Over the years I've had experience three times with lengthening the freebore in order to seat long bullets out as far as possible. The first was in my own TRG to make use of the 3.750 long magazine. The long sloping approach to the lands was preserved, and the cut was reasonably smooth and matched the depth of the grooves. The was no effect on that fine Krieger barrel's accuracy and now I had better velocities at the same pressure levels.

The second was a 330 Dakota. Not my rifle, but this time a .5MOA shooter transformed into a 3.0MOA shooter. A borescope showed a smooth cut, but the front edge of the lands ended abruptly. The freebore of throat was .004 larger in diameter than the grooves. It looked like a second neck area. The owner had to replace the barrel.

Next is a 6.5-284. The chamber the reamer cut was too short in the throat, forcing 140 Partitions about .200 deep. The reamed area looks like it was cut by a bulldozer. Again the lands end abruptly. The new freebore is visibly deeper than the grooves (.002-.004?) And the rifle is 3.0MOA.

So what's the secret? Never throat ream? Or custom chamber reamer? Why did the first attempt work so well?

A properly reamed throat will be no more than .0005 over nominal bullet dia (eg. .3085 for a 30 cal) and have a 1 1/2 to 3 degree lead to bore diameter. A chamber with a badly oversized throat will be difficult to get to shoot. Many chamber reamers which do have a reasonably shaped throat will be oversized. I have been caught by this myself when I have failed to measure before use.
Reaming throats seperately is usually no problem providing the reamer is good. Regards, Bill.

And, the bore is dialed in...

The throat/freebore needs to be tight enough to pass the bullet from the case mouth to the bore as straight as possible so that the axis of the bullet remains true. Too large and long a throat can impart a false axis to the bullet and cause it to wobble off target. Needless to say, a non concentric bullet spinning around a false axis results in misses.

Malm

I'm assuming the barrel is scrap as it's a featherweight and can't be turned back enough to eradicate the cobbed up reamed area. Too bad as it is straight and smooth, a really terrific job of reaming before the button was pulled.

So the best way to avoid the problem in round two is to find a chamber reamer with adequate freebore? And check the reamer specs for .2645? I really don't want to have the throat cut separately again.

[ 01-13-2003, 11:44: Message edited by: Rod@Mountain_of_Dreams ]

A properly reamed throat will be no more than .0005 over nominal bullet dia (eg. .3085 for a 30 cal)

Hence some people say Wbys shoot well and some others pull their hair out while the rifle continues to give them hope

Don't see why cutting the throat is such an issue since very common practice is for the gunsmith to have a reamer with removable pilot, at least in Australia, but also suspect America and Canada.

Mike

I had a freebore on my voere 300 Win magnum and it game me 12mm groups all day longs so if done the correct way it must work

Rod,
Yes. The thing to do is to locate a 6.5/284 reamer with a longer throat. I ream all of my own match rifles with a separate throater, because I vary throat length accordingto the bullet, and always have. It truly should be no problem. Regards, Bill.

Rod---

It sounds like the throating reamer wasn't cut right. The reamer cuts to the profile it's ground to. A throating reamer should always be piloted, too.

I backtracked this. What was done: the smith did not have a throating reamer, so he used a 6.5-06 chamber reamer with a solid pilot. I'm assuming the barrel was still in the lathe in it's original chambering set up, but it looks like the reamer, unsupported, chattered on the lands. Can't say if the 6.5-06 reamer was smaller or larger than the short-throated 6.5-284.

Starting over. New "right" reamer. Sending a dummy round to Dave Kiff. 1:9 twist stabilizes 140gr Barnes (worst case) at 2825fps. Partitions were good down to 2600. SST at 2750. Now I have to find another blank that is .2636-.264.

[ 01-14-2003, 09:03: Message edited by: Rod@Mountain_of_Dreams ]

Rod, 'Afore you go a trashin that gas pipe you might get on the horn with Dennis Olsen. He has considerable experience snatching things like you describe back out of the dumpster. If you like sausage and know enough not to watch how its made,dont ask for details. his solutions DO work.
tomas

Well Thomas, I do like sausage. That's why there's a package of sheep "skins" in my freezer and a meat grinder with a sausage stuffer in a cabinet close by.

And a borescope in the garage shop.

Dennis may get the nod for the "next" chambering job, but, on this one, I wouldn't sleep well knowing that blemish resides inside. Life is short and time at the range comes at a premium. When it throws them high, low, and wide, it has to be powder or bullet. If there's anything else in the equation, I'm defeated before I start.