AusVarmint

A mate got a new 308 LG some time back with a new barrel and new match chamber which was the same as the one in his old LG.

Thought he would use the fairly new brass from the old gun but was a bit puzzled when it wouldn't chamber in his new gun..... so anyhow he dropped the old barrel over on the weekend and I got to have a look at it and I think I found his problem

It seems the old chamber has grown a bit over time at the back end

Photo is of a new unfired 6br case in the chamber which I know it is a couple of thou smaller but it has gone in a loooonnnggg way

Amazing what a few thou on a taper will do.

So I presume that 6BR brass shouldn't go that far into a 308 chamber ?

Wow I would not have thought that was possible.

Missed

Yeah that barrel has gone about just on 3500 rounds and has grown a bit over time.....

The BR case measures 471 and the chamber measures 480 as best I can measure it at the back of the chamber which is 0.007" over original chamber dimensions

I type this for kickinback. I recently experienced a much smaller chamber on a rifle I purchased recently an had some trouble using my older brass when I tiightened the barrel

G'day Albow.

I am a bit confused.. If that barrel back end had grown by 0.008" how did you manage to remove the barrel from the action? That much expansion would have well and truly locked the threads together..
Are you sure the chamber wasn't always oversize?

Cheers
Leeroy

Leeroy,

Wouldn't surprise me that the chamber has grown, I've had 300 Redneck chambers on 1.25" tenon grow 4 or 5 thou, to the point where you had to resize the web to get the case back in. Funny stuff steel, but it seems to find a way to move itself under 65000 psi. And yes, the barrel screwed out fine.

Jeff

justjeff wrote:Leeroy,

Wouldn't surprise me that the chamber has grown, I've had 300 Redneck chambers on 1.25" tenon grow 4 or 5 thou, to the point where you had to resize the web to get the case back in. Funny stuff steel, but it seems to find a way to move itself under 65000 psi. And yes, the barrel screwed out fine.

Jeff

Interesting.. I certainly don't dispute what 65,000 PSI can do but where did the steel go? The tenon OD must grow in dia or perhaps it lengthened?

I'll be checking the Match barrels i take off in future for this..

Cheers
Leeroy

Leeroy, you being an expert in all things like this, would the action ring be getting larger by the same amount, thereby making it the same to remove the barrel ??

Camel wrote:Leeroy, you being an expert in all things like this, would the action ring be getting larger by the same amount, thereby making it the same to remove the barrel ??

It would be a very dangerous development if that was the case don't you think?
No the action wouldn't be growing, the forces developed in a normal load are well under the Yield strength of typical receiver steel at around 38 Rc.. The barrel it's self may well be growing as it's only around 25-28 RC, but if it were true, there would be a measurable difference in the thread dia right at the chamber mouth end vs the shoulder end.. Perhaps the OP can measure it with a mic for us??

Cheers
Leeroy

G'day Leeroy

Yeah I had a good look at the barrel when I got it and the area that has grown is the first 0.190" of the chamber which is the same length as the section of barrel that has been turned to fit inside the adaptor (came off an omark action) so not knowing the original OD of this section of the barrel it could have had an overall OD growth and still not had an issue with screwing out as this is smaller than threads on the adaptor. Similarly I am not sure if there has been a growth lengthwise either as do not know the original dimension on that either.

Thanks for that Leeroy, I never thought about the tensile strength thingo.

Looking back at the picture there does appear to be quite a long thread relief at the chamber mouth.. The wall thickness is quite thin here and so this probably contributed to the expansion as there is no support from the receiver.

Cheers
Leeroy