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.451 vs .452 velocity difference?


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Last fall I was comfortably making major with rainier 230gr RN bullets (.451). 4 grains of clays gave me 173 pf.

I've been using the exact same load but with 230gr RN xtreme bullets (.452), and chrono'd more like 160 pf. Bumping up the load to 4.1 and even 4.2 grains still left me short of major. Before I go buy some .451 bullets to re-test with, has anyone else ever noticed a significant velocity difference like this?

I'm pretty sure it's the same lot of powder, not sure about the primers tho. Could primers result in a difference of that much.

fwiw, temps and weather were similar.

Edited by motosapiens
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I've noticed velocity difference between plated and lead of about 50fps. I have been using nothing but .452's so I've never really thought much of it. Seems odd unless that last little bit of copper is causing extra friction. Seems silly, though...

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You're having troubles figuring out why you're getting slower velocities when you're not increasing charge but increasing the diameter of the bullet's entire riding surface by .001?

Sounds like you already answered your own question to me but you aren't seeing the forest through the trees. It's not just a tiny line around the "width" (a little bigdawgbeav video joke where he interchanges that with diamiter for 18 minutes) that gains that .001, it's the entire riding surface which can be a pretty significant amount on various .40 bullets.

I suck at formulas so I can't give you one to figure out how much more material resistance you're actually adding but I ASSuME it's quite a bit more than you're imagining.

FWIW in regard of primer's effect on results: when I switched from WSPP to FSPP with the same powder, bullet, & gun I lost enough velocity that I had to increase the charge by .2 grains to keep a 170pf. That was brand change not lot change though.

Edited by dzhitshard
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Thanks for sharing your experience dzhitshard. I'm not sure I'm 'having trouble', I think I'm observing empirical data and formulating a hypothesis, and to possibly save some work, asking if any of my other friendly internet reloader-scientists have observed a similar phenomenon.

fwiw, i got higher chrono readings today, but interestingly the first shot in every chrono string is noticeably lower than the rest. I thought I was being careful with charge weights on the last batch, but I'm going to back up and do another series with n320 and a series with clays, and i'm going to use matching headstamp brass (the same stuff I plan to use for the state match and for nationals) and try again later this week. Historically, my chrono readings have been exactly what I test at on match days and courtesy chrono checks, but it's still possible I could have made a mistake somewhere.

Unfortunately, I couldn't chase down any rainier .451 bullets. That would have made an interesting back-to-back comparison, keeping everything else identical. If anyone wants to mail me 15-20 rainier 230gr roundnose bullets, I will test them under the exact same conditions and report my findings, and buy that person a beer if we ever meet in person.

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  • 2 weeks later...

I believe I have found the problem with low velocity (and erratic velocity). It turned out I was putting almost no crimp at all on my 45 loads. I readjusted my press to put a light crimp (1/2 turn or so down from contact on my fcd) on a handful of rounds, and the chrono was higher and more consistent.

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