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Headspace and OGIVE ???

scsbronco

scsbronco

Sergeant
Full Member
Minuteman
Jun 15, 2010
367
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Michigan
I picked up a set full set of gauges and comparers. So, I set out to get measurement of the lands on all of my rifles. Ill use my XCR LRT 300wm as the example.


Hornady Brass gauge headspace 2.255"

Once fired brass headspace 2.271"


208gr Amax Ogive to the lands in the Hornady brass gauge 2.906"

208gr Amax oal 3.637"

All measurements were taken from the base of the brass.




So, my question is ...... Do I add the difference of the two headspaces to the bullet ogive for the Once fired brass?



Thanks in adavanced
 
Re: Headspace and OGIVE ???

What're you trying to figure out? Headspace has nothing to do with seating depth.
 
Re: Headspace and OGIVE ???

The headspace on the Special Hornady Brass gauge is 2.255" (bullet seating depth brass)

My Brass is 2.271"


If they are both measured from rim to headspace they are different.



Wouldn't that mean the bullet would be .026" set back from the lands in the once fired brass?
 
Re: Headspace and OGIVE ???

You're missing something here. Headspace doesn't have anything to do with distance to lands. Headspace is how much room there is between the case shoulder and the shoulder of the bore. This is determined by how deeply you set the shoulder back with your FL die. The distance to lands is determined by how deeply you seat the bullet into the case neck (how far the bullet will travel once fired before the bullet's ogive hits the lands).
 
Re: Headspace and OGIVE ???

Gene poole

So, you are saying that if the bullet touches the lands at 2.906" in the gauge it will in my brass?

*It doesn't make sense to me. If the cases are two different lengths the bullet will be different spacing off the lands.

*If it spaces off the case shoulder in the barrel and I have two different length cases from the shoulder they'll be different.



I think I figured it out
 
Re: Headspace and OGIVE ???

The bullet seating die doesn't care about case length. It seats the bullet based on the position of the shell holder which indexes off the base of the case. Case length never enters the equation.
 
Re: Headspace and OGIVE ???

I get what your saying scsbronco, that's why I tap my own case after firing it. I might be wrong but using one of hornadys threaded cases seems to defeat the purpose
 
Re: Headspace and OGIVE ???

What size tap do you use and do you need to size the neck any to get the pullet to stay in?

Alternately sinclair makes a good tool for this but its a two step operation.
 
Re: Headspace and OGIVE ???

5/16-36 uns
Don't size the neck, you want to feel the bump at the touch.
 
Re: Headspace and OGIVE ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: scsbronco</div><div class="ubbcode-body"> Ill use my XCR LRT 300wm as the example </div></div>

Bad choice for what you are asking as belted Magnums headspace off the belt not the shoulder.

300wm trim length is 2.610" in every reference I have read.

Seating depth should be tailored to each rifle using the appropriate measuring device but what you are using the information for is to determine the set back of the ogive to the lands. This should also be tailored to the specific chamber as some like to touch and others like a bit of of jump FWIW mine likes .01 off the lands.

So using the numbers you provided;

Hornady Brass gauge headspace 2.255"- Dosnt matter as this is simply a tool to measure the seating depth. Obviosly you wont be loading this case to shoot.

Once fired brass headspace 2.271"- This sounds like the case length not the headspace. So trim to 2.610 after neck sizing


208gr Amax Ogive to the lands in the Hornady brass gauge 2.906"- So take this number and use it as your seating depth but if it were me I would bump it back .01

208gr Amax oal 3.637"- As long as your seating depth is correct and it fits your magazine COAL dosnt matter. I'm loading 230 Berger OTM's and those bad boys are sitting in the barrel fairly deep but again my seating depth from the ogive is all that matters and since I'm using a DBM made for 338LM the longer rounds have no issues feeding.
 
Re: Headspace and OGIVE ???

To be concise you WOULD factor in the difference between between the cases you are using and the hornady case. The hornady case is really allowing you to find the distance from your shoulder datum to the bullet ogive. Taking the hornady modified base to ogive distance at face value, you would actually end up with more jump than what you think you have, this errs on the side of caution and hornady admits this (about .016" more jump in your case it sounds like). The goal is to have all dimensions of your reloaded cartidges the same, this includes case length, base to shoulder, shoulder to ogive and base to ogive.

The easiest and probably the best practice would be making your own modified case like mentioned above that matches your fired case dimensions. This accounts for the base-shoulder length difference between your cases and the hornandy case.

As for the belt, I would pretend it isn't there. Just focus on the cartridge base to shoulder "headspace". To think that the shoulder doesn't stretch to fit the chamber (or that shoulder position doesn't matter because it headspaces on the belt) is false. When FL sizing brass just push the shoulder back .001" or enough so that the bolt closes freely (or with little resistance). For this the tapered 25 degree sinclair bump gages are better than the hornady headspace gage in my opinion. FL sizing is needed in belted mags to size the body and keep the shoulder at a consistant distance from the cartridge base.

My $0.02.
 
Re: Headspace and OGIVE ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: QuiggyB</div><div class="ubbcode-body">bump, trying to verify this is the correct tap if anyone knows

http://drillsandcutters.com/qualtechdwtst516-32p516-32hssplugtapspecial.aspx </div></div>
Sorry about the delay QuiggyB, I couldn't really say, I don't think that's it. I took the hornady tool to an engineer with some cases and asked him to thread them. He gave me the tap and mentioned it was pretty obscure so he had to make it himself. Im in New Zealand, so it may not be so uncommon in your part of the world.
 
Re: Headspace and OGIVE ???

For the tap I bought one of these from Enco.com (below). The description for the other one looked right but the picture looks like a pipe tap or something bigger.

891-4932
5/16-36 HSS HAND PLUG TAP
$13.64

It's an oddball thread so you won't find it at a hardware store.
 
Re: Headspace and OGIVE ???

would a taper tap be easier for hand tapping a couple of cases?
drill size needed and whats the best way to hold the brass?
 
Re: Headspace and OGIVE ???

I couldn't find a taper tap in this size but yes it would be easier.

I believe somewhere between 9/32" and 19/64". Use a size "L" drill (or 7.3mm) or hog out with a 9/32" bit. Mine threaded on a bit loosely but it snugged up solid to the gage's thread shoulder.

Drilling out the primer pocket can get ugly fast. I wrapped the case with tape and tightened it in a vise as lightly as possible but it probably wasn't the best way. You may want to practice on an older peice of brass.

You can also send Hornady your brass and they will drill/tap it for you for a small fee. It will probably look prettier that way. I figured if I had the tap and drill I could convert any case I wanted to in the future, so I went that route.
 
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