The age old discussion of excess headspace in chambers for belted cartridges has surfaced in the "Medium Bore" section again. While reading through this a question arose in my mind. I have never seen a go or no-go gage that was designed to measure anything but the belt in reality. It also appears to me that the same gauges are used for pretty much all belted rounds. Please correct me if I am not correct on this.

Further, when you cut a chamber for a belted cartridge are you relying on the reamer to be ground to exacting specifications or do you have a special gauge, either go or no-go, to measure the depth of the shoulder after the chamber is cut? I can see where a non belted round which headspaces on the shoulder would make for a more exacting chamber to measure with the proper gauge, hence finding out quickly if a reamer is off, but am wondering if there are any gauges that measure both the shoulder and the belt on belted rounds? I realize all reamers should be ground to certain specs, but how can you tell for sure if you only measure headspace on the belt?

I do not wish to further the argument about whether there is a problem with headspace in belted rounds, I just am curious how this is controlled if the reamer is a tad off and all you are really checking is the headspace on the belt.

Many thanks

When I installed a new, take-off PSS 300 Win mag on my PSS I discovered that the shoulder of new, factory ammo would be blown ahead about .026 upon firing. The belt area in the chamber was within the "go" and "no-go" gages. So I put the barrel in a lathe and took material from the barrel thread shoulder, the rear and counterbore sections and bored the belt area so that the "go" gage would just go. Now the new fired cases are not blown-out more than a few thou.
Next step was to make a "go" gage, shoulder style, that just allowed the bolt to close. Using this gage, I then checked 6 different .300 Win Mag F.L. sizing dies. They were all over the place. Some would not touch the shoulder and some would push the shoulder back more than I wanted. Plus, the depth of the belt area was way more than needed in all of the dies.
The "go" gage for belts is .220" from boltface to front of belt and the "no-go" is about .224 or .226" (I think). Most brass is about .212" to .215" so you have a lot of "rattle room" in all chambers.
I chose to modify a shell holder such that my chosen die bumps my fired cases about .002-.003". This (and a .300 BAR) are the only belted chambers that I have, now. I really hate the belts and hope that the new cases based on the .404 Jeffrey cases makes them as obsolete as rimmed cartridges.

Jay

If I were to order a new barrel chambered for a standard bottlenecked belted round I would ask that it be done just as Jay did it above.

This may be one reason why some report no problems. Heck any gun and ammo combination can have headspace problems and the post above is the cure for this one.

When I designed my belted wildcat I had it chamber on the shoulder and the belt cleared. On this particlar wildcat custom dies were required.

Some have picked up on the fundimental problem of the clearance to the shoulder that the cartridge and chamber drawings give belted cartridges. They have called this sloppy chambers by the manufacturers. Now the chamber on any gun may be "sloppy" but there is a fundimental problem with that clearance to the shoulder on belted rounds. It's in the design and it must be in the design. You can't headspace on the belt and also headpace on the shoulder what with the accumulation of cartridge manufacturing tolerances.

This all got started when some gunsmiths like Ackley and Powell/Miller got lazy. They should have followed what Kilbourn did.

Manufacturers are notorious for making chambers for belted cases VERY long and large, since the belt serves as a "fail safe" headspacing mechanism and 90% of the shooters who don't reload never know the difference. Making oversized chambers has two manufacturing advantages: First, the chambering reamer can be very oversized and thus you get many more chambers out of it before it wears down below minimum specs and must be discarded. Second, big chambers allow the largest ammunition to still chamber easily; shooters would scream about factory ammunition chambering "tight" in their rifles, but are happy when a shell "falls" into the chamber without resistance. Bottom line: Factory belted chambers are lacking from the reloader's view point.

The discriptions of proper belted chambering above are the proper way to go. Treat any belted (and shouldered) case just as you would a rimless, and you'll live happily ever after.

When I had my 7mag rebarreled, the smith headspaced it off a factory cartridge (shoulder). That was Jim-Dandy for US brands, and the chamber prevents blown-out shoulders. Unfortunately, now the chamber will not accept Norma brass, because it has a couple thou larger belt than the domestic stuff. Bugger! FWIW, Dutch.

SAAMI and CIP specs for a belt are not all .220. I believe there are some calibers as small as .218. Not sure what the biggest is.

The best approach to belted cases is a combination of the above posts. Cut the chamber using the appropriate headspace gauge and, once the cases are fireformed ,treat them the same as a rimless case. JMHO

I have always chambered belted magnums to the standard .220 figure. When the barrel is installed the crush results in a true figure of about .218. Since I have never seen a belted case which measured more than .216 (with most being around .213-4) I figure this is OK.
When building a hunting rifle one simply cannot try to custom fit the head to shoulder measurement. All a gunsmith needs is to have a customer buy some ammunition which will not chamber. This shortcoming (no pun intended) will always be discovered when trying to get a shot at a 370+ bull elk or while a bear is chewing on the hunter's foot! For match rifles it's quite another matter and the shooters usually don't mind having to dick around (advanced reloading term) with brass.
Headspacing on the shoulder subsequent to fire forming is common practice and probably necessary if one wants any kind of brass life. Regards, Bill.

Bill, if you'd like, I'd be happy to send you some Norma (Weatherby headstamp) 7mm Rem Mag that measures right at .220..... Dutch.

Dutch,
As a matter of fact, I just checked some new Winchester 300 brass which measures right at .218 which is much greater than some older Winchester brass at .214 and the largest measurement I've seen to date. My 308 Norma brass is .216 while some 7x61 brass I have is .214. Also some .270 Weatherby at .216. The smallest measurement I've seen is some old Remington 7mm which is .211! I'll take your word on the dimensions of your Norma brass. It just goes to show anything can happen.
By the way, I check the dimensions with a gauge and depth mike because, when measuring with calipers, it's too easy to get an error from angling the instrument. Regards, Bill.

Gentlemen,

We have not chambered as many belted magnums as some of you, may be around 200 or so, and have always followed our own method of chambering them

We use a new empty case as a go gage. We cut the chamber until the bolt will just close on it, and stop right there.

We have never had any problems with any factory ammo or our own reloads to chamber and fire in these rifles.

And we got a lot more firings from our brass than with rifles that have been chambered by the factories.

I have seen some which have such sloppy chambers, that after a couple of firings the cases get a second belt!

I just went and checked my Norma 240 Wby, and it runs something like .219. Go figure.... Dutch.