New 223 FTR Barrel FB?

[Sumtoc]

Is there a optimal/recommended FB to be able to shoot all the 80-90 gr bullets? Mainly the Berger 85.5 and 90.....

Thanks

 

[CADDIE5]

ISSF reamer 0.169" freebore starting point to 0.180-0.190" reamer freebore

 

[XTR]

The 169 ISSF reamer will work with 80s and 90s. Ideally if you are shooting only 90s another 10 to 20 would probably be better but that will be too long for then 80s.

 

[mike mccormick]

A .175 freebore puts the 85.5 just in front of the neck/ shoulder junction. A little more would not hurt

 

[Ned Ludd]

I've run the 90 VLDs in F-TR rifles chambered in both 0.169" and 0.220" freebore. Both work, but the 0.169" freebore is a little too short to be "optimal" for the 90 VLDs, IMO.

The 90 VLD and 85.5 Hybrid have BTO dimensions of 0.622" and 0.585", respectively, or a difference of .037" (~.040"). A 0.220" freebore puts the boattail/bearing surface junction of the 90 VLD somewhere close to the middle of the neck, or just short of it, when they are seated at .021" off the lands. At the same seating depth, the 85.5 would therefore be seated approximately .040" farther out the neck at the same CBTO measurement. That would translate to the 85.5 having roughly 0.110" (half the neck length) - .040", or about .070" or so worth of shank in the neck seated at -.021". That is a little short of the desired minimum "half a caliber bullet shank in the neck", but not by too much. As a crude estimate, you should be able to run the 85.5s fairly close to optimally in a rifle having from 0.180", to as much as 0.200" freebore. That would also be a little better for the 90 VLDs, having from ~.011" to .031" more freebore than would be cut by the 223 Rem ISSF reamer (0.169" fb). No single freebore length will be "perfect" for both bullets, as their BTO lengths differ by almost .040". So choosing a compromise that will work reasonably well for both is really the only option.

Possibly even more critical than freebore is the barrels' bore/groove configuration if you're planning to run the 88 ELDMs, or 90 VLDs. It is not uncommon to experience jacket failures with these two bullets in barrels of 30" length (or more) when running faster than a 7.0-twist when using a 0.218"/0.224" bore/groove configuration. It is much safer to use a 0.219"/0.224" barrel configuration with these long heavy bullets to minimize the chances of jacket failure, especially if planning to run relatively warm loads in F-TR rifles. The extra half thousandth bore diameter on each side doesn't seem like much, but it apparently makes all the difference in the world, even allowing twist rates as fast as 6.5-twist to be used with minimal odds of jacket failures in 30" barrels. Nonetheless, a 7.0-twist will work just fine, although around 6.8-twist is pretty near optimal for the 90 VLDs. If you don't already have the barrel in hand, consider going with a 0.219" bore.