.270-7mm-300 Winchester Magnum!

[TresMon]

Tomorrow I will be shooting my .270-7mm-300WM! Yippe.

So your wandering what I'm up to? I'll tell you. My 7mm-300 WLM is built with a tight neck chamber. I have to turn/machine my case neck to a precision fit to the chamber.

What I had tried was to take a stock 300WM case, anneal it and neck it down to 7mm. This worked, except in the necking down process the necks were no longer concentric to the body of the case. That's BAD for accuracy!

So I was trying to straighten all the neck by hand.. it was SLOW and not perfect. Then when I turned the necks- the neck walls were not perfectly uniform in thickness all the way around- UGH!

It would be nice if I could just fire form them but I can't. The neck diameter in my chamber is .312"

If I load an unturned neck with a bullet I get this: the neck wall thickness on this brass I'm working with is about .0145" thick so:

.0145 neck wall on one side plus
.284 bullet diameter plus
.0145 neck wall on the other side equals
------------------------------------
.313" neck diameter for the loaded round.

So theoretically an unturned laded case will not fit in my chamber- not to mention your supposed to have at least .003" clearance on the neck for safe bullet relief.
So I can't fire form unturned cases. Crap.

Or can I?

The minor bore diameter of a 7mm bore is about .276 -.277.

Hmm... .277 is a familiar number thinks me- oh yeah the good old .270 winchester bullet is actually .277 dia...

So I ran the math:

.0145 x 2 for wall thickness Plus
.277 dia bullet equal
---------------------------
.306 neck dia for a loaded round!

So yep I loaded up all my brass with ultra el-cheapo 270 deer bullets and am headed to the range tomorrow. The .270 will just barely drag the riflings- not even enough to get a great gas seal. But my brass will fire form perfectly- then I can turn the neck perfectly- and make perfect 7mm-300WLM ammo.

And the nearly "slip" fit of the bullet in the bore shouldn't add wear to the barrel.

Fun fun. In all my days I have never shot a "wrong" bullet in a gun. I feel like a mischievous little kid.

 

[Bloody_Tailgate]

Re: .270-7mm-300 Winchester Magnum!

Is that going to torch your throat?

 

[TresMon]

Re: .270-7mm-300 Winchester Magnum!


It may, it WILL if I fire all the rounds hot & fast. But I'm running them through the 18 twist barrel, so who cares!
http://www.snipershide.com/forum/ubbthre...173#Post2466173

 

[TresMon]

Re: .270-7mm-300 Winchester Magnum!


I fire formed the brass yesterday. The rifle actually kicked pretty good and the cases are formed. I was even able to hit a steel silhoutte some what consistent even though the .270 bullets were tumbling in flight from the slow 18 twist barrel.

 

[bohem]

Re: .270-7mm-300 Winchester Magnum!

Why waste the bullets, why not just neck down to 270, put in 12iish grains of Bullseye, and fill up the rest of the case with Farina?

No barrel wear, no copper fouling, etc.

I've been down this road, after you're done necking and turning, you should anneal the necks. It makes a big difference when the brass is getting this much initial work and your neck walls are pretty thick.

Contrary to common conception, neck tension is not really as dependent upon the sizing as much as it is the material stress state.

A thick neck material with 0.001" of "neck tension" is going to hold the bullet a lot more than a very thin neck with 0.002"+ of "neck tension".

 

[armorpl8chikn]

Re: .270-7mm-300 Winchester Magnum!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Why waste the bullets, why not just neck down to 270, put in 12iish grains of Bullseye, and fill up the rest of the case with Farina?

No barrel wear, no copper fouling, etc.

I've been down this road, after you're done necking and turning, you should anneal the necks. It makes a big difference when the brass is getting this much initial work and your neck walls are pretty thick.

Contrary to common conception, neck tension is not really as dependent upon the sizing as much as it is the material stress state.

A thick neck material with 0.001" of "neck tension" is going to hold the bullet a lot more than a very thin neck with 0.002"+ of "neck tension".

</div></div>
Probably because this is far more destructive to a barrel than almost anything else! I don't know why people still do this.

 

[bohem]

Re: .270-7mm-300 Winchester Magnum!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: armorpl8chikn</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Why waste the bullets, why not just neck down to 270, put in 12iish grains of Bullseye, and fill up the rest of the case with Farina?

No barrel wear, no copper fouling, etc.

I've been down this road, after you're done necking and turning, you should anneal the necks. It makes a big difference when the brass is getting this much initial work and your neck walls are pretty thick.

Contrary to common conception, neck tension is not really as dependent upon the sizing as much as it is the material stress state.

A thick neck material with 0.001" of "neck tension" is going to hold the bullet a lot more than a very thin neck with 0.002"+ of "neck tension".

</div></div>
Probably because this is far more destructive to a barrel than almost anything else! I don't know why people still do this. </div></div>

The cream of wheat fireforming method is destructive to the barrel?

 

[kyreloader]

Re: .270-7mm-300 Winchester Magnum!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: armorpl8chikn</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Why waste the bullets, why not just neck down to 270, put in 12iish grains of Bullseye, and fill up the rest of the case with Farina?

No barrel wear, no copper fouling, etc.

I've been down this road, after you're done necking and turning, you should anneal the necks. It makes a big difference when the brass is getting this much initial work and your neck walls are pretty thick.

Contrary to common conception, neck tension is not really as dependent upon the sizing as much as it is the material stress state.

A thick neck material with 0.001" of "neck tension" is going to hold the bullet a lot more than a very thin neck with 0.002"+ of "neck tension".

</div></div>
Probably because this is far more destructive to a barrel than almost anything else! I don't know why people still do this. </div></div>

The cream of wheat fireforming method is destructive to the barrel? </div></div>

First I have heard of COW being destructive to a barrel also, any elaboration would be helpful.

 

[ida83704]

Re: .270-7mm-300 Winchester Magnum!

Is this running .277 bullets?

Why would you do that, the bullet choices in .277 really pretty much suck.
.257 has some pretty small BC choices also

.264 and .284 have better choices...........

 

[725franky]

Re: .270-7mm-300 Winchester Magnum!

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Poster: ida83704

Is this running .277 bullets?

Why would you do that, the bullet choices in .277 really pretty much suck.
.257 has some pretty small BC choices also

.264 and .284 have better choices........... </div></div>


The .277 bullets were to allow him to fire-form the brass while maintaining safe firing conditions. The final chambering is 7mm-300WM which is running a .284 bullet diameter.

 

[725franky]

Re: .270-7mm-300 Winchester Magnum!

TresMon, what kind of barrel life are you expecting out of a caliber like this? It sounds interesting and this should make for one fast 7mm!

 

[Stick Around]

Re: .270-7mm-300 Winchester Magnum!

It's very tough to trump a 7mmRemMag,if/when forced to suffer a belt.

The melding of quality brass and COAL latitude,in conjunction with the nice BC's available,do rain upon many a parade.

 

[XTR]

Re: .270-7mm-300 Winchester Magnum!

I know it will vary between brass but approx case volumes are:

300WM = 89 gr
7mm RUM = 110.2 gr
7MM STW = 93.3 gr
7mm WbyMag = 87.5 gr
7mm RM = 83.2 gr


So, based on volume it sounds like it's going to be pretty close to the Weatherby 7mm. I think most of these are based off of the 375 H&H if I remember correctly so it's really making a longer version of the 7mmRM that's somewhat shorter than the 7MM STW

 

[XTR]

Re: .270-7mm-300 Winchester Magnum!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: armorpl8chikn</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Why waste the bullets, why not just neck down to 270, put in 12iish grains of Bullseye, and fill up the rest of the case with Farina?

No barrel wear, no copper fouling, etc.

I've been down this road, after you're done necking and turning, you should anneal the necks. It makes a big difference when the brass is getting this much initial work and your neck walls are pretty thick.

Contrary to common conception, neck tension is not really as dependent upon the sizing as much as it is the material stress state.

A thick neck material with 0.001" of "neck tension" is going to hold the bullet a lot more than a very thin neck with 0.002"+ of "neck tension".

</div></div>
Probably because this is far more destructive to a barrel than almost anything else! I don't know why people still do this. </div></div>

Since when did we discover that using cream of wheat to fire form is bad? The guys over at Accurate Shooter and 6mmbr still endorse it as far as I know.

 

[armorpl8chikn]

Re: .270-7mm-300 Winchester Magnum!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: XTR</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: armorpl8chikn</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Why waste the bullets, why not just neck down to 270, put in 12iish grains of Bullseye, and fill up the rest of the case with Farina?

No barrel wear, no copper fouling, etc.

I've been down this road, after you're done necking and turning, you should anneal the necks. It makes a big difference when the brass is getting this much initial work and your neck walls are pretty thick.

Contrary to common conception, neck tension is not really as dependent upon the sizing as much as it is the material stress state.

A thick neck material with 0.001" of "neck tension" is going to hold the bullet a lot more than a very thin neck with 0.002"+ of "neck tension".

</div></div>
Probably because this is far more destructive to a barrel than almost anything else! I don't know why people still do this. </div></div>

Since when did we discover that using cream of wheat to fire form is bad? The guys over at Accurate Shooter and 6mmbr still endorse it as far as I know. </div></div>

Pulled directly from the 6mmbr website in reference to the Dasher "skeeter" was fireforming brass for:
*Skeeter did have a fire-forming barrel, but it was reamed with a .269 chamber like his 10-twist Krieger “good” barrel. If he fire-formed with bullets, he would have to turn all 300 necks to .267&#8243; BEFORE fire-forming so that loaded rounds would fit in the chamber. Judging just how far to turn is problematic. There’s no need to turn the lower part of the neck that will eventually become shoulder–but how far down the neck to turn is the issue. By fire-forming without bullets now he only has to turn about half the original neck length, and he knows exactly how far to go.


Now why in the hell would he have a "good" barrel and a "fireforming" barrel. You think he was going to shoot COW in his 10 twist Krieger? Not a chance. Argue anything you like here. Matter of fact shoot all the COW in your high dollar match barrel you would like in the name of "saving the barrel". This is what is known as the rest of the story. If the absolute need to fireform using COW arises I will gladly use it to fireform loads but NOT in my match barrel.