Author Topic: Belted case's (Read 825 times)

Jim n Iowa · « **on:** November 16, 2005, 01:58:57 PM »

In reloading belted case's for me 7mm mag, 338 mag, it has come to my attention that you should "head space off the shoulder". Ok how do you do this?
For my 7mm I neck size, the 338 I full size, as it was related to me the bigger case's are better off full sized. The cost of shooting the 338, while fun in the winter, is not feasible when compared to a 223 or 243 for coyotes all year, which is all we have to shoot with high power.
So how do ensure that you are head spacing off the shoulder? If this is what happens in a neck size, how do you do it in a flsize?
Jim

Iowegan · « **Reply #1 on:** November 16, 2005, 03:22:11 PM »

Jim, First let's define headspace. If you could measure the gap between the case head and the breach face when the bolt is closed, this gap would be the headspace. When a case is chambered, what stops it from going deeper into the chamber is the belt on your 7mm Mag and 338 Mag. Non-belted rimless cases stop when the angle of the shoulder contact the corresponding area in the chamber (datum point). Rimmed cases such as a 30-30 are stopped by the rim and cases like a 30 Carbine are stopped by the case mouth. When you see reference to cartridge headspacing, what is usually meant is "what keeps the case from going too far into the chamber?".

No, you do not want to headspace off the case shoulder with a belted case, you want to headspace off the belt.

You want a few thousandths of headspace just so the case doesn't bind up when the bolt closes. Excessive headspace will cause all kinds of problems including head separation, splitting cases, and a loss of accuracy.

In a belted magnum, the optimum case-to-chamber fit occurs when the belt contacts the chamber, the shoulder angle is a few thousandths off the datum point and the case mouth is .005" short of bottoming out. The gap between the case head and breach face should be about .005". This gives the case the necessary space to expand when fired and not seize in the chamber.

You can buy go / no-go headspace gages that look like a cartridge. The no-go is set at .006" so when you chamber it, the bolt should not close. The go gage is set at .004" and should allow the bolt to lock in place.

Another good reference is the Wilson case gages. You can place a loaded round in the case gage and get a good idea of your case measurements. The head of the case gage has a channel cut in it. The case head should be lower than the top of the channel and higher than the bottom of the channel. On the bullet end of the case gage, you have a similar channel. The case mouth should be lower than the top and higher than the bottom for proper case length. This length is not the same in all guns and yours may be deeper, thus allow a slightly longer case.

Unless you are a bench rest competition shooter, you're better off to full length size your cases. This will insure chambering without forcing the bolt. Accuracy and case life is a little better with neck sizing but not enough to notice in a field grade gun. When you fire a cartridge, the case puffs up and "fire forms" to the chamber. Neck sizing leaves the body of the case the same and only resizes the neck tight enough to hold a bullet. A full length sizing die will squeeze the case back to factory specs and will fit a little looser in the chamber.

Hope this helped.

Jim n Iowa · « **Reply #2 on:** November 17, 2005, 05:43:36 AM »

In the Speer manual #13 regarding the 338 "Like other belted magnums, we recommend that you set your dies so that the case headspaces on the shoulder, not the belt."
This was what I was refereing to as" how to headspace off the shoulder."
In the first part of the manual they state"7mm mag and the300 Winchester have adequate shoulders for headspace control so the belt is actually more a cosmetic feature than a design necessity."
My query was without buying more tools would I be better off neck sizing the 338 or partial sizing to headspace off the shoulder? Now I am confused. I am not a bench rest shooter but I want the best accuracy that I can achieve.
I am not disagreeing with you just stating what I had previously read in the manual.
Jim

ricciardelli · « **Reply #3 on:** November 17, 2005, 06:56:11 AM »

I have used belted cases in many different calibers over the years, and I always size off the shoulder.

How?

I neck-size only, and then only 1/2 to 2/3 of the neck.

Lawdog · « **Reply #4 on:** November 17, 2005, 12:11:58 PM »

Old benchrest shooters trick.

I do this with all my belted cartridges. I set the die so it sizes on the belt and shoulder at the same time. Now the cartridge fits the chamber perfectly by also resting on the shoulder. This will help with downrange accuracy. It only takes a little playing around with the die adjustments. Been doing this for over 40 years. Lawdog

Steve P · « **Reply #5 on:** November 17, 2005, 04:02:23 PM »

Iowegan and Lawdog make some good points. I set my full length sizing dies for my two belted mags (7mm, 338) so the case will easily chamber, and so that a little smoke from a candle will just rub off the shoulder when it is chambered. I will usually use a fired round (spent primer), run it up into the die so that I size the neck enough so I can seat a bullet. I light a birthday candle and smoke the shoulder and neck. I then try it from magazine into chamber and close the bolt. If bolt closes a little hard, I pull the bullet, wipe off the smoke, set the die down another 1/8 to 1/4 turn and try it again. When set just right, the dummy round should come out with the smoke scraped or rubbed off (You may need to run a rag in the chamber to remove soot if it takes you more than 3 or 4 trys to set the die). It may take you 45 minutes to set up your die, but once done, your brass should last a long long time.

Good Luck,

Steve

Lone Star · « **Reply #6 on:** November 17, 2005, 05:02:12 PM »

Strange, a double post - my first in over 700 posts here.

Lone Star · « **Reply #7 on:** November 17, 2005, 05:05:59 PM »

Quote

First let's define headspace. If you could measure the gap between the case head and the breach face when the bolt is closed, this gap would be the headspace.

No, that is excess headspace. Headspace is the distance from the breech face to the cartridge datum line, either on the rim, on the belt or on the shoulder.

It is virtually impossible to have both the shoulder and belt establish headspace at the same time while obtaining the optimum minimum excess headspace measurement. We have no control over the length of the belt cutout in the chamber, and we have no control over the length of the case belt from rim face to top of belt. These are manufactured to tolerences, and sometimes these tolerences will add up to near-perfect headspacing, but most of the time, the result is considerable excess headspace resulting in short case life. Measure the lengths of the belt on cases of different manufacture and you will usually find several thousandths difference between brands. This means that if headspacing off the belt, different case brands will heasdspace differently. We cannot control this with die adjustment.

Speer is right, belted cases (not the .458) should headspace off the shoulder, ignoring the belt, It is not needed, and we cannot effect the belt headspacing anyway. Back off the FL die by 1/16th inch and size the case, Chamber it, if it chambers hard, turn the case in 1/16th turn and try again. Once the case chambers with almost no resistance, lock down the die and subsequent cases wil headspace off the shoulder. Smoking the case is a good idea and works very well. The shoulder will contact the chamber first, the belt will be left hanging - just as it should be.

.

beemanbeme · « **Reply #8 on:** November 18, 2005, 04:25:26 PM »

I've always headspaced my belted cases on the shoulder.

Slamfire · « **Reply #9 on:** November 18, 2005, 05:19:28 PM »

A LOT of belted cartridges have generous chambers, ahead of the belt. That's ok for factory cartridges, because the belt stops the cartridge from going in too far. However, the the original case's shoulder is pushed forward to meet up with the chamber. If you full length resize cases fired in these chambers you'll push this brass that has migrated forward back to SAMMI specs.This pushed back brass tends to pile up on the belt and eventually you'll be unable to chamber the round, due to this "false belt". Additionally this brass has to come from somewhere and it comes from the part just ahead of the belt. This weakens the case just at the spot that expands the most. If you set your sizing die so it just kisses the expanded shoulder you'll get longer case life. The folks who publish reloading manuals recognize this, and they want you to keep on reloading and buying their products, hence their recommendation. You got a lot of good responses, but sometimes a bit more data helps you picture the problem.

PaulS · « **Reply #10 on:** November 19, 2005, 03:29:22 PM »

As I understand it, the only belted cases that headspace on the belt are the old H&H cartridges. All of the more modern belted cases are suposed to headspace on the sholder like any other bottleneck cartridge.
The problems that arise from necksizing these cases is, more often than not, excessive pressures.

sgtt · « **Reply #11 on:** November 19, 2005, 05:58:33 PM »

Why would neck sizing create excessive pressure?

Jim n Iowa · « **Reply #12 on:** November 20, 2005, 01:46:52 PM »

Well This has been a healthy thread, and thank you all for the input. I neck size for my 7mm mag for 5 or so reloads, then full size (not to many make it that far). I may invest in a neck size die for the 338. It has become one of my favorite down range target guns.
Jim

PaulS · « **Reply #13 on:** November 20, 2005, 05:39:44 PM »

Quote from: sgtt

Why would neck sizing create excessive pressure?

It doesn't - the guy dumping powder in the case causes high pressure if he ignores the max listed loads in favor of the highest velocity.

Arrroman · « **Reply #14 on:** November 20, 2005, 07:08:32 PM »

Quote from: Jim n Iowa

In reloading belted case's for me 7mm mag, 338 mag, it has come to my attention that you should "head space off the shoulder". Ok how do you do this?
For my 7mm I neck size, the 338 I full size, as it was related to me the bigger case's are better off full sized. The cost of shooting the 338, while fun in the winter, is not feasible when compared to a 223 or 243 for coyotes all year, which is all we have to shoot with high power.
So how do ensure that you are head spacing off the shoulder? If this is what happens in a neck size, how do you do it in a flsize?
Jim

The full length sizing die will size the whole case if the die hits the shell holder.

If you back the die off the thickness of a dime away from the shellholder you will only size the neck of the case.

Proper neck tension on the bullet should be maintained if you want the case to hold the bullet in a uniform fashion.

Good luck hunting! >>>------------>

Jim n Iowa · « **Reply #15 on:** November 24, 2005, 03:00:57 PM »

Well I thank all of you for your input. I already neck size for 7mm mag. As for the 338 mag I think I will try Arroman's suggestion on backing it off some. The 338 is a rifle I use in the winter for coyotes, as the wind blows hard, and if I can find them laying down on the sunny side, well you get the picture. Love the gun and maybe I will be able to put it to better use some day.
Jim

Dand · « **Reply #16 on:** November 24, 2005, 11:11:28 PM »

I have done like Arroman for 24 years with my 300 win mag and have excellent results. Brass often lasts over 10 (15??) reloads and I load some of it pretty hot. I regularly get .8 to 1.25 inches at 100 yards. I like the idea too that the full length die can help resize the most of the body of the case if for some reason its needed.

I've never had a problem while hunting either, but I usually run all rounds through the chamber before I go out just to be sure.

Heck, I'd think the 7mm mag would be plenty for coyotes even in the wind! But if you're having fun with the 338 - that's cool too.

Good luck.

Arrroman · « **Reply #17 on:** November 25, 2005, 09:00:09 AM »

You should definately run alll of the loaded cases through the action of the gun you are reloading for to insure they will chamber properly.

Cases that have been fireformed in one gun may not chamber properly in another gun; if the brass came from a different gun it may need to be full-length sized in order to work.

Good luck hunting! >>>------------>

Jim n Iowa · « **Reply #18 on:** November 25, 2005, 02:28:54 PM »

I am a one gun one cal. guy, not by choice but affordablity. So neck sizing would be a easy option. The 338 is a way far gun to shoot as I have not had to many chances to hunt anything but deer with it. I know even that is over kill, and Dand your right the 7mm does a great job on the song dogs in the wind and at long range.
By the way where abouts are you in Ak? We try to go up and rent a RV and "Poke Around" every couple of years. The Homer Spit, and the "Salty Dawg" are always a must see.
Jim

Robert357 · « **Reply #19 on:** January 28, 2006, 08:42:33 AM »

This was a very interesting read and I want to be able to find it for reference. That is why I am doing this reply