COAL for Zero 200 grain LSWC

First topic message reminder :

Hi,

I've order a box of the 200 grain Zero LSWC to test at 50 yards.  What COAL are you folks using with that bullet?

Thanks,
DF

james r chapman wrote:Hmmm... so many opinions,
so few targets....

Jon and I aren't voicing opinions..Hard won experience, and years of testing.. That reamer is one of many custom ground in search of a better way.. It works and does so better than anything else we have tried.. Two more test reamers are in the works..They cost money...   so most smiths are using SAAMI spec.   .903 was once considered the shortest headspace. We are now running guns in .low  .890s and going shorter with the next gun..I can site many championships, and records..Jon can do the same..  If we aren't, progressing, we are standing still.

noylj wrote:Your COL (OAL) is determined by your barrel (chamber and throat dimensions) and your gun (feed ramp) and your magazine (COL that fits magazine and when the magazine lips release the round for feeding) and the PARTICULAR bullet you are using.
...
Take the barrel out of the gun. Create two inert dummy rounds (no powder or primer) at max COL and remove enough case mouth flare for rounds to chamber (you can achieve this by using a sized case—expand-and-flare it, and remove the flare just until the case "plunks" in the barrel).
...
Drop the inert rounds in and decrease the COL until they chamber completely. This will be your "max" effective COL. I prefer to have the case head flush with the barrel hood. After this, place the inert rounds in the magazine and be sure they fit the magazine and feed and chamber.

All of this makes sense to me, until we get to "decrease the COL until they chamber completely".  What does "chamber completely" mean, exactly?  Is that DEFINED by the case head being flush with the barrel hood, or something else?  In other words, do you mean "keep setting the bullet seating die shorter and re-seating the dummy rounds until the rear of the case is flush with the barrel hood, as shown in the third example of this diagram https://s673.photobucket.com/user/nhblaze/media/1911BULLETGAUGE.jpg.html"?

I'm surprised by this idea of adjusting the bullet seating depth to control the headspace, because I thought that 45 Auto rounds are positioned in the chamber by the case mouth (the front of the case, the part that goes around the bullet and gets crimped).  So I figured that with 45 Auto, the headspace was controlled by the exact length of your case and the exact depth to which the chamber is cut, and so there wasn't anything you could do to adjust headspace when reloading (other than buying longer or shorter cases, or getting a new barrel).  So, I figured this procedure of seating the dummy round's bullet deeper and deeper was to get to a point where seating it deeper does not allow it to go in further, with the intention of making sure that we are seating the round in the chamber by the case mouth (i.e. the bullet is out of the way, and not affecting how the round seats in the chamber, or the headspace).  In other words, I thought the point of this procedure was to seat the bullet as far out as possible WITHOUT affecting the headspace.

Or is the idea that, yeah, 45 Auto rounds SHOULD be positioned in the chamber by the case mouth, but lots of barrels have chambers that are too long, so we cheat by seating the bullet out too far, so the round is positioned in the chamber by the bullet, allowing us to minimize the headspace?

Any clarification would be appreciated.

Dave

P.S. I must admit that I'm starting to get fuzzy on what people mean when they say "headspace" sometimes.  I thought headspace was the distance between the case head (which is the bottom/back of the case, where the primer goes) and the breech face (which is the part of the slide that sits right behind case head when the round is chambered).  No?

Yeah, in a perfect world, our perfect 1911 would have a perfect barrel with a perfect chamber reamed by the perfect reamer used by Jerry Keefer. But, Jerry's retired so most of the masses make due with "close enough" barrels with factory headspace and too short brass. The solutions usually are to seat the bullet out a bit to adjust for the variance. .01-.02 is what we're generally talking.

BDAS,

Correctly done, the round headspaces on the mouth of the case. As noted, previously, not everything is done correct, so the methodologies described are used by some to make up for the other variations.

Look at the chamber that Jerry shows pictures above, and compare it to what you have in your pistol.  His chamber is not the SAAMI specification industry standard, it is a custom chamber for maximizing precision.  In Jerrys' photos, you will see the step where the case mouth will stop against. He controls that depth to a minimum and the other features that I am about to describe are cut that way because of the reamer that he has.  Looking at the chamber in front of the first step you will see a straight section, "freebore" if you will. You can tell that it is cut at a larger diameter than the bore diameter by the next little tapered step going into the rifling that also includes/forms the leade of the rifling.  Jerry has previously mentioned that he has the freebore to help guarantee that his tight headspacing works on the case mouth as opposed to the long bullet methodology for making up for poor chamber/ammo dimensions. The freebore and shallower leade angle allow the bullet to start moving without as much force before entering the rifling, which also has the benefit of reducing initial pressures/accelerations and consequently, recoil.  Jerry has reduced the leade angle to also minimize bullet deformation, and make that portion of the change less dramatic.

SAAMI spec chambers, or along those lines are what are put in almost all factory barrels. Saami specifications for chambers and loaded ammo dimensions are sloppy, and are there to let mass manufacturers combine ammunition and guns be freely interchanged. Most standard reamers sold by the various reamer companies are to SAAMI Specs. A .308 Winchester reamer that I once measured was .312 on the freebore section meant for a .308 diameter bullet, and would allow one to let the brass length grow over .030" beyond what is listed as maximum case length. I have over 5 different .308 reamers from when everyone shot that in hipower competition. I also have more than that in various .22LR reamers....this is part of what you get and pay for when you use a (serious/technical/precision/specialized/knowledgeable/been around awhile) gunsmith.

-Ron

Some wise sage on here (I forget who...) said "Measure from base to shoulder of the bullet .925".  That's what I use and it shoots very fine indeed.  I have an STI Trojan.

What are using to measure? An optical comparator?
A calibrated gaging device?

james r chapman wrote:What are using to measure? An optical comparator?
A calibrated gaging device?

Back to the first response. A fingernail

OldMaster66 wrote:

james r chapman wrote:What are using to measure? An optical comparator?
A calibrated gaging device?

Back to the first response. A fingernail

I'm inclined to agree that's good enough for the general equipment we have available.

That's what I was told a couple years ago just use your fingernail for a seating depth gauge on lead SWC's .

It's important to remember that not just any fingernail will do.



I may have too much free time today.

You failed to include the temp, humidity, & barometric pressure during the calibration process.  Now go have a beer and ponder your failings.

Rob Kovach wrote:^^^SOOOO NICE^^^^^

Thanks Rob..
I am presently waiting on a reamer with approx. 3 times that amount of free bore, and  only " minutes " of leade angle.. Can't wait to try it..

But, but, but, what about your case length variable? 

An uncalibrated case length plus a calibrated fingernail is what?

Jack H wrote:But, but, but, what about your case length variable? 

An uncalibrated case length plus a calibrated fingernail is what?

Wait, I'll ask my wife....