300 Wby match reamer throat

Tumbleweed

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Tillamook, Oregon
Hi guys.
Looking to set up a 300 Weatherby for my uncle using either 215 Hybrids or 200.20x Hybrids. These will need to fit in the Mag box which should be around 3.7".

When I set up a dummy round to 3.650" with either bullet, the end of the bearing surface is right at the case mouth. I want to use a match chamber reamer for the new barrel that will provide a .3084" diameter throat. If I were to optimize the throat length for either of these bullets I would have no throat, only leade basically at the end of the neck.

Obviously I don't want to do this in case he ever needs to use factory ammo in a pinch. So the question I'd like to know is what would be the minimum amount of throat length I should use and still be safe/compatible with factory ammo? Would .125" be enough?
Thanks!
 
.300 Weatherby Magnum and "match reamer" or "minimum throat" don't even belong in the same sentence, if you want to be able to use factory loaded ammo....…. If you want to shoot factory ammo, use a SAAMI spec finish reamer. Weatherby 'controls' pressure with the long throat. If you shorten the throat, factory ammo will create more pressure. With the higher pressures, safety becomes a concern. You would experience hard bolt lift and short(er) case life, at minimum. The finish reamers made by JGS and Manson Precision are of minimum dimension as provided by the Sporting Arms and Ammunition Manufacturers Institute. The Weatherby family of cartridges were not designed with the "do it all" capability in mind. A good chambering job in a quality made barrel blank, properly fitted to the action , will most certainly exceed performance expectations. It is a 'hunting' round, treat it as such!
 
........ I want to use a match chamber reamer for the new barrel that will provide a .3084" diameter throat...........
The spec on a standard SAAMI reamer for the freebore diameter of a 300 Weatherby Mag is .3084".
 
The spec on a standard SAAMI reamer for the freebore diameter of a 300 Weatherby Mag is .3084".

By golly you're right. I guess I had never looked at a SAAMI print for the Weatherby. Had always been told it had a sloppy throat, guess they were referring to length at around .346".
 
.300 Weatherby Magnum and "match reamer" or "minimum throat" don't even belong in the same sentence, if you want to be able to use factory loaded ammo....…. If you want to shoot factory ammo, use a SAAMI spec finish reamer. Weatherby 'controls' pressure with the long throat. If you shorten the throat, factory ammo will create more pressure. With the higher pressures, safety becomes a concern. You would experience hard bolt lift and short(er) case life, at minimum. The finish reamers made by JGS and Manson Precision are of minimum dimension as provided by the Sporting Arms and Ammunition Manufacturers Institute. The Weatherby family of cartridges were not designed with the "do it all" capability in mind. A good chambering job in a quality made barrel blank, properly fitted to the action , will most certainly exceed performance expectations. It is a 'hunting' round, treat it as such!

Pressure. Yes, exactly why I'm worried about messing with throat length much. I don't want to jump these bullets nearly .346" either. Thinking about all of this last night...I'm gonna see if we wants to do a 30 Nosler. I just completed a build for myself and I have the match reamer set up for 215's and everything already. Then there will be no pressure issues with factory ammo either. Thanks for the reply.
 
Shortgrass Nailed it !!!!

Don't mess with the Weatherby reamer, and don't mess with the Weatherby free bore. The dimensions are there for a purpose (They add velocity to the round without excessive pressure). if you decrease any of these, they go critical.

I have several and get extreme accuracy from them using the SAMMI spec reamer. The best one is a 30/378 hunting rifle that has shot sub 1/10 of an inch 5 shot groups.

On one of my 300s I "added" freebore to seat the bullets to .400. this requires a little machining of the bolt stop groove, changing the mag to a 378 mag, removing the third screw tang (For 2 piece floor metal). and adding free bore to keep it at factory spec with bullets seated to .400. This allows me to use maximum powder charges without going over the limit.

The belief that you must seat the bullet close or touching the lands for accuracy is a thing of the past especially with the Weatherby designed cartridges. With new powders, dies, better loads, accuracy is up to the re loader.

Just my opinion

J E CUSTOM
 
Thanks guys!
You kinda confirmed my concerns with modifying the 300 Wby throat. I've worked up loads for 2 factory 300's now and they can be a real bear to tune being that far off the rifling. Seem to be picky about powders they like when jumping that far too.
We're just gonna scrap this idea and use an older Remington 700 BDL in a 30 Nosler using 215 Bergers. We'll push it through a 27" SS 5R Bartlein.
I already have the match Rhiann/Brozovich reamer so it makes sense. No fighting mag length issues either, with the 215 touching the lands the cartridge still fits in a 3.7" box.
Thanks again
 
All of my Weatherby chambers run .0004"-.0005" straight clearance in the throat.
All but my 375 Weatherby run 3/8"/.375" throat lengths. The 375 runs 1/2"/.500" which it really needs to get 260's to 3000fps, 270's to 2950fps and 300's to 2850fps out of a 24" barrel.
I wouldn't mess with the clearances, too much pressure is leaked even bringing throat diameter to .001" over bullet diameter.
Interestingly, my 270 Weatherby has .00035" throat clearance and is rack driver even with a throat length of .375".

Cheers.
 
All of my Weatherby chambers run .0004"-.0005" straight clearance in the throat.
All but my 375 Weatherby run 3/8"/.375" throat lengths. The 375 runs 1/2"/.500" which it really needs to get 260's to 3000fps, 270's to 2950fps and 300's to 2850fps out of a 24" barrel.
I wouldn't mess with the clearances, too much pressure is leaked even bringing throat diameter to .001" over bullet diameter.
Interestingly, my 270 Weatherby has .00035" throat clearance and is rack driver even with a throat length of .375".

Cheers.
I apologize for a different cal question briefly but MM thank you for including some info for 270!Wby. I own two factory but am planning a build with match barrel can you suggest a couple actions to start with. Thank you.
 
Thanks guys!
You kinda confirmed my concerns with modifying the 300 Wby throat. I've worked up loads for 2 factory 300's now and they can be a real bear to tune being that far off the rifling. Seem to be picky about powders they like when jumping that far too.
We're just gonna scrap this idea and use an older Remington 700 BDL in a 30 Nosler using 215 Bergers. We'll push it through a 27" SS 5R Bartlein.
I already have the match Rhiann/Brozovich reamer so it makes sense. No fighting mag length issues either, with the 215 touching the lands the cartridge still fits in a 3.7" box.
Thanks again

Not to deter you from wanting a Wby but have you looked at the 300 PRC as an option ?
 
I apologize for a different cal question briefly but MM thank you for including some info for 270!Wby. I own two factory but am planning a build with match barrel can you suggest a couple actions to start with. Thank you.
I am very biased when it comes to building rifles. I own custom M700's for target/comp work that are far from stock.
For my LR hunting I only build on CRF actions. I use S/S Win Model 70 actions almost exclusively. But when I build for a .589" rim or larger, I use CZ 550 Safari Magnum actions.
If you want a bespoke action, I hear they are all very good.
Unfortunately for me, the cost of obtaining bespoke actions scares most people away here in Australia. Most supply M700 actions to me, but some listen and build on Model 70's.

Cheers.
 
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