Brass Stretching Question

[duurmeehr]

I have a new Browning BLR Model 81 LT WT in a Win .308. After an initial sighting in a question has arisen that I need some advice on. It appears to be stretching the brass more than I am accustomed to.

A new piece of Winchester brass factory loaded reads 1.5715" from base to shoulder with a Sinclair bump gauge.

A fired piece of Winchester brass full length resized on my RCBS standard resizing die comes in at 1.5695".

In my Winchester Model 70 .308, when I measure a fired reload that I resized full length, the case is 1.573" to the shoulder which appears to me I moved the shoulder forward .0035".

Now the part that I am not sure of.

When I fire that same load in my new BLR, the fired case measures 1.5825" to the shoulder which appears to me I moved the shoulder forward .0135" which is .01" more than my Model 70 moves it.

Is .0135" excessive stretch in a chamber or is my Model 70 just a better headspacing job than the BLR is?

Any advice is appreciated. I am trying to determine if there is really a problem that would warrant a call to Browning.

 

[ronemus]

Are you using the correct bushing ().400" ID)? SAAMI spec for the chamber is 1.630 -40", so your brass should be a couple of thousandths shorter after firing.

That aside, it's not unusual for factory chambers to differ by a few thousandths, but one of them is seriously out of spec. You should have them checked using GO, NO-GO, and FIELD gages; a correctly dimensioned new chamber should allow the bolt to close on the GO gage, but not the NO-GO. A well-used rifle may close on the NO-GO, but not the FIELD. A gunsmith will probably have the gages, and somebody in your shooting community may have them. The test is quick and easy, so it shouldn't cost much to have it done professionally if need be.

 

[ronemus]

Are you using the correct bushing ().400" ID)? SAAMI spec for the chamber is 1.630 -40", so your brass should be a couple of thousandths shorter after firing.

That aside, it's not unusual for factory chambers to differ by a few thousandths, but one of them is seriously out of spec. You should have them checked using GO, NO-GO, and FIELD gages; a correctly dimensioned new chamber should allow the bolt to close on the GO gage, but not the NO-GO. A well-used rifle may close on the NO-GO, but not the FIELD. A gunsmith will probably have the gages, and somebody in your shooting community may have them. The test is quick and easy, so it shouldn't cost much to have it done professionally if need be.

Repeated reloading with 0.015" of stretch will result in a case head separation (very bad juju) after relatively few firings. You can either have the rifle repaired or adjust your sizing die so that the shoulder is bumped 0.001-2"; if you choose the latter, you'll have to dedicate brass to a particular rifle.

 

[whatsupdoc]

When you are measuring a fired case from the BLR are you removing the primer before measuring?
The primer will skew the numbers.

 

[duurmeehr]

The insert I have is a Sinclair #20. It is supposedly tapered to match the dimension of the cartridge shoulder.

This is my first lever action rifle and is more difficult to work with than my bolt action and single actions. It will close on the go gauge but not on the no-go gauge. It comes close to closing on the no-go gauge but it won't lock up. It's hard to feel that in the bolt action.

The BLR has a rotating bolt face, not like a regular lever action. At this point I don't know if the chamber would be out of spec or the bolt not engaging fully.

 

[duurmeehr]

When you are measuring a fired case from the BLR are you removing the primer before measuring?
The primer will skew the numbers.

Yes, I removed the primer with a decapping die. I've seen that little bit protruding skew the numbers.

 

[duurmeehr]

Repeated reloading with 0.015" of stretch will result in a case head separation (very bad juju) after relatively few firings. You can either have the rifle repaired or adjust your sizing die so that the shoulder is bumped 0.001-2"; if you choose the latter, you'll have to dedicate brass to a particular rifle.

So what I am hearing is that .013" is on the long side so something is amiss. That is where I was leaning.

This isn't going to be a range gun, just a long time itch to own one that got scratched. It's sole purpose will just be a couple rounds a year hunting in the rotation with the others. I think for now I will just decicate a set of brass for that rifle and just bump the shoulder. For what they sell for, you would think they would be better quality control. I am going to give Browning customer service a call and just feel them out.

 

[jimmymac]

I guess I'm not seeing the problem. I wouldn't expect the two factory chambers to be the same. I'd just set up the resizing die for the new gun to provide a few thou of shoulder bump and call it a day.

Better yet, grab another sizing die and dedicate it to the new gun to eliminate fiddling around with the die too much.

Obviously, the brass won't be interchangeable between the two guns, but this is pretty normal when dealing with factory chambers.

 

[jackieschmidt]

I guess I'm not seeing the problem. I wouldn't expect the two factory chambers to be the same. I'd just set up the resizing die for the new gun to provide a few thou of shoulder bump and call it a day.

Better yet, grab another sizing die and dedicate it to the new gun to eliminate fiddling around with the die too much.

Obviously, the brass won't be interchangeable between the two guns, but this is pretty normal when dealing with factory chambers.

^^^^^^^^

 

[243winxb]

in my new BLR, the fired case measures 1.5825" to the shoulder

Bump the shoulder back to 1.580" see if the sized brass will chamber? You do NOT want a crush fit.

Keep brass separate for each gun.

 

[fkimble@charter.net]

Another easy way is to adjust your die for the short chamber and use some "Skips Shims" to space the die up for the long chamber. Pack of 9 or 10, from .003 to .010. You can double up on them if needed. Makes it quick and easy and less expensive.

Frank

 

[Coyotefurharvester]

Since you have/had the go no go did you measure them using your Sinclair and get an actual number for your brass/die adjustment? Saves time and guessing.

 

[Webster]

I have a new Browning BLR Model 81 LT WT in a Win .308. After an initial sighting in a question has arisen that I need some advice on. It appears to be stretching the brass more than I am accustomed to.

A new piece of Winchester brass factory loaded reads 1.5715" from base to shoulder with a Sinclair bump gauge.

A fired piece of Winchester brass full length resized on my RCBS standard resizing die comes in at 1.5695".

In my Winchester Model 70 .308, when I measure a fired reload that I resized full length, the case is 1.573" to the shoulder which appears to me I moved the shoulder forward .0035".

Now the part that I am not sure of.

When I fire that same load in my new BLR, the fired case measures 1.5825" to the shoulder which appears to me I moved the shoulder forward .0135" which is .01" more than my Model 70 moves it.

Is .0135" excessive stretch in a chamber or is my Model 70 just a better headspacing job than the BLR is?

Any advice is appreciated. I am trying to determine if there is really a problem that would warrant a call to Browning.

Not sure if I am following the details but you compare new brass to fired and FL resized. What's the measurement fired but not resized? I would think the measurement after fired and no sizing would be the number to compare to. If you didn't have a bump gauge you wouldn't think you had a problem. The new brass measurement is probably meaningless since factory loaded brass always has excessive clearance so the ammo will chamber in any rifle that is made.

I would only measure as fired brass as a reference. The fired brass should easily chamber. FL resize with no shoulder bump chamber and fire. The fired brass should still chamber easily. Only when you begin to see a little effort to close the bolt measure the length. This is your reference number to bump back from.

 

[Twicepop]

Some cases by design will stretch because of their design. The worst offenders seen to be are those designed prior to about the year 2000, and especially those design for military use. The military want's their cartridges to feed, fire and extract/eject one time only with no regard to reloading them. These usually have "generous" body taper and gently shoulder angles that promote case growth. Even many of the cartridges designed up through the 80s and 90s followed this design also. Only the past few years has cartridge design favored the handloader with minimum body taper and shoulder angles that limit case growth. Loading to higher pressures along with the aforementioned issues will cause case growth and eventual case head separations unless sizing is kept to a minimum.

 

[Ccrider]

Use new brass for the one or two shots hunting a year. That way you can be 100 percent sure of what will happen.

 

[duurmeehr]

Another easy way is to adjust your die for the short chamber and use some "Skips Shims" to space the die up for the long chamber. Pack of 9 or 10, from .003 to .010. You can double up on them if needed. Makes it quick and easy and less expensive.

Frank

I think this is a good solution for me.

I had never heard of the "Skip's Shims". What a great idea.

A separate set of brass for the long chamber.

Set the die up to bump the short chamber back and when I load for the long chamber use the shims.

Thanks all for the great answers.

 

[Coyotefurharvester]

Or don't move the shoulder(FL)of fired brass that will still chamber easily without sizing, or just neck size. All new brass is "short" of factory chambers.

 

[Ned Ludd]

It's caused by the more generous chamber dimensions on the new Browning rifle as compared to the Model 70 chamber. An increase in the CBTS of .0135" seems like a lot to me. My .308 Win rifles generally show an increase in CBTO measurement after firing virgin brass of around .005" to .006". The CBTS measurement of the virgin brass also has something to do with this; some brands start out noticeably shorter than others. I do have a couple .223 Rem bolt rifles in which the brass grows from .008" to .009" at the shoulder, which also seems like a lot. Nonetheless, the application for all of it is always the same: I set the die to bump the shoulder back only .0015" to .002" from the fired CBTS measurement on all subsequent firings, and this seems to work just fine.

FWIW - I have never had a case head separation. From those I know that have, it always turned out to be caused by repeatedly bumping the shoulder back much more than .002" after each firing. In some instances, it only took three or four firings before case head separation reared its ugly head. The repeated [over] sizing and compression of the brass puts a lot more strain on the initial region of the case wall just above where the case head/webbing thins out. Minimizing this repeated stretching/compression after the first firing seems to do the trick. However, there is probably some amount of stretching on the first firing that is large enough to cause problems even though the shoulders are only bumped back .002" or less on subsequent firings. I do not have any idea how close your specific situation might be to that. I'd simply resize the cases with </= .002" shoulder bump, and pay careful attention on subsequent firings. A paper clip with a short right angle bend near the end can sometimes be used to "feel" the beginning of case head separation inside the case. Alternatively, a borescope can also be used to examine the region just above the webbing inside a fired case (after cleaning) for the beginning of a crack or similar anomalies. Either one of those approaches may help ease any trepidation you might have about firing these re-sized cases.

 

[duurmeehr]

It's caused by the more generous chamber dimensions on the new Browning rifle as compared to the Model 70 chamber. An increase in the CBTS of .0135" seems like a lot to me. My .308 Win rifles generally show an increase in CBTO measurement after firing virgin brass of around .005" to .006". The CBTS measurement of the virgin brass also has something to do with this; some brands start out noticeably shorter than others. I do have a couple .223 Rem bolt rifles in which the brass grows from .008" to .009" at the shoulder, which also seems like a lot. Nonetheless, the application for all of it is always the same: I set the die to bump the shoulder back only .0015" to .002" from the fired CBTS measurement on all subsequent firings, and this seems to work just fine.

FWIW - I have never had a case head separation. From those I know that have, it always turned out to be caused by repeatedly bumping the shoulder back much more than .002" after each firing. In some instances, it only took three or four firings before case head separation reared its ugly head. The repeated [over] sizing and compression of the brass puts a lot more strain on the initial region of the case wall just above where the case head/webbing thins out. Minimizing this repeated stretching/compression after the first firing seems to do the trick. However, there is probably some amount of stretching on the first firing that is large enough to cause problems even though the shoulders are only bumped back .002" or less on subsequent firings. I do not have any idea how close your specific situation might be to that. I'd simply resize the cases with </= .002" shoulder bump, and pay careful attention on subsequent firings. A paper clip with a short right angle bend near the end can sometimes be used to "feel" the beginning of case head separation inside the case. Alternatively, a borescope can also be used to examine the region just above the webbing inside a fired case (after cleaning) for the beginning of a crack or similar anomalies. Either one of those approaches may help ease any trepidation you might have about firing these re-sized cases.

.135" seemed a lot to me also but after reading al the reply's and thinking about it, it's not really that big a deal other than not being able to interchange ammunition between my two .308's. The only real working the case received will be from the factory to chamber dimension. As long as I don't completely resize, the case won't be worked any more after that first good stretch. Am I correct in that?

I just checked the once fired cases in my rifle and they chamber smoothly and completely without any full length resizing so I am going to neck size them, trim to length and let them go.

That set of cases will just be dedicated to that rifle.

 

[Coyotefurharvester]

Yes, especially if your chambers fit go-no go correctly.