300 WSM throat depth???

[Laguna Freak]

I'm a barrel delivery away from being ready to start my 300 WSM long action build. This is my first custom build. I'd like to get the benefit of experience from y'all.

I'd like to throat for the 200 and 210 Accubonds, if possible. My best guesstimate says that there is about 0.070" bearing surface delta between the 2 designs. Though I may be way off. I have 200's on hand to measure but had to use the old eyechrometer on images of the 210 LR along with oal dimension to come up with this delta number.

My only remotely close throat reference is that I shoot .308 x 150 Accubonds loaded for 0.074" jump out of a Steyr 30-06 that shoots 0.2 moa +\- at 300 yards.

What does your experience with the .308 x 200 or 210 LR Accubond indicate is the preferred jump to lands?

Thanks for the help!

 

[MagnumManiac]

Regardless of cartridge, the 210g ABLR requires a throat length around .220"-.240" to have the heal below the neck juncture.
Seat a couple with the heal just below the neck/shoulder juncture and measure.
This is how I figure it out for throating reamers.

Cheers.

 

[MagnumManiac]

I forgot to mention that touch between the 2 bullets is vastly different. The 200g Accubond WILL be further into the case even with the longer throat due to the ogive differences.
I would base all throat dimensions on the 210g ABLR and compromise with 200g Accubond.

Cheers.

 

[tobnpr]

I have a SAAMI chamber on mine, used for LR target (208 ELDM's). Limited by mag length on the short action, but I could've easily throated it longer, seated the bullet out where it "should" be by conventional wisdom (boattail at neck/shoulder junction) and single loaded as it's a target rifle but decided against it after reading this. Real deal, scientific testing done at Nosler.

 

[Laguna Freak]

I have a SAAMI chamber on mine, used for LR target (208 ELDM's). Limited by mag length on the short action, but I could've easily throated it longer, seated the bullet out where it "should" be by conventional wisdom (boattail at neck/shoulder junction) and single loaded as it's a target rifle but decided against it after reading this. Real deal, scientific testing done at Nosler.

Interesting read. Thanks for posting. I too shoot 180's seated 0.020" off lands in a saami throated 300 WSM. I get 2925-2932 fps with 66.2 gr RL 23 out of a 24" barrel. Lots of bearing surface below the neck:shoulder junction and no sign of donut in 3 firings of Winchester brass.

I believe physics precludes such velocity from a saami throated 300 WSM with a 200 or 210 gr bullet at "safe" pressure. To my knowledge, the 1000 yd Benchrest competitors have pretty much proved this as ballistic fact. Hence, my quest…

 

[Laguna Freak]

I forgot to mention that touch between the 2 bullets is vastly different. The 200g Accubond WILL be further into the case even with the longer throat due to the ogive differences.
I would base all throat dimensions on the 210g ABLR and compromise with 200g Accubond.

Cheers.

Have you measured it in your rifle? Is it greater than the 0.070" I guesstimate?

 

[MagnumManiac]

Have you measured it in your rifle? Is it greater than the 0.070" I guesstimate?

If you mean OAL, then yes, I have loaded both and .070" with a .020" jump sounds about right. It will obviously change as OAL differs at different jump lengths.

Cheers.

 

[Laguna Freak]

If you mean OAL, then yes, I have loaded both and .070" with a .020" jump sounds about right. It will obviously change as OAL differs at different jump lengths.

Cheers.

My bad. Seems I was kinda vague in my OP. I'm trying to determine the probable range of jump to lands that may be best for each bullet. My concern is the high BC bullets have a reputation for liking a really long jump. I'm uncertain as to whether the 210 AB LR throating will be good for the 200 AB, and vice-versa. My only personal experience with .308 AB design is the 150 which likes 0.074" jump in my 30-06.

I guess I need a BTO measurement for the 210 AB LR but I don't have any on hand. I do have 200 AB on hand so I have that BTO measurement.

 

[MagnumManiac]

OK, I see what you're getting at.
Having used the 210g ABLR in several 300WM rifles now, most of them have liked a jump around .030" with only one performing well at .050" but is dismal in all other jumps tested and I quit trying to get them to group better than .75MoA.
That particular rifle needs a lot more running in, so I will wait and see.
Throating for touch then adding .020" is normally what I do.
You can't get around the fact that with some chamber throats not all bullets are gonna be near the rifling. You have to compromise, which is why you need to load up some dummy rounds with the preferred bullet and throat it for that.
My F-class rifle barrels are all throated for 230g Berger's…..can't get them anymore, so I use Sierra 210g Match, my rifles don't like the 220g.
I can still jam, but it leaves so little bullet in the neck it's not worth trying, so I compromise on jump length.
Hope this is what you need to contemplate.

Cheers.

 

[Laguna Freak]

OK, I see what you're getting at.
Having used the 210g ABLR in several 300WM rifles now, most of them have liked a jump around .030" with only one performing well at .050" but is dismal in all other jumps tested and I quit trying to get them to group better than .75MoA.
That particular rifle needs a lot more running in, so I will wait and see.
Throating for touch then adding .020" is normally what I do.
You can't get around the fact that with some chamber throats not all bullets are gonna be near the rifling. You have to compromise, which is why you need to load up some dummy rounds with the preferred bullet and throat it for that.
My F-class rifle barrels are all throated for 230g Berger's…..can't get them anymore, so I use Sierra 210g Match, my rifles don't like the 220g.
I can still jam, but it leaves so little bullet in the neck it's not worth trying, so I compromise on jump length.
Hope this is what you need to contemplate.

Cheers.

That fits with about half of the posts I found on accurate shooter last night. Those guys were pretty evenly split between 0.020 to 0.050 jump and 0.070 to 0.125 jump for the 210 AB LR. I guess like all other bullets it may be decided by the individual rifle.

 

[MagnumManiac]

Well, it's all about compromise, like most things in life.
What would you prefer, a bullet that gives mediocre precision all the time, or a bullet that groups very well all the time?
I don't look for that miraculous ONE 3 shot group that goes into one hole, I look for that 10 shot group that stays the same throughout everyday it is fired. This goes for my hunting rifles too.
Precision over an average is what counts at LR.
Others will look at it differently, but F-class has shown me that a load combo that shoots a little larger than a finicky load combo that changes during an event is not the one you want. You want it consistent from day to day, month to month and year to year.
The ABLR does not like jammed, touch or closer than about .020" in my experience and as I said .030" is where it starts for seating depth.
Benchrest shooters want one hole precision, this is not necessary for hunting, no matter who you are.
Those on Accurate Shooter are sticks in the mud, they poo poo everything that they don't agree with, which is why I got banned from there, I called out those so called gifted shooters who know ONE WAY to do things and if you don't agree with them you were ostracised. They never even gave different methods a try, so who are they to question anyone?

Cheers.

 

[Laguna Freak]

Shootersproshop had some 210's that actually went in my cart and checked out.

 

[Laguna Freak]

I took some comparative measurements of these two Nosler bullets that may help others in a similar circumstance to mine.

200 Accubond:
bullet oal ~ 1.485" (per Nosler)
base to ogive ~ 0.084"
boat tail length ~ 0.115"

210 Accubond LR:
bullet oal ~ 1.570" (per Nosler)
base to ogive ~ 0.090"
boat tail length ~ 0.290"

Interestingly, it appears to me that throating for the 200 AB will provide ample throat for the 210 AB LR due to the 200 exhibiting longer bearing surface when boat tail : bearing surface junction is seated at the case neck : shoulder junction. In the first image the base of the 200 is ~ 0.145" off the micrometer.

 

[Laguna Freak]

Oops! Just noticed my typo above. The bto should be 1.0xx