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.311 Bullet In A .308 Bore?


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#1 ken98k

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Posted 12 October 2009 - 09:28 PM

Just a hypotheticle qusetion but what would happen if someone was to fire a standard 7.62x39 in a rifle with a .308 bore?

Would it cause a serious pressure spike?

I was thinking about putting one together similar to this one- http://www.sporteriz...?showtopic=7580

#2 lemski4

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Posted 13 October 2009 - 05:18 AM

Ruger Mini30's use a 308 bore

#3 tinkerfive

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Posted 13 October 2009 - 09:36 AM

About a year and a half ago I built 2 7.62X39 guns. One using a remington 30-06 barrel (.308 bore ), one using an Enfield barrel (.311 bore).
Supposedly the 7.62 is to have .311 bullets. The ones I bought had .308 bullets.
My intent was to use which ever gun matched the ammo that I found.
I've got 400+ rounds left of the stuff with .308 bullets, so I won't be looking for ammo for a little while.
Otherwise .311 to .308 isn't a huge swage. If you are using something like a large ring Mauser as a action, I doubt that
you will exceed it's pressure limits. Just pay attention to the throating/freebore and I think that you can manage pressure
spikes. I didn't want to play with the throating, that's why I built 2.

Now feeding the little round is iffy.
I intend to go back at some point and try to add in a sheet metal lining to the mag box to extend the tighter
portion of the lips forward before they open up. The problem being that if you cycle the bolt too slowly
the round will fly out as soon as it reaches the wider portion of the feed lips.

Best of luck!
Tinker

#4 odies dad

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Posted 13 October 2009 - 06:28 PM

Try my 223 feeding technique and use a Ruger Mini-30 mag in the Mauser well.

#5 Sailormilan2

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Posted 13 October 2009 - 08:26 PM

.311 in a .308 bore shouldn't be a problem, as long as the case neck has enough space to expand to release the bullet. A tight chamber neck will cause high pressures.
I remember reading years ago, that during WW1, the Germans were hurting for rifles so badly, that they took Rifles with the older small .318 bore and throated them so they could shoot the newer .323 bullets in them. With enough freebore, the bullet would pick up enough velocity to swage down without causing excessive pressure.

#6 Vladymere

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Posted 14 October 2009 - 08:07 AM

German military rifles never used a .318" bore. This is a common misconception/myth. The Gew.88 rifle that your are refering to used a .318" diameter bullet in .320" bores. The theory was, and it may have been true with the thinly jacketed bullets of the time, that the bullet would "slug" up and fill the bore on firing.

Vlad

#7 Sailormilan2

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Posted 15 October 2009 - 11:31 AM

I may have mispoke regarding "bore" size, using the word the wrong way.
The 1888 Mauser 7.9mm cartridge had a bullet diameter of .318", .003" smaller than barrel groove diameter. The 88 Commission rifle had lands with a diameter of .311", and grooves with a diameter of approx. .321"(.318" + .003").
In 1905 7.9 mm S cartridge was developed. It had a .323" diameter bullet. When this bullet was adopted, the groove diameter was deepend approx. .0018"(from .0047" to .0065").
Commission 88 and Model 91 Mausers were altered to accept the new cartridge by enlarging the neck. No changes were done to the groove diameter. So, essentially the Germans were putting a .323" bullet down a .321" "bore".

In 98 Model Mausers made to fire the "S" cartridge, the barrels had a very long forcing cone of about 4 1/2 calibers to keep the pressures down. No mention is made that the retro-modified 88s and 91s were so done.


Olsen's MAUSER BOLT RIFLES, pp. 42, 104, 130.

#8 odies dad

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Posted 15 October 2009 - 08:23 PM

In case anyone else is looking for the 223 mauser project link, I couldn't find it here, but I did find it on another forum.
http://www.mausercen...0936921&t=10813

#9 Doble Troble

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Posted 17 October 2009 - 06:43 PM

My 1917 won't shoot unless I load 303 bullets for it (0.312 diameter). But the bore was in pretty bad shape when I got it.

#10 karlunity

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Posted 17 October 2009 - 07:52 PM

DT.

Sir, I owe you a beer.

Boris, my first Mil sup, is a 1917 enfield and has been losing accuracy for some time.

By accident, I loaded a .311 and it was dead on at 100 meters but I have been leery to try it again.
As soon as I can find a new range, I will try a few..If it restores Boris......: )

Karl

#11 Doble Troble

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Posted 18 October 2009 - 09:43 AM

karl,

I don't *think* the 0.311s will hurt :). I've shot probably 100 150 gr 0.312s through mine (the Hornady 303 SPs that I had on hand for my SMLE) at Garand velocities (47ish grains of 4895).

The only difficulty was I had to expand the necks more - I took the expander/decapper out of my 303 sizing die and put it into my 30-06 sizer die.

It made a huge difference. I shoot a lot of cast, which makes you pay close attention to bore and bullet diameters. In additon to accuracy problems, skinny cast bullets lead bores - which is a real PITA that you learn to avoid.

My 1917 was inaccurate and copper fouling with 308s. So I tried bigger bullets = improved accuracy and less fouling (I think - it still has a nasty bore - It was used for salutes with blanks by veterens groups. The blanks used must have been really corrosive.




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