Headspacing REMAG Belted Magnum

[hoz53]

There can be as much as .026" difference in minimum factory ammo and a maximum SAMMI chamber in the bolt face to shoulder datum dimension. This holds true for 300 Win Mag, 7 Rem Mag, 264 Win Mag, and 6.5 Rem Mag., and probably many other belted cases. The simple solution is to size to YOUR shoulder and ignore the belt entirely. The belt is a hold over from adapting flanged H&H mag cartridges to feed in a bolt action. A factory load (or equivalent hand load) in a max chamber will fire form the first shot, then size accordingly.

I agree I think that's what I posted except I just didn't have the .026 figure available.

 

[hoz53]

Some time back, a friend, who is very good about small details and careful about procedures asked me to design a tight necked shorter throat .300 Weatherby reamer. It was set up so that 180 gr. hunting bullets could touch the lands and fit in the magazine of the German Mk. V action. I moved the shoulder so that there would only be a .006 difference between the head to shoulder dimension of unfired brass and the rifle's chamber. Based on experience, I avoided tight clearances for the body diameter at the shoulder and .200 from the head, and used the standard Weatherby dimensions. We also ordered a FL die reamer. Because we had not data for the chamber design, the first thing that we did after the rifle was together was to do some pressure testing, using belt expansion and other indicators to judge pressure levels. The last load tested expanded the belt a second time and was well past the point where an ejector mark appeared. We had moved up by half grains. loading at the range. Sizing was done with a one piece neck die, that just happened to give very straight sized brass (Remember, tight neck.) All the way through the test, seven shots I believe, the bolt close was OK, at the end, after the case had cooled, but without sizing, it chambered easily. There are issues involved in reamer design that are not commonly understood, or discussed. I will not digress into why I decided to use the body dimensions that I did, but it was not a wild guess. It was based on a friend's experience, and it worked. The first time that the rifle was used on a hunt, my friend's son shot a 4x4 elk, high in the shoulder, at 600 yd. dumping it on the spot. End of story. PS Yes I know that it wandered a bit off of topic, for the curious, after our exploration to the outer limits, we stepped back from the edge and designated the max load at what appeared to be a sane pressure level. The testing was purposely done in warm weather to avoid the kind of surprises that cold weather testing can result in when things warm up. This has to be the longest example on record to back up the idea that while it may or may not be necessary to reduce body diameters slightly after the first firing, it is highly unlikely that the shoulder would need bumping, which is why when I don't have a tight case to use as a reference, I set FL dies to give sized cases the same head to shoulder dimension as it had after firing. Try it; you might like it, and you can always reset the die if you don't.

In the past when loading for my 7mm RM I just pushed the shoulder back enough to just chamber in the rifle. That seemed to work good and did away with the incipient rings I was getting before I started sizing that way. That was before I had a bump gauge. As long as the cases are a close fit to the chamber( head to shoulder) after the first firing things should work good. Sizing the shoulder back excessively like I did when I first started loading a belted magnum in 1978 and I got rings within 2 or 3 firings. I never measured to find out .021 was the amount of stretch in the cases and I was surprised it was that much. The OP is just trying to set the headspace of his barrel. Setting it with a new piece of brass and then sizing the fired cases to just fit the chamber should work for him. If he buys a bump gauge and uses that it would be better. I'm ready to find out about reamer design specifics you mention. Thanks for the info

 

[RonAKA]

At this point I have concluded that there are too many possibilities to reasonably consider; long belt depth in chamber, short belt depth, long shoulder depth in chamber, and short shoulder depth, and then the same combinations on the cartridge brass, and again in the sizing die and that overlayed with using standard go no go gauges vs headspacing off the brass. Makes my head spin to even think about figuring out all the possible permutations and combinations... However, it would seem on a probabilistic basis, SAAMI chose those dimensions in the case of a belted magnum to virtually assure it will headspace on the belt, not the shoulder.

The thing is that I have little control over any of this other than how I headspace it. If I resize brass to make the shoulder distance shorter I can only increase the chance it will seat on the belt.

To give my head a break, I am going to wait until my brass and sizing dies arrive, which could be later today. I do appreciate and understand all the suggestions though. One of the things I concluded in writing the original post was that using a standard go, no go, gauge was that you should be able to eliminate the tolerance of the SAAMI chamber issue. To cut down on the brass tolerance issue you have to go into the tape method, which is where I will probably end up.

It also looks like I may have to get the Stony Point shoulder length gauge. The standard bushings however don't seem to work for the 6.5 Rem Mag as the SAAMI spec is at 0.440" rather than the 0.420 for the other magnums. I guess it is all relative though, and it will still work. I just won't be able to correlate the measurment back to the SAAMI spec., unless I do a little math. Ouch!

 

[RonAKA]

Brass and RCBS dies arrived today. The brass looks fine and is new. Tried some quick checks to measure the belt headspace dimension. However my crude tool - a washer I reamed out to about 0.511 to fit my .264 brass is a bit too big. The 6.5 RM brass is 0.5065 or so. This confirms to me they have never been fired. But the washer fits too loose to make a good measurement on the 6.5. Will have to make a new one, or think up another idea. Overall length is 2.161, so just about bang in the middle of the SAAMI spec. No idea on the other measurement to the shoulder. I did realize I have the Hornady base to do shoulder measurement. I use it for measuring bullet lengths. I just need the bushing now for shoulder length.

Not too impressed with the RCBS dies though and what they may do to the brass. The expander ball is small, in my opinion, at 0.2616. I think that is going to provide way too much grip on the bullet. And the brass looks undersized already in the neck with an OD of 0.292", and it still does not fit into the neck of the sizing die. So it seems it is going to reduce the neck even more than it is now. The combination is going to work the crap out of the brass in the neck! Perhaps I will have to get an expander from a .270 and turn it down to .263 or so, and I may have to figure out how to hone up the neck size in the die. Flex-Hone?

 

[LARRY TAYLOR]

Go away from expander ball dies. Bushing dies are much more flexible in fitting necks and shoulders.
Bushings are available in 0.0005 increments.

 

[hoz53]

At this point I have concluded that there are too many possibilities to reasonably consider; long belt depth in chamber, short belt depth, long shoulder depth in chamber, and short shoulder depth, and then the same combinations on the cartridge brass, and again in the sizing die and that overlayed with using standard go no go gauges vs headspacing off the brass. Makes my head spin to even think about figuring out all the possible permutations and combinations... However, it would seem on a probabilistic basis, SAAMI chose those dimensions in the case of a belted magnum to virtually assure it will headspace on the belt, not the shoulder.

The thing is that I have little control over any of this other than how I headspace it. If I resize brass to make the shoulder distance shorter I can only increase the chance it will seat on the belt.

To give my head a break, I am going to wait until my brass and sizing dies arrive, which could be later today. I do appreciate and understand all the suggestions though. One of the things I concluded in writing the original post was that using a standard go, no go, gauge was that you should be able to eliminate the tolerance of the SAAMI chamber issue. To cut down on the brass tolerance issue you have to go into the tape method, which is where I will probably end up.

It also looks like I may have to get the Stony Point shoulder length gauge. The standard bushings however don't seem to work for the 6.5 Rem Mag as the SAAMI spec is at 0.440" rather than the 0.420 for the other magnums. I guess it is all relative though, and it will still work. I just won't be able to correlate the measurment back to the SAAMI spec., unless I do a little math. Ouch!

Ron- I feel like I have wasted my time replying to your thread. I guess it's just not sinking in. You're making it way more complicated than it is.

 

[hoz53]

Go away from expander ball dies. Bushing dies are much more flexible in fitting necks and shoulders.
Bushings are available in 0.0005 increments.

^good advice

 

[RonAKA]

Go away from expander ball dies. Bushing dies are much more flexible in fitting necks and shoulders.
Bushings are available in 0.0005 increments.

Who makes a good bushing bump die for a 6.5 Remington Magnum? I have a Forster for my 6BR, and I still use the expander ball in it. The ball just kisses the ID on exit, and on the Forster you can locate the ball really high in the die so it is still being guided by the bushing. This minimizes the potential for inducing any non concentricity in the neck.

My rational for still using the expander ball is that the ID of the neck is the most important variable, and needs to be the most consistent, if you want consistent bullet pull away force.

 

[RonAKA]

Ron- I feel like I have wasted my time replying to your thread. I guess it's just not sinking in. You're making it way more complicated than it is.

Actually it is sinking in. There is almost no way I can headspace on the shoulder with unfired brass. Of course I will "headspace" on the shoulder once it is fired. I think I said that was my intention from the start. And your comments are appreciated and valid.

 

[hoz53]

Actually it is sinking in. There is almost no way I can headspace on the shoulder with unfired brass. Of course I will "headspace" on the shoulder once it is fired. I think I said that was my intention from the start. And your comments are appreciated and valid.

Alot of guys with savages dont own or use any headspace gauges and headspace with brass all the time.

 

[RonAKA]

Alot of guys with savages dont own or use any headspace gauges and headspace with brass all the time.

Perhaps you misunderstood, what I was saying. I suggested it is almost impossible to set my barrel headspace based on the shoulder using unfired brass. At this point I do in fact plan to set barrel headspace with the brass, but using the belt. After the first firing, I will then set shoulder bump based on the shoulder, and the case will headspace on the shoulder.

 

[fguffey]

What do you think? Will it work? I've tested the idea out with my .264 and it looks like it would work when the ejector is removed.

What do I think? I believe there is more going on than most reloaders can keep up with. There is at least three different ways to measure the length of the chamber and then there are belted cases, chambers and dies; problem, the reamer comes in one piece.

F. Guffey