Should I have my .308win free bore increased?

[stinnett1981]

So I have had my custom .308 for several months now. I have 200+ rounds down the barrel. I shoot 175g SMK's and 178g Amax's. The rifle is chambered with a 308 Bisley reamer which has a .080" free bore. It seems like the free bore is a little short. With a 175g SMK loaded touching the lands the COAL is 2.798". I load them 2.78" with 44.7g of Varget and it shoots amazing. This load has the bullets boat tail/bearing surface junction sitting just above the neck/shoulder junction and the base of the bullet sits just above the shoulder/body junction. With the 178g Amax its a different story. It sits a little too deep in the case. The COAL touching lands is 2.830" and I load them 2.812" with 44.3g Varget and it also shoots amazing. My gunsmith said he can easily increase the freebore for me. My issue... this rifle shoots both of these loads in the .2moa and .3moa at 100 yards and well under .5moa at long ranges which scares me to mess with it! My barrel is a 10 twist and I would like to try out some heavier bullets, but I cant because my free bore is to short. What is your guys .308win COAL with 175g SMK's and 178g Amax's and your chamber free bore? Thanks guys!

 

[stinnett1981]

My free bore is a little bit to short, but not by much. I only want it to be lengthened .010" or .020". A loaded 175g SMK touching the lands is 2.798ish. I would like it to be 2.818" so I could load it right at 2.800" I would be able to load the 178g Amax's correctly too. I'm just wanting to know fellow shooters COAL touching the lands with 175g SMK'S that ALSO have a Bisley chamber that is .080". I wanna make sure theirs is the same as mine.

 

[Erik Cortina]

Leave it alone! .010" or .020" increase in freebore will do nothing for you.
If you only want .010" freebore growth, keep shooting your gun, you'll get there for free!

 

[Laurie]

Leave it alone! .010" or .020" increase in freebore will do nothing for you.
If you only want .010" freebore growth, keep shooting your gun, you'll get there for free!

+ 1 on this view. You don't say what distances you're using the rifle over. I'd only advise contemplating a change here if you plan on serious F/TR competition at 900 and 1,000 yards, and even there I'd say leave well alone but revert to a good long-range 155gn bullet, the 155.5gn Berger BT Fullbore is ideal, and look to get over 3,000 fps if feasible in your set-up. (You don't say what length barrel you're using either.)

Don't worry about 'over-stabilising' 155s in a 1-10 inch twist - modern match grade models are so well made and designed they cope fine with being spun considerably faster than the theoretical optimal.

If you really want to go down the heavier bullet route, one option / compromise is to have the gunsmith increase the freebore just enough to handle the 185gn Berger Juggernaut. This amount of freebore will still work very well with the longer 155gn match bullets.

The Bisley 150 chamber IS just a tad on the short side but still copes better than many imagine with longer / heavier bullets. It was designed to be optimal for our Radway Green ammunition factory 155gn British forces 7.62mm sniper round. This bullet has a similar shape to the older 155gn Sierra MK, but is an FMJBT rather than a hollow-point BT match (or OTM as this form has somehow been rechristened recently). UK 'Target Rifle' competitors now mostly use German RWS manufactured .308 Win cartridges loaded with the older model (p/n 2155) 155gn Sierra MK. These cartridges are supplied through our NRA and the Bisley 150 chamber works very well with them indeed. Those who handload and have tried the newer 155gn SMK, the current 'Palma' version (p/n 2156) have found the chamber less than ideal and it can take a bit of work and luck to get this higher BC bullet to group as well as its older stablemate.

 

[stinnett1981]

Leave it alone! .010" or .020" increase in freebore will do nothing for you.
If you only want .010" freebore growth, keep shooting your gun, you'll get there for free!

+ 1 on this view. You don't say what distances you're using the rifle over. I'd only advise contemplating a change here if you plan on serious F/TR competition at 900 and 1,000 yards, and even there I'd say leave well alone but revert to a good long-range 155gn bullet, the 155.5gn Berger BT Fullbore is ideal, and look to get over 3,000 fps if feasible in your set-up. (You don't say what length barrel you're using either.)

Its a 24" Bartlein and I plan on shooting it mostly at 600 yards and occasionally at 1000 yards. Thanks for the input guys

 

[savageshooter86]

I would leave it be. 24" won't be optimal to 1000 yards from everything I have been told and have read. Is the OAL now giving you donuts or something funny? If it shoots in the 2s and 3s I wouldn't touch a thing.

 

[stinnett1981]

I would leave it be. 24" won't be optimal to 1000 yards from everything I have been told and have read. Is the OAL now giving you donuts or something funny? If it shoots in the 2s and 3s I wouldn't touch a thing.

Not that I can see. When developing loads for the 175g SMK and 178g Amax it actually shot best on the warmer side. I load 44.7g Varget for the SMK and 44.3g Varget for the Amax. I was VERY cautious when developing the load for the Amax because the bullet sat a little deep in the brass which decreases volume and increases pressure. But I slowly got up to 44.3g and it shoots 5 shot groups into 1 little hole. I figured I would get pressure signs early ???

 

[Laurie]

Yes, with 24 inches, you'll struggle at 1,000. As Gstaylorg says the 175gn Berger Tactical OTM may offer an advantage for 1,000 yard comps as it's designed to work with 20-24 inch barrel velocities and remain stable through the transonic speed zone and the drop through the sound barrier. It is designed though expressly for the US military's recently adopted 1-11.25 inch rifling twist rate in its 7.62 sniper and marksman rifles, and 1-10 inch spins it rather (actually a lot) faster than it was designed to give this high degree of stability with.

Another 175gn option for longer ranges is the 175gn Berger LR BT, not as well known as the 185gn Juggernaut, but a proven LR performer amongst sling Fullbore / Palma Rifle shooters in US Rules / any bullet weight matches, many of whose rifles will have your chamber form or similar designs such as the Palma 95. It has a higher BC than the 175gn Sierra MK and is an excellent performer in most barrels.

 

[savageshooter86]

reason I asked was most throat out to get the pressure ring above the neck/shoulder junction and to move the bottom of the bullet out of that case to increase powder capacity if they are not reaching the velocity needed due to this powder room being taken up.

If you are not having any issues and getting velocity and accuracy, stick with it

 

[Shynloco]

Like the other have said, leave it alone. Might I make one suggestion... and that is try changing your bullet to a 168gr HPBT IF you are going to shoot 100 - 200. A few years ago one my Benchrest buddies spoke to one of the bullet guru's at Sierra who told him the 168 gr HPBT was designed for distances UNDER 400 yds. The 175's are designed for 400 yds+ and more like 600 yds to 1K. When I ordered my reamer from PTG, I told Dave Kiff I was intending to shoot strictly 100 - 200 yds using the 168's and he sent me a .308 Bisley, the same as your's. As for powder loads, I'm getting 1's and 2's @ 100 yds using right at or around 42 grs of Varget, IMR 4895 and RE15. Obviously you have to test to see what your baby likes. Just something to think about.
Alex