.298" Bore .30 Caliber Obermeyer Barrels...

[Matt in Virginia]

Gentlemen,
This will likely not result in a bumper sticker answer, however, I would greatly appreciate your input on .298" land diamerter "Tight" .30 Caliber Barrels from Obermeyer(amongst others). The three chamberings would be M118LR/.308 Win, A-191/Mk248 Mod 0/.300 Win Mag, and finally a Custom .30-06' Chamber throated for 208 grain A-maxs at maximum sub half MOA accuracy.

I should note the M118LR is a known quantity and have exhibited no pressure signs via either strain gauge or reading tea leaves on the case head. The A-191 .300 Winchester Magnum/190 SMK @3050 plus via Oehler 35P Proof Chrony, is an entirely different animal. It is clearly hot and shows pressure signs under normal usage without extreme temps. That said both ATK and Winchester loaded the round to similar velocity(if not accuracy). The WCC version is markedly more accurate than the early Federal. The .30-06' would be setup with lapua brass and a custom reamer to run 208 grain A-Maxs at reasonably warm velocity with the best repeatable accuracy available...

What are the dangers, benefits, and general take home messages on running a .002" tighter .30 Caliber Match Barrel with these three loadings? Your input is greatly valued...

Best Regards, Matt Garrett
Chesapeake, Virginia

 

[Larryh128]

The only down side to a tight bore is pressure. You will never be able to run the same loads as in a .300 bore barrel. I have owned .298 barrels and everyone was super accurate BUT I would end up selling them because I couldn't use the same loads as the .300 bores. Most of the top loads were 1-2 grs below the .300 bore to keep the pressure in line. Of course velocity was lower.

 

[Matt in Virginia]

Gentlemen,
That makes sense... Appreciate the input and open to more...

Best Regards, Matt.

 

[Bugholes]

I've found the velocities to be comparable but the tighter bore requires less powder (as previously mentioned) to get there. Boots swears the tighter bore lasts longer because there is "more rifling to wear away", and I would have little concern for this with hand loaded ammunition. That being said, I'd be a little uneasy shooting the navy ammo, which I believe is a bit on the hot side (and their spec seems to change).

There has been discussions about longer bullets in tight bore barrels, the bullets wil get more compressed and therefore lengthened because of the tighter bore. The flip side of that, and the reason why boots wasn't concerned about these higher pressures, is that the additional land height is the thinnest part of the R profile rifling, the top of the "trapezoid". Borescoping his barrels you will see that the land tops are quite narrow compared to other mfgs

 

[watercam]

I was always under the impression that the reason for the tight bores was to help compensate for variable bullet diameters when the Palma Teams traveled to other countries where QC was, uh, also variable. Having used both lately I do not see any accuracy difference between the tight bore vs. conventional when using quality bullets. I am not saying that there is no difference in bullet diameters occasionally but the variance is so small as to be naught in a practical world.

 

[TonyR]

I was always under the impression that the reason for the tight bores was to help compensate for variable bullet diameters when the Palma Teams traveled to other countries where QC was, uh, also variable. Having used both lately I do not see any accuracy difference between the tight bore vs. conventional when using quality bullets. I am not saying that there is no difference in bullet diameters occasionally but the variance is so small as to be naught in a practical world.

I heard something along the same lines. I head that the tight bore was used because one very popular bullet had a smaller diameter than most of the others. In 7mm, one very successful barrel maker only makes a .276/.284 while most of the others are .277/284. I've shot both and both have worked well for me.

 

[Matt in Virginia]

Gentlemen,
Much obliged...

Regards, Matt.

 

[Rustystud]

Done a lot of experimenting with 30 caliber barrels. .298" tight bore barrels are great for short bearing surface bullets, ie: 155 grainers. If you shoot long bearing surface bullets you will be well served to shoot .3000"-.3008' barrels. Bore diameter along with land groove ratios have a lot to do with your rifle making velocity before having pressure signs.
Nat Lambeth

 

[Matt in Virginia]

Mr. Lambeth,
That makes a whole lot of sense actually. Going to the 208 A-Max for the 06' so that makes one decision very clear. Thank you for the heads up...

Regards, Matt Garrett

 

[SBS]

Krieger's website does not recommend the tight bore (.298) for anything over 175 gr.

 

[Dangarusmc]

Having owned a 300 win mag with an Oby tight bore ,excessive copper fouling using 208 Amax . Very accurate but wouldn't do tight bore again unless it was a short barrel 308.

 

[Laurie]

I was always under the impression that the reason for the tight bores was to help compensate for variable bullet diameters when the Palma Teams traveled to other countries where QC was, uh, also variable. Having used both lately I do not see any accuracy difference between the tight bore vs. conventional when using quality bullets. I am not saying that there is no difference in bullet diameters occasionally but the variance is so small as to be naught in a practical world.

On the right lines but more to do with many countries using military arsenal loaded 7.62mm in their 'Target Rifle' discipline. This applied in the UK until very recently, and although the Radway Green 155gn FMJBT sniper round bullet (packaged as 'Bisley Match' for the civilian market) was much closer to 0.308" than earlier 146gn 'Green Spot' ammo's bullets, was still a little skinny.

It is self-perpuating of course. The GB NRA now sources its 308 Win from RUAG (RWS brand) and the ammo is loaded with the older 155gn Sierra MK (#2155), the loading and resulting MAP had to assume that it would be fired in tight-bore rifles. If used in a SAAMI spec barrel, pressures and velocities are sub-standard, so people keep on having TR rifles built or rebarreled with tubes on the tight side (though nothing like as tight as prevailed in the early 7.62mm days).

I understand that this is the case in the US too for serious Palma shooters where there appears to be less rationale. I assume that this is to accomodate the supplied ammunition in other countries as when Bisley hosts the competition.

I have found that both the old RG 155gn 'Bisley Match' and current GB NRA RWS match ammo give very low MVs when fired in normal 308s. A Howa 1500 22-inch barrel Varminter in good condition won't achieve 2,600 fps with the RWS ammunition, some 350 fps down on what the cartridge should produce and only around half the shortfall can be accounted for by the short barrel.