally thinner in diameter. This could be why as they dont create the same resistance in the barrel to keep the pressure up. Garry Link to comment Share on other sites More sharing options...
Elwood Posted August 31, 2011 Report Share Posted August 31, 2011 How far are the two projectiles sitting in the case? if the Lapua is taking up more room this will increase your pressure and should in theory increase velocity. Link to comment Share on other sites More sharing options...
6.5shooter Posted August 31, 2011 Report Share Posted August 31, 2011 Scenars are known for being marginally thinner in diameter. This could be why as they dont create the same resistance in the barrel to keep the pressure up. Garry Sorry I read youre post wrong this mornin, was still half sleeping. Garry Link to comment Share on other sites More sharing options...
264wm Posted September 1, 2011 Author Report Share Posted September 1, 2011 OAL is 3.322,seated.502 thou inside case. Scenar is only 39 thou longer than the accubond. What I am struggling to come to terms with is that a bullet that is nearly 10gn heavier with the same powder charge is 100fps faster. Also when I pulled the accubonds and replaced them with Scenars they were 100fps slower, I can ony put that down to the neck tension would change if as explained earlier that the scenars are slightly thinner. rewgards Griff Link to comment Share on other sites More sharing options...
Chris-NZ Posted September 1, 2011 Report Share Posted September 1, 2011 What is the relative bearing surface of the two projectiles? Can you post a pic of them standing side by side (unseated)? Chris-NZ Link to comment Share on other sites More sharing options...
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