Push test, OAL Peculiarities?

[IDescribe]

Well, back home after 9 weeks offshore, and I did the push test this morning with my 75 Shadow Line and 7 different bullet types.    I don't know if what I'm getting is peculiar or not.  The BBI's and Xtreme plated came in about where I expected, but I got some differences from what I expected with Berry's bullets, so I thought I should ask.

I expected the Berry's Round Nose bullets of various weights to push test somewhere in the range of 1.135-1.15 range because once the .015 is subtracted for a safe jump gap, that would put the OAL in the 1.12-1.135 range, which is where I see a lot of RN rounds for CZ getting loaded.  Mine pushed considerably longer, however, with RN's.  And it seems like FP's are commonly getting loaded in the 1.06-1.08 range, so I expected something in the 1.08-1.0 range.  My FP's pushed shorter.

These are the measurements they pushed to, on average:

Berry's 115RN ---- 1.180
Berry's 124HBRN - 1.209
Berry's 147RN ---- 1.198

Berry's 124HBFP -  1.067

Each bullet type got push-tested and measured 9, 12, or 15 times, depending on how consistent the results were, with different bullets and different brass.  When the Berry's RN's were coming out that long, I thought "Great, all the legroom I could want, AND I'll get above average room with the FP's."  WRONG.  Cutting 0.015 off that FP measurement is going to yield 1.05 (and I probably need to drop back more than 0.015, more on that later), which seems extremely short to me.  I know it's within Saami specs, but it still seems awfully short.

My surprise, and the reason I'm questioning things is that I don't get why the RN's would come out higher than average, and the FP's lower.  Both longer or both shorter, sure, that makes sense, but not one type longer and one shorter.  Or is that my problem: I'm wrong about my RN's being higher than average.  Or wrong about my FP's being lower than average.  My expectations were based off my memory of what others had reported, which I realize is pretty imprecise/unreliable, so feel free to let me have it on that point.

Also, as far as dropping off the recommended .015 for a safe jump gap, I may need to make that .025.   With several individual bullets, if I dropped off .015, they would spin freely about 320 degrees, then slow down (meet a little resistance) over a short stretch.   I assume that's the result of the lands extending out a tiny bit more in a small range AND bullets not being perfectly concentric.  If I drop back .02 off the pushed-to measurement, I spin freely all the way around.  I figure making that .025 would be playing it safe enough, but maybe not -- .03?  I've got plenty of room with the RN's, but that would cut my FP OAL to 1.037, which I really don't see myself doing.  That's far shorter than what I'm comfortable with.

Any thoughts?

[Wobbly]

Rest easy, friend, your numbers are highly consistent with mine.

The numbers are different because the full diameter of the rifling strikes the RN on the ogive, while the FP strikes on the periphery at the root of the rifling. Two different interference types; two different lengths. See the cartoon below.



We load Berry RN in the 1.140" OAL range not because of the push test results, but rather to support the bullet better inside the case. We're not trying to get close to the rifling, we're trying to make sure we always steer clear of the rifling.

We do the "push test" as the first step in loading a new bullet because you simply never know how the bullet will react to the CZ chamber. Take a look at your own numbers for the 115gr RN and the 124gr HBRN. To the eye those 2 nose shapes look exactly the same, and yet we get 2 vastly different numbers. I rest my case.


 

[IDescribe]

We load Berry RN in the 1.140" OAL range not because of the push test results, but rather to support the bullet better inside the case. We're not trying to get close to the rifling, we're trying to make sure we always steer clear of the rifling.

That clears up my main question perfectly.

In regard to my particular issue where I need to back off .02 to get the bullet to spin freely, is .020 enough?  Or would .025 or .030 be prudent?  From what you would recommend with the RN's, that won't come into play, but with some of the other bullets that are measuring out at 1.113 or shorter, I won't want to go shorter than necessary.  AND what about those FP's?  If I knock off .020 and load those at 1.047, isn't that REALLY short?  Seems too short to me.

Thanks for your response, by the way.  Helped a bunch.

EDITED for type-o

[1SOW]

re spinning freely:  I've run into that too.  Sometimes the bullet isn't seated "centered in the case" with the push test.  This can influence the spin part of the test.
I would load up some no primer and no powder dummy cartidges "with a proper crimp" and redo the spin test.

-.015" from contact should supply ample clearance and margin for error.

If not, it could just be your chamber is tighter.  With three 75s mine are pretty consistent.  One does test maybe a thousandth+  longer than the other two.

Added:  I also 'suspect'  a blown open unsized case with no taper crimp can influence the spin test.  Think about the jams that occur when reloaders don't taper crimp properly to within SAAMI specs.

I'm also stubborn.  I load to less than the  .015" margin for error with the FN/ HP/ conical nose  bullets that require oals under 1.105".  I offset this shorter margin for error by measuring EVERY oal.  Yeah, I know; but I'm fully retired and enjoy reloading MY AMMO for MY PISTOLS.
I strongly suggest following Wobbly's advice unless you are also anal and have the extra time to do otherwise. 

[Riptide439]

re spinning freely:  I've run into that too.  Sometimes the bullet isn't seated "centered in the case" with the push test.  This can influence the spin part of the test.
I would load up some no primer and no powder dummy cartidges "with a proper crimp" and redo the spin test.

-.015" from contact should supply ample clearance and margin for error.

If not, it could just be your chamber is tighter.  With three 75s mine are pretty consistent.  One does test maybe a thousandth+  longer than the other two.

+1 on 1SOW's dumy cartridge.  Every new bullet test should include this (learned that from Wobbly & 1SOW - Thanks guys)

[IDescribe]

I would load up some no primer and no powder dummy cartidges "with a proper crimp" and redo the spin test.

Thanks, will do.

[Wobbly]

In regard to my particular issue where I need to back off .02 to get the bullet to spin freely, is .020 enough?  Or would .025 or .030 be prudent?  From what you would recommend with the RN's, that won't come into play, but with some of the other bullets that are measuring out at 1.013 or shorter, I won't want to go shorter than necessary.  AND what about those FP's?  If I knock off .020 and load those at 1.047, isn't that REALLY short?  Seems too short to me.

People who are starting out with reloading want to know hard numbers they can measure and use right away. So I made up the .015" number as the setback distance. I believe this number is large enough to cover all the "sins" of the beginning reloader. You'll remember that novice reloaders have multiple issues holding their OAL to a minimal number. It does no good to tell anyone to back off .005" if their finished ammo OAL varies wildly, and ends up .008" longer than the OAL they were aiming at. They'd be right back into the rifling by .003" if that were the case. Follow?

There are other ways to screw up too. (I've managed to find most of them.  ) Some are dependent upon the bullet you use, some are dependent upon the dies. Until novice reloaders get enough "time in the saddle" to sort all these things out in their head, a large number like .015" is very safe and extremely helpful. I use it with bullet brands that are new to me. It's helpful.

However, there comes a point when you've settled on one bullet supplier, you've graduated to a "feature loaded" die set, and your reloading process is well defined and refined. At that point in time, you can throw the .015" setback distance out the window any time you wish. In other words, you've matured and you no longer need crutches to walk. The proverbial 1Corinthians 13:11 moment.

I don't think going from .015" to .010" is going to give you any abrupt change in chamber pressure, but it could be used to improve feeding or other helpful things. So whenever you're ready....