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#6055491 - 11/28/15 10:02 PM 300wm custom throat length??
tx hunter Offline


Registered: 08/11/09
Posts: 250
Loc: Ft. Worth/Pidcoke
I'm having a new barrel (Krieger 26" m24 contour 1-10" twist) installed on an old Remington 700 300wm and I have a question. How do I determine what length to have the throat cut at? I don't hand load at the moment (that will change soon) so, I'm not set on just one bullet or max length for that one bullet. For the time being I'd like to just shoot off the shelf ammo and hopefully in the near future I can reload a custom round for this rifle. I kinda need a "middle of the road" throat length lol. Hopefully that makes sense to someone. Advice is greatly appreciated. Thanks!

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#6056831 - 11/29/15 06:11 PM Re: 300wm custom throat length?? [Re: tx hunter]
tx hunter Offline


Registered: 08/11/09
Posts: 250
Loc: Ft. Worth/Pidcoke
Thoughts?

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#6056841 - 11/29/15 06:15 PM Re: 300wm custom throat length?? [Re: tx hunter]
Tff caribou Online   content
Veteran Tracker

Registered: 08/27/12
Posts: 2997
Loc: Watauga, TX
Your gunsmith should know what you need.
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#6056876 - 11/29/15 06:29 PM Re: 300wm custom throat length?? [Re: tx hunter]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2579
If you have a dbm I wouldn't go longer than magazine length

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#6056990 - 11/29/15 07:17 PM Re: 300wm custom throat length?? [Re: tx hunter]
Ritter Online   content


Registered: 02/15/09
Posts: 246
Loc: Southern Oklahoma
Short answer;
Let the gunsmith decide.

Long Answer;
You will need to pick out one bullet and hand load for the rifle.
There is really only one way to figure out the throat length you need for a custom barrel, the base to ogive dimension. the BTO will be dictated by the bullet you choose and in large part by the cartridge overall length. The COAL will be restricted by the magazine length unless you plan on shooting the rifle as a single shot and load each round through the ejection port.

If you go this direction you start with the length of the magazine, then determine the maximum COAL and then the BTO. From there your gunsmith will determine the length of the throat.
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#6057017 - 11/29/15 07:29 PM Re: 300wm custom throat length?? [Re: tx hunter]
MacDaddy21 Online   content
Pro Tracker

Registered: 08/19/11
Posts: 1654
Loc: CO
If you go with a DBM, go with an extended length magazine if you have the option. I should have done this when I was building my 300WM. Instead I ordered the standard length McRees Chassis and mags. When I developed a load, they ended up being too long (3.649") to fit in the standard mags. So I had to order the extended length mags and mill my chassis to allow the bigger mag to fit.

I do not know what specific reamer my smith used but my rifle loves the 208 Amax and 210/230 bergers seated pretty long. Its been awhile since I developed the load but I think they are seated about .010" off the lands.

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#6057380 - 11/29/15 10:07 PM Re: 300wm custom throat length?? [Re: tx hunter]
tx hunter Offline


Registered: 08/11/09
Posts: 250
Loc: Ft. Worth/Pidcoke
It's an old bdl model so it has the hinged floorplate. I don't really have a need for detachable mags so I'm probably gonna keep it as is. I measured the internal length of the box mag and it measured out to 3.69. That seemed fairly generous to me. I want this rifle setup for long range hunting/tactical so, the coal doesn't need to exceed the mag length.

Now, it makes sense that one needs to pick out a desired bullet and load to further determine chambering. What troubles me is, what happens if i pick a bullet and load that just doesn't shoot well or what if I wanna experiment with a variety of bullets and loads? Maybe I'm overthinking it?

FWIW I've found three bullets that peaked my interest:
208gr. Amax
200gr matchking
210gr berger vld
Thanks for the help


Edited by tx hunter (11/29/15 10:13 PM)

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#6057816 - 11/30/15 09:12 AM Re: 300wm custom throat length?? [Re: tx hunter]
ChadTRG42 Offline
THF Trophy Hunter

Registered: 09/16/09
Posts: 9433
Loc: Lewisville, TX
At 3.690" COAL length, you are good. That's plenty of room for a standard chamber in 300 WM. My 300 WM is a normal chamber, and I am seating a 225 BTHP about 3.540". The bullets you have listed will all work with your magazine length and allow you to seat them at or near the lands. With the 10" twist, look into the 230 grain Berger! That's the Cadillac of the 30 cal bullets.
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#6057903 - 11/30/15 09:57 AM Re: 300wm custom throat length?? [Re: tx hunter]
charlesb Offline
Pro Tracker

Registered: 04/07/10
Posts: 1408
Loc: West Texas mountains
Just a thought, but why not give the gunsmith an example of a loaded round with the longest (heaviest) bullet that you intend to shoot?

Have him set it up for that.
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#6058628 - 11/30/15 03:51 PM Re: 300wm custom throat length?? [Re: charlesb]
tx hunter Offline


Registered: 08/11/09
Posts: 250
Loc: Ft. Worth/Pidcoke
Originally Posted By: charlesb
Just a thought, but why not give the gunsmith an example of a loaded round with the longest (heaviest) bullet that you intend to shoot?

Have him set it up for that.



Wouldn't have a problem with that if it'll get me where I need to be. I understand this stuff to a degree....still eagerly trying to learn lol.

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#6058859 - 11/30/15 05:39 PM Re: 300wm custom throat length?? [Re: tx hunter]
charlesb Offline
Pro Tracker

Registered: 04/07/10
Posts: 1408
Loc: West Texas mountains
Well, with a gunsmith, you are paying for his expertise. But he needs good information from you as to what you want. By handing him a round that you want it set up for, you've done your part and the rest is up to him.

Later on when you are reloading, you'll be taking measurements and seating the bullets into the case so that they work well with whatever throat setup you have. For now though, using factory rounds, I'm thinking that your best bet is to have him set it up for the factory round that you intend to use the most. - I would assume that would mean a 180 grain load since that's the best all-around loading for a .300 WM owner. - It will do just about everything well.
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Kind regards, charlesb

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#6059693 - 11/30/15 11:09 PM Re: 300wm custom throat length?? [Re: tx hunter]
tx hunter Offline


Registered: 08/11/09
Posts: 250
Loc: Ft. Worth/Pidcoke
Ok, I've been reading some more on this and the more I read the more it makes sense to me. This has already been said but, why couldn't I take the heaviest bullet that I'd ever want to experiment with (230 berger) find the longest coal that will feed reliably from my internal magazine, load a dummy round and have my smith work his magic based off the dummy round?

I've also read where some will load a dummy round with their desired coal and have it chambered where the bullet just touches the lands. This give them the ability to set the bullet back however many thousandths they wish to experiment with while still feeding from their magazine system. My knowledge is limited but that seems like a good idea. Thoughts? Thanks for your patience smile

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#6060036 - 12/01/15 08:21 AM Re: 300wm custom throat length?? [Re: tx hunter]
ChadTRG42 Offline
THF Trophy Hunter

Registered: 09/16/09
Posts: 9433
Loc: Lewisville, TX
With a standard SAAMI length 300 WM reamer, the ogive area will have plenty of room for throat erosion to seat the bullet out further.

Generally, you don't mess with a dummy round and a custom throat when there is plenty of magazine room. Most of the time you provide a dummy round when the magazine is short and you are planning on running an aggressive bullet, like a VLD. For example, when I shot my 260 Rem, I provided a dummy round with a 140 VLD at 2.860". The gun smith chambered the barrel with a throatless reamer, and went in with a throating reamer to get the lands where I wanted, to allow the bullet to touch at about 2.860".

Since your 300 WM has plenty of room in the mag, and a standard reamer will accommodate your needs, I wouldn't mess with a dummy round and special throating.

Also, remember that different bullets have different ogive to tip lengths. For example, you mentioned a 200 grain SMK and a 230 Berger. The ogive to tip length on a 190 grain SMK is .710". (The 200 grain will be very close, but I don't have this measurement for the 200 SMK, only the 190 SMK). The ogive to tip length on the 230 Hybrid is .905". If you seat the 230 Hybrid to 3.600", this puts the ogive at about 2.695". If you put the 190 SMK at the same 2.965", the COAL would be 3.405" (2.695" +.710"). You can seat the Berger out a little further if you want to gain some case capacity, but it's really not needed. I am seating my Hornady 225 BTHP at 3.580" in my SAAMI chamber, and it works great.

IMO, a custom throat is not needed, and would be time spent unneeded making this special chamber. Sure, you can make one, but why do you need one?
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www.DallasReloads.com
Type 01 and Type 06 FFL

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#6060297 - 12/01/15 10:12 AM Re: 300wm custom throat length?? [Re: tx hunter]
FiremanJG Offline
THF Celebrity

Registered: 12/16/08
Posts: 17893
Loc: Wolfe City, TX
To mirror what Chad said, we chambered my 7 Rem Mag with "0" free bore, knowing Ibwas going to run the longest 7mm hunting bullet on the market at the time, the 18 gr. VLD. Once the rifle was complete, I found my lands and started load development with the bullet even with the lands. The zero free bore means I have room left in the magazine. Worked up the load, and as usual, it started shooting best once on a compressed load of Retumbo. Looking at a cartridge you would never guess the bullet sitting in it is 1 1/2" long, simce so much of the bullet is in the case sitting right on top of the powder column. It is a beutiful thing to see all that horse power stack bullets into one hole at 100 yards. Then run out out to 500 and see it punish steel. Sure does wonders on large mammals too!
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#6060467 - 12/01/15 11:32 AM Re: 300wm custom throat length?? [Re: tx hunter]
trigger time Offline


Registered: 08/05/09
Posts: 30
Chad, your 300 is not a SAAMI chamber. It's a match chamber cut with a 0 throat reamer then we cut the throat to the bullets you wanted to shoot.

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