JimGnitecki
Member
- Joined
- Mar 28, 2010
- Messages
- 1,258
I did just a tiny bit more experimentation tonight which got me some findings that I want to add to the body of knowledge building here.
I have some Federal 147g JHP FACTORY ammo, with both unfired cartridges and cases that were fired in my SIG P210A Target, I took a close look at both.
The tapered crimp diameter of the unfired factory cartridges at the casemouth is very consistently 0.376". That's .002" larger diameter than my .374" taper crimped loads.
BUT, in measuring the wall thickness of the Federal cases, I see that they are pretty consistently .011", which is almost exactly .001" thicker than the .0101" wall thickness of my Hornady cases. .374" + (2 x .0011") = .3762". So, Federal is crimping those factory cartridges to pretty much exactly the same .001" crimp as I am. This makes me think that maybe I am on the right track with my crimping.
By the way, let's make sure you understand what this means: Since the bullet diameter pof .355 plus TWICE the Federal wall thickness (because the case walls SURROUND the bullet) totals to .355" +(2x.011") = .377". But the taper crimped OD is .376", which means Federal is applying .001" crimp across the total diameter, which means .0005" actual crimp on each arc of the wall. NOT .001" crimp on any arc of the wall. So, this is indeed a pretty mild crimp.
Someone pointed out that the 9mm case tapersto a smaller ID as you travel down the case wall, but when taking the ID measurements on both the Federal cases and my cases, I always make sure that I have the caliper jaws in deep enough to go to the depth that the bullet is seated at. So, no, the actual ID is NOT smaller than what I am measuring.
Next, I tried dropping first several of my completed unfired cartridges down the WRONG end of a 9mm go-nogo cartridge case gage. Interestingly, the cartridges drop in until the CASE, not the ogive of the bullet, catches on the case gage. Same with the Federal cartridges. Tis makes sense when you think about it, because the end of the case gage has to be able to handle bullet ODs on the hIGH end of the SAAMI standard, not just average or smaller OD bullets.
But this raises an important point: If you try to literally measure from base to ogive on any tool that uses a gage opening capable of accepting any in-spec 9mm bullet diameter, your efforts will be futile, becsause just as in my testing, the tested cartridges will drop in until their CASES hit the gage.
So, this implies, if I am correct, that the only practical way to measure consistency of bullet seating, using ANY tool you make or buy, is to measure from the base to some consistent diameter point on the ogive that is slightly smaller than the maximum diameter of the bullet, and just make sure that this measurement is consistent, or darn close to being consistent, for all the cartridges you test.
I emailed Hornady though to ask what the slope of the HAP coned ogive is. If they give me that, I can then calculate what the actual true base-to-ogive measurement would be. That, coupled with an accurate plunk and rotate test, provides guidance for calculating the "jump" in whatever firearm you load the cartridges into.
Jim G
Hornady replied. They said that the ogive angle on the 115g .355" HAP is 15 degrees.
Jim G