As others have stated, the problem is most likely case buckling due to excessive crimp. It is not “case springback” nor does the OP need a set of expensive case gauges. The easiest solution may be to simply run the loaded cases into the FL sizing die a bit to iron out the case buckling enough...
The .303 Savage (virtually identical to the .30-30) used a 190-grain jacketed bullet just fine. I once loaded a 173-grain cast bullet in a .30 WCF using Unique, it shot very well. What will you use the load for? Do you want plinking or hunting loads?
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I’m glad you are happy with your 2400 loads, but the OP wants velocities between 700 and 900 fps. 2400 is not a very good choice for him, although it will go bang.
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2400 is not an appropriate powder for reduced loads, it will have inconsistent ignition and plenty of ash left in the barrel and cylinder. I don’t have experience with Zip, it is far faster than 2400 and might be able to be reduced below book levels. But for the OP’s use fast powders like...
Such a slow, heavily deterent-coated powder would likely not even ignite or burn well in low pressure .45 LC loads. As above, don’t try it. The slowest powder I’ve used successfully in my various .45LCs is AA-1680.
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No wonder the OP got the brass for “a good price”. Nothing really wrong with FC brass in my experience, but I wonder what cartridge the OP is using....a big secret I guess.
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Any load data for revolvers will be safe in your Ruger, worked up to as usual of course. The use of the slower powders like H110 and AA1680 should high velocities in the longer barrel.
One thing to watch out for is bullet construction if you intend to hunt with it. Muzzle velocity will be...
Best to slug both the bore and the cylinder throats. If the latter are smaller than the former, you’ll need soft bullets or leading and iffy accuracy may result.
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I used the Lee 150 FN over 10.0 grains of Unique. I sized them at 0.310” with gas check. It was accurate in my M94 and produced about 1500 fps. I never used it on game, but it approximates the ballistics of the .32-40, which killed a lot of deer when fired from M94s.
IMO, your belief that “there must be something else going on” is unfounded. Looking back over the past two decades we have seen very similar shortages before- high demand, fear of short supply and hoarding were the causes. This time we have to add the millions of new gun owners buying due to...