30 Cal. .299 vs .300 bore diameter

[JayCutright]

Anybody know that one's better than the other?
I've been using .300x.308 but I've noticed some shooters are big on .299x.308, what's up with tighter bores?

 

[Laurie]

Jay,

to get higher velocities. Tight bores, even tighter than 0.299", were a particular feature of UK and British Commonwealth 'Target Rifle' barrels as shooters were mostly restricted to 7.62mm military ammo until recently and their bullets are often undersize, running in the high 0.307s, while commercial nominally 0.308" dia. match bullets usually run in the low 0.308s, but can be up to 0.0005" 'oversize'. Even with the adoption of the 155gn Radway Green FMJBT sniper round bullet in British ammunition, and hence Target rifle, it was a true 0.3080" dia. bullet, but users and their gunsmiths seemed to want to stay a bit 'tight'.

The tight bores were originally needed to get over 2,900 fps from standard NATO milspec 144-146gn FMJBT 7.62mm ammunition. Over here, TR barrels have virtually standardised on the 0.298" bore size and RWS loaded its NRA contract .308W ammo with the old 155gn Sierra MK to suit, the objective being around 2,950 fps in a 30" barrel in good condition.

You should get the same MVs from .300/.3080 but needing a little more powder probably. Our .308W F/TR shooters have mostly abandonned thes etioght bores and can get 155s up to nigh on 3,100 fps and 210s at well over 2,600, so it's not true you need a tight barrel to get really high MVs with quality bullets.

There is a lot of information on 'tight' Target and Fullbore Rifle barrels and the rationale thereof on the US Rifle Teams' Long-Range Shooting forum including the results of tests carried out in England some years back on MVs and pressures with different .30-cal barrel dimensions. That showed that commercial match ammunition could significantly exceed allowed CIP Maximum chamber pressures in overly tight barrels.

See:

http://www.usrifleteams.com/lrforum/index.php?showtopic=12800


Generally speaking, it doesn't help accuracy either if you're swaging a 0.3083" dia bullet down 0.002" +, but that's what happens in many TR rifles over here, the 0.298 / 0.299" bore diameter having become the standard.

Laurie,
York, England

 

[Rustystud]

Tight bores are the norm for Palma rifles. They normally shoot 155s. With long bearing surface bullets you will experience pressure issues with tight bores. I use .3000s through .3008s and .3076 through .3008s.
Nat Lambeth

 

[rcw3]

We sell a lot of .299" x .308" Bartlein 5R 30 caliber barrels. I would not exactly call that a "tight bore", especially since the groove size is the full .308" and the 5R land configuration is not as aggressive as many of the conventional rifled bores (i.e. you are only looking at a miniscule .0005" additional height on the top of each land and with 5R rifling that is the thinnest part of the land). I realize the nominal spec. is .300" x .308" but as far as I know that was originally set up with conventional opposing land 4 or 6 groove barrels and things have also changed in barrel making and rifling over time.

Any talk of increased or excess pressure with this set up in a 30 Caliber 5R land configuration is conjecture and not reality. Many of the 30 caliber rifles currently produced by GA Precision use this exact bore dimension and configuration and they are producing some of the finest and most accurate 30 caliber rifles in the U.S. right now and they are built to shoot factory 308 Win. or 300 Win. Mag. ammo. with no issues. With the less aggressive land configuration of the 5R lands, the prevailing thought is a little more bullet grip is good on many levels and for barrel longevity and wear.

I know one thing for sure, barrels wear as more rounds are shot through them, and when a bore is loose you can have a rifle that shoots big loose groups. From that perspective I would always err on the side of a little tighter bore than a looser one.

Robert Whitley

 

[jo191145]

I have a Kreiger .298 /.3065/ 1-13 Palma barrel chopped off at 26''. $50.00 for the blank I could'nt pass it up.

It does seem to ramp up the velocitys and pressures a bit. Usually seems only slightly higher than book data at low charges. When you get up near book max its howlin.
I've been 3100+ with a 155 out of a 26" tube with Varget. Most folks claim short barrels can't get to 2950. :-\
FWIW accuracy bites at high velocitys. It seems to like 2750fps with Lapua brass.
A small batch of old Winchester Match brass showed signs of a node at 2950 but the pockets loosened up. Not worth it for me.
Its not something I've done a lot of work with. Not an expert on the subject by any means.

 

[Larryh128]

I had both a .299 & a .300 barreled 300WSM. I would consider MY .299 to be slightly more accurate BUT the .299 max load was 2 grs less than the .300. I ended up selling the .299 & replacing it with a .300 so I can shoot the same load in both rifles. Barrels were the same manufacturer & NOT 5R.