Noticed a lot of chatter about headspace. One thing to keep in mind about belted cases is they have a built in headspace problem!

Here goes:

The go gauge is 0.220" thick. Most rifles are chambered so the bolt will close on the go gauge. And a lot of them have 3 to 5 thou axial bolt float over a go gauge.

Average case belt thickness is 0.213" to 0.215". I have seen as low as 0.209" and a high of 0.218".

So, if the go gauge is a little loose with the bolt closed, and a thin belt case is fired, guess what: The case starts stretching, after a couple of firings the head seperates.

Below photo shows a gauge I made that measures case belt thickness. Case show is a R-P and the belt is 0.209" thick. The dial indicator is zeroed on the gauge, then a case is inserted and the belt thickness measured with the indicator. So, if this case is fired in a chamber where the bolt closed on a go gauge, you automatically have 0.011" excessive headspace, maybe more!!!

When chambering a belted case, the way I set the headspace depends on several items: Is it a match rifle, a hunting rifle, or a DGR? Is the owner experienced in case prep? Will this be a tight neck/tight base/tight belt chamber? Must any and all cases fit, or will a specific lot of brass be preped for the rifle?

Having the chamber cut for specific brass dimensions is OK for that 1000 yarder the owner carefully prepares brass for. But, for a rifle that travels to other countries, the chamber must accept any and all cartridges that are brought, borrowed, loaned, or scrounged from under the seat of the Landrover.

I will post some more comments in future posts.

John If I read you right you recommend measuring the thickness of a given number of the brand of cases the customer intends on using; then figure the average thickness then use that your headspace target? Thats what I do if the customer is a vetern reloader & knows what he's doing.

I am looking forward to this thread.

I measured the headspace in two M-70's by soft soldering a dab of solder to a case just at the forward part of it's belt and filing it to be a crush fit. I believe the chamber tolerance is .220-.227 and mine both measured .228"

Doug, yes, if we are building a match rifle. Best way is to buy a large lot of cases, and sort for belt thickness. And you gotta stick with one manufacturer!!! When chambering a rifle of this type, I check 50 or so cases for belt thickness and select a "norm". (Only takes a few minutes with the gauge in the photo). Once fireformed, in a tight belt chamber, one is home free. If it is to be a long range precision hunting rifle, non-dangerous game, and the owner is experienced in case prep and snug chambers, then we will discuss the minimum chamber settings.

A hunting rifle that must digest any and all cartridges is chambered so the bolt will just close on a go gauge. This makes darn sure that if ammo is lost in transport to the hunting area, the ammo one borrows or buys will chamber. Not very nice if you have a snug chambered 416 Rem, head to SA, the ammo is lost, and all you can find is Winchester, RWS, etc., ammo. Won't chamber. Verrrrry important in a DGR.

I chambered a 460 Weatherby yesterday. The belt thickness is only 0.003" less than a go gauge. So, I set the headspace so the bolt just closes on the go gauge.

I will post more later and get into how to check headspace with the barrel in the lathe and using a dial indicator, what to allow for "draw up" when the barrel is torqued, how to measure the receiver and calculate all the dimensions, etc. And how to check the headspace with a dial indicator when the rifle is assembled. Techniques for chambering a M700 Rem are different that for a M70 Win or a Mauser. And a lot depends on what the rifle will be used for. And I will include some info on designing a tight necked and tightbase chamber for match rifles.

It's all "different strokes for diferent folks", the intended use of the rifle dictates the chamber and headspace specifications.

John, you've got a great website! The rifles look good too. Regards, Guy

John,

Thanks for shining your "reality spotlight" on the belted cartridge headspace issue.

jim dodd

John,

On the 0.209 Rem case you mentioned and .011" excess headspace, would that be a reality or would the shoulder of the case have come into play.

Mike

With today's cases, one never knows unless the shoulder length is measured also. I have a 375 H&H gauge that is adjustable and allows the measurement of the shoulder with respect to the belt. I have seen shoulders on belted cases as much as 0.014" too far back. Looks like the case makers do not pay much attention to the shoulder position on belted cases. One reason to use fire formed cases!

[QUOTE]Originally posted by Mike375:
[QB]John,

On the 0.209 Rem case you mentioned and .011" excess headspace, would that be a reality or would the shoulder of the case have come into play.
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Mike375,

As I have said before again and again the chamber tolerance is -.000", + .010" and the cartridge headspace dimension is -.007", +.000". This is compounded by the cartridge belt tolerance and the chamber belt tolerance's of .000, -.008" and .220-227" respectively.
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John Ricks,

Thank you so much for this effort. Please go on!

John and Don,

I have a 375 H&H here to bed for a friend. The barrel maker chambered it with a JGS reamer. Tomorrow I will check how much headpace there is on a few new cases. I would expect it will be around .005" or so, about coke tin thickness.

I will then grind the belts off a few cases and see what happens to the headpace. Any guesses?

My 416 Wby Euromark will not quite close on coke tin and it feels about the same on several cases. I don't think I will grind the belts off any of the 416 cases

Several years ago in a 460 Wby I owned, I had some new brass that was originally purhcased in the early 1970s. That had a few thou more headspace than brass purchased in the early 90s. But I have seen the same variarion on rimless cases. Although of course if the rifle is chambered with only 0.0" to say .003" or so with rimless, a longer case can still be cammed in by the bolt.

Mike

Some belted chambers are quite good. I have had bad ones and good ones. I had a Ruger #1A in 7mm Rem Mag rebarreled and one of the reasons was that it always had short case life. In the end I used .300 Win Mag cases to make brass for that one.

I have another #1 in .300 Win Mag and the chamber is tight and the cases last quite a long time. The satisfaction with this chamber has a lot to do with the fact that it is "tight" and round and square. This rifle will chamber fired brass which for a #1 with full pressure loads is quite a surprise after having one in the aformentioned 7mm Mag for 25 years.

I think this fitting of the chamber is very valuable and it's what Mr Ricks offers and can do. With a belted chamber made with common sense and thinking as offered here all of the problems with a belted case will hardly be noticed as long as informed reloading proceedures are followed.

Don Martin 29--

Good points.

The "problem" with belted mag headspacing of the cartridge being less than the .220 of a GO gauge is exactly the same as for all other cartridges.

Ammo is made SMALLER than a GO gauge. Chambers are the same as, or larger than, a GO gauge. That's why they all fit together the world over.

When a case is resized, the die resizes the fired brass ROUND. The shoulder is NOT affected unless you have moderately to severe excess headspace to begin with. I've NEVER owned a rifle that the FL die affected headspace on. The die makes the case ROUND and SMALL again, not shorter.

That's why a custom chamber job will almost always re-chamber a fired case and a factory rifle wont. The custom chamber is round and the bolt face is more likely to be square the the bore/chamber.

I'll stick my neck out and say that 99% of Ruger Number Ones have a breech bolt out of square with the chamber. That means the base of the case fireforms crooked. (It takes a hot load to do it). Test it by marking TDC on the case and fire it, then remove and rotate the case 180 degrees and see if the breech closes without dragging on the case.

Fireformed cases have less movement in the chamber during the ignition sequence......they are more "Solid". That means less vibration. That means the bullet is more likely to exit the barrel when it's pointed at the same place every time.

Truly accurate rifles shoots all ammo well....some ammo better.

Inaccurate rifle *somtimes* shoots *some* ammo well, but it's not a regular thing.