303 brit in a .308 barrel?

[Ballistics in Scotland]

I think you have something wrong.
A .303 bullet measures .311 to .312. By definition the chamber is large enough for a .308 projectile.

To get a .303 reamer to work the pilot must fit a .300 land diameter. A .303 reamer with interchangeable pilot bushing would work fine.

The other issue is whether .303 dies will reduce the case neck enough to grip the bullet. I would prefer to reduce it a little undersize, even if it is only a thousandth or so, and use an expander button. If you simply rely on the die alone and insert the bullet, a trivial difference in loaded neck OD can be translated into a non-trivial difference in its grip on the bullet. I think most commercial dies will do this, but it is something to watch out for.

One of the big myths we often hear about the .303 is that it was originally a black powder round. In fact it was used as a stopgap for a brief period, in the form of a single pierced pellet loaded before the case was necked, a thing obviously unsuited for the recreational shooter today. They knew perfectly well from the start that a smokeless powder would be used, and even calibrated the sights of the Lee-Metford for a luckily-guessed fifty or so more ft,/sec. than the black powder would provide.

So it isn't designed the way a black powder cartridge would be. It is true that the amount of lube is a problem, and the short neck more or less prevents the use of a card and wax "cookie" behind the bullet, as was often used in longer necked rounds. It is possible to make a bullet with a single very large lube groove, which works well in low pressure cartridges such as the 8ga and 4ga big game rifles. But I don't like the idea for this one. In the original load, even with that slow-burning pellet, the peak pressure wasn't significantly lower than with smokeless, and there is a strong likelihood that the bullet base would cant, or be irregularly deformed into that large groove. If I wanted to use black powder in a .303, I believe I would paper-patch the bullet.

[EDG]

This is not a problem. I have a set of .001" increment pin gauges that I use to check the necks of my loading dies. I have several sets of RCBS .303 dies and the neck of the FL sizer is the exact same size as the neck of .308 Win size dies. All that happens is the .303 expander expands the case more than the .308 expander.
It seems that when they make .30 cal, .303 and 7.65 Mauser dies they use the same dimension for the neck in all of them.

The other issue is whether .303 dies will reduce the case neck enough to grip the bullet. I would prefer to reduce it a little undersize, even if it is only a thousandth or so, and use an expander button. If you simply rely on the die alone and insert the bullet, a trivial difference in loaded neck OD can be translated into a non-trivial difference in its grip on the bullet. I think most commercial dies will do this, but it is something to watch out for

[Ballistics in Scotland]

This is not a problem. I have a set of .001" increment pin gauges that I use to check the necks of my loading dies. I have several sets of RCBS .303 dies and the neck of the FL sizer is the exact same size as the neck of .308 Win size dies. All that happens is the .303 expander expands the case more than the .308 expander.
It seems that when they make .30 cal, .303 and 7.65 Mauser dies they use the same dimension for the neck in all of them.

That is about what I would have expected, and I also know of someone finding Lee dies satisfactory that way. Indeed I did, when I loaded some cases with his dies for experimentation with .308 bullets in a .303 P14 Enfield I had bought to rebarrel in .300 H&H. Those dies were made a long time back, but it is unlikely that they have changed.

Incidentally I got good accuracy, for a frosted bore, with lightly jacketed sporting bullets (though more testing might have revealed the odd rogue shot, and hunting would then have revealed it at the worst possible moment.) Nosler solid based boat-tails, excellent bullets when not misused, almost all tumbled, with one-sided engraving to show that centrifugal force had pressed them very hard against one side of the bore. Just the occasional one behaved impeccably. I had a flat piece of steel with .004in. deep grooves from playing around with acid etching, and it took quite a bit of force in an engineer's vice to make a bullet engrave as precisely as centrifugal force had done.

[DrLiberty]

I am planning my work for the winter and my next project is a 95 mauser with a barrel (was a 30-06 cut at chamber leaving .455 to start with). I thought I would chamber this one for 300 savage but that cartridge looks boring to me in my present emotional state. I have plenty of 303 reloading goods and I would love that cartridge in a .308 bore. I know this whole deal is screaming 30-40 but I don't have those dies. Any one do the 303 into a .308 bore?

Yes, I have and with disastrous results. While some .308 barrels MIGHT be ok with the.311 diameter slug, you run two major risks loading the larger .303 into the .308 case. 1: the slug will lodge in the barrel, causing excessive back pressure to the bolt, turning g it into a mini grenade. 2: the case will separate due to the slug lodged in the barrel, and the next round can fire out of battery, again creating a mini grenade right near your face / hands. I learned this the hard way.
Now, I can say that my Savage 99 WiIl fire this configuration, although it Chambers hard. Conversely, I turned a HK 91 into a mini grenade with this configuration.
Why? Well, ignorance and thrift. In the mid Obama years, slugs, powder, etc are expensive, if not impossible to find. I had some .303 rounds, which I disassembled and used the slugs to build .308.
At the time I was unaware that the Brits measured ".30 Cal" from the groove, not the lands.
Keep the .311 slugs for the .303 and .30-40's...

[Outpost75]

Regarding the left-offset scope mount in my No.4 bush rifle, this is to permit top reloading with chargers and alternate use of either the battlesight or scope. I have a Sako M28/30 Civil Guards rifle set up the same way.

[samari46]

Outpost75, thanks for the answer. Somewhere around here I have a bunch(never counted them) MKVII British bullets. Years back bought a large lot of WWII and later 303 British ammo and even though it was in the unopened 48 round boxes it had a less than ideal storage life. Gave up trying to clean off the corrosion and some cases actually had pinprick holes in them. So saved the bullets, destroyed the cordite and scrapped the brass. Frank

[john.k]

Ive fired thousands of 303 Mk 7 military bullets in a number of 30-06s and .Ive also used 303 military rounds in a Win 95 in 30/40 Krag,by simply setting the shoulder back 1/8" .No signs of any pressure issues.And from what I have read,a tight chamber and neck will boost pressure far more than a slightly oversize bullet.Ive also reloaded a 30-06 with cordite as well as 303 bullets.

[Outpost75]

Yes, I have and with disastrous results. While some .308 barrels MIGHT be ok with the.311 diameter slug, you run two major risks loading the larger .303 into the .308 case. 1: the slug will lodge in the barrel, causing excessive back pressure to the bolt, turning g it into a mini grenade. 2: the case will separate due to the slug lodged in the barrel, and the next round can fire out of battery, again creating a mini grenade right near your face / hands. I learned this the hard way.
Now, I can say that my Savage 99 WiIl fire this configuration, although it Chambers hard. Conversely, I turned a HK 91 into a mini grenade with this configuration.
Why? Well, ignorance and thrift. In the mid Obama years, slugs, powder, etc are expensive, if not impossible to find. I had some .303 rounds, which I disassembled and used the slugs to build .308.
At the time I was unaware that the Brits measured ".30 Cal" from the groove, not the lands.
Keep the .311 slugs for the .303 and .30-40's...

What you are describing above is the result of a chamber with a lack of neck-release clearance, not being a factor of barrel groove diameter. Firing cal. .30 M72 or 7.62mm M118 Match ammo in a TIGHT-NECKED target chamber will do the same thing. As long as the chamber NECK diameter had adequate release clearance for the larger bullet there is no hazard in a strong-actioned rifle which supports the case well.

When the German Army modified older J-bore 7.9mm rifles to use the larger bullet diameter S-bore ammunition, earlier '98 Mauser rifles had the chamber necks enlarged, and the throats reamed to a more gradual angle, to ease transition of the .325" diameter bullet into the .320" groove diameter barrel. While Type-S ammunition did exceed safe pressure in the Modell '88 Commission rifles so-altered, the stronger '98 actions tolerated the change with no issues.

[Texas by God]

And that is why 8mmMauser U.S. commercial ammo is loaded light with a soft core .321" 170 gr bullet. In case it finds its way into an 88 Commission rifle.

Sent from my SAMSUNG-SM-G930A using Tapatalk

[vzerone]

Yes, I have and with disastrous results. While some .308 barrels MIGHT be ok with the.311 diameter slug, you run two major risks loading the larger .303 into the .308 case. 1: the slug will lodge in the barrel, causing excessive back pressure to the bolt, turning g it into a mini grenade. 2: the case will separate due to the slug lodged in the barrel, and the next round can fire out of battery, again creating a mini grenade right near your face / hands. I learned this the hard way.
Now, I can say that my Savage 99 WiIl fire this configuration, although it Chambers hard. Conversely, I turned a HK 91 into a mini grenade with this configuration.
Why? Well, ignorance and thrift. In the mid Obama years, slugs, powder, etc are expensive, if not impossible to find. I had some .303 rounds, which I disassembled and used the slugs to build .308.
At the time I was unaware that the Brits measured ".30 Cal" from the groove, not the lands.
Keep the .311 slugs for the .303 and .30-40's...

The metric designation for the 303 British is 7.7x56R. 7.7 to inches is .30315 so that means it's measured on top the lands. You know the groove to groove is lot deeper then .30315. .308 does have a top of land measurement of .300. The groove to groove would be .308. The 30-40 Krag land to land is suppose to be .300 and the groove to groove is .308, but do to manufacturing tolerances and worn bores you'll find the groove diameters larger. I have one and my measurement is .3095. One should really shoot the correct diameter bullets in their rifle, although you can get away with a fatter bullets sometimes.