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Old January 8, 2013, 03:31 PM   #1
HShack
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Chamber reaming

Am about to have my GS re-barrel my Rem. 700. Trying to decide betwwen .308 Win. or .260 Rem. [Leaning toward this].

When doing the chamber reaming, can the leade be adjusted to suit the necessary cartridge length?

I am assuming that the bullet needs to be seated so as to use all the bearing surface of the cartridge neck as possible, yes?

This gun to do double duty as a Light Varmint -for- score [benchrest] and to do some long range shooting.

Any advice appreciated.
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Old January 9, 2013, 01:39 PM   #2
Unclenick
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Not normally. Normally the throat profile is ground into the finish reamer. You could get one made with no throat, like a roughing reamer, or else with a minimum throat with no freebore, then get a separate throating reamer made, but it's quite an investment and it is usually more economical to adjust your loads to match a standard chamber geometry.

The neck portion of a chamber reamer can also be altered per special order, as many custom rifle makers have for clients who are going to outside turn their case necks to thinner-than-average wall thickness. Neck length is usually ten or twenty thousandths longer than case neck maximum to allow for neck pull during start pressure build-up and before the bullet is released, but you could get it made shorter if you were controlling your neck lengths tightly.

I'd suggest you call Manson reamers and talk to Dave Manson. Describe what you are trying to do and he will know the prudent limitations.
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Old January 9, 2013, 10:42 PM   #3
Jimro
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Quote:
I am assuming that the bullet needs to be seated so as to use all the bearing surface of the cartridge neck as possible, yes?
No. The bullet needs to be seated only deep enough that it doesn't fall out. The 30-06 M2 ball load did not use the full neck, and millions of Garands cycled that load just fine without the bullet coming loose, but a crimp and sealant help out in that load.

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Old January 10, 2013, 06:24 AM   #4
Bart B.
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Note also that most cartridges are such that as the barrel's throat erodes away, bullets can be seated out further so their jump to the lands distance remains about the same. For example, with a .308 Win, after 4000 to 5000 rounds the throat's eroded away about 1/10th of an inch or so. There's usually enough bullet bearing surface length to let them be seated out 1/10th inch further than when the barrel was new.
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Old January 10, 2013, 08:20 AM   #5
jaguarxk120
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The best answer will come from the reamer mafgr., why not give Clymer Reamer a call and ask, 248-853-5555.

What your getting here is a opinion, the guy that makes the reamer can tell you just as unclenick suggests.
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Old January 10, 2013, 11:51 AM   #6
James K
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You can get special chamber reamers that will give a tight leade, but they are made for one bullet shape. If you decide to use another brand of ammo or another bullet, the round might not fit. I would stick to the SAAMI specs, which are built into the standard reamers.

But distinguish between a tight leade (where the bullet fits) and a tight chamber neck (where the neck of the case fits). If the chamber neck is too tight, the case neck can't expand to release the bullet and pressures go quite high.

Jim
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Old January 10, 2013, 09:34 PM   #7
HShack
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O.K. SAAMI specs. it is, now that I know I can vary seating depth so much.

Thanks for all the input.
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