Brass Stretch

[Coltdriver]

I loaded up a fresh bag of remington brass for my 30-06.

Prior to loading I trimmed all of the brass that needed trimming. I used the lee tool.

After firing there was no uniformity in the stretch. Some needed no trim, some got a good kiss all around the edge. I was using 59 grains of H4831 under a 165 Grain Nosler Partition. This is well under max load but it is very accurate from my old Model 70. I was hitting a 2 inch target from 100 yards very easily.

Does anyone know if brass fired from a hot chamber will stretch more than brass fired from a cool chamber?

I fired 50 rounds over two hours. A few times it got pretty hot.

 

[The Bushmaster]

Aah...My favorite load for my Browning A-bolt .30-06. Only I use 59 grains of H4831SC and a Sierra 165 grain HPBT.

I really haven't paid that much attention to whether a cold or a hot chamber might effect fired case length, but I can see where it might. Hotter the chamber the longer the case might get. Expantion of the chamber would be my guess. Never really paid any attention to that though. I just trim those that need it and let it go at that. I do, however, try to let my rifle cool down between every 3 shot series. Always someone at the range to shoot the breeze with that is also letting his rifle cool down...

 

[Shoney]

Please clarify what you mean by

Prior to loading I trimmed all of the brass that needed trimming.

How do you determine which ones need trimming?
Do you trim the brass before or after sizing?

 

[peterotte]

How smooth (or rough) is your chamber? How well do you clean the case lube off the loaded cartridges? The dryer your brass the more it can be expected to stretch due to more grip on the chamber walls. I find it easier keep residual case lube constant by 're-lubing' loaded cartridges. This also eliminates case stretch in both my rough chambered 303Brit and 22 hornet. I do find, however, that even with an un-resized and lubed case, the hornet case will stretch when pressures are too high. But - this stretch is predictable and proportional to the degree of overload.

Inconsistent case stretch could also result from full length resizing then firing in a 'loose' chamber.

Hope this is of some help.

Peter

 

[Coltdriver]

I trimmed the new unfired brass out of the bag. Some needed it, some did not.

The point on brass not being previously stretched is interesting. They were new and this was the first firing for the brass.

For the second reload of the brass I am neck sizing only.

I will drop a note back here after I fire them again.

 

[snuffy]

Please clarify what you mean by
Quote:
Prior to loading I trimmed all of the brass that needed trimming.
How do you determine which ones need trimming?
Do you trim the brass before or after sizing?

I can answer that one. Coltdriver is using the lee trimmer system. The pilot bottoms out on the case spinner, if the case is not long enough, it just doesn't get trimmed. If however, it is longer than the pilot, it is trimmed until the pilot bottoms out on the case spinner spud.

 

[tkendrick]

As you mentioned in your later post, neck sizing is the way to go in your model 70. Always check your overall length, but unless you are shooting the same ammo from different guns, you usually don't need to full length size.

There are some exceptions, (aren't there always?).

I have two Krags, one of them is notoriously bad for stretching the brass, even with mild loads the brass has to be trimmed after each use, and after the third or forth firing, I start to see case head seperation.

I also load .300 Savage for a Savage 99 which always stretches the cases, and for a Remington 81 which will not chamber any round that has not been full length sized or exceeds SAAMI length.

In short, every rifle is going to be different to a certain extent. Keep tabs on what you Model 70 requires the first few times you load for it, and you'll figure it out.

 

[Shoney]

Coltdriver
Case necks stretch during the full length sizing process, usually, the longer the neck the more the amount of stretch. The amount the cases stretch can vary from case to case. To verify this, mike your cases before and after full length sizing.

My standard procedure is case trimming after sizing. That insures that all cases are uniform.

 

[peterotte]

tkendrick

You say;

I have two Krags, one of them is notoriously bad for stretching the brass, even with mild loads the brass has to be trimmed after each use, and after the third or forth firing, I start to see case head seperation.

Perhaps you should try lubing your ammo for that particular rifle. The lubing is the same as for sizing but with less lube - the case should feel 'sticky'. This will prevent the case from binding on the chamber wall during the initial pressure build-up during firing. My 303Brit went from case head separation after three firings to indefinate life. (Occasionally I get a split neck if I don't anneal - at least when I still re-sized. Now I use paper sabots to secure the bullet in the case).

Regards
Peter

 

[snuffy]

Perhaps you should try lubing your ammo for that particular rifle. The lubing is the same as for sizing but with less lube - the case should feel 'sticky'. This will prevent the case from binding on the chamber wall during the initial pressure build-up during firing. My 303Brit went from case head separation after three firings to indefinate life. (Occasionally I get a split neck if I don't anneal - at least when I still re-sized. Now I use paper sabots to secure the bullet in the case).

I wouldn't! You could end up eating that bolt, or have it take the right side of your head off as it leaves the receiver! The Krag has only one locking lug and the bolt cut as a second locking lug, lubing a case would vastly increase bolt thrust. Those minimal lugs could let loose, allowing the bolt to be thrown back towards your head.

 

[Walkalong]

I don't like the idea of lubing the case either. There are almost always better ways to limit case streching. I know some folks do and more power to them, but I would not just throw that around as a way to reduce streching of cases. It will get someone in trouble.

As snuffy says, it could ruin your gun or you as well. The case grabbing the chamber walls is crucial to sealing the chamber ( sealing off the gases), and keeping much of the force off of the bolt as well.

 

[The Bushmaster]

You might try this...My 1949 Winchester mod 94 has a small problem with head space (about .025 to .030"). A gunsmith recommended that I move the shoulder of the case up just that much (.030) by fire forming the case then resizing with the die set .030 off the shell holder. In my case I had primers backing out a bit and this solved the problem and minimized case stretch. It might work for this problem too...You will need to measure your chamber dimensions from bolt face to chamber shoulder.

 

[Walkalong]

That's it. Size the case to match the chamber.

 

[peterotte]

.... lubing a case would vastly increase bolt thrust. ...

No, it won't. As I explained, lubing prevents that initial binding of the case on the chamber wall. The case itself plays no role in bolt face thrust reduction. BUT, and this is meant to be a strongly worded warning, head separation will DOUBLE the bolt face thrust!
Brass is a self lubricating material but with a rough chamber, the brass is forced into the irregularities of the chamber walls which binds the brass, preventing normal longitudinal case stretch over it's full length, forcing a concentrated stretch just where the case body thins. Remember that the case is thrust forward into the chamber by the firing pin where it is held during that initial pressure build up, before the head can reseat against the bolt face. In a stronger case such as the 308 Win, the case wall as thicker and stronger and thins gradually towards the shoulder. This results in sufficient pull away to spread the load evenly, keeping the elongation within the elastic limit of the brass, so it springs back. But our thin walled, rimmed cases give us an extra problem.

Having said all that, there is truth in the belief that lubricating a cartridge could cause injury. This is due to oiling the cartridge or chamber. Never fire a rifle with oil in the chamber. It can cause diesel detonation by injecting oil mist into the chamber. This is not good!

To sum up - it is safer to lube than to risk head separation. But use small amounts of case lube or a dry lube. NEVER USE OIL!

Regards
Peter

 

[Walkalong]

Sounds like a rifle that needs work, or put out of service, except for folks who know what they are doing. I am glad to see you explain the difference between lubing the case carefully and just oiling it up. It can be very dangerous. Not for the novice.