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  #41  
Old 10-03-2013, 10:28 AM
ETicket ETicket is offline
 
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Quote:
Originally Posted by en bloc View Post
Nice work Ericc.
This post should be made STICKY for posterity.

~Matt
I agree with this, it should be a sticky. It explains the procedure very clearly.
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  #42  
Old 09-10-2015, 03:53 PM
Coastal190 Coastal190 is offline
 
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Location: St. Marys, Georgia
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I should have read this post before I tried to check my headspace. I thought I had a problem but after performing this procedure I know now that I don't have a problem.
A BIG Thanks!!
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  #43  
Old 04-21-2017, 05:43 PM
HB of CJ HB of CJ is offline
 
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Default Incomplete Description And Why ...

Couple things to add. Rotate the gage about 1/10th circle each time pressing the bolt. You want an average of at least 10 different placements. Yes it makes a difference.

You do not have to disassemble the bolt. There is a trick to this. But you do have to remove the bolt and snap or place the gage in the bolt face. Check for engagement.

Make sure the ejector is compressed fully. Make sure the extractor rim is not obstructing the gage pressing completely flat against the bolt face. No slide or op rod with this.

Repeat the gage rotation again. You are establishing an average of 10 checks. To be sure repeat with a different manufacture gage. More better. Get an average.

Yep .... just a few pounds of pressure needed. Do not force. Like said, the bolt must lock up completely. Repeat with longer gages until you determine the head space.

Why all of this? You need to determine a measurement. With only one gage and one check, statistically it MAY not be valid. Using several different manufactures helps.

Hope this helps. Passing it forward. Respectfully.
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  #44  
Old 05-31-2017, 03:11 PM
Kestrel4k Kestrel4k is offline
 
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Location: Oregon
Posts: 1,685
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I was trying to put '06 headspace gauge measurements in order; came across this thread in a search so figured I'd ask here.

From perusing the various 'Navy' threads in past years here, I put together the following specs to help me keep track of .308 & 7.62NATO:

1.630": .308 Go
1.634": .308 No-Go
1.6355": 7.62 Go
1.6375": 7.62 No-Go
1.638": .308 Field
1.640": .308 Max
1.6455": 7.62 Field

I would like to put together the same listing for '06; I'm thinking it should be simpler as the civilian & military spec seems to be the same ?

A brief search of Forster gauges didn't turn up the '06 measurement specs, and was hoping someone here could point me in the right direction for a definitive '06 listing comparable to the one above?
So far, for .30-06 I have:

2.049": Go
2.055": No Go
2.058": Field

Sounds right?

Last edited by Kestrel4k; 05-31-2017 at 03:19 PM.
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  #45  
Old 06-01-2017, 12:21 PM
Unclenick Unclenick is offline
 
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Both .30-06 and .308 have case dimensions identical to their military counterparts. When you examine the SAAMI standard you find a little bit of shoulder and chamber interference is allowed (a small overlap in minimum chamber and maximum case) for the ability of a rifle bolt to compress and upset the case diameter outward a little. As a result, rifle operation is not certain to be impeded until the case body has expanded to fill the minimum chamber diameter.

In the 7.62 gauge numbers you found, that SAAMI overlap is eliminated. I surmise it is because the extra chambering effort from a maximum length cartridge getting into a minimum size chamber would increase the chance of a fixed-firing pin gun design igniting primers before the action is fully locked, increase the chance of a slamfire in a floating firing pin design, and because the extra effort increases the likelihood of a jam even if firing is not affected. Again, that is surmise on my part, but it makes sense to me.

The .30-06 is older and dates to when headspace was taken from the breech to the shoulder and case body intersect, which was used as the reference diameter back then. In .30-06 that diameter is 0.4425", and Hatcher gives the headspace to that point from the breech as 1.940". SAAMI calls that dimension as 1.9399", so they are within a tenth of a thousandth of one another and for all practical purposes are the same number.

From the SAAMI drawing, the minimum chamber is 2.0487", which would be the GO gauge carried to one more decimal place than you did. The maximum they give is 2.0587", or 0.010" bigger than minimum. That's the same minimum to maximum difference the standard has for .308 Win. On page 214 (page 226 in Acrobat Reader's page counter) of the 2015 standard I linked to, they give those two dimensions as minimums and maximums for gauges.

You'll have noted with the .308 that the FIELD REJECT gauges are -0.002" shorter than the SAAMI maximum. I believe that's an industry consensus number that has developed among the gauge makers over time, as it does not appear in the SAAMI standard. I don't know where it originated. The .308 Win NO-GO gauge is simply 0.004" shorter than FIELD REJECT length. The NO-GO applies only to a newly cut chamber's maximum, thereby reserving at least 0.004" of space for a little lug setback and other size settling to occur as the gun is used.

For .30-06, that -0.002" adjustment to maximum number is not employed, and the FIELD REJECT number matches the SAAMI maximum. The NO GO is, again, 0.004" shorter than FIELD REJECT, so the same growth allowance is used.

Based on the above, my expectation would be the nominal gauge numbers would come out as:

2.0487+0.0002" GO (2.0487"—2.0489")
2.0547-0.0002" NO-GO (2.0545"—2.0547")
2.0587-0.0002" FIELD REJECT (2.0585"—2.0587")

I suggest you call Manson Reamers or someone else actually making the gauges to ask how the particular allowances and .308 Win numbers evolved.
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  #46  
Old 06-01-2017, 12:51 PM
Kestrel4k Kestrel4k is offline
 
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Thank you for the very good explanation, UN.
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  #47  
Old 03-12-2018, 06:53 PM
1deborah 1deborah is offline
 
Join Date: Feb 2013
Location: Frisco, Texas
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Default headspacing

I have a straight bolt handle I'm wanting to switch with a swept back, 1903. If the headspace needs to be changed to fit the new swept back bolt, will that ruin the original bolt for use with the rifle? Best regards, Paul
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  #48  
Old 03-16-2018, 11:39 AM
Unclenick Unclenick is offline
 
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"Ruin" is an overstatement. The odds are a bolt swap will happen with the chamber still inside military specifications for both. If you go on to lap the lugs of the bolts with the receiver lugs to get a matching fit, that can open up headspace a couple of thousandths for both. Chances are, you will change the headspace of the chamber by some amount with a swap, but you want to know how much before you get concerned.

To determine that, get a piece of 1/4" diameter cold rolled steel (CRS) rod from the hardware. These are usually 36" long. CRS is too soft to damage a bore and usually has an even softer zinc surface plating. Square one end and file it smooth and deburr the edge of the cut and, after checking no live ammo is around, close the bolt and place the cleaned end of the rod in the muzzle until it stops on the bolt face. Mark the rod where it is flush with the muzzle. Remove the rod and cut it off a half an inch below the mark and dress the cut end, too. Perfectly square is ideal. Put it back in the barrel and set the muzzle upright. Open the bolt to check the rod is in place over the firing pin tunnel and close it again (this also double-checks that no gremlin placed any live ammo inside). Use a depth micrometer to measure how far below the muzzle the end of the rod is. You can do this with the depth probe of a caliper, but it is harder to get that perfectly square unless you also have a depth measuring adapter for it. Note your measurements and without recalibrating anything, switch bolts and measure again. The difference in the measurements will tell you the difference in headspace you will have.

If the difference isn't too big, say, a couple of thousandths as I mentioned, once you have both bolt's lugs fitting well, you can take the bolt that reduces the headspace most and have the face cut back (Dave Manson has a handtool that does this, or someone with a lathe can do it for you) to match the other bolt. Then you'll have matching headspace with both bolts for any chamber you cut for the gun. But that's not something to do to adjust a big difference. I would not want to true or cut a case-hardened bolt face back more than about two thousandths because the case may be no more than five thousandths thick if you don't have specific information to the contrary.

Assuming a bigger difference in headspace, you may also want to ignore the error and just segregate your brass. Brass will fireform to substantially different dimensions than originally intended, as happens when parent cartridges are fired in Ackley Improved chambers to create the brass for them. Hatcher's Notebook includes a description of him cutting a '03 chamber's headspace way too deep to see what happened. IIRC, it was to 0.050" oversize, and new ammunition fired in it just fine, likely headspacing on the extractor hook. But nothing catastrophic occurred.

Changing bolts isn't going to make a difference nearly as large as Hatcher's experiment. So, if the new bolt tightens the headspace enough that a reamer has to be applied to the chamber to lengthen it a little to get to the minimum length (desired to be sure new ammo will always chamber), then when you put the old bolt back in, the headspace will be larger. The cases will fireform to that larger size and you will be able to get a reasonable reloading life out of them by keeping the brass that was fired with old bolt segregated for use only with it. Conversely, if it's the new bolt that makes headspace too great, the same thing applies. Resize the longer brass with the sizing die not screwed down all the way or by using the Redding Competition Shell Holders selected so you only push the shoulder back a couple of thousandths and not all the way back to factory size. That is to avoid over-working the brass at each reloading cycle. Overworking will lower the number of load cycles you get before incipient head separation begins to appear.

If the chamber has to be shortened for the new bolt by using a new barrel or setting back the old one (if this '03 is sporterized), then you may have a situation in which the old bolt becomes too tight for reliable rapid feeding (new brass may fit snuggly). At that point, you want to look at the rod measurement you made of how many thousandths of a difference the two bolts make the headspace. If it isn't too much, you may find carefully further cutting the chamber so it becomes a minimum chamber for the old bolt gives you a longer, but not excessively long chamber for the new bolt.
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  #49  
Old 03-16-2018, 06:08 PM
mycanoe44 mycanoe44 is online now
 
Join Date: Feb 2016
Location: Southern MN, Owatonna
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I purchased the Manson Reamers "Down & Dirty" headspace gauge set. It includes all 3 gauges for $70. Pretty good deal and they are very nice fit and finish.

https://mansonreamers.files.wordpres...8-catalog2.pdf
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  #50  
Old 05-02-2018, 02:51 PM
Lukester Lukester is offline
 
Join Date: Feb 2012
Location: Texas
Posts: 111
Default Mansonreamers review?

Anyone out there with thoughts/opinion/review on the Manson Reamers "Down & Dirty" set?...
They do look like a good value.

Quote:
Originally Posted by mycanoe44 View Post
I purchased the Manson Reamers "Down & Dirty" headspace gauge set. It includes all 3 gauges for $70. Pretty good deal and they are very nice fit and finish.

https://mansonreamers.files.wordpres...8-catalog2.pdf
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