Hi everyone. i just had my 260 Rem reamed to 260 Ackley Improved. Dave Kiff recommended .100 free bore. I hope to find a 140 Gr. bullet recipe that works well.With the bullet seated at the lands approx .130" of the bearing surface of the bullet is into the case past the neck/shoulder junction. Obviously this reduces case capacity, dont yet know if enough to matter. I am hoping to achieve an accurate load in the 2950-3000 Fps range. What would the negative effect be if you increased the free bore to approx .230" so that if the bullet were seated at the lands only the boat tail section would be into the case past the neck/shoulder jnct. Is there a point of diminished or negative return with increased free bore? The gun is a savge Mod 10 & the mag will accept an OAL of up to a full three inches which is more than enough to accommodate this scenario. Hope the old adage about no dumb questions still holds true, any input is appreciated.
Free Bore, how much is to much?
- Thread starter Lucky
- Start date
Lucky: I like to spec my pacific reamers so the first bullet of intended use is touching the lands with the full shank diameter of the bullet just far enough in front of the neck/shoulder junction to avoid the donuts that may form there. To my way of thinking anything much more than that is little different than firing 500, 800 or ? rounds down the barrel with all the resulting erosion. I've had chambers cut that had more freebore than I would have preferred and with normal throat erosion, it was not long before I could not touch the lands & still keep a good part of the bullet in the case neck. Especially important with a ctg. that has a short neck length, like the 223 Rem., for example.
Why any freebore beyond normal throating for a .260 rem? Would not consider any freebore, unless was chambering a hunting rifle for one of the weatherby ctgs and chose not to work up my own loads.
Just thinking outloud here, but Rem 700 short action IE is shorter than the Win 70 SA. Might want the freebore to allow seating bullets at optimum length when single-loading??? Or is customers goal to maximize velocity? Freebore was Roy Weatherby gimmick to max-out velocity by effectively stretching chamber to reduce immediate pressure.
Just thinking outloud here, but Rem 700 short action IE is shorter than the Win 70 SA. Might want the freebore to allow seating bullets at optimum length when single-loading??? Or is customers goal to maximize velocity? Freebore was Roy Weatherby gimmick to max-out velocity by effectively stretching chamber to reduce immediate pressure.
NorCalMikie
Gold $$ Contributor
Lucky: I'am thinking the first thing you would need to know is if your bullets prefer to be jumped or jammed into the lands. Some of the larger calibers prefer a good jump to the lands compared to the smaller calibers that work well being jammed.
A bullet seated at the shoulder/ neck junction and jammed into the lands would be my prefered choice.
Nothing worse that having a chamber cut then discovering the freebore is too long and you can't shoot the 140s and still have enough bullet in the case neck. And there's a chance that the OAL of the round being set to the longer freebore may not fit the mag?
A "dummy round" sent in and the chamber cut to those specs would my choice. YMMV, Mike.
A bullet seated at the shoulder/ neck junction and jammed into the lands would be my prefered choice.
Nothing worse that having a chamber cut then discovering the freebore is too long and you can't shoot the 140s and still have enough bullet in the case neck. And there's a chance that the OAL of the round being set to the longer freebore may not fit the mag?
A "dummy round" sent in and the chamber cut to those specs would my choice. YMMV, Mike.
OK,im back. Thanks again for the feedback. i think i first need to clarify why i am asking this question. with my current chamber & freebore,.100" i have to seat the bullet so deeply in the case that it is compressing a 44.5 gr charge of H4831sc. Approx. .130" of the shank or bearing surface of the bullet is inside the case below the neck/shoulder jnct.. this is with the bullet at the lands. I dont want any extra freebore,just want to know if there is any drawbacks to having enough additional cut in to allow me to seat the bullet out so that the boat tail/bearing surface junct. of the bullet is at the neck/shoulder junct. of the case. this would require a total freebore of around .230" unless i am completely screwed up in my understanding which is entirely possible. Since my original post i have fired a few test fire forming rounds & am a little concerned about pressure. anything over about 44 gr. starts causing some cratering of the primer & backs it out of the pocket. i am shooting new Lapua brass chambered in 260 Rem. Even after fire forming 44 gr. seems to be the limit before i start seeing slight signs of pressure. I have not chronied the loads yet but 44 gr. seems like a fairly mild load even with the Lapua brass. Any thoughts?
Hmmm... looking at Hodgdon's suggested loads for 260 REM there aren't too many that push past 44.5 grains with 140+ grain bullets. 260 AI ought to be good for a little more. Looking at their suggested cartridge overall length, they pretty much stick with 2.780" from the Sierra 107 up to their 142 grain HPBT. How does this compare to what your's is?
To me, 0.130" of any seated bullet below the case shoulder is too much. All the cartridges I shoot for long range currently (6XC, 308 for Palma) have chamber throats cut so that bullets seated 0.020" off the lands end up with not more than maybe 0.20" of their bearing surface inside the case neck, or less up to a minimum of about 0.10".
Obviously what works for me may not work for others, so take this all with a grain of... powder.
To me, 0.130" of any seated bullet below the case shoulder is too much. All the cartridges I shoot for long range currently (6XC, 308 for Palma) have chamber throats cut so that bullets seated 0.020" off the lands end up with not more than maybe 0.20" of their bearing surface inside the case neck, or less up to a minimum of about 0.10".
Obviously what works for me may not work for others, so take this all with a grain of... powder.
For what it is worth, my Tikka T3 stainless/synthetic in 6.5x55 Swede has a ginormous long throat for the WWI heavy RN bullets. Don`t ask me why Tikka and Sako continue to this. Must be some sort of tradition thing.
Believe it or not, the most accurate bullet in this rifle is the 95 gr VMax. I seat it so that one bullet diameter is in the neck. Have never calculated the jump to the lands. Tell my buddies it is 1/4 mile for effect. Load it to 3000 fps and hammer the coyotes.
Given my druthers, I would have a shorter throat in this rifle but that would require a rebarrel.
Good luck in your quest.
Bill
Believe it or not, the most accurate bullet in this rifle is the 95 gr VMax. I seat it so that one bullet diameter is in the neck. Have never calculated the jump to the lands. Tell my buddies it is 1/4 mile for effect. Load it to 3000 fps and hammer the coyotes.
Given my druthers, I would have a shorter throat in this rifle but that would require a rebarrel.
Good luck in your quest.
Bill
NorCalMikie
Gold $$ Contributor
Adding a "little more" freebore to what you already have wouldn't be too bad if you never planned to change bullets.
Adding another .130" to what you already have might be a bit too much?
Load a dummy round with the bullet seated to touch the lands. Lay one of the same bullets next to the dummy round. That should give you an idea as to where it seats in the case for comparison. See where an extra .130" comes out. Will the round still fit in the mag? Could you get by with say just another .050" past where you started from?
Better to think it out now then go longer. You can't go back.
Adding another .130" to what you already have might be a bit too much?
Load a dummy round with the bullet seated to touch the lands. Lay one of the same bullets next to the dummy round. That should give you an idea as to where it seats in the case for comparison. See where an extra .130" comes out. Will the round still fit in the mag? Could you get by with say just another .050" past where you started from?
Better to think it out now then go longer. You can't go back.
Thanks NorCalMikie, i appreciate your stickin with me on this. Your suggestion is how i arrived at those dimensions, approximate as they are.My mag would accept an OAL clear up to 3". I probably would not go the full additional .130 as you suggest so i could go to a lighter,shorter bullet down the road if i wanted to. i was mostly just wondering if there was a problem with cutting that much freebore if you did know for sure you were only going to shoot that 140 gr. bullet seated out to the lands.
NorCalMikie
Gold $$ Contributor
Lucky: Again,with the bullets you're shooting "now", do they prefer to be jumped or jammed? Have you figured that out yet?
I would get that figured out before I tried to figure out how much freebore to finally go with.
Like I mentioned before, dummy round set (jam or jump) where you like it, loose bullet laid next to it for comparison. Will it fit the mag?
You've got a little more work before you can make your decision.
Nothing wrong with asking the guys at PT&G (or whoever) their opinion. I just like the idea of knowing ahead of time what I want. Cut too much freebore and you can't go back.
I don't claim to be an expert, just been there, done that and sold off my 6BR barrel because it was throated too long to shoot the bullets I wanted. It's your barrel so have it set up the way "you want it".
I would get that figured out before I tried to figure out how much freebore to finally go with.
Like I mentioned before, dummy round set (jam or jump) where you like it, loose bullet laid next to it for comparison. Will it fit the mag?
You've got a little more work before you can make your decision.
Nothing wrong with asking the guys at PT&G (or whoever) their opinion. I just like the idea of knowing ahead of time what I want. Cut too much freebore and you can't go back.
I don't claim to be an expert, just been there, done that and sold off my 6BR barrel because it was throated too long to shoot the bullets I wanted. It's your barrel so have it set up the way "you want it".
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