Any actual compairison between a tight bore 308 ..

[JJones75]

I was wondering if anybody here has actualy done a compairison between a standard bore 308 and a tight bore 308 barrel? I know that the thigher bore is supposed to give you a little more velocity from a shorter barrel just wondering if anybody has any solid testing on this?

My next build is gonna be a 18" 308 probably a Kreiger or Bartlein. 98% of the shooting will be under 500yds but I would like to be able to bring it out to 1k if the chance comes up. Most of the ammo will be factory loaded match stuff.

 

[Hummer]

Re: Any actual compairison between a tight bore 308 ..

I guess that is me. I have maybe a dozen barrels on target rifles that measure all variations. In 30 cal for instance I have one barrel that is .298"X.3055", a number of them that measure .299"X.307" and others .300"x.308"and some .300" by .309"+.
If I order barrels I ask for .299"X.307". As well I load bullets from .308" to .309" thusly there is a large variation possible but attention to detail allows for such.

What I have determined is each barrel is a story unto itself which is confirmed by a good borescope. For instance I see "factory" 30 cal barrels that have evidence of scant contact by the bullet with the bottom of the groove. Others have medium contact and others have heavy contact and even then the entire bore is not "sealed" thusly there is gas blow by between the opening left at the bottom of the rifling.

This is where the 5R design tends to help as this design tends to "seal up" better than conventional rifling. I guess I have about a dozen 5R barrels as well most being from Boots and others from Kreiger.

As a general rule I back off my loads starting with a "tight" bore just to see where I am. I do the step load series at 300 and or 600 to see which gives the smallest SD for long range shooting. I don't load anything to max levels. They don't shoot that much better and why risk injury to gain a few more FPS. As well it shortens barrel life.

Contrary to popular belief the danger I am afraid of does not come from blown primers. You are not going to shear the lugs but the biggest danger is stringers in the barrel steel.

Normally a split barrel (not occurring from in bore obstructions) will fail in the 9:00 to 3:00 orientation. Rarely does one occur in the 6:00 to 12:00 direction.

If you happen to be shooting prone with a sling and you get a barrel failure (AND IT DOESN'T HAVE TO BE FROM A HOT LOAD) YOU ARE LIKELY TO LOSE ALL FOUR FINGERS BETWEEN HE FIRST AND SECOND JOINT. Should a 6 to 12 failure occur you are likely to lose half your hand.

Barrel failures were rampant in the Pattern 14 barrels and while there are those that will say "I've never heard of such." I happen to have a copy of the Brit Ordnance Board Minutes "DECLASSIFIED" about sixty years after their acceptance of the weapons that clearly states barrel failures were sustained from all three vendors all during production with failure initiation beginning at the muzzle.

PO Ackly at Trinidad (early 1950s) told his students that under no condition would a US gov't barrel be rechambered to a magnum in the school as he realized resulhurized steel was used in the gov't barrel billets and while that was acceptable for 30.06 pressures it was not for magnum pressures and one of his students lost all four on left hand when he converted a M1917 to a 300 Win Mag.
He thought the old man didn't know what he was talking about and he had seen others do it.
Canadian Target barrels are known to be tight as well as Swiss Rifles have tight bores.
A very knowledgeable friend just the other night told me he had a custom reamer design that allowed him to fire milspec 303 Military bullets in standard 30 cal barrels with no pressure signs at all.
The 30-40 Krag was known to be a weak receiver (by 1903 Standards) and they had a throat in them that went all the way to next year to keep the pressures down.

Mosin Nagants are known to have large bores to allow them to fire the Russian MG ammo in them that had tight bores as they needed the pressures to drive the MGs. I know a guy who has a Mosin that was never rifled. It was drilled but never rifled. I tried to get him to let me have it and he wanted to keep it. You could never shoot it but would be a nice demo piece to show just what can happen in gun plants.

 

[DMS]

Re: Any actual compairison between a tight bore 308 ..

The reason behind tight bore barrels was due to the Radway ammo being issued at Palma matches. This ammo had bullets that were small in diameter. By going to tight bore barrels better accuracy was achieved. Manufactures continue to make tight bore barrels although Palma rules state that handloads may be used as some shooters continue to feel the need for tight bore barrels.

 

[300sniper]

Re: Any actual compairison between a tight bore 308 ..

i don't have a non-tight bore comparison but maybe someone else has their results. with my 18.5", .299/.308 bartlein barrel and factory federal match 168 .308 ammo, i was getting 2645 fps.

 

[Luvman]

Re: Any actual compairison between a tight bore 30

my 20" savage only gets about 2615FPS with 168gr GMM. it still wears a factory tube.