Sleuth this headspace question for me

[aquinas]

So I have this new gun. Autoloader. Had all sorts of strange behavior regarding case growth (there was none) so I popped a Forster 1.630 Match Headspace gauge in the chamber. New gauge. Forster sells them in .001 increments.

Bolt wouldn't close on gauge. Gun is going back to manufacturer. So here's the can of worms I opened. I should have never done this, but...

I popped the gauge in my hornady headspace gauge. For those of you not familiar with this tool, it clips on a pair of caliper blades. It comes with a bushing that corresponds to the datum line of that particular cartridge. Here's a really lame video on the gauge if you don't know exactly what I'm talking about

http://www.youtube.com/results?search_query=hornady+headspace+gauge&aq=1

By the way, regarding the video...get a digital caliper. That way you can zero it on the gauge and it gives a number that (should) corresponds to headspace.

The gauge should have read 1.630. It didn't. It read 1.622.

Spoke with some industry professionals. They told me what I alreay knew: Hornady gauge is not an exact number. So here's my question: why not?

It's all relative. In other words, it doesn't matter what the hornady gauge says, as long as you keep it consistent. In other words, if the gauge reads 1.622 and you resize and get a reading of 1.618, you've bumped the shoulders back .004, enough for an autoloader and you should be happy. But I'm not.

I want my gauge to read the same as the forster headspace gauge. If i pop a 1.630 gauge in my hornady gauge, I want it to read 1.630.

Bushings are only 6 bucks, so I think I'll order a few more of same caliber and see where those read versus the Forster gauge.

Any thoughts for this really anal retentive handloader?

 

[Lumpy Grits]

Re: Sleuth this headspace question for me

Your brass is NOT "growing" and you think you have a problem

Don't fix what's NOT broken

BTW, how did the stick shoot with factory ammo?
Respectfully,
LG

 

[Fuzzball]

Re: Sleuth this headspace question for me

"Any thoughts for this really anal retentive handloader?"

Yeah -- forget it, you're retaining the wrong stuff.

All reloaders need IS a relitive measurement. Paying for .001" accuracy by SAAMI specs for a cheep but plenty functional Hornady tool would make them ten times more expensive than your Forster headspace plug/gage and for no benefit at all.

IF you want to use that Forster gage as a comparision just do it as a measurement relitive to what the Hornady tool says. But it won't do a thing for the quality of your reloads if the dial reads 1.620" or 1.630".

I have both digital and dial calipers and don't find one much different to use than the other for smallish relitive measurements. I lock the dial face for "0" where ever I want it and the difference is immediately appearant.

Not many folks would send a tight chambered rifle back to the maker for the chamber to be cut sloppier. ??

 

[country888]

Re: Sleuth this headspace question for me

I agree with Fuzzball! If it shoots well and the chamber is tight, dont mess with it. As far as the Hornady gauges, I love them. Wish I had got them a long time ago, but you have to know how to use them! Good luck with your loading

 

[Jerkface11]

Re: Sleuth this headspace question for me

You sent your gun back because the chamber was too tight? Even though it chambered ammo?

 

[aquinas]

Re: Sleuth this headspace question for me

Don't you think a .308 should close on a GO gauge?

I'd feel pretty stupid explaining that one..."I lost my eye because the gun fired out of battery. And I even checked the chamber with a GO gauge and it didn't close on the gauge, so I still fired it anyway."

 

[Jerkface11]

Re: Sleuth this headspace question for me

Unless the gun is broken it won't fire out of battery. The worst you would get is a bolt that won't close. You weren't having that problem were you?

 

[aquinas]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jerkface11</div><div class="ubbcode-body">Unless the gun is broken it won't fire out of battery. The worst you would get is a bolt that won't close. You weren't having that problem were you? </div></div>

It's an autoloader; said so in the first post. Unless I'm a total moron (which is possible), what do you mean, "unless the gun is broke, it won't fire out of battery."

There's no way to tell if it's in battery or out on an AR type gun. The only way you know is if the gun goes KABOOM when you pull the trigger. M14's are a little different. You can glance at the lugs and tell if they are all the way locked. Can't do that with an AR.

I'm guessing you are thinking it's a bolt gun. No. If that were the case, I might just keep it as is. I don't mess around when it comes to gas guns. Life's too short and unlike a crab, I won't grown a new eye or finger.

 

[jacq220]

Re: Sleuth this headspace question for me

even on an AR you can see that its not in battery by looking at the bolt. also, the way the bolt carrier is designed, the hammer will not strike the firing pin unless its all the way into battery, so unless you gun is broke then the gun wouldnt have fired if it were not locked up.

 

[Jerkface11]

Re: Sleuth this headspace question for me

No I didn't think it was a bolt gun. AR's do in fact have bolts. And if they aren't in the closed position the gun won't fire. So as I said if the gun isn't broken it won't fire out of battery. If it will fire out of battery you're screwed no matter what the headspace is.

 

[aquinas]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: lumpy grits</div><div class="ubbcode-body">Your brass is NOT "growing" and you think you have a problem

Don't fix what's NOT broken

BTW, how did the stick shoot with factory ammo?
Respectfully,
LG </div></div>

It's worse than that, amigo. Brass comes out shorter than it goes in. That tells me it's getting whacked hard when it seats. The fact that it won't close on a 1.630 gauge, which is the smallest any autoloader chamber should be cut, says a lot.

You also may be confused with short throating and short chambering. They are not the same. Short throating is fine as long as you know the specs from the smith and load accordingly (and tell the guy you sell the gun to that it's short throated). Short chambers are dangerous. It's an autoloader.

It does not chamber all ammo, either. It chambers LC M80 ball just fine, but LC is sized small.

I don't want to get into all that. That wasn't the reason for this post. I wanted to know why there is .008 between my Hornady gauge and my Forster gauge. I know the Forster gauge is spot on. I confirmed it with a Wilson. I've also been told by other industry professionals the Hornady gauge is relative.

But I measured the bushing on the Hornady and it's spot on .400 which is the correct datum line measurement for that caliber. The Forster gauge has to space on that line also. So why the discrepancy? Everything is squeaky clean.

 

[aquinas]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JACQ</div><div class="ubbcode-body">even on an AR you can see that its not in battery by looking at the bolt. also, the way the bolt carrier is designed, the hammer will not strike the firing pin unless its all the way into battery, so unless you gun is broke then the gun wouldnt have fired if it were not locked up. </div></div>

Ok, I am a moron. How do you see if the bolt's not in battery? You look through the ejection port. But it only needs to be slightly out to cause trouble. What am I looking for to see if it's not locked?

Bear with my ignorance, here. What mechanism causes it not to fire when out of battery? How would you know if it's malfunctioning (before ya get blowed up)?

 

[jacq220]

Re: Sleuth this headspace question for me

The cutout on the bottom of the bolt carrier group that the hammer goes through when fired. if the bolt is not fully closed the hammer will strike the bolt carrier NOT the firing pin. it still may leave a VERY LIGHT mark on the primer, but is in NO way hard enough to set it off.

 

[Jerkface11]

Re: Sleuth this headspace question for me

The bolt on an AR rotates and retracts into the carrier. If it isn't locked into the lugs the firing pin can't reach the primer.

 

[aquinas]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jerkface11</div><div class="ubbcode-body">Unless the gun is broken it won't fire out of battery. The worst you would get is a bolt that won't close. You weren't having that problem were you? </div></div>

Yeah, I was. On some, not all resized cases it would not close. And the shoulders were getting hit about .004 during resizing.

Now, lemme splain something. I popped resized brass in the chamber and tried to close the bolt. Bolt wouldn't close. When I let the carrier zing home on magazine fed round, it closes. And the shoulders also get hammered back as well a couple thousandths! At the very least, it can't be good for accuracy and I think it could be a safety issue. I'm not the sharpest stick in drawer, so I try to be careful, knowing that if an idiot induced error can occur, it will occur to me.

 

[Jerkface11]

Re: Sleuth this headspace question for me

Well if you couldn't get ammo to chamber by all means it needs repaired. Just know you weren't in danger of getting blown up.

 

[blakheaven]

Re: Sleuth this headspace question for me

kinda highjacking the thread aren't we? The Op even restated he wanted to know the discrepancy in the gauges (as would I). I wish I had the answer but don't but will be checking this post in hopes of finding out.

 

[ChrisGarrett]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: himaster</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: lumpy grits</div><div class="ubbcode-body">Your brass is NOT "growing" and you think you have a problem

Don't fix what's NOT broken

BTW, how did the stick shoot with factory ammo?
Respectfully,
LG </div></div>

I don't want to get into all that. That wasn't the reason for this post. I wanted to know why there is .008 between my Hornady gauge and my Forster gauge. I know the Forster gauge is spot on. I confirmed it with a Wilson. I've also been told by other industry professionals the Hornady gauge is relative.

But I measured the bushing on the Hornady and it's spot on .400 which is the correct datum line measurement for that caliber. The Forster gauge has to space on that line also. So why the discrepancy? Everything is squeaky clean.

</div></div>

The datum line isn't a 'always' a consistent spot, halfway up a shoulder, is where you're getting confused. It varies from cartridge to cartridge, or can vary.

If the Forster gage is set to measure at a point different than the .400" Hornady gage, you'll get a variance, is my thought on the matter.

.008" is about three sheets of typical printer paper, so they're not off by much, but it is a head scratcher.

I don't have the drawings of any cartridges in front of me, showing where the datum line is for each, so I can't comment. I remember reading in one of my reloading manuals, that it's 'usually, but not always' at the halfway point of the shoulder.

Chris

 

[doc76251]

Re: Sleuth this headspace question for me

To the OP.

The discrepancy between the Go/No Go gauge and the Hornady measuring tools is simply in WHERE it measures the datum line on the shoulder. No more or less than that. The datum line is a somewhat nebulous measurement used to give some reference point on an angle. You will note that the Hornady tools cover a multitude of cartridges (many w/ different shoulder angles).

FWIW I would bump the shoulders back on the brass so's yer not mashing them, trim the necks as needed and carry on. It is not unusual for an auto gun to mash shoulders even on a properly headspaced rifle so some experimentation w/ empty rounds may net you some answers (or more questions).

Cheers,

Doc

 

[BCP]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: himaster</div><div class="ubbcode-body">
Yeah, I was. On some, not all resized cases it would not close. And the shoulders were getting hit about .004 during resizing.
</div></div>

I had/have the same issue with mine.

I found the main issue was base diameter. To reliably chamber in my rifle they have to be less than or equal to .470. Mil brass by and large after running it through a regular die was still .472-.473. Also the regular dies didn't bump the shoulder nearly enough. Small base dies cured that.

I don't notice much growth with mine either.

1300+ rounds later still works fine.

 

[aquinas]

Re: Sleuth this headspace question for me

To the above last three posters-thank you. Those are good posts. It gives me something to chew on. Now I gotta lay in bed tonight and scratch my head about the datum line discrepancy discussed above. But, hey, I love this stuff.

To the last poster, thank you and I am using a Redding Small Base die and it actually shoots better with a small base die than a regular die. Go figure.

 

[Fuzzball]

Re: Sleuth this headspace question for me

"The datum line is a somewhat nebulous measurement used to give some reference point on an angle."

That datum line comment is sorta true in reloading practice but it's quite specific in SAMMI dimensions. But, all we need is a reference to some consistant point on the straight part of the shoulder so we can compare the length of our sized cases to the same length on our fired cases. Size 'em to match for bolt guns, size 'em a couple-three thou shorter for autoloaders.

 

[aquinas]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: doc76251</div><div class="ubbcode-body">To the OP.

The discrepancy between the Go/No Go gauge and the Hornady measuring tools is simply in WHERE it measures the datum line on the shoulder. No more or less than that. The datum line is a somewhat nebulous measurement used to give some reference point on an angle. You will note that the Hornady tools cover a multitude of cartridges (many w/ different shoulder angles).

FWIW I would bump the shoulders back on the brass so's yer not mashing them, trim the necks as needed and carry on. It is not unusual for an auto gun to mash shoulders even on a properly headspaced rifle so some experimentation w/ empty rounds may net you some answers (or more questions).

Cheers,

Doc </div></div>

Doc, I've read your posts in the past and think you are one of the more intelligent posters here, so I need to pick your brain a little on this one.

Let's call our bottleneck case that headspaces on the shoulder a "cone." It's an apt description.

Somewhere on that cone it measures .400. From that point back to the case head determines headspace. If my Forster gauge is cut to headspace on a chamber at .400 and my Hornady tool is .400 (which it seems to be. I confirmed with two calipers-one of which was a nice Mitutoyo- and the measurement right at the rim of that gauge measure .400)why would there be any discrepancy?

Shoulder angle should not matter: .400 is .400.

Here's what I think, and the only way to confirm this is to order another .400 bushing from Hornady. I think these bushings are purposely undersized to keep idiots like myself from getting blowed up.

Here's the problem with just bumping the shoulders back. It's not uncommon for brass to stick in a chamber upon firing. The bolt twists and jerks the brass, causing more case growth.

Let's say the chamber is 1.631. Sized Brass goes in at 1.627.
Fired, it comes out at 1.624 due to normal case growth and then additional case growth due to extraction. You size it down .004 (normal for a gas gun) and now you have a problem. You only have a realistic .001 clearance on brass going into a gas gun.

The Hornady gauge has (mine, anyway) .008 safety factor built into the gauge. Even in he above scenario, I would still be .007 under minimum headspace.

So it could be Hornady is doing this for a reason.

On the other hand, it presents a problem for guys like me who want to size a true .003-.005 under fired dimensions.

If anyone out there has match headspace gauges (in .001 increments) and a Hornady gauge, test them against one another and tell us what you get.

In the mean time, I'm ordering a few more bushings. Midsouth has them for $5.95. Cheap

 

[doc76251]

Re: Sleuth this headspace question for me

himaster,

I appreciate your accolades but I dunno if I'd qualify as more intelligent than many or any considering today I just had my intelligence lowered by completing my degree and to prove I'm dumber than a box of rocks they told me that they thought so much of my efforts that there was "Some Cum Load" on it

My initial thought is to take the Hornady gauge and measure the head space gauge and see just where .400" hits on it. Since the Hornady gauge is made to measure any of a family of cartridges and as such it is an arbitrary number that will hit the shoulder on a .260, 7mm-08, 308 and .35 Rem (which ain't got very much shoulder at all) IIRC. It essentially gives you a reference number based on the fact that it will chamber in your stick and not much more.

Headspace gauges on the other hand are cut to very exacting standards as are barrel chambers, both of which are subject to rumor and conjecture based on the sharpness of ye' old blade and machine doing the cutting. If you think a chamber is the same from the same cutter you would be poorly informed. Nobody said anything about your headspace gauge being .400" at a certain distance, nor did they tell you what that distance was.

There is another tool from Sinclair's that will let you measure the Exact length of the neck of your chamber, a little plug looking thing. If you have a snug chamber this is a good thing to have because it will keep you from smooshing (precision technical term there) the neck into the leade of the chamber, which is bad for your health and complexion.

Disregarding all of the above..........

You know how big the brass is going in......
You know how big the brass is coming out.....

Make the brass going in .002 - .005" (I would say .001 - .003 but this is a gas gun) smaller than the brass coming out to make sure it goes in but not into the leade and drive on.

This part requires conceptualization:

Does water get bigger or smaller when you freeze it?

Sooooo, at the instant of firing, the brass blows up to fill the available space (bigger), then it immediately gets pulled and turned, once the pressure goes down in the chamber, and gets chucked on the floor where it begins to cool (more bigger).

How much bigger? You got me, its your rifle.

If it is timed incorrectly (fast) it could be HUGE. Slower, not so much.

You have said that you get something to feed (most of the time) and that you have sticky extraction or FTE. Taking measurements from letting the bolt fly will not net you any gains. Either the brass gets smooshed via the inertia or it gets pooshed (more precision technical jargon) via the inertia. To correctly ID your headspace will require a pair of calibrated fingertips to insert the bolt and find out what "empty" feels like and then find out what your headspace gauge feels like. Oh and then a sh!t ton of brass re-sized incrementally down so's you can find out exactly where your headspace is so that you can make more.

I would say that you have two issues. One is good and one not so good.

1. Nice snug chamber (good)
2. Gas system out of time (too fast)[not so good]

I hope the above made sense, it did to me while typing it but I'm celebrating my decrease in intelligence at the moment

Cheers,

Doc

 

[aquinas]

Re: Sleuth this headspace question for me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: doc76251</div><div class="ubbcode-body">himaster,

I appreciate your accolades but I dunno if I'd qualify as more intelligent than many or any considering today I just had my intelligence lowered by completing my degree and to prove I'm dumber than a box of rocks they told me that they thought so much of my efforts that there was "Some Cum Load" on it

Cheers,

Doc </div></div>

Doc, at least it wasn't a MAGNA CUM LOAD!!!

Some interesting things have developed regarding this thread. I'm still sleuthing and it looks promising. Will know answer by weeks end. I'll let ya'all know and the answer may surprise you, but I gotta be sure before spoutin' off.

 

[Innovative]

Re: Sleuth this headspace question for me

Look into the <span style="font-weight: bold">Digital Headspace Gauge</span>. There are no bushings required, it's very simple to operate, and it's 100% repeatable. It's designed for the reloader (not the barrel installer).

There's no need to find the datum line, and it works on ALL different calibers.

 

[aquinas]

Re: Sleuth this headspace question for me

Looked into it years ago. Larry Willis makes it.

Is all it does is tell you the difference between fired and resized cases. It is of little value for those of us who shoot autoloaders. Would work fine on a bolt gun, but so does the hornady, at half the price.

See, an autoloader can jerk the brass out so violently that it adds additional case stretch. If you really want to load correctly for a gas gun, you need to know what actual chamber headspace is and then have a way of comparing fired brass to that headspace. Just knocking the shoulders back the "safe" distance may not always be enough. The Willis gauge does nothing in that regard.

If you get a hornady gauge and a Match headspace gauge to confirm on another, that's all you need.

 

[doc76251]

Re: Sleuth this headspace question for me

OK after re-reading this a couple of times what exactly is it you are trying to accomplish?

It's a gas gun.

You have a small(er) chamber which is preventing you from chambering some ammo.

When you let the bolt fly it chambers it but you are concerned that the chamber is setting the shoulder back.

So I A$$uME that you are attempting to establish exactly the point that you can set your dies up so that you can reload consistently so that each round doesn't get "grown" or "smooshed" when you let the bolt fly or when it operates as designed.

Nice concept but impractical if you intend to shoot this stick in anything other than a controlled environment.

By the very virtue of the fact that it is a "gas gun" you need some tolerance built in to make sure there is enough "slop" to make the thing run with springs and gas pressure. Then there are changes in atmospherics, dirt, carbon etc... (remember gas guns sh!t where they eat)

Headspace gauges are worthless in this endeavor unless you are checking the relative operating range of the chamber against SAMMI specs. Headspace gauges will only tell you if the chamber is too long or too short. As you surmised having incremental gauges will tell you "possibly" where the shoulder actually hits.

In a gas gun this is particularly difficult since there is no consistent method to get the camming force of the bolt the same every time you manually close the bolt. Add to that the vagaries of machining involved in the bolt, pin, carrier, upper, barrel extension and the chamber itself. Then of course there is the compressibility of the grease / oil you use on your bolt and carrier.

Then there is the whole reloading thing with brass spring back and neck tension etc. etc. etc.

So what exactly are you measuring and comparing again?

Cheers,

Doc