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Old September 8, 2012, 02:08 PM   #1
Marco Califo
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Trimming 308 - when too?

The trim to length is 2.005"
Case length is stated at 2.015"
Some I just resized are around 2.02 to 2.025, but they drop into the chamber just fine and the bolt closes.
I have no plans to trim every time I shoot these, or more often than I absolutely need to.
Should I plan to trim these when they go over:

2.035?
2.030?
2.025?
2.020?
2.015?
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Old September 8, 2012, 02:34 PM   #2
Jimro
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You won't know when you need to trim without knowing your chamber dimensions.

I trim to minimum on the first reload.

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Old September 8, 2012, 03:23 PM   #3
dahermit
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Quote:
I trim to minimum on the first reload.
Excellent advice. This makes all the case lengths as uniform as possible...which is you want for accuracy purposes. Accuracy is all about uniformity. I have always considered the first loads in new cases only for fire-forming the cases anyway.
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Old September 8, 2012, 07:37 PM   #4
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I trim on the first reload and every reload after that. My Giraud trimmer makes trimming a snap, I will buzz through 88 cases in less than ten minutes from the time I go find the thing to when I put it back up. I figure it takes less than five minutes once I start trimming. It is as fast as a pencil sharpener.

I learned decades ago that long cases will blow primers.

Incidentally, I trim to 2.000". Too long is a safety risk as the neck will pinch the bullet in the throat but too short, as long as it holds the bullet I don't know what too short might be.
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Old September 8, 2012, 09:35 PM   #5
603Country
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What dahermit said is exactly 100% of what I do and why.
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Old September 8, 2012, 09:51 PM   #6
Powderman
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Using .308 as an example, I load new cases and fire once, as is. Same, of course, for factory new ammo.

During the first reloading process, I trim to the minimum length (2.000). I'll then shoot the lot and measure until I have to trim again. When I have to trim again, I'll reload and shoot once afterward, then the case gets scrapped.

I usually average 5-6 reloadings of fired cases after the first trim.
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Old September 8, 2012, 10:24 PM   #7
Marco Califo
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Quote:
When I have to trim again????
I am pretty sure that was the OP's OQuestion.
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Old September 8, 2012, 10:31 PM   #8
Ideal Tool
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1+ on what Jimro said..Sinclair International sells chamber length gages. Far better to determine the length of YOUR rifles chamber rather than blindly go by some wide-open tolerance SAAMI specs in a reloading manual.
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Old September 9, 2012, 05:17 PM   #9
dacaur
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max case length is 2.015"... when a case exceeds that, trim it. seems pretty simple....

If you are loading for only one rifle i guess you could measure your chamber and trim for it, but I dont know that i see the point to that.... case length in a bottleneck cartridge only matters if its too long. too short isnt going to affect anything....
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Old September 11, 2012, 11:33 AM   #10
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I have a Dillon trimmer set up on my 650 with casefeeder and case prep toolheads with trim dies for 30-06, .308, .223/5.56, and even 30 Carbine (special thin toolhead and CH4 trim die). That was I set the trim length at near the maximum case length. Because my cases are trimmed every time I resize and deprime them (if needed) I ensure that the cases are both all the same length as well as having the best neck grip on the bullet. In addition, longer necks help to slow throat erosion.
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Old September 11, 2012, 01:38 PM   #11
Marco Califo
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So, what Max case length do you use for 308?
2.015?
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Old September 11, 2012, 01:53 PM   #12
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I don't go over 2.015". No need to. A blown primer chews up the bolt face with gas cutting and really isn't worth risking to save a little trimming work. And if you have a chamber with a ball throat (taper from neck diameter, no freebore) it can wedge a long neck in, raising pressure. Keep in mind that chambering a round can set the shoulder back a few more thousandths (Hatcher measured 0.006", IIRC, on an Enfield chambering a .30-06, presumably done by someone who could work the bolt fast), so what fits when you drop it in the chamber empty might not do so during actual shooting.

SAAMI minimum case length is 1.995". Military minimum is 2.000". The usual 2.005" "trim-to" length given is simply half way between SAAMI minimum and maximum. Nothing magic about it. SAAMI is a manufacturing association, and manufacturers typical aim for the middle of a spec range to allow a maximum of wiggle room for error so they don't have to measure every cartridge case for length. No reason the handloader has to copy that.

Some M14/M1A competitors used to trim .308 Win to 1.975"-1.980" just so they were sure never to go over 2.015" and have to trim again during the life of the case. I heard it suggested that can eventually wear the chamber a little wider, increasing gas bypass during bullet jump, but I've never seen it demonstrated to make any difference during a barrel's normal lifetime. If someone else knows otherwise, please speak up.

Needless to say, you can't trim cases extra short and expect crimping dies to work normally with them. If you don't crimp normally (the guys using extra short trim didn't and neither do I) it doesn't affect you that way.
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Old September 11, 2012, 04:38 PM   #13
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I also trim after every round. Uniformity= sweetness down the range
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Old September 11, 2012, 09:30 PM   #14
TheTinMan
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Full length resizing for an M1A, I had to trim almost very case every time until I switched to an RCBS X-Die for sizing. In a semi-auto, I see no reason to mess with cases longer than spec and lots of reasons not to.
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Old September 12, 2012, 05:31 PM   #15
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Yes but you do still have to trim cases to the SAAMI minimum once (1.995" for .308) before you start sizing them with the X-die, per the instructions.
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