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Make my own headspace gage?

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Waffentag
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Make my own headspace gage?

Postby Waffentag » Tue Sep 05, 2017 3:41 pm

Here is my dumb question of the week.

Can I make my own Go, No Go Gages for matching up my MG42/3 Bolt heads and 7.62 Barrels?

I am going to borrow a friends 7.62 GO/NO GO Gages. I have a Dillon 308 Case Gage. I would size one empty 7.62 Case to the same size as the Go Gage and one for the No Go Gage and mark them.

I should be good if the self made cases match how the 7.62 GO/NO GO Gages fit in the Dillon Case Gage?

So, what is wrong with my plan? I don't think that a placing a bolt head by hand in a barrel to see if the rollers lock up with change the case dimensions?

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Re: Make my own headspace gage?

Postby JBaum » Tue Sep 05, 2017 10:43 pm

Cases stretch and shrink. They also compress, such as when they are resized in a reloading press. How many times it takes to do that (be resized) by being pushed into a chamber, which may or may not be worn or within specs, is anybody's guess. I suppose it would be good for at least one use. After that, could you really trust it to be accurate to with thousandths of an inch?

Headspace gauges are extremely hard, i.e. they don't wear (for all practical purposes).
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Re: Make my own headspace gage?

Postby Waffentag » Wed Sep 06, 2017 8:56 am

John, you are right as usual, I just need to buy some 7.62 gages.

I was just re-reading some of your earlier posts and found the good article on the difference between .308 Winchester vs. 7.62x51mm NATO that you had provided the link for.

http://how-i-did-it.org/762vs308/chamber.html

"If you're read all the way through the admonitions about not using .308 Winchester in a 7.62x51mm chamber, then you know that 7.62 chambers are dangerously long compared to what's allowed for .308 Winchester. Interestingly, the cartridge dimensions themselves for 7.62x51mm are identical to .308 Winchester. All that extra space is just to improve reliability of feeding and prevent headspace issues in firearms that love to slam the case into the chamber with enormous force; e.g. machineguns."

"7.62x51mm chambers get away with being so loose because 7.62 ammo is made thicker at the base than .308. The extra brass provides enough material to prevent ruptures, and is the reason why most reloading manuals advise downloading by about 10% when using military brass. Conversely, thinner .308 brass provides more case room, but less leeway in chamber dimensions."

I use only Military 7.62 Brass. Last time, I gaged all my cases with the Dillon 308 case gage at the minimum headspace. In the future, If I go to the Max Head Space in the 308 Gage, then I should be good for 7.62? After I check my barrel and bolt combos again with some 7.62 Head Space Gages, I need to test a 7.62 NATO Go, No Go Gages in my Dillon 308 case gage so that I know how to set my case sizing die.

For my MG 42, I have four West German 7.62 barrels and five 8MM Barrels (3 German WW2, and 2 M53) and four M53 Bolts. They are not all the same, I have numbered the barrels and have an index card with the different barrel bolt combos. I have one barrel bolt combo, that will not lock up on factory 7.62. When I get the gages, I am going to recheck the combos of barrel and bolts and verify my index cards.

I will re-read the link on testing headspace. Do you have any additional advice on how the rollers should feel when testing?

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Re: Make my own headspace gage?

Postby JBaum » Wed Sep 06, 2017 12:03 pm

" If I go to the Max Head Space in the 308 Gage, then I should be good for 7.62? "
I have no idea. I never wanted to play with the tolerances like that.

"Do you have any additional advice on how the rollers should feel when testing?"
Rollers should go 100% outward. A little extra play doesn't seem to make must difference on headspacing the MG42, but you get to decide what's acceptable. A little short on headspace is not tolerable, and can cause a ruptured case blow back.
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Re: Make my own headspace gage?

Postby 42rocker » Wed Sep 06, 2017 3:24 pm

Another dumb question
Is this for Full Auto or Semi Auto. I believe that also makes a minor difference. In Full Auto don't play games.

That said there are folks out there that make their own go, no-go, field gauges. Are you that good?? I buy mine, not worth the opp's factor.

Later 42rocker

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Re: Make my own headspace gage?

Postby hakentt » Thu Sep 07, 2017 2:20 am

Waffentag wrote:Can I make my own Go, No Go Gages for matching up my MG42/3 Bolt heads and 7.62 Barrels?
?


Yes. You can just use one live round and lock it by hand, with light push of a finger, rollers should lock. JBaum will tell you it is a rocket science but its really easy to check if you understand the technical concept of headspacing. Do you know where can I find me one 7.62 barrel?

download/file.php?id=16094&mode=view

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Re: Make my own headspace gage?

Postby Waffentag » Thu Sep 07, 2017 8:57 am

Ok, that photo is helpful. I got one barrel from RTG, was on a waiting list. I got the other 3 from a local dealer who just happened to have them. I bought all that he had.
You may look here,
viewtopic.php?f=80&t=2501&start=20

So, in the photos, one looks like you are looking for the gap without a round in the chamber?

I have a 7.62 case gage on the way. At the last shoot, I fired almost 2000 rounds and it was a mix of factory and my reloads. I had a couple of cases separate and get stuck in the chamber. They were LC Brass that had been fired twice. In the past, I would check every reload in the barrel with a bolt head.

Since I was checking every case in the Dillon 308 Case Gage, I did not check every case in the barrel like I have always done. I was more concerned with them being too long, than too short. I sized them to minimum length for 308. So, I think that the brass was too short and stretched too much and gave out? I did have a few rounds that were the max 308 length in the gage, but they were in specs. The ruptured cases happened in the afternoon, so the chambers may have gotten dirty with all the shooting. I had no issues with factory brass.

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Re: Make my own headspace gage?

Postby hakentt » Thu Sep 07, 2017 2:07 pm

got to have new quality military ammunition with these. Home reloads are for bolt actions

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Re: Make my own headspace gage?

Postby JBaum » Thu Sep 07, 2017 5:36 pm

When reloading brass, an inspection before they are reloaded is necessary, especially if you're shooting in an MG34 or 42. Look for slight discolorations in a lengthwise line, or a slightly dark ring about 1/8" above the extractor groove. Brass can only take just so much strain before it separates.

I shoot nearly all reloads and never have a problem, but the brass can only be reloaded twice (plus the original shot, when new) before it becomes likely to have a case separation. Sorting out anything with 3 hits on the base from the feeder on front of the bolt eliminates a lot of problems. Bolt actions give the brass time to shrink before being extracted. Machine guns don't give the brass the time to stop pushing on the sides of the chamber before they are extracted. When it is extracted less than 1/100th of a second after firing, there's a lot of damage done on the microscopic level, which weakens the shell.

Brass will only take a little abuse before it cracks.

I'm sure it seems like rocket science to hakentt, but it's just simple common sense.
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Re: Make my own headspace gage?

Postby Waffentag » Thu Sep 14, 2017 6:58 pm

Got my 7.62 NATO headspace Gage's, and tried them out.

I placed the min 7.62 head space Gage in my 308 Dillon case Gage. Wow, there is a big difference between 308 and 7.62. The min 7.62 Gage sticks up above the max in the 308 case Gage.

I tested all combinations of my 5 bolt heads and 4, no combo had too much head space. One bolt head had too tight head space with all barrels, one barrel was too tight with all bolt heads.

Maybe I can find another bolt head to go with that barrel? I may be able to use that too tight head space barrels for a bunch on reloads that that I sized too tight? For the too tight bolt head, I need to test that in my 8mm barrels,

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Re: Make my own headspace gage?

Postby JBaum » Thu Sep 14, 2017 9:45 pm

I don't know what kind of reloading press and dies you have, but it's impossible to size the brass too small with my Dillon set up. The bottom of the die comes to rest on the shell plate. You can't compress past that.

A different bolt head gives different headspace results. It would likely be all you need to make the combination work. It may space on an 8mm just right. There's no telling until you try it.
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Re: Make my own headspace gage?

Postby Waffentag » Fri Sep 15, 2017 8:56 am

I have a Dillon 550B, But not 308 Dillon, dies, I need to order Dillon Dies,

However, all rounds were within spec and checked using the 308 Dillon case gage. The lesson learned is that minimum 308 headspace is excessive for 7.62 NATO. Even though it Gage's, OK, for 308, you end up pushing the shoulder down too far for the long 7.62 NATO chamber.

I will upload some photos of the 7.62 Gage's in the 308 case length Gage to show my point.

I can not got bolt lock up with one barrel with any of my five bolt heads with the minimum 7.62 headspace Gage. However, I have 500 hundred rounds that I loaded and pushed the shoulder down to min 308 specs. I tested these rounds in this too tight barrel and get good bolt lock up on these rounds. So, I will try a few and make and check for stretching, if they are good, I will shoot them off and toss the brass when I am done.


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