M1 Garand shoulder setback, 0.010" too much for a one time firing?

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That pressure ring's a very good indicator of case wall thickness uniformity. Neck wall thick and thin parts tend to align with those at the pressure ring. On cases I've measured, those with uniform pressure ring heights have uniform neck walls too that seldom have more than a .001" spread. They don't need turned 'cause they're uniform enough.
 
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There are some who think that cases lie on the bottom of the chamber when fired and only the top of the case expands.

I was one of them decades ago until someone showed me the forensic method of reading firing pin and bolt face imprints in the dented primer cups. Orienting cases to align the prints at the same place showed that high point of the pressure rings were all around a clock face. 'Twas easily seen that pressure ring high points were not all at 12 o'clock nor low points all at 6 in the chamber.

That was my first lesson of the details of what happens when a round fires. That nice old man next proved to me that those new 270 Win cases from my Winchester 70 touched nothing in the chamber when fired except a contact circle at the chamber shoulder and where the extractor pushed its pressure ring area against the chamber wall. And, of course, where the firing pin dented the primer cup.
 
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Not sure how much this helps or even fits in this thread . I've found gauges , comparators , dies and chambers all have different dimensions or angles at the shoulder . It may not be much but it's there . I can size a case to measure the exact same length as my Forster NO-GO gauge when compared using my Hornady head space gauge ( same as shown in OP ) When I try to chamber my NO-GO gauge the bolt will not close . How ever that sized piece of brass the measures the exact same size will chamber ( it's snug but I can get the bolt to close with out excessive force ). How can two seemingly same sized objects not fit in the same space ?

I concluded that my chamber and gauge are closer in correct dimensions to one another then my sizing die is to either . I'm assuming the sizing die puts a slightly different angle on the shoulder causing it to contact the chambers shoulder at a different point to where the case can sit a tad deeper allowing the bolt to close . Even though when comparing the two ( sized case & No-Go gauge ) they measure the exact same from head to there respective datum point .

I also have a case gauge that my NO-GO gauge sits flush with the top step . How ever I can chamber a case that sits visibly higher then that top step .

What does that all mean ? There are no absolutes when it comes to gauges and how they transfer to another object that is supposed to have the same dimensions .
 
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Metal God said:
What does that all mean ? There are no absolutes when it comes to gauges and how they transfer to another object that is supposed to have the same dimensions .
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There are absolutes that mean there are tolerances in anything mechanical. That's the biggest absolute. Now consider the following:

One can use high school trig to figure out where a 20 degree case shoulder will contact a 21 or 19 degree chamber shoulder. Same if the numbers are reversed. Then you will understand that the same interference with the case shoulder next to the case neck diameter is easier to squeeze back than the case shoulder at the body diameter. If the neck diameter's half that of the shoulder, it'll have half the area to get pressed back. This paragraph is related to the next one.

A brass case can be compressed a thousandth or so as the bolt binds a bit closing into battery, but a steel headspace gauge of the same dimensions won't compress and the bolt won't close short of a healthy smack with a sledge hammer or 5-foot long cheater bar.

A case with headspace equal to that of the chamber whose head is out of square .001" on one side from being slammed against a bolt face that made it that way will chamber easily when it's clocked in the chamber to match the bolt face. 180 degrees out and there'll be a .002" interference fit and the bolt will bind when closed. How much depends on what the chamber and case shoulder angles are.

Hope this helps. Need more facts?
 
I did not consider the idea of the case flexing , springing or compressing . If so that could very well be the difference . :)
 
Metal God said:
I did not consider the idea of the case flexing , springing or compressing . If so that could very well be the difference .
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Consider this - If actions open a little to soon, the head to datum measurement on fired brass can be longer then the actual chamber.

The comparitor measurement have nothing to do with the SAAMI drawing measurements. :)
 
lol well I was speaking of one of my bolt actions so if the action opened early I'd be in big trouble :confused:
 
Metal God said:
When I try to chamber my NO-GO gauge the bolt will not close . How ever that sized piece of brass the measures the exact same size will chamber ( it's snug but I can get the bolt to close with out excessive force ). How can two seemingly same sized objects not fit in the same space ?
Click to expand...

The brass is being sized when closing the bolt. Shorted head to datum measurement.


That Hatcher guy claimed as much as .006" shoulder setback when closing some bolt actions. The M16 will set the shoulder back a thou or two, if you let the bolt slam on a long head to datum round.

But as you said, changing the angle of the shoulder figure's into the equation.
 
How do you get the quote box ?

(The M16 will set the shoulder back a thou or two, if you let the bolt slam on a long head to datum round.)

Yes they do . I actually did my own test on this to include complete bolt , stripped bolt as well as every configuration in between .My results showed the BCG slamming home would set the shoulder back as much as .002 with most being .001 to .0015

There were three interesting things that I found as a result of these test .
1) If you continually chambered the same cartridge it would continue to have it's shoulder set back in the increments stated above .

2) The continued set back would stop happening at around .004 to .006 of total cumulative set back . After the cases reached a total on .004 of set back it dramatically dropped off , with some but very few being set back more then that .004

3) The set back would only happen if you started with minimum set back . Meaning you started with the cases shoulders only bump .002 to .003 from fire formed measurements . If you first sized the case .006 short of fire formed size . The case had no shoulder set back

There is actually a forth . That is I was able to get a case sized to long ( about .002 ) to still be forced into the chamber by the force of the BCG slamming home although I did not test that more then twice .
 
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243winxb said:
Consider this - If actions open a little to soon, the head to datum measurement on fired brass can be longer then the actual chamber.
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The five 7.62 Garands I used on USN teams had one thing in common shooting normal max loads and their bolts all opened when bullets were some feet out the barrels. All fired lcases from them would not rechamber from whence they commeth. Case headspace and body diameters were greater than the chamber's by a thousandth or more. Same thing with 30-06 Garands.

One guy I shot with had his Win 70 bolt gun and Garand chambered with the same 30-06 reamer. Bolt gun's fired cases rechambered easy again. Garand's fired cases would not. Both barrels same except for profile and gas port. Same ammo used in both.

30-06 case shoulders set back from firing pin impact, too. Couple thousandths is common.
 
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Or click the reply button in the bottom right hand corner of the comment & edit as needed if you don't have those options.

Interesting on the shoulder set back in a auto. When I first started with 223 I only had a bolt action & unless the shell plate bumped the die the bolt was hard closing. I now load for 7 of them with 2 being bolt actions. I occasionally have one that has enough spring that it won't chamber in my AR. I place it in one of the bolt actions after closing the bolt on it I can get it to chamber in an AR most of the time. When I can't it takes a hammer to open that bolt.
 
kingmt said:
shell plate
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Beware of shell plates. The deck height should be around .125" at each station.

Each station may be different. More or less thickness.
If my FL die was adjusted on the bad station, i got a total of .014" shoulder set back. The die produced .005" + .009" from the shell plate. Leading to case separations. One station was normal, the other 3 were all different.

Mostly my fault for not having an L E Wilson cartridge gage back in the 1980s. But instructions said nothing about a gage. Live and learn.
 
While that Wilson case gauge is appealing to many, it's always best to use your own barrels' chambers as the gauge to fit your cases to. Along with a good understanding of how case dimensions relate to chamber dimensions when the round's fired after the rifle's moving parts position the case before it's fired.
 
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I made a mistake in saying shell plate. I meant shell holder.

I also only have my barrel as a gauge.
 
If you use Redding's competition she'll holders, you may be able to set 'em back only .001".
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I've gotten to really like the Redding competition shell holders. They make Precision sizing more repeatable, by keeping you from adjusting the die, and instead changing the shell holder to the needed size.
 
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Walkalong said:
The reason some things were consolidated into one thread was that the stickies were starting to take up the hole screen.
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Certainly understand desire to save bandwidth, especially with this site's high popularity.

Thanks,
Russellc
 
Some people never pass the first page & if it's all filled with pinned threads it gets cluttered. The Mods are doing a good job here.
 
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