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Deliberately throating a match barrel long

 
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  #8  
Old 01-31-2013, 05:00 PM
Edd Edd is offline
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Re: Deliberately throating a match barrel long

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Originally Posted by MontanaRifleman View Post
Because the throat/freebore area is a larger diameter than the bullet. If the bullet leaves the neck before engaging the lands, it is essentially floating uncontrolled and might "wobble", entering the lands slightly cocked.
The case has more room to wobble in the chamber than the bullet has to wobble in the freebore.
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Old 01-31-2013, 05:08 PM
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Re: Deliberately throating a match barrel long

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Originally Posted by Tumbleweed View Post
Hi guys. I will be re-barreling my 300Rum with a 31+" Broughten 5C 12.4 heavy palma 9 twist in a couple of months as well as blueprinting the receiver and bolt. Found my smith for the job, he seems more than qualified. I will be setting this up to run the 230 Hybrid Targets. Here is my question:

I want some feedback on the 'idea' of deliberately throating the chamber .25-.5" longer than a standard chamber with a match reamer that would allow say .0005-.001" bullet side clearance in the throat portion. I'm sure it would lend itself to very nice velocity above a standard chambering but my question and concern is would I be giving up any accuracy even with the very tight throat? With .0005-.001" throat clearance the bullet should still start out lined up with the rifling straight right? Would the heavy hybrid put up with this kind of jump without giving up any accuracy? I do have a Wyatt's box it my 700 now and it measure right around 3.860". I will probably keep it magazine feedable, so yes that's a lot of jump. I am going all out on this build looking for max accuracy, if I would need to sacrifice accuracy in any way I will not do it. Does anyone have experience with setting up a chamber this way and what kind results did you get? (Accuracy, velocity, ES, pressure, ect)

P.S. I know a guy that built a 7STW with 1" of freebore along with a special i.d. bore and claims to have been able to run 3600fps with a 175 grain gameking with .5MOA accuracy.
The bearing surface of the 230 Hybrid is .495" When the bullet is fired, the ogive will engage the lands just forward of the bearing surface, maybe .050 give or take. If you make your freebore longer than that, you might loose accuracy.

I just ordered and 300 RUM reamer and I am going with a .200" throat which was designed for the CE 200 gr Max Agg bullet. I also have an additional .018" from my trimmed necks to the end of the neck of my chamber for a total of .218" of actual freebore It will also be good for the 230 Hybrid as I will be seat that bullet so the the junction of the bearing surface and boattail are even with the junction of the neck and shoulder of the brass leaving some jump to the lands.
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Old 01-31-2013, 05:18 PM
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Re: Deliberately throating a match barrel long

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Originally Posted by Edd View Post
The case has more room to wobble in the chamber than the bullet has to wobble in the freebore.
That depends on chamber and throat specs. It also depends on how and to what degree the brass was sized. if there is a misalignment of the brass in the chamber, it would not likely exceed .001, especially if it were a match chamber.
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Old 01-31-2013, 05:24 PM
Edd Edd is offline
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Re: Deliberately throating a match barrel long

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Originally Posted by MontanaRifleman View Post
That depends on chamber and throat specs. It also depends on how and to what degree the brass was sized. if there is a misalignment of the brass in the chamber, it would not likely exceed .001, especially if it were a match chamber.
There is always the possibility of exceptions but that isn't what is being discussed. A typical freebore spec is .0005". A typical chamber to case clearance is at 6-8 times that.
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Old 01-31-2013, 05:35 PM
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Re: Deliberately throating a match barrel long

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There is always the possibility of exceptions but that isn't what is being discussed. A typical freebore spec is .0005". A typical chamber to case clearance is at 6-8 times that.
Typical freebore clearance from what I've seen on prints is .001 Match is .0005

My Chamber clearance will be .002 all around for .004 total after sizing.
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Old 01-31-2013, 05:50 PM
Edd Edd is offline
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Re: Deliberately throating a match barrel long

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Originally Posted by MontanaRifleman View Post
Typical freebore clearance from what I've seen on prints is .001 Match is .0005

My Chamber clearance will be .002 all around for .004 total after sizing.
Some of them are .001" , a 300 RUM happens to be one of them, but many of them are closer .005". Most of the Weatherby's are .004", including the 300 and 30-378.

Even in your example the chamber clearance is 4 times as much as the freebore.
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Old 01-31-2013, 06:27 PM
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Re: Deliberately throating a match barrel long

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Some of them are .001" , a 300 RUM happens to be one of them, but many of them are closer .005". Most of the Weatherby's are .004", including the 300 and 30-378.

Even in your example the chamber clearance is 4 times as much as the freebore.
My reamer is a match and the throat clearance is .0005, so it is actually 8 times. When the firing pin strikes the primer, it drives the case forward which then centers it up as the shoulder comes in contact with the chamber shoulder.

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