Hi All,

Does anyone have experience with using a Lyman 180gn SP mold in a fast twist 308 Winchester (8")
Accuracy has been ok so far with 1700-1800fps loads, but I would like a faster load closer to 2400fps.

25gn of H4895 yields 1700-1800fps, with reasonable groups, 33gns of H4895 had fairly large groups.

There was no leading at 33gns, so
I'm guessing it's something else.

Projectiles are all weighed, and made as identical as I can make them, lead tests 22brn, gas checks are seated separately.

Any suggestions?

I have not shot the combination you speak of, but in my mind, with that fast a twist and that velocity, your bullets might not be quite hard enough. There is a lot written about bullets becoming elastic when driven too hard (especially the nose section...) and the subsequent yawing destroys groups.

Not all designs are equal due to fit. Use of a slower powder will give better results also.

At that fast twist you may need to find a 220 grain bullet.

Jim

Seems like I might have heard something about an rpm threshold???/ Maybe I didn't and thought I did.

quote:

Originally posted by carpetman1:
Seems like I might have heard something about an rpm threshold???/ Maybe I didn't and thought I did.

I seem to remember someone said that they made that up. No substance to it when you think about it.

quote:

Originally posted by carpetman1:
Seems like I might have heard something about an rpm threshold???/ Maybe I didn't and thought I did.

Here's what you thought you heard Ray. Giboon admitted he made it up. Here's his post here on Accurate:

Larry Gibson
one of us

posted 07 September 2012 01:18 Hide Post

quote:
Originally posted by SmokinJ:
Gibby...RPM Threshold book and Author?????



Make it easy on yourself by reading this book first;

Understanding Firearms Ballistics by Robert A. Rinker

When (IF) you can then understand the basics of ballistics (yes the info of how the RPM threshold works is in there) try;

Applied Ballisitcs for Long Range Shooting by Brian Litz

In there you'll also find how the adverse effect of RPM adversely affects the flight of bullets.

If you really think you can assimilate the information then try a graduate study with;

Centrifugal Effects in Rotating Convection: Non-linear Dynamics by J.M Lopez & F. Marques

Now before you come back and say there is no "RPM threshold" mentioned in those let us realize your BS here. In an earlier post you quoted one of my 1st post on the topic from a thread of some years ago on the CBF. In that thread I was discussing the cause and effects of RPMon cast bullets. In a later post I, for lack of better terminology, name it the RPM threshold.

So no you are not going to find the title, RPM threshold because I made that title up for use on the CBF. However, in the above references you will find all the ballistic facts that support the title and "theory", especially in the last reference. I doubt you be able to understand the last reference as it is detailed and technical but the facts are there. Thus before you comeback with "ah ha, there is not RPM threshold mentioned in those", beware we are all aware of your childish attempt at this stupid subtrafuge. You, the fool, fool no one.

I assume, since I have once again satisfied one of your inane questions, you will skip over this and go back to you personal attacks and BS.

Wouldn' you and everyone else be better served to just not mention me, RPM or the RPM threshold again and get on with your "discusson" as such? The rest of the world would prefer you did just that.

Larry Gibson

Posts: 1489 | Location: University Place, WA | Registered: 18 October 2005 Reply With Quote
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I highlighted it in red. Most the dumbasses on CB believed him.

I just reread the post and saw that x-rings is in Australia. Would that make his bullet spin backwards from what it does here in North America? If so how would that effect the rpm?

What no RPM threshold? Next I guess you'll be talking about Santa Claus.