Request advice on trim tolerance

bow shot · March 23, 2010, 12:03 PM

How close to my target trim length do I need to keep, really?

What generated this question is this: I have high quality (Nosler) brass, and much of it was below the spec. trim-to length before the first firing. Now, after firing, the range of the case lengths has increased to 0.010" (with a few outliers that would actully make the spread 0.020").

This brass is very uniform in neck wall thickness and TIR. but as you can see, the trim length is all over the map. Or would a good, bug-shooter say, "Dude, 0.010" tolerance is fine and will have no effect on accuracy."?

This is .204 Ruger, case length specs are: 1.850 max 1.840 trim-to and 1.830 min. I'm expereincing 1.830 - 1.840 (with a few in the 1.825-1.8.0" range)

**Unclenick** · March 23, 2010, 12:31 PM

Only measure trim length after resizing. As-fired can be shorter or longer, depending on circumstances. The sizing die squeezes it back to length. Some rounds vary quite a bit, case-to-case, in how they respond to being fired.

Lots of guys who shoot .308 in matches used to ignore the -0.020" spec limit and trim about twice that far back just so they wouldn't have to trim again during the life of the brass in a self-loader (about 5 cycles, pretty commonly). You lose some grip on the bullet, but if you use the standard magazine-compatible COL's, it doesn't make any more difference than a lot of other load variables.

bow shot · March 23, 2010, 01:50 PM

So far these were measured before firing, after firing, and then again after sizing (neck sized with Lee collet die).

I don't like the spread, but if it doesn't matter (accuracy), then I'll just go back to bed...

Slamfire · March 24, 2010, 02:36 PM

Every new case I have every fired, on the first firing and resizing was all overlength.

Trim the stuff down so the case neck does not pinch the bullet in the throat.

Trim length below max is not safety critical. Trim length variations do not make a difference on paper, at least in my rifles.

Maybe in a bench rest gun.

Toddco · March 24, 2010, 07:39 PM

Bowshot, are you able to get these rounds out to around .020 thou from the lands or at least as long as you want to make them? The trouble I had with my savage model 12 flv was that the new nosler brass i bought was so short that i could not load bullets out far enough for my liking. So what i did was make a chamber length guage from an old piece of brass. I cut half of the neck off of it, split the ring i had just made, resized the brass, reamed it out so the bullet would slide in and out, put a bullet in the brass leaving it out as far as i could, slipped the ring over the bullet, put the bullet in my rifle. This gave me my chamber length. I did this 5-10 times to get a precise measurement. Once i had the chamber length, i then shortened the brass .007 thou and this has become my trim to length for my .204

bow shot · March 26, 2010, 12:20 PM

Toddco:

As I recall, when I first started with this rifle, If I got to the lands, the 32 gr VMax bullets were barely in the case, and that was with Hornady brass that was plenty long, in the 1.840- 1.850" range. The number in my head for OAL that I settled for is 2.400", I'll have to check my notes when I get home.

The sierras 32s a a tad longer, which helps a bit. I just loaded those into Nosler brass @ appx 2.405" a couple nights ago, and they chamber fine.

I did the thing where you put the bullet in a case with a split neck and chamber it several times. Your method sounds great!

As you mention, the Nosler brass is shorter, and thats the thing that generated my post. I really didn't like trimming that stuff down, because real estate there is scant to begin with!

Slamfire: Believe it or not, mine actually got shorter after firing? I guess its not uncommon? I almost always see it grow if I full length size though. As a matter of fact, in the past I've FL sized cases they've come up shorter than I like. Not that what I like is always based on the best of wisdom...

March 23, 2010, 12:03 PM	#1
bow shot Senior Member Join Date: March 26, 2009 Posts: 263	Request advice on trim tolerance How close to my target trim length do I need to keep, really? What generated this question is this: I have high quality (Nosler) brass, and much of it was below the spec. trim-to length before the first firing. Now, after firing, the range of the case lengths has increased to 0.010" (with a few outliers that would actully make the spread 0.020"). This brass is very uniform in neck wall thickness and TIR. but as you can see, the trim length is all over the map. Or would a good, bug-shooter say, "Dude, 0.010" tolerance is fine and will have no effect on accuracy."? This is .204 Ruger, case length specs are: 1.850 max 1.840 trim-to and 1.830 min. I'm expereincing 1.830 - 1.840 (with a few in the 1.825-1.8.0" range)

March 23, 2010, 12:31 PM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,732	Only measure trim length after resizing. As-fired can be shorter or longer, depending on circumstances. The sizing die squeezes it back to length. Some rounds vary quite a bit, case-to-case, in how they respond to being fired. Lots of guys who shoot .308 in matches used to ignore the -0.020" spec limit and trim about twice that far back just so they wouldn't have to trim again during the life of the brass in a self-loader (about 5 cycles, pretty commonly). You lose some grip on the bullet, but if you use the standard magazine-compatible COL's, it doesn't make any more difference than a lot of other load variables. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

March 23, 2010, 01:50 PM	#3
bow shot Senior Member Join Date: March 26, 2009 Posts: 263	right.. So far these were measured before firing, after firing, and then again after sizing (neck sized with Lee collet die). I don't like the spread, but if it doesn't matter (accuracy), then I'll just go back to bed...

March 24, 2010, 07:39 PM	#5
Toddco Senior Member Join Date: August 7, 2009 Location: Stony Plain, Alberta Posts: 108	Trim length Bowshot, are you able to get these rounds out to around .020 thou from the lands or at least as long as you want to make them? The trouble I had with my savage model 12 flv was that the new nosler brass i bought was so short that i could not load bullets out far enough for my liking. So what i did was make a chamber length guage from an old piece of brass. I cut half of the neck off of it, split the ring i had just made, resized the brass, reamed it out so the bullet would slide in and out, put a bullet in the brass leaving it out as far as i could, slipped the ring over the bullet, put the bullet in my rifle. This gave me my chamber length. I did this 5-10 times to get a precise measurement. Once i had the chamber length, i then shortened the brass .007 thou and this has become my trim to length for my .204

March 26, 2010, 12:20 PM	#6
bow shot Senior Member Join Date: March 26, 2009 Posts: 263	OAL Toddco: As I recall, when I first started with this rifle, If I got to the lands, the 32 gr VMax bullets were barely in the case, and that was with Hornady brass that was plenty long, in the 1.840- 1.850" range. The number in my head for OAL that I settled for is 2.400", I'll have to check my notes when I get home. The sierras 32s a a tad longer, which helps a bit. I just loaded those into Nosler brass @ appx 2.405" a couple nights ago, and they chamber fine. I did the thing where you put the bullet in a case with a split neck and chamber it several times. Your method sounds great! As you mention, the Nosler brass is shorter, and thats the thing that generated my post. I really didn't like trimming that stuff down, because real estate there is scant to begin with! Slamfire: Believe it or not, mine actually got shorter after firing? I guess its not uncommon? I almost always see it grow if I full length size though. As a matter of fact, in the past I've FL sized cases they've come up shorter than I like. Not that what I like is always based on the best of wisdom...

March 24, 2010, 02:36 PM	#4
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	Every new case I have every fired, on the first firing and resizing was all overlength. Trim the stuff down so the case neck does not pinch the bullet in the throat. Trim length below max is not safety critical. Trim length variations do not make a difference on paper, at least in my rifles. Maybe in a bench rest gun.