Help with an older 6br rem chamber

[khoffx2]

Boy I thought this was going to be easy. Was I wrong. I purchased a used Cooper M22 in 6br Remington some time ago, but due to medical issues I haven't been able to do anything with it until now.

Anyway, I contacted Cooper for any information that they had on the chambering, and they sent me a print of the reamer dimensions. Yiks!

The chamber is nothing like I expected, and I don't understand the half of it. Can anyone take a look at this print and tell me what I've got and how to proceed with loading cartridges for this rifle?

Thanks,

Ken

 

[highlife]

To tight and to short. Rebarrel it or take it to a confident gunsmith for a new chamber. Or see if you can get ahold of some Remington BR brass. See if that’ll work for you. Short story of it.

 

[gunsandgunsmithing]

Judging by the print, trim to 1.520 and shoot it.

 

[khoffx2]

I see what you're saying about trimming to length and I think that makes sense. How about the neck at .262? Will I be able to resize Lapua brass down to .261 without turning the necks? I say that, even though I don't know what the heck I'm talking about. I'm used to loading standard calibers with standard chambers, the keyword being "standard".

Thanks

 

[Terry]

With a .262 neck you need to turn the necks. .008 necks would be safe.

 

[khoffx2]

Looks like I have something new to learn. And since this is a hobby (although a potentially dangerous one) I'll enjoy the learning. I have 3 reloading manuals (Burger, Nosler & Hornady) and a couple of how to's (Ratigan's Extreme Rifle Accuracy & McPherson's Metallic Cartridge Handloading) so I should be able to get what I need from them.

Thanks.

 

[gunsandgunsmithing]

I see what you're saying about trimming to length and I think that makes sense. How about the neck at .262? Will I be able to resize Lapua brass down to .261 without turning the necks? I say that, even though I don't know what the heck I'm talking about. I'm used to loading standard calibers with standard chambers, the keyword being "standard".

Thanks

I'm wrong and you're absolutely right about the neck diameter. Yes, you'll need to turn necks. I didn't even look at the neck diameter but you should be good on headspace and diameter at the other critical dimensions. I'm sorry for the confusion on my part.
You have more than one option here...You can turn necks, which involves an equipment and learning expense, or you can let a good smith open the neck up a few thou. You have a nice rifle but it's not a br rifle and you won't see any benefit from turning Lapua case necks, IMHO and IME.

I have two rifles chambered in 6 Grendel on Borden BR actions. One is a HV rifle with a min turn neck chamber. I did just win a UBR Nationals with it! The other is a UBR Unlimited. It has a no turn neck. Guess which one I consider the best rifle...the Unlimited, by a little bit.

 

[jrm850]

Looks like an old school rem chamber with a tight neck. Lapua brass would not fit my old .262 Rem Br, but Norma cases would. The base is too fat on the Lapua. I just found 30 of the Norma cases that will fit it with .007" neck walls. If you are interested, I'll donate them to the cause. They measure .4675 at the base.

 

[jrm850]

New Lapua brass measures .4720 at the base which will not fit in that chamber. Anyone have any other brands they can measure?

 

[Terry]

I have some Remington brass, if you really need it.

 

[Dusty Stevens]

You should really eliminate your future headache and get somebody or cooper to rechamber that

 

[khoffx2]

Based on all the responses from those of you who know about this stuff, and looking closer at the diagram, let me see if I've got this right. Comparing the SAAMI cartridge specification to the chamber specifications it appears that the SAAMI rim measurement is .473 but the chamber is cut at .4719, which is too small for the cartridge to fit. Next, the SAAMI spec for the cartridge base to shoulder is 1.075, but the chamber is cut at 1.071, which is too short. Then there is the COAL in the SAAMI spec of 1.560, but the chamber is 1.530 which is also too short. Finally, the SAAMI spec for the neck is .270, but the neck is reamed at .262 which is really tight.

Do I have that right? Is there any way that I'll be able to use Lapua brass in this chamber. And how will the shorter COAL and tighter neck affect accuracy? I'm not trying to win any matches, but considering Cooper's reputation for accuracy I'm wondering whether I should try to make this work, or just have a new barrel installed.

I think I'll call Cooper tomorrow and go over all of this with them, and talk with them about options.

Thanks for your help and advice.

Ken

 

[khoffx2]

First, I want to thank everyone for their advice and then I want to apologize for wasting your time. Something didn't seem right about this chamber so late last night I dug into my reloading stuff (we just moved and it was all stored away) and found some 6mm BR brass that the seller sent to me when I purchased the rifle. I got my micrometer out and took some measurements on the spent brass, and found that the measurements didn't match up to the chamber diagram that Cooper sent. The measurements seemed to match pretty accurately with the SAAMI spec for the caliber (neck-.270, case length 1.553, etc.). So this morning I called Cooper and found that they had sent me the wrong chamber diagram. The diagram they sent was for a customer that wanted a custom chamber back in 2001.

I just received the correct chamber diagram (attached) and it seems to fit for a SAAMI compliant 6mm BR Rem cartridge. It looks like the neck is .271 so I was thinking about getting a .270 bushing for the sizing die that I'll be purchasing. Also, from what I see, I'll be able to use the Lapua cases in this chamber (note: the spent brass that the seller sent was both Lapua and Norma). Does that sound right?

Again, thanks and sorry.

 

[gunsandgunsmithing]

First, I want to thank everyone for their advice and then I want to apologize for wasting your time. Something didn't seem right about this chamber so late last night I dug into my reloading stuff (we just moved and it was all stored away) and found some 6mm BR brass that the seller sent to me when I purchased the rifle. I got my micrometer out and took some measurements on the spent brass, and found that the measurements didn't match up to the chamber diagram that Cooper sent. The measurements seemed to match pretty accurately with the SAAMI spec for the caliber (neck-.270, case length 1.553, etc.). So this morning I called Cooper and found that they had sent me the wrong chamber diagram. The diagram they sent was for a customer that wanted a custom chamber back in 2001.

I just received the correct chamber diagram (attached) and it seems to fit for a SAAMI compliant 6mm BR Rem cartridge. It looks like the neck is .271 so I was thinking about getting a .270 bushing for the sizing die that I'll be purchasing. Also, from what I see, I'll be able to use the Lapua cases in this chamber (note: the spent brass that the seller sent was both Lapua and Norma). Does that sound right?

Again, thanks and sorry.

Your bushing should be nominally .002 smaller than you loaded round, regardless of chamber dimensions.

 

[Dusty Stevens]

^ beat me to it

 

[khoffx2]

I know what your saying, but I don't have a loaded round and can't manufacture one until I buy the die & bushing. I wonder if I can calculate the bushing size based on the neck thickness of the Lapua case, but I don't know what that thickness is. Or is there another way to calculate the bushing size? And wouldn't there be a standard size of the loaded ammunition using new Lapua brass and a standard .243 bullet? Does Lapua make case neck thickness dimensions available to the public for their brass?

Thanks.

 

[gunsandgunsmithing]

I know what your saying, but I don't have a loaded round and can't manufacture one until I buy the die & bushing. I wonder if I can calculate the bushing size based on the neck thickness of the Lapua case, but I don't know what that thickness is. Or is there another way to calculate the bushing size? And wouldn't there be a standard size of the loaded ammunition using new Lapua brass and a standard .243 bullet? Does Lapua make case neck thickness dimensions available to the public for their brass?

Thanks.

A .268 will be a good starting point but you're gonna need brass anyway. Order it and a .267 or .268 bushing, or both.. then measure and fine tune if needed. You don't absolutely need a die yet, to seat a bullet. But, get a redding type stuff full bushing die while you buying brass and bushings

 

[khoffx2]

A .268 will be a good starting point but you're gonna need brass anyway. Order it and a .267 or .268 bushing, or both.. then measure and fine tune if needed. You don't absolutely need a die yet, to seat a bullet. But, get a redding type stuff full bushing die while you buying brass and bushings

Gunsandgunsmithing, thanks. What you're saying makes a lot of sense. I just knew that, based on the chamber dimension, the bushing needed to be less than .271. I need to learn a lot more about case neck sizing before I go too much further, but this is a good start.

Thank You,

Ken

 

[Webster]

Boy I thought this was going to be easy. Was I wrong. I purchased a used Cooper M22 in 6br Remington some time ago, but due to medical issues I haven't been able to do anything with it until now.

Anyway, I contacted Cooper for any information that they had on the chambering, and they sent me a print of the reamer dimensions. Yiks!

The chamber is nothing like I expected, and I don't understand the half of it. Can anyone take a look at this print and tell me what I've got and how to proceed with loading cartridges for this rifle?

Thanks,

Ken

Remember a 6mm Remington and a 6mm BR Norma are not the same cartridge. Also it's not the 6mm Rem BR. I have owned both. I'm sure Lapua doesn't make 6mm Rem brass. The 6mm Rem is considered obsolete.

 

[khoffx2]

Yes, I'm aware of the differences. What I have is a 6mm BR Remington, the precursor to the 6mm BR Norma which is also commonly known as the 6mm BR or just 6BR and which has a longer COAL than the 6mm BR Remington. The 6mm BR Remington is considered to be obsolete by most modern 6BR shooters, but since I'm only shooting at 100 and 200 yards, the 6mm BR Remington with the 14 twist barrel is perfect for what I want to do. The attached test target came with the rifle, and although it was only a three shot group and shot only at 50 yards the group is still pretty impressive.

Thanks.