Modern Sporting Rifle Evolution
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His$Her277

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Reply with quote  #1 
Been trying my hand at some 120 SST’s. I almost religiously use 1680 as my go-to for super and sub powder. Problem is, these 120’s are sittin pretty deep (COAL 2.140 - best accuracy) and I’m compressing the poo out of my powder @ 21 grains but still not showing any signs of pressure. I guess perhaps any advice on an alternate powder that’s gonna fit, cycle and not blow up my gas tube? I’m achieving 2100+ FPS out of the 8.5” but the compression of this load is pretty sketchy, like butt hole clenched sketchy when I’m seating.... Thoughts?

As always thank you to the awesome WLV community!!

-Mark

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Gusmeister

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Reply with quote  #2 
I'll take a distant shot at helping you.  I have not used your bullet but have worked with the 115gr Gold Dot.  It is seated to 2.150".  IMO the Gold Dot bullet seems quick to spike pressures as it is a softer plated bullet rather than a harder jacketed bullet.  But to be fair that is only a guess.  But here is what I have.

I loaded 1680 with CCI 41 primers and with 1680 from 21.3gr to 21.9gr.  21.3gr would not lock to bolt back on the last shot (16" AR).  21.9gr blew primers out with nutty pressures.  The brass is hornady.  So my guess is you are at least near max pressure.  

Then I went to SWBO powder.  I went from 21.5gr to 22.6gr.  21.5gr gave an easy 2,400 fps (16" bbl) and 22.6 gr gave 2,478 fps with waaaaay too much pressure.  One of the more subtle pressure signs is primer pockets opening up.  It varies with brass and typically requires multiple loads with the same brass to judge it.  I tried to settle on 21.9 gr of SWBO for 2,401 fps as it was very accurate.  But with only 2 or 3 loads it was opening many of the primer pockets up with my Hornady brass.  Certainly I would pick SWBO over 1680 with this bullet... and it is perfect for 90gr TNT's.  

Finally I went to AA 2200 powder. I knew I'd run out of room for the powder pretty quick so the LOA was increased to 2.170".  The best load ended up being 24.8gr of 2200 for a mv of 2,386 fps.  Primer pockets are good for 5 or more loadings.  It is a very accurate load.  

In retrospect this has all been a "learn as I go project".  Looking back I think 1680 is simply not appropriate for heavy supersonic bullets.  I thought SWBO was too fast for too little velocity and moved on to AA 2200.  But the numbers say SWBO is as good as AA 2200 or a bit better for heavy supersonic bullets.  This assumes accuracy and everything else being equal (they never are).  Personally I would try SWBO before anything else.  This is certainly not an apples to apples comparison but just some general thoughts you may be able to pull out of my experience.
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RangerJoe

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Reply with quote  #3 
Gus - good report; well documented and consistent with my limited testing and other reports.  A2200 has provided stellar accuracy for me in several 5.56/.223-based cats (e.g., WLV, X40) but always on the lower end of the velocity scale and with very full (i.e., compressed) loads.  Although SWBO seems to be faster than A1680, it also seems to have a flatter pressure curve.  So far, I've not been able to obtain the "one-ragged-hole 5-shot groups" with SWBO that I have with A2200 or A1680, but I've not spent as much time with it yet either.
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His$Her277

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Reply with quote  #4 
Gusmeister, thank you for the reply. Like you said I’m sure I’m near max pressure however I’m not yet experiencing pressure signs, I suppose only time will tell. In contrast to your experience I’ve had nothing but excellent results including lock back from 1680 and I suspect it could be due in part to me using an 8.5” barrel. I’ve looked a little into AA 2200 but have yet to use it. I’ve also seen a growing popularity in SWBO, I think I’ll pick some up and see what I can come up with.
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BIGGDAWG

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Reply with quote  #5 
to avoid compression you can step to a faster burn rate but you will then have to worry about pressure spikes. if you go to a slower powder then you will have more of the same issues. one reason i don't like the 120 sst for the wolverine it eats up too much case capacity. much better off running the 110 vmax or the all coppers form mdws for  hunting bullets they were designed for the wolverine.
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Gusmeister

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Reply with quote  #6 
H$H,

I think you're getting 2100 fps with that 120gr bullet in an 8.5" barrel is pretty good. I would not have guessed 1680 could do that but you never know.  Whenever I think I have a solid load I'll take the same 20-30 cases and reload them over and over. It's a good chance to test for accuracy and reliability.  If, after the 5th reload, everything is still tight and the brass has not weakened or massively stretched, then it is not an over pressure load at least in your rifle.  At least at the temps you are testing in.  This test has caught my kidding myself a few times.  

Oh, and for what it's worth, my 16" bbl gives 2,740 fps with a 90gr TNT bullet with safe pressures using SWBO.  Imagine what it could do in your 8.5".
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