7mm Rem Mag Throat

[denphillips2]

Now that you helped with barrel length.

How about throat? I am setting it up for 180gn Berger VLD.

Would the ideal seating length put the boatail/body junction of the bullet at the shoulder neck junction of the case?

There is plenty of room in the magazine. (700LA)

I have a short throat reamer with a throating reamer to set the lenght.

Thanks!
Denny

 

[rscott5028]

I don't have an answer, but I also am curious as I recently saw where someone raised the issue of throat errosion and suggested not making the throat too long for initial chambering.

 

[denphillips2]

That is a good concern. Too short and you are just shooting yourself in the foot though.... Reduced powder capacity and possibly velocity. I have done nothing with a 7mm Rem Mag before, so this is new to me. Most of my custom builds have been 6.5 and under and defiantly not magnums.

 

[denphillips2]

Where is that thread about throat erosion you talked about?

 

[rscott5028]

Just brief mention made by SBruce... http://www.longrangehunting.com/forums/f28/question-jump-77587/#post545166

 

[J E Custom]

That is a good concern. Too short and you are just shooting yourself in the foot though.... Reduced powder capacity and possibly velocity. I have done nothing with a 7mm Rem Mag before, so this is new to me. Most of my custom builds have been 6.5 and under and defiantly not magnums.

Throating a chamber short has it's advantages but it also has its disadvantages to.

If you build a rifle around a particular style and weight of bullet it will sometimes come back
to haunt you because the barrel may not like the bullet and your stuck with rechambering
or at least re throating the chamber.

If you are lucky and the barrel likes that bullet Great. But if it doesent hang on.

Most of us like velocity and more free bore/throat is one way to get it without excessive
pressure.

This will always be a debate and there are lots of opinions as to which way to go. I prefer
building a rifle that will shoot most any bullet well, rather than build one for one bullet and
risk getting one that wont shoot anything with out re doing it.

Free bore is not a problem if the rifle is built correctly (Just like the belted cases) and in many
cases it is a plus.

I recomend a standard chamber to all but the most experanced who can trouble shoot a problem
and work it out.

There are many reasons to use a special throat dimension but none that can't be overcome
with proper planing In My Opinion.

So be prepared for issues if you short throat your mag.

J E CUSTOM

 

[rscott5028]

JE,

I think the OP was about using a longer throat to accomodate VLDs.

I was pointing out that too long might be a problem over time as the throat errodes.

Are you recommending a standard throat length with sufficient freebore to accomodate VLDs seated a little further out?

thanks!
Richard

p.s. to your point about taking a chance on rechambering, I imagine Shawn Carlock and Kirby Allen just consider barrels expendable in their R&D with throat designs for the +P, etc...

 

[denphillips2]

Good food for thought J E.

What is considered a "standard throat" for a 7mm Rem Mag? I would guess it to be in the .200-.300" FB range.

I just looked at my reamer, and it is a 0FB.

So if you were to seat a bullet in and use it for your gauge for throating, how deep would the bullet be in the neck in your ideal world?

If I have to rechamber, so be it. I know the throat will erode, but fast enough to worry about on a hunting gun?

I guess I am trying to get to a point of not being too short, but not being too long either. I only have the 180 Bergers to gauge off of.

Maybe I'll seat the bullet in .050 past the shoulder neck junction.
I guess it is always easier to lengthen the throat out vs. lengthening the chamber to shorten the throat.....

Thanks!
Denny

 

[rscott5028]

I need to shut up and listen. But, I thought this was an intersting interview with Dave Kiff at PTG...

Chambering the 6BR and 6 Dasher

Q: Without revealing any trade secrets, what throat lengths do you recommend for a 6mm BR case?

We normally go with a 1.5 degree lead angle, unless the customer wants something different. For 60-68gr bullets we recommend a .060" freebore. For the 80gr bullets, .080" is a good setting. For the 100-107gr VLDs, a .115" -.120" freebore will allow you to get the base of the bullet up out of the doughnut area. This will save you lots of aggravation over the life of the barrel.

-- richard

 

[denphillips2]

Yes, Dave knows what he is talking about. The last 6mm BR I did was set up with an .080" FB. Works perfect for the 80-90gn bullets, but still handles up to the 107s. I just chambered a 6x47L with a .100 FB and it is about perfect for the 105-107 class.

The doughnut is what I was thinking of when planning to set up this way. Now is the doughnut a concern on a no-turn hunting round like this? I don't know.

If I get time, I'll give him a call.

 

[J E Custom]

JE,

I think the OP was about using a longer throat to accomodate VLDs.

I was pointing out that too long might be a problem over time as the throat errodes.

Are you recommending a standard throat length with sufficient freebore to accomodate VLDs seated a little further out?

thanks!
Richard

p.s. to your point about taking a chance on rechambering, I imagine Shawn Carlock and Kirby Allen just consider barrels expendable in their R&D with throat designs for the +P, etc...

Sorry , I thought he was talking about shortening the neck to allow the VLDs to be seated close
to the lands there fore making it to short for standard ojive bullets unless seated deep.

The standard throat is .071 before the start of the leed. the neck is .272 +.000 - .020 long

The standard leed angle is 3 degrees and with the secant ojive of the VLD it would have to be
seated long to get close to the lands.

But if this is done it will make it to close for the standard ojive bullets and pressures will go up
(Or powder loads will be reduced) slowing velocities.

J E CUSTOM

 

[rscott5028]

Sorry , I thought he was talking about shortening the neck to allow the VLDs to be seated close
to the lands there fore making it to short for standard ojive bullets unless seated deep.

The standard throat is .071 before the start of the leed. the neck is .272 +.000 - .020 long

The standard leed angle is 3 degrees and with the secant ojive of the VLD it would have to be
seated long to get close to the lands.

But if this is done it will make it to close for the standard ojive bullets and pressures will go up
(Or powder loads will be reduced) slowing velocities.

J E CUSTOM

No doubt I'm the one that's confused. But, once I finish diagraming your explanation, I will have learned something valuable here.

thanks!
richard

 

[denphillips2]

I just talked to Dave Kiff.
He said if he was building a reamer for the 180 Berger it would have a .180FB and 1.5deg Lead.

He said that should be about right to put the boattail/body junction of the bullet at the shoulder/neck junction of the case.

I was going to make a seating gauge to match the chamber, but I think I am going to make the seating gauge first.

I have a 180 Berger seated about .020" deeper than what is mentioned above. I am going to use this as my gauge to set the throat depth.

When I get it cut, I will let you know what I have.

Thanks for all your help!
Denny

 

[denphillips2]

I ended up running the throater in an additional .210 to get the 180VLD to touch the lands where I had them seated. Hoping to get some loaded for it this week and get it out to shoot. Proof will be in the pudding.

Denny