Can you guys advise me on this ? I have an old 700 classic w/a full length heavy factory target barrel. The gun is very accurate, sub-moa since the 70s. BUT, the chamber is a little long, and thus the case life was short when I used to reload for it. I can't remember if it came that way from the factory, but the gun will barely close on a no-go chamber gauge.

So here is my question:

I'd like to rebarrel the gun with a different cartridge based on the same medium length case and head. But, I'd like to know if it is possible that this chamber "stretched" in the past, and if it did, would it have been the bolt lugs themselves that stretched, the lug recesses themselves, or the tubular action itself ? The implication being that depending on the "type" of stretch, so to speak, would make it inadvisable to rebarrel the action. For the moment I'd like to concentrate on the technical question itself versus the cost justification of rebarelling vs replacing the whole gun.

The barrel itself still shoots, last time I shot it it shot 1/2 moa at 200. But I no longer like the cartridge and the barrel leade is heavily fire-cracked, thus with rebarreling I can kill two birds with one stone. The barrel is probably near the end of it's life as a target gun anyway, and I'll never take it hunting, it's too heavy.

Any advice appreciated.

Thanks.

quote:

. But, I'd like to know if it is possible that this chamber "stretched" in the past, and if it did, would it have been the bolt lugs themselves that stretched, the lug recesses themselves, or the tubular action itself ?

Very unlikely. Far more likely that the chamber was reamed just a bit too deep when the rifle was being built.

quote:

Originally posted by IndianaBoy:

quote:

. But, I'd like to know if it is possible that this chamber "stretched" in the past, and if it did, would it have been the bolt lugs themselves that stretched, the lug recesses themselves, or the tubular action itself ?

Very unlikely. Far more likely that the chamber was reamed just a bit too deep when the rifle was being built.

Agree. If the brass didn't last, most likely bumping the shoulder/headspace too much or more then .002.

Headspace will stretch over the life of the barrel and I'd expect to see about 0.002" stretch over a couple thousand rounds, depending on the cartridge. I also suspect that there will be a little initial compression of the recoil bearing surfaces of the receiver lugs and bolt lugs, but I don't expect it to be more than 0.001" or so.

If it's barely closing on a NO-GO gauge, then it's still under NO-GO spec. When it closes freely without resistance, then it's over the NO-GO spec for a new chamber.

Keep in mind that a NO-GO gauge is used to indicate the MAXIMUM headspace of a NEW RIFLE. A rifle can still swallow a NO-GO gauge but be safe to shoot. It's not unsafe to shoot until it swallows a field reject gauge. But as you have already discovered, cases don't last when reloading.

Here's an example of lengths for 308/7.62 NATO...(quoted text from Master Gunnery Sergeant Gus Fisher, USMC)

.308 Win. GO 1.630"

7.62mm GO Gage........1.6335"

.308 Win. NO-GO 1.634" - This was the "Old Common Length."

.308 Win. NO-GO 1.636" - This is the "New" Common Length?

7.62mm NO Go Gage.....1.6375"

.308 Win. FIELD REJECT 1.638" - This has been THE standard or common length for decades.

.308 Win. FIELD REJECT 1.640" - New Length SOME manufacturers are using. This may have been the result of the GI Rock Island Arsenal going to that for the EBR? It ALSO is the SAAMI standard Field Reject limit for .308 Win.

7.62mm Rebuild Maximum Gage......1.6415"

7.62mm Field Reject Gage.............. 1.6455"

There are three basic types of “fit” when metal parts fit together. They are:
1. A clearance Fit (loose)
2. An interference Fit (tight)
3. A transitional Fit (between loose and tight)

What we want when we use the GO Gage is a Clearance Fit so that you can not feel any more friction or resistance as you close the bolt on the gage. That and ONLY that is the proper way to ensure you have minimum headspace.

If you have a Transitional Fit, then you can feel some additional friction or resistance as the bolt closes on the Gage. This is NOT acceptable when you close the bolt on a GO Gage and it doesn’t pass the GO Gage inspection. What is going on is that while you can close the bolt all the way down, the metal in the bolt and chamber actually are bending ever so slightly so the bolt can close on the gage. This is because the barrel is softer than the headspace gage and while the bolt has a hard surface, it has a soft inner core so it doesn’t shatter when the cartridge is fired. There is a little “give” even from the bolt for that reason.

If you have an Interference Fit, you sometimes can still force the bolt closed down over the gage. However, you usually then have to use a screwdriver of some kind of small pry bar device to get the bolt to open. This comes from the metal in the barrel and the bolt having to bend or “give” even more so the bolt can close on the Go Gage. This is even less acceptable with a GO Gage than a Transitional Fit.

Now, I have heard even some people who SHOULD know better say that as the bolt closes on the GO Gage (no matter if there is a transitional or interference fit) then Headspace is still good. They can’t be more mistaken because in both cases metal has to be slightly bent or “give” for the bolt to close on the gage.

As far as the Field Reject Gage goes, the best is the bolt doesn’t go all the way down to the flat shoulder on the receiver. However, as long as you have either a Transitional Fit (additional friction) or BETTER STILL an Interference Fit (really tight and you have to pry the bolt open) then Headspace is still safe.


Tony.

It didn’t stretch, it may be that the throat got worn further into the barrel, or that the gun had a long chamber to begin with, or the bolt lugs have worn or were lapped too much to give the same long chamber...

Get a new barrel in the caliber you want and don’t worry about it.

Another possibility is that you were pushing the shoulder back too much when resizing. That will kill your brass quick as well.

quote:

Originally posted by cas:
Another possibility is that you were pushing the shoulder back too much when resizing. That will kill your brass quick as well.

This is why when I'm loading for my 308 I use fireformed cases and don't bump the shoulders back until the bolt closing gets too tight BTW I consider light drag as perfect and anything needing a bit of strain to get the bolt closed is too tight. By doing this I don't see any observable case stretch in the overall length for 3 or 4 cycles after a size and trim.