Modern Sporting Rifle Evolution
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Reply with quote  #1 
I posted these 2 blurbs on 6.5creedmoor forum, but didn’t get replies that helped me very much. There is such great knowledge on this forum that I thought I would post it here. I know cases have different capacity and wall thickness and I’m sure different hardness. As I say in the post, there is a lesson here that I am putting together, I just think it goes a little deeper than I am seeing. Thanks for the help

shooting 140 Nosler RDF over 43.0 gr RL16 and Seller Beloit primers. I thought there would be a difference in the load due to case capacity, but I was surprised how much. Hornady brass had avg fps of 2850 while Norma had fps of 2900 and showed some slight signs of pressure. Both were once fired brass from factory rounds shot in my gun and then shoulder bumped.

I feel like I am on the verge of learning a big lesson and gaining some great experience, BUT I just can't quite put the pieces together. With both Hornady and Norma brass I try to bump the shoulder to 1.5300 although I have a VERY hard time getting this consistent which I do not understand. I am using a Hornady Die and shell holder in a Lee Classic Turret press and measuring with the Hornady 400 headspace gauge. Measuring the shot brass after decapping gives me a shoulder of 1.5305-1.5320.

I went to the range today to rework up the load using the Norma brass, RL 16, Nosler 140 RDF and Seller Belloit LR primers. I started at 41.5 and stepped up in .3gr steps until 42.7 seated at 2.210 ogive which should be a jump to lands of .03. Some of the rounds were a little tight to chamber which tells me that I need to bump shoulder back even more (in fact I will probably FL size next time). I had some swipe marks at every load. There was very little vertical dispersion, but I was only shooting 100 yards. The velocities are what I found really interesting because of the swipe marks. 43.0 was giving me 2898 fps and 42.7 dropped all the was down to 2837.

Please help me make sense of all of this

Today's loads were all 3 or 6 rounds so SD and ES are pretty meaningless.
load shots avg: sd ES increase
41.5 3 2770 4 9
41.8 3 2785 6 12 15
42.1 6 2798 5 15 13
42.4 6 2825 11 30 27
42.7 6 2837 12 27 12

43.0 5 2898 9 20 61

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Reply with quote  #2 
you don't say if you measured the case capacity of both cases?  that is the first thing i would do that will help you figure it out. i would be willing to bet that the norma brass has .5-1 grain less capacity than your other brass.

on the big velocity jump that is where max is. when you have consistent rise of velocity then a large jump that tells you normally you have really raised pressure which normally means you hit max

another sign is the swipes either over gassed if a gas gun or way over on pressure on a bolt gun.



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Reply with quote  #3 
^^^ What he said!  ^^^ 
Sua Sponte | Ranger Joe

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Reply with quote  #4 
Yep Norma brass usually assumed or measured as slightly thicker than competitors (I dont know for Creedmoor) so Hornady may be as much  powder and easier to mold in all aspects but Norma fired into final shape and annealed, forever brass.... well a good many loads...

Without freedom of choice all is left is Tyranny!  [thumb]

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