Brass trimming tolarances

eowiggy · March 4, 2013, 01:56 AM

When trimming my .223 brass, I noticed that I was getting a variance in my trim length of about 2-3 thousandths. Is this normal. Should I expect 1.750 exactly with every case I take off the trimmer. I am fairly new to reloading and I am trying to figure out if I am being a little too OCD when it comes precision for rounds that I am going to put through a recreational/pig killing AR.

Are there any tips to more consistant trimming? I try to put the same pressure on each case, but hell I see folks using power drills while trimming brass.

GTOne · March 4, 2013, 02:18 AM

What trimmer are you using?

eowiggy · March 4, 2013, 02:28 AM

Forster Original with a brand new 3-in-1 cutter. I adjust it to 1.750, tighten the set screws and after about a dozen cases most are +/- .001, but sometimes 2-3 thousandths more

GTOne · March 4, 2013, 04:54 AM

I'm not familiar with how the forster holds the case.

It should not vary that much, for sure. +/- .001 is normal, but not .003

Sport45 · March 4, 2013, 05:45 AM

Quote:

I am trying to figure out if I am being a little too OCD when it comes precision for rounds that I am going to put through a recreational/pig killing AR.

You are. If you are +/-0.003 of your trim to length you are fine. Just don't let them grow more than the max case length.

Your problem is probably irregularities on the base caused by the extractor.

Bart B. · March 4, 2013, 06:53 AM

I doubt there's a problem with as much as .010" spread in any bottleneck rifle cartridge case length. As long as the length of the longest one is at least .007" shorter than chamber length (bolt face to chamber mouth), accuracy will not be hampered.

One exception. . . If 35 caliber or larger cartridge with heavy bullets need to be crimped in place to prevent magazine held round's bullet movement in recoil, then a case length spread of no more than .005" may be best. That enables more uniform crimping of the case mouth in the bullet's cannelure.

GTOne · March 4, 2013, 02:53 PM

Quote:

If you are +/-0.003 of your trim to length you are fine.

No.

While usable in most situations, it isn't fine. I use a lyman universal and if I was getting +/- .003 I'd be complaining to someone somewhere. I'm getting measurments that are right on with my dial and digital..

I trim my .223 to 1.755 sometimes, it would be laughable(unacceptable) if I trimmed and the case measured 1.758. I didn't buy a lathe trimmer for that.

Something in the process would have to be wrong. Either operator error or machine error. Maybe something is loose in the assembly somewhere.

Magnum Wheel Man · March 4, 2013, 03:29 PM

I was having the same issues with the RCBS trimmer I got from my FIL... now I buy a file trim die for as many calibers as I can, & mine are all good to .001"

AllenJ · March 4, 2013, 03:46 PM

+/- 2-3 thousandths is an acceptable varance in my opinion for your purpose. As stated above, as long as you are at or below the max case length you are not going to have any problems.

10 Spot Terminator · March 4, 2013, 07:52 PM

I have the Forster trimmer but not the new 3 way cutter head. I find that the chamfer and deburring of the necks after trimming can alter the oal reading slightly as can rotatng the brass 360 degrees while in the calipers. I will attribute this to the headstamping on the brass. Only one end gets uniformed . Getting an .003 variance has not created any issues I can see to include crimping and performance over the chronograph. You should do fine. I would love to try that 3 way cutter. Brass prep is my biggest pain but I dont short cut cuz I'm too anal .

10 Spot

hooligan1 · March 4, 2013, 08:06 PM

When I trim, (any brass) I trim .010 below book length, and I have always done this, and I think its because I don't like to trim, so I knock enough off to be clear for a couple turns.

wncchester · March 4, 2013, 09:18 PM

".. getting a variance in my trim length of about 2-3 thousandths. Is this normal. Should I expect 1.750 exactly with every case I take off the trimmer."

Agonise over such tiny trivia if you wish but it won't matter how precise you get, after it's been fired and resized the case lengths will vary that much or more. And it won't affect your accuracy.

Reloading precision matters -- to a point. After which you're just fanning the wind; our cases and powder and primers and common bullets just aren't made with the precision of a Swiss watch! Proper load development and good shooting are far more important for accuracy than 5 thou of case length variation but it's easier to agonise over such trivials at home so that kind of tiny stuff matters to some folk.

eowiggy · March 5, 2013, 11:37 AM

Thanks for the response folks. Extra input helps alot. Most of the .223 bullets I am loading have a cannelure. Doesn't look like the small variances I was getting will affect my seating that bad.

BTW the 3-in-1 cutter is awesome! I prepped a few hundred rounds back in Dec. and this thing would have saved me a few hours. Now the cases come off clean and ready for loading. I just received another for .308 brass.

March 4, 2013, 01:56 AM	#1
eowiggy Junior Member Join Date: January 25, 2013 Posts: 8	Brass trimming tolarances When trimming my .223 brass, I noticed that I was getting a variance in my trim length of about 2-3 thousandths. Is this normal. Should I expect 1.750 exactly with every case I take off the trimmer. I am fairly new to reloading and I am trying to figure out if I am being a little too OCD when it comes precision for rounds that I am going to put through a recreational/pig killing AR. Are there any tips to more consistant trimming? I try to put the same pressure on each case, but hell I see folks using power drills while trimming brass.

March 4, 2013, 03:29 PM	#8
Magnum Wheel Man Senior Member Join Date: July 26, 2006 Location: Southern Minnesota Posts: 9,333	I was having the same issues with the RCBS trimmer I got from my FIL... now I buy a file trim die for as many calibers as I can, & mine are all good to .001" __________________ In life you either make dust or eat dust...

March 4, 2013, 08:06 PM	#11
hooligan1 Senior Member Join Date: July 18, 2010 Location: Independence Missouri Posts: 4,586	When I trim, (any brass) I trim .010 below book length, and I have always done this, and I think its because I don't like to trim, so I knock enough off to be clear for a couple turns. __________________ Keep your Axe sharp and your powder dry.

March 4, 2013, 02:18 AM	#2
GTOne Senior Member Join Date: December 28, 2011 Location: IL Posts: 210	What trimmer are you using?

March 4, 2013, 02:28 AM	#3
eowiggy Junior Member Join Date: January 25, 2013 Posts: 8	Forster Original with a brand new 3-in-1 cutter. I adjust it to 1.750, tighten the set screws and after about a dozen cases most are +/- .001, but sometimes 2-3 thousandths more

March 4, 2013, 04:54 AM	#4
GTOne Senior Member Join Date: December 28, 2011 Location: IL Posts: 210	I'm not familiar with how the forster holds the case. It should not vary that much, for sure. +/- .001 is normal, but not .003

March 4, 2013, 06:53 AM	#6
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	I doubt there's a problem with as much as .010" spread in any bottleneck rifle cartridge case length. As long as the length of the longest one is at least .007" shorter than chamber length (bolt face to chamber mouth), accuracy will not be hampered. One exception. . . If 35 caliber or larger cartridge with heavy bullets need to be crimped in place to prevent magazine held round's bullet movement in recoil, then a case length spread of no more than .005" may be best. That enables more uniform crimping of the case mouth in the bullet's cannelure.

March 4, 2013, 03:46 PM	#9
AllenJ Senior Member Join Date: December 11, 2009 Location: Northern California Posts: 1,766	+/- 2-3 thousandths is an acceptable varance in my opinion for your purpose. As stated above, as long as you are at or below the max case length you are not going to have any problems.

March 4, 2013, 07:52 PM	#10
10 Spot Terminator Senior Member Join Date: January 3, 2008 Location: Central Oregon Posts: 348	I have the Forster trimmer but not the new 3 way cutter head. I find that the chamfer and deburring of the necks after trimming can alter the oal reading slightly as can rotatng the brass 360 degrees while in the calipers. I will attribute this to the headstamping on the brass. Only one end gets uniformed . Getting an .003 variance has not created any issues I can see to include crimping and performance over the chronograph. You should do fine. I would love to try that 3 way cutter. Brass prep is my biggest pain but I dont short cut cuz I'm too anal . 10 Spot

March 4, 2013, 09:18 PM	#12
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	".. getting a variance in my trim length of about 2-3 thousandths. Is this normal. Should I expect 1.750 exactly with every case I take off the trimmer." Agonise over such tiny trivia if you wish but it won't matter how precise you get, after it's been fired and resized the case lengths will vary that much or more. And it won't affect your accuracy. Reloading precision matters -- to a point. After which you're just fanning the wind; our cases and powder and primers and common bullets just aren't made with the precision of a Swiss watch! Proper load development and good shooting are far more important for accuracy than 5 thou of case length variation but it's easier to agonise over such trivials at home so that kind of tiny stuff matters to some folk.

March 5, 2013, 11:37 AM	#13
eowiggy Junior Member Join Date: January 25, 2013 Posts: 8	Thanks for the response folks. Extra input helps alot. Most of the .223 bullets I am loading have a cannelure. Doesn't look like the small variances I was getting will affect my seating that bad. BTW the 3-in-1 cutter is awesome! I prepped a few hundred rounds back in Dec. and this thing would have saved me a few hours. Now the cases come off clean and ready for loading. I just received another for .308 brass.