Shortest safe .308 case length

deepcore · May 17, 2011, 09:52 PM

I have a few .308 cases below 2.005 in case length (in the mid-ish 1.9s).
Got that way when my RCBS trim Pro adjustment collar "walked" on me while using it. Part of the reason I changed to Lee cutter.
I think with re-sizing they'll lengthen a bit.
Need to know which to throw out though.

89blazin · May 18, 2011, 07:21 AM

IMHO, whether they will be safe to use or not is dependent on your rifle's chamber. I've had a similar experience and used brass trimmed to 1.97" with no problems. Did you trim before resizing? I always resize first. By all means, resize them if you haven't.

Slamfire · May 18, 2011, 08:36 AM

Brass holds the powder, primer, powder all in one package. Without brass cases we would be back to powder horns, spit patches, ramrods and percussion primers.

Very importantly brass acts as a gas seal. The most important and safety critical section of a brass cartridge is the unsupported part. The part that is not surrounded by steel, the unsupported part, is the case head. If the case head develops a leak then there is nothing keeping the gas from escaping back into the action. Actions are not designed to take the loads when 50,000 psia pressure gas goes from a small surface area (bolt face) to a large surface area, like the receiver ring.

So what has this got to do with trim OAL?

If you trim so much that the bullet falls off because there is not sufficient case neck to hold it, well that should be obvious to all that is a problem: , “look Mom, no bullet!"

The forward 2/3’s of the case is useless for pressure purposes. It is the back 1/3 which is the pressure vessel. If you look at what is going on in fluted chambers, the front 2/3 rds is floated off the chamber walls. The only function for the front is to hold the bullet in place and keep the powder from spilling.

If you trim so much that you are cutting into the case head and I don’t know how you would load a cartridge without a case neck or a body, then you will have a safety issue. Because there is nothing to keep gases from escaping into the action.

So how did anyone establish a “minimum trim length”?, heck if I know. I know seating depth makes a difference in pressures, but just how much, I don’t know. Might make a difference if you trimmed a tenth of an inch off a centerfire rifle case, but if you are over trimming by .005”, or even .01” I would not be worried.

wncchester · May 18, 2011, 01:36 PM

"If you trim so much that the bullet falls off because there is not sufficient case neck to hold it, well that should be obvious to all that is a problem"

That's the bottom line.

deepcore · May 18, 2011, 08:48 PM

Thanks guys.
Yes I sized before I trimmed.
Just over trimmed because I didn't tighten the locking collar on my RCBS Trim Pro enough and the setting moved while I was trimming.
I measured the 10th case trimmed and noted the "shortness".
I back measured from the 9th to the 1st case and noted the gradual increase shortening.
The remaining 90 cases went fine after I cranked on that tiny set screw.

4runnerman · May 18, 2011, 08:50 PM

I just got a box of new Nosler brass in 308.New they measure 1.9975. I have shot them all once and had zero issues.

May 17, 2011, 09:52 PM	#1
deepcore Senior Member Join Date: July 24, 2010 Posts: 364	Shortest safe .308 case length I have a few .308 cases below 2.005 in case length (in the mid-ish 1.9s). Got that way when my RCBS trim Pro adjustment collar "walked" on me while using it. Part of the reason I changed to Lee cutter. I think with re-sizing they'll lengthen a bit. Need to know which to throw out though.

May 18, 2011, 08:36 AM	#3
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	Brass holds the powder, primer, powder all in one package. Without brass cases we would be back to powder horns, spit patches, ramrods and percussion primers. Very importantly brass acts as a gas seal. The most important and safety critical section of a brass cartridge is the unsupported part. The part that is not surrounded by steel, the unsupported part, is the case head. If the case head develops a leak then there is nothing keeping the gas from escaping back into the action. Actions are not designed to take the loads when 50,000 psia pressure gas goes from a small surface area (bolt face) to a large surface area, like the receiver ring. So what has this got to do with trim OAL? If you trim so much that the bullet falls off because there is not sufficient case neck to hold it, well that should be obvious to all that is a problem: , “look Mom, no bullet!" The forward 2/3’s of the case is useless for pressure purposes. It is the back 1/3 which is the pressure vessel. If you look at what is going on in fluted chambers, the front 2/3 rds is floated off the chamber walls. The only function for the front is to hold the bullet in place and keep the powder from spilling. If you trim so much that you are cutting into the case head and I don’t know how you would load a cartridge without a case neck or a body, then you will have a safety issue. Because there is nothing to keep gases from escaping into the action. So how did anyone establish a “minimum trim length”?, heck if I know. I know seating depth makes a difference in pressures, but just how much, I don’t know. Might make a difference if you trimmed a tenth of an inch off a centerfire rifle case, but if you are over trimming by .005”, or even .01” I would not be worried. __________________ If I'm not shooting, I'm reloading.

May 18, 2011, 08:50 PM	#6
4runnerman Senior Member Join Date: January 16, 2010 Location: Minnesota Posts: 3,577	I just got a box of new Nosler brass in 308.New they measure 1.9975. I have shot them all once and had zero issues. __________________ NRA Certified RSO NwCP- Performance Isn't Optional

May 18, 2011, 07:21 AM	#2
89blazin Senior Member Join Date: March 13, 2009 Posts: 107	IMHO, whether they will be safe to use or not is dependent on your rifle's chamber. I've had a similar experience and used brass trimmed to 1.97" with no problems. Did you trim before resizing? I always resize first. By all means, resize them if you haven't.

May 18, 2011, 01:36 PM	#4
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	"If you trim so much that the bullet falls off because there is not sufficient case neck to hold it, well that should be obvious to all that is a problem" That's the bottom line.

May 18, 2011, 08:48 PM	#5
deepcore Senior Member Join Date: July 24, 2010 Posts: 364	Thanks guys. Yes I sized before I trimmed. Just over trimmed because I didn't tighten the locking collar on my RCBS Trim Pro enough and the setting moved while I was trimming. I measured the 10th case trimmed and noted the "shortness". I back measured from the 9th to the 1st case and noted the gradual increase shortening. The remaining 90 cases went fine after I cranked on that tiny set screw.