7mmbr questions

[janderson0]

Just bought a 7mmbr pistol. and looking for some info. It has a no turn neck. Question is will I get too thin a neck if Lapua 6mm brass is used?

Also need help with what loaded rounds will measure so I can get a couple of bushings in that size range.

any tips welcome.

Thanks,
Jim

 

[Preacher]

That depends on your Lapua brass lot number, the neck thickness, and the neck on your chamber.
If it's a old pistol it may have a Remington chamber for the old Remington brass..
Take a chamber cast to find out all the info you need as far as what exact chamber you have.
If your necks measures .013.5 per side and your bullet measures .284, then the total is .311, and your bushing should be .002 to .003 under that, so you want a .308 and a .309 bushing, IF that is your chamber size...

 

[65BR]

Jim,

I used 6BR lapua brass in my 7br rifle that had a no neck turn chamber, did fine, very good brass.

Cannot be more detailed as I never turn cases but I think you will be ok.

 

[RickB]

It would be nice to make a cast of your chamber and find out just what you are working with. What pistol is it anyway?

 

[janderson0]

It's a Wichita pistol. Notes on the owners manual say it's been re-barreled with a Pac-Nor "regular neck"

I have both 6br Lapua and 7br Rem brass coming. I can get a good guess on neck size from fired brass. I'll just need to load a few and make sure they chamber.

I just assume 6br Lapua that measures .013 to .0135 would be something less after opened to 7mm. how much less is the unknown to me.

Jim

 

[RickB]

One of the reasons I think that it would be useful to make a cast of the chamber is that there is a difference in the case length between a 7mm BR and a 6mm BR necked up to 7mm. Whether the reamer that was used to chamber the barrel takes this into account is unknown. There is also the possibility that the rear of the chamber may be on the tight side for Lapua brass, but that would become obvious when chambering a case. The problem with case length is that you could wind up with the case mouth jammed into the chamfer of the chamber and raise pressures.

If you are unable to make a cast of the chamber, I would suggest making up a dummy round...a bullet, but no powder or primer...and mark the case mouth and front part of the case neck with Marks-a-lot to see if there is any inappropriate contact when you try to close the bolt. You might as well mark up the base of the case neck while you are at it to make sure that you do not have a tight area there also.

You will need to figure out bullet seating depth by trial and error as it is entirely possible that the throating was something different than the Remington factory spec.

The Wichita action was a good one and should serve you well.

Edit:

I would not be concerned about the neck becoming thinner necking it up to 7mm. I would be concerned about the section of the should that becomes the base of the neck being too thick. Lapua brass is known to have that problem with some lots of their brass for various cases.

Please take care with this. There are many, many variations in chambers that are cut for silhouette guns.

 

[Preacher]

Opening up a 6mm Lapua case to 7mm will thin them up over .0005, and I've seen them up to .001 thinner on .013 necks...
I would really check the chamber, I've seen a few normal neck P-N chambers that needed turning to be correct to that chamber.....
Any chance of the previous owner helping out ?
Just hate to see you get in trouble with it....

 

[65BR]

Janderson,

Pac-Nor barreled my 7BR rifle, and I'd bet it's the Same reamer. Doubt they barreled enough to have worn it out, likely same reamer or spec, MY guess. Chris might know if you ask him, likely FEW if any other 7BR's done by them, in a rifle. Not common, in rifles.

 

[janderson0]

Today I got my Rem 7mmbr brass. It looks like its based on the old 6mmbr Rem case. Measures about 1.510 long. But quality is not there.

Necks measure from .0098 to .0125 on the same case. And I was worried what a 6mmbr Lapua would loose going up to 7mm!

Primer pockets are bigger than my 6mmbr Lapua that has been fired 17 times.

I should fire it Saturday, and get some rough neck measuremnets from the fired cases.

Thanks for all the help,
Jim

 

[janderson0]

Fired the gun today. Fired brass measures just under .310, and the loaded rounds,Rem brass) are only .306-.307. Plenty of room.

If I make any from Lapua I will shorten them to 1.510 and make sure they are about .308.

My bullets did not come in the mail, and all I had was 28 rounds of 120g Vmax and Nos 120 BT that was pulled from my old 7tcu that I no longer have.

Using H322 and loads 1/2 grain apart I had one group well under 1/2 inch. But I was at the 50yd range as a match was being held on the 100yd range.

Jim

 

[65BR]

janderson,

I found a few pcs of brass I had left,sold gun/all brass...almost I guess)

nickel RP miked .308 neck fired
Nickel resized around .304-.305

The Lapua case, found one that was fired miked .309.

I think the Lapua must be a tad thicker in the neck, as it was 6BR necked up.

Hope that helps.