6mm arc, headspace gauge issues, oversized chamber?

[Shadow9mm]

So I am prepping to start reloading for 6mm arc, hopefully this week if all goes well.

I just got in my LE wilson headspace gauges today and decided to check the headspace on my bass. However the brass did not want to go into the gauge. I ended up putting the brass in, and dropping it, brass down, onto my table a few times which caused the brass to seat. had to use and allen wrench down the inside with a few taps to get it back out.

as near as I can tell its binding just below the shoulder.

I measured 7 cases and as best I can tell the fired bras is 0.017 over max headspace length.

Factory brass drops in the die and it fits like a glove. almost no wiggle room. In my past experience the gauges were a bit loose on the body to allow for once fired brass to drop in easily. but with the way factory ammo fits i am almost wondering if the die is just a bit on the snug side.

Or based on the headspace measurements, it may be that my chamber is a bit overly generout.

and before you ask, I did buy and use headspace gauges while assembling, it closed on the go, and did not close on the no-go.

Also begs the question. If it want to preserve maximum brass life, should I just bump the shoulder a few thousandths? or should I take it to max headspace per the gauge to ensure reliable feeding in my semi auto platform? Iv honestly never really though about how much brass grows. is 0.17 a lot or a little relatively speaking? I know if you bumping the shoulder 0.003 I would assume that's the grown vs neck sizing fire formed brass....

I did contact LE wilson. Waiting to hear back. Just figured I'd pick your brains while I was waiting.

 

[Unclenick]

The headspace measurement won't tell you anything about how wide the chamber is. If someone cut it with the reamer directly chucked in a lathe tailstock chuck or collet without using a floating reamer holder or first aligning the lathe, a chamber that is the right length but growing too fat as you progress from the shoulder to the back end is exactly what you get. My dad bought an M1 Garand that was chambered for 308 Win by a local guy who made exactly that mistake, and none of his fired cases would drop into a gauge, nor would they fit into an RCBS Precision mic base.

Looking at the SAAMI drawing, a dead minimum diameter cartridge case (-0.008" below the dimension given, which is a maximum dimension for cartridges) and a maximum diameter chamber (+0.002" above the dimension given, which is a minimum dimension for chambers), would be 0.0116" of growth in the cartridge case diameter. At 0.017" growth, you are 0.0054" over that maximum if your measurement is correct, indicating the oversize chamber diameter.

At this point, I would look at making a chamber cast and comparing it to the SAAMI drawing I linked to. Remember, the diameters for the chamber are minimums with a +0.002" tolerance. If you are exceeding that, the chamber was incorrectly cut.

 

[Shadow9mm]

The headspace measurement won't tell you anything about how wide the chamber is. If someone cut it with the reamer directly chucked in a lathe tailstock chuck or collet without using a floating reamer holder or first aligning the lathe, a chamber that is the right length but growing too fat as you progress from the shoulder to the back end is exactly what you get. My dad bought an M1 Garand that was chambered for 308 Win by a local guy who made exactly that mistake, and none of his fired cases would drop into a gauge, nor would they fit into an RCBS Precision mic base.

Looking at the SAAMI drawing, a dead minimum diameter cartridge case (-0.008" below the dimension given, which is a maximum dimension for cartridges) and a maximum diameter chamber (+0.002" above the dimension given, which is a minimum dimension for chambers), would be 0.0116" of growth in the cartridge case diameter. At 0.017" growth, you are 0.0054" over that maximum if your measurement is correct, indicating the oversize chamber diameter.

At this point, I would look at making a chamber cast and comparing it to the SAAMI drawing I linked to. Remember, the diameters for the chamber are minimums with a +0.002" tolerance. If you are exceeding that, the chamber was incorrectly cut.

LE wilson states their gauges are not made with chamber reamers, "but with special reamers giving extra clearance both in front of and behind the shoulder so as to eliminate any posibility of contact except at the gauging point" However my cases dont fit without force, which has me a touch concerned. I have their gaugeds for 223 and 308 and have never had this issue before.

Ok this is how I understand the headspace portion of the gaugegauge. the instructions state "top of gauge = min/max headspace 0.005" groove. My understanding was bottom of the notch was minimum headspace and the top of the notch was maximum. I measured from the bottom of the groove and got 0.022. accounting for the 0.005 depth that put me 0.017 over max.

Lastly, per the instruction, they recommend a shoulder bump of 0.002 for bolt guns and 0.004 for semi auto guns from where they gauged out at.

Thanks for the help. If i am understanding the sammi specs headspace is 1.190 +/- 0.007.

so min 1.183
max 1.197

is that correct?

meaning I am in theory at 1.214 if I am in fact 0.017 over max?

saami drawings and blueprints were never my strong suit.

 

[Unclenick]

No. The SAAMI tolerances are unilateral, meaning they only apply in one direction. They are either minus or they are plus. This is an engineering practice used for what are called critical dimensions, in which the numbers given are not-to-exceed maximums if the tolerance is minus and not-to-go-below minimums if the tolerance is plus. In this case, the designer feels it is critical that the head-to-shoulder datum dimension never exceed the minimum chamber's headspace, so the number given in the drawing is the maximum, and then a minus tolerance shows it can be smaller than that maximum but not bigger. So, the case head-to-shoulder datum dimension (aka case headspace) can be 1.1831" to 1.1901". The chamber is the opposite. It cannot be smaller than 1.901" but can be bigger by up to +0.002" or 1.921".

Looking back, I misread your post. You are talking about 0.017" growth in case length and for some reason, on the first read-through, I took it to mean diameter. Sleepy brain, I suppose. Whether that is too much or not depends on what the starting length was. If the new case was at -0.007" from HS and your chamber is at the maximum 1.2001", then an increase of 0.0017" is exactly what you would get, but it is, at that length, too big for the gauge, which doesn't want to see over 1.9001". In other words, it needs more resizing.

 

[Shadow9mm]

Looks like i need to get more gauges.

 

[stagpanther]

I'm guessing UN has posted pics that illustrate what he is talking about at some point--sometimes pictures make these concepts easier to understand. I'm far from an expert on these things--but I have twin "goals" in getting measurements; the first is to confirm that my chamber and bolt combination results in maximum expansion of the case that is safely within the SAAMI specs--and secondly to size the brass so that the degree and frequency of sizing down "growth" or flow is minimized thereby prolonging brass life and strength (that is particular to my rifle--not a gauge). I can add that even SAAMI specs isn't an ironclad guarantee that everyone always follows as I rudely found out when an early 350 legend AR blew up on me.

 

[tangolima]

Be careful talking about headspace of brass. Some folks here don't like that.

Is the brass sized, or it came out of firing? The gauge is for sized brass. If the sized brass doesn't fit, size it down a bit more. That's how it is supposed to work, I think.

However, why bother with the gauge? Why not the rifle's chamber? Keep sizing the brass down till it chambers, and then go further 2-4 thous more. You don't manufacture ammo (you need license for that). No point meeting saami specs.

-TL

Sent from my SM-N960U using Tapatalk

 

[Shadow9mm]

The brass is fired, nothing done to it. The gauge is for fired brass.

I was hoping to measure and do a 0.005 bump since its a semi auto. Gauge also does max case length. Its just more convenient than pulling the rifle out every time.

 

[ocharry]

i agree with tangolima...the rifle chamber is the gauge you need to worry about....unless it is WAY out of spec....and even then you can load for that chamber, just wont fit nothing else

unless you have multiple rifles chambered in the cal you only need to worry about what fits that chamber

i would measure to the shoulder and size to bump... -.004 is where i like the auto shoulder to be bumped to...but you do you on that..but that -.004 seems to work well for me...trim and load them

it may only work in that rifle but you only got one so it really dont matter... i use whidden case gauges...you can use what ever you want i guess to measure the shoulder bump...the whidden gauges are not cheap but they give you a fast easy to read measurement...i just like them over the other ways to measure shoulder bump

i think you are over thinking this.....if you are sizing to that chamber everything else is moot....size to that chamber and trim and load and shoot..lol

i could be wrong but that is my take...i have been wrong before and prolly will be again

ocharry

 

[tangolima]

The brass is fired, nothing done to it. The gauge is for fired brass.

I was hoping to measure and do a 0.005 bump since its a semi auto. Gauge also does max case length. Its just more convenient than pulling the rifle out every time.

It is a brass gauge, to verify a sized brass meets saami specs or not. That's why the factory round drops right in and within limits. By default, chamber dimensions are slightly larger than brass. A fired brass would always be slightly too big to drop in. The gauge is never the same as the rifle chamber. I don't know where you are going with it.

I used to have a couple of such brass gauges. Very quickly I realized they were totally useless till I start manufacturing ammo for sales.

-TL

PS To determine whether the rifle chamber meets spec, proper way is chamber cast.

Sent from my SM-N960U using Tapatalk

 

[Brian Pfleuger]

The gauge is pretty meaningless for your rifle.

Unless the chamber is dangerously over (or under) sized, or you need this brass to work in multiple rifles, it really doesn't matter.

Measure your fired brass at the shoulder datum and size it back 0.005, or whatever number you choose.

I've literally never once "gauged" a single case.

 

[44 AMP]

Looks like i need to get more gauges.

OR

consider that the only "gauge" that really matters if the chamber of your rifle.

 

[HiBC]

Different strokes for different folks,I guess. I find the bushing type cartridge headspace gauge quite useful.
Following this project, IIRC, I'd consider the barrel as a POSSIBLE variable in the equation. No,I'm not trashing it!. "Trust but verify"

UncleNick reminded us of an important chambering technique.Use a floating reamer holder. The proper fit reamer pilot will follow the bore. But what is driving the reamer into the cut? From the tailstock to whatever method is used to keep the reamer from spinning,any side load to the reamer will cause the chamber diameter to be cut oversize. A clue might be how the reamer flutes fill with chips.. Heavy on one side?
Good help is hard to find. A guy can go from flipping burgers to chambering $165 AR barrels by the hundreds pretty quick.

The idea that a fired ,unsized case won't fall full depth into the bushing gauge leaves me suspicious.
As the bushing gauge literature said,the diameters are cut oversize. There should be no interference on fired case. The case shoulder must come to rest on the bushing datum.
It needs to work on an unsized fired case so you can measure how much you are reforming the shoulder. I use the tool to measure "before" and "after" sizing. I have a dial indicator comparator stand on my loading bench I can just slide the bushing gauge under, I can set the indicator zero on the top of the bushing gauge. In my notes I can record " AR-15 #1 set to size --.003"
and three years later I can return to that setting from the bushing die as my standard. Another rifle? No problem! It might be --.001. Its recorded and repeatable.

If you understand using the Stony Point or Hornady setup that clamps on dial calipers or Uncle Nick's hardware store bushing, I use the bushing gauge the same way. Its just ,for me,far less clumsy to use. No disrespect intended,but not understanding a tool does not make the tool useless. I don't know how to play a violin. That does not make the violin useless.

I suspect the place to start is making sure the unsized fired case diameters fall within acceptable limits . You may have an oversized chamber. Maybe your barrel maker will take care of you.

The bushing gauge you have is probably just fine.

As far as using the rifle chamber as a gauge...What do you measure? From what to what? With what tool? Very long rods in your depth mic? From the rear of the receiver? I suppose you could do that. How do you set .002 or .004 head clearance on your brass when setting up your sizing die? Sounds like a PITA

Or are you just confirming your bolt will close?

 

[tangolima]

No need to measure anything. Keep sizing down till bolt closes without resistance, just like with go-gauge, best without extractor / ejector. Then turn the sizing die down 3-6 thous further to have head clearance 2-5 thous, assuming the brass bounces back by 1 thous.

The thread on sizing die has pitch of 14tpi. I subdivide the circumference into 24 divisions and mark them on the lock ring with electric pencil. Each division turns the die down by 3 thous. Why 24 divisions? Because the lock ring is hexagonal. 4 x 6 = 24.

Op said a factory round fitted the gauge with no slop. A fired brass has little or no chance to drop in.

Different strokes for different folks indeed.

-TL


Sent from my SM-N960U using Tapatalk

 

[Shadow9mm]

Update: It seems to keep going back and forth that this gauge is intended to check sized ammo only. I would like to put this to rest if possible. It is intended for use in checking both fired and resized brass and is intended to measure the fired cases as a basis for resizing.

Also, at this time all brass has been resized to just below the maximum indicated by the gauge to ensure proper feeding and reliability. I will be ordering the Hornady headspace comparator gauges next payday. I will measure the few rounds of factory ammo I have left. My size casings, and all the casings after being fired.

From the gage instructions
Step 2: Check Headspace in Gage
Hold the gage in a horizontal position and insert the AS-FIRED case into the gauge so it rests firmly against the shoulder of the Gage. Always check as-fired cases before sizing. This provides a basis for sizing. ALL chambers are NOT equal in headspace!

(Please see the forum policy on posting copyrighted materials.)

 

[stagpanther]

A certain Bart B on the this forum turned me onto Larry Willis' belted magnum cartridge collet die--it turned out to be a Godsend and I use it when resizing all big belted magnums now. While on the website I noticed his digital headspace gauge and that's also become an indispensable part of my tool arsenal--and both tools are really inexpensive IMO compared to the return I get on them. I also have a big box full of the wilson gauges and they are useful for "quick and dirty" checks--BTW I've found that using a razor blade edge over the top of the wilson gauge can reveal a gap that you might not otherwise see.

 

[HiBC]

I don't use the slot and straight edge.
On my bench is a small (about 8 in square) flat granite plate with a 1/2 in diameter vertical post. I can attach a dial indicator to the post. Its called a comparator.
If I stand the bushing gauge on the granite flat surface, the bushing gauge gives me a simple,convenient way to hold the brass stable and vertical for measurement with the indicator,with the brass shoulder resting on the datum ring. When setting my sizing die initially, I can zero my indicator on the case head. After sizing,the indicator will tell me the shoulder setback. Its as simple as dropping the brass into the bushing then sliding the bushing under the indicator,with the indicator contacting the case head. We get a direct read (in theory) of the sized case head clearance.
Verify the results in your rifle chamber if you wish,any way you want to.
OK,we just compared the cartridge case before and after sizing , We adjusted the sizing die to give us what we want. Great!

Now rezero the indicator to the top surface of the bushing gauge. That is a repeatable constant. Now slide the gauge so the indicator reads on the case head. Write the number down. Lets say its ,004. Great!

Suppose the last 3 digits of that rifle SN are "632" OK. Take a sharpy and write " 632 --.004" inside your die box.
In 7 years you can resize any headstamp of fired brass and if it gauges .004 shorter than the bushing gauge you are good to go for that rifle because you have a standard to return to.

Thats how I do it. You can do whatever makes you happy.

And,fwiw,if I want to check 100 cases, I just drop them in the bushing and slide them under the indicator. Any time I want to re-zero the indicator, I just zero to the top of the bushing.

50+ years ago, I was candle smoking the case shoulder to find when I contacted the die shoulder. My horrid,PITA,messy way to find zero head clearance.

Not great. But with no internet and no mentor and no UncleNick I figured out that was one way to make my 7mm Rem Mag brass last longer. On my own,I figured out controlling head clearance.

Over time I found a better way.

 

[Unclenick]

 

[HiBC]

More than one way to skin a cat!
Thats a good way!

 

[stagpanther]

Thanks UN--for further clarification (for a simpleton like me ) I assume this is a fired case indicating your headspace (minus a bit since a case likely does not fully "snap back" to unfired dimension)?