Wednesday, June 29, 2011

Update: The Best Way to Tumble Lube the Best Cast Bullets

Lube testing with 357 magnums has produced some fascinating results. This is an update on the prior lube posts.

For target loads with fast powder:  The top 2 tumble lube variations of lube are JPW/Xlox mixed 3/1 and also pure JPW.  They are so close in performance and accuracy that they are really equivalent.  The JPW/Xlox (or LLA, it doesn't matter) gets the very slight nod because the best grouping I've ever shot used it.  Also, after shooting many groups and taking all the measurements, the results are, on average, within .1 inch of each other.  That's from 25 yards off a rest.  This shooter isn't good enough to call that conclusive.

This is with the Lee TL358-158-SWC, lapped to drop 166-7 grain bullets.  The most accurate design for a light-fast-powder load in a 357 magnum. (another test result is coming...)

Added later:  I'm using up the Xlox/Alox that I have, using it to stretch my JPW.  Once it's gone, I'll be using pure JPW again.  I just hate to waste anything.

  • Note:  Tumble lubing standard groove bullets, for the light loads, may work well.  However I haven't spent much time testing this combination.  There is no leading, but accuracy may drop off.  It would be slight, less than 1/4 inch at 25 yards.  But that's speculation, since I haven't found a better more accurate bullet.  I don't plan to test this more.  Shooting less accurate bullet designs is not high on the list of ways to spend my time.

Heavy magnum loads using slow powder are most accurate with a heavy bullet.  Using a 358-429 lapped mould, that drops 178 grain bullets has proven to be the most accurate.  Using Darr lube has produced the best results with this combination.  Other conventional lubes may work too, there are too many to test them all.

NOTE: Tumble lube on a large-groove bullet, with a magnum load, is proven to loose accuracy.  This is not speculation.  Up to 1/2 inch at 25 yards.  Not that the TL fails to lube as there is no leading.  I suspect the huge empty lube groove doesn't support the bullet base adequately.  Causing the accuracy to drop off.  That is with very soft bullets, so it may not apply to shooting WW or harder.  Since the harder bullets have also proven to be less accurate, I won't spend time doing additional tests with them either.

Some general comments:  That doesn't mean tumble lubing a with a small conventional-lube-groove will be less accurate.  But it might, at longer distance.  If you measure 25 yard groups with a caliper, and care about fractions of an inch in group size, it's worth testing.

If you shoot at 15 yards and do an eyeball, "looks good to me", you probably can't tell the difference so it doesn't matter.

The results in your gun, based upon lube groove design, lube, alloy, and charge should be similar to mine.  Or said another way, a huge lube groove (like a Keith) with a soft bullet and TL may not be the most accurate combination, depending on the charge.  So try it out, at some distance.  When a tumble lube design proves to be extremely accurate, try some JPW/Xlox 3/1, or pure JPW.

I hope this is useful information that helps you shoot tighter groups with your 357 Magnum.

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