.308 case length over spec. . .big deal???

[magyarbetyar]

Hey Guys, new to the forum and reloading and have a question. I am reloading .308 for one firearm only, an AR-10. I have FL sized all my brass and measured the case lengths. They range from 2.005 all the way to 2.035 with the majority falling into the 2.010-2.025 range.

Now just out of curiosity I took one of the cases that measured 2.035 and chambered it in the rifle and the bolt closed with no resistence whatsoever. I did removed the ejector from the bolt to make it easier.

Now my question is why should I trim the case length if it fits in my chamber fine?

Oh, I am using all Lee reloding equipmet including their 3 piece rifle die set.

 

[Wil]

Re: .308 case length over spec. . .big deal???

consistency is key... much to that

 

[427Cobra]

Re: .308 case length over spec. . .big deal???

Sinclairs sells a little tool to measure your chamber to determine trim length, I trim mine back to 2.015, like Sir Wil said, consistency.

 

[buffybuster]

Re: .308 case length over spec. . .big deal???

Whether it is safe or unsafe is dependent on your chamber. If your chamber is cut long then it's not an issue until it reaches the end of the chamber. If your chamber is cut to minimum spec then you have a potential safety issue. With a longer than spec case, the casemouth will be pinched in the throat of the chamber. Upon firing, the casemouth will have no room to expand and release the bullet. The pressures will eventually release the bullet but excessive pressures may result.

From an accuracy perspective, the more consistent you can be, the more precise your rounds will be.

 

[Victor N TN]

Re: .308 case length over spec. . .big deal???

Like stated above. You really need to measure your chamber. I have 2 rifles chambered in 308. I have to label everything this or that.

 

[Swan]

Re: .308 case length over spec. . .big deal???

Just trim it to something under max length, and be consistent with all the brass. Don't worry about it.

 

[magyarbetyar]

Re: .308 case length over spec. . .big deal???

I am just trying to dial in the reloading to that one particular rifle. I also tried checking to see how far out the bullets would have to be to touch the lands and they were way to long for the magazine. So will not be able to play with that really.

Thanks for the help. I will go ahead a trim them to SAAMI spec for my first batch and see what happpens.

 

[AXEMAN]

Re: .308 case length over spec. . .big deal???

i just started reloading but i figured that when they give you a maximum and minimum case length, they do it for a reason. brass is soft. you go shoving a long case in there and you and your rifle bolt will make it fit. but to be safe, trim to the min after it goes over the maximum.

 

[Clark]

Re: .308 case length over spec. . .big deal???

The book may say "2.015" max, trim to 2.005", but your rifle's chamber neckspace is longer than 2.015".

Trimming is a pain we would all like to skip until the brass gets as long as the chamber.

The trouble is, the firing pin pushes the case forward. The rifle headspace minus the cartridge shoulder space is how far forward the case gets pushed.
The headspace on .308 Win chambers, per SAAMI, can be from 1.630" to 1.640".
The shoulder space on .308 Win cartridges, per SAAMI, can be from 1.627" to 1.634".

So if your sloppy gunsmithing reamed to 1.640", it is still Kosher.
If your sloppy case resizing pushed the shoulder back to 1.627", that is still Kosher too.
But the firing pin is going to push the case forward 1.640" - 1.627" = .013".

If the firing pin pushes the cartridge forward, and the case neck runs into the end of the chamber neck, the bullet will be pinched. This will damage the bullet, making a decrease in accuracy, and make a spike in pressure causing an increase in velocity and may shorten brass life with loose primer pocket and/or jam the rifle with stiff bolt lift.

So if your chamber neckspace is longer than 2.015", and you think you don't need to trim, you may be right. But you need to consider the firing pin pushing the case forward is eating into that safety margin.

 

[1911.it]

Re: .308 case length over spec. . .big deal???

Get a Giraud!

 

[gnfiter3]

Re: .308 case length over spec. . .big deal???

The infor here will prevent you from sharing an embarrasing moment (with me) on the firing line. While all chambers have a tolerance, and you're maybe getting by with the, 2.035 for now; avoid this! Bolt goes home, will not lock, pull charging handle to rear and it won't move. Now you're on the range with a rubber hammer, tapping on the charging handle to get the case out of your $1,900 plus dollar rifle. It was recommended that you trim shorted than the specified 2.015, great idea, IMHO. Found this to be true with AR-15 also.

I'm a brass hog at the range. Shooters love me picking up their spent brass, so they don't have to do it. My work starts with measuring and trimming it, esp AR15 Brass. Love that once fired, FREE brass.

Find the specification on your AR-10 and keep the specs within tolerance. Egg should be on your plate, not on your face

 

[magyarbetyar]

Re: .308 case length over spec. . .big deal???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gnfiter3</div><div class="ubbcode-body">The infor here will prevent you from sharing an embarrasing moment (with me) on the firing line. While all chambers have a tolerance, and you're maybe getting by with the, 2.035 for now; avoid this! Bolt goes home, will not lock, pull charging handle to rear and it won't move. Now you're on the range with a rubber hammer, tapping on the charging handle to get the case out of your $1,900 plus dollar rifle. It was recommended that you trim shorted than the specified 2.015, great idea, IMHO. Found this to be true with AR-15 also.

I'm a brass hog at the range. Shooters love me picking up their spent brass, so they don't have to do it. My work starts with measuring and trimming it, esp AR15 Brass. Love that once fired, FREE brass.

Find the specification on your AR-10 and keep the specs within tolerance. Egg should be on your plate, not on your face

</div></div>

LOL nice post! I am going to start with all SAAMI specs and then dial in the rounds for my rifle from there. I will invest in some measuring equipment so I can get my ture chamber dimensions later on down the line.

Better safe than sorry I alwyas say.

Thanks for the advice guys.

Although I will not get a Giraud $$$$$$$$$ too mucho. Possum Hollow here I come

 

[sobrbiker883]

Re: .308 case length over spec. . .big deal???

I set my Possum Hollow's cutter to cut at 2.005" and trim when they reach 2.015"

I watched a buddy have a long two days at the Vegas Halloween match from not trimming his brass for his AR. Its not a lesson he will soon forget.