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 Precise case trimming?
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roysclockgun
New Member

USA
22 Posts

Posted - May 21 2017 :  07:16:35  Show Profile Send roysclockgun a Private Message  Reply with Quote
I am not a bench rest shooter, so maybe I worry about this issue to much.

I trim my rifle brass on a Lyman trimmer driven by an electric drill. I have the drill set up to slide in and out on a piece of 2"x4" wood, set up to align the chuck with the arbor of he trimmer.

I trim the first case to exactly the length recommended in the loading manual. I, of course, then tighten down on the stop rings with the Allen wrench. However, to get all brass trimmed to that length, within .001" to .002", I have to *feel* when to stop holding the cutter against the case mouth. My deviation varies up to .0004" shorter than the book "trim to" length.

Is there a more accurate way to get precise case length when trimming? Or should I continue my current process and not worry about the slight deviation in the trimmed case length??

Best, Steven

Shastaboat
Advanced Member



USA
9125 Posts

Posted - May 21 2017 :  13:17:56  Show Profile Send Shastaboat a Private Message  Reply with Quote
Steven,
I experience similar results trimming .223 mixed brass on a Lyman Power trimmer. Theoretically all brass should come out the same length once you tighten the lock adjustment rings down. I think it has to do with how much pressure you put on the tool. Since I don't crimp .223/5.56 loads, I don't worry about the length differences. Mine end up between 1.745 and 1.750. With that dimension they all run through my LEE Pro1000 progressive press without a problem. My rounds are accurate enough for minute of ground squirrel out to 300 yards.

For other calibers I use a hand driven Lyman trimmer with similar results but a lot less quantity.

Edited by - Shastaboat on May 21 2017 13:19:31
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Scardycat
Junior Member

USA
48 Posts

Posted - May 22 2017 :  05:08:10  Show Profile Send Scardycat a Private Message  Reply with Quote
I use a lyman universal hand powered trimmer as well, i get variation also. I agree with shasta that i beleive it comes from the pressure you put on it. I havent had issue with the ones i crimp. I dont benchrest shoot either but the accuracy seems fine. cant say that what i have experienced with it ever caused problems for me. I use lighter pressure then check them, trim more if needed.

I have enough guns now...OOh look at that one.
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Hockeynick39
Advanced Member



USA
4690 Posts

Posted - May 22 2017 :  06:26:55  Show Profile  Send Hockeynick39 an AOL message Send Hockeynick39 a Private Message  Reply with Quote
I use this one to trim:
http://www.hornady.com/store/Trimmer-With-Cam-Lock-1-Each/

I put a sized case in it and lock the mandrel to that length. Every case comes out the same length. I do crimp, everything, but am not worried about .001 or .002 differences. If I was .010 off, then I might start to buck a bit.
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Ireload2
Senior Member

USA
286 Posts

Posted - May 28 2017 :  13:38:15  Show Profile Send Ireload2 a Private Message  Reply with Quote
You might look at the SAAMI drawings for your chambers and your cartridges and look at the tolerances.
Then measure the actual length of the chamber. I think you will find your chamber is usually .010 to .015 longer than any ammo.

For the most part case length does not have significant effect on accuracy as long as the case mouth is square.

Because of this I let my cases on ordinary ammo grow a bit over length. I then trim when they get out of square or get close to the length of the chamber. This reduces labor from excessive and unproductive trimming of cases that do not really benefit from trimming.

When I trim I use a Forster trimmer powered by a drill motor.
As long as I do an accurate job of chucking, the FL sized cases trim to very uniform lengths with about .001 total variation according to my dial calipers.

Edited by - Ireload2 on May 28 2017 13:45:43
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Zero333
Advanced Member



Canada
812 Posts

Posted - May 28 2017 :  20:25:01  Show Profile Send Zero333 a Private Message  Reply with Quote
Again, Ireload2 is spot on. Most of the chamber in my rifles are 0.020" longer than the max case length. Some are even 0.030" longer than max case length. So I let the brass grow between 0.010" and 0.015" short of the chamber neck length.

Here is a link on how to make a gauge to measure the chamber neck length. All you need is 1 piece of brass ,1 bullet and a dremel or other type of small cutter.
http://bulletin.accurateshooter.com/2016/11/measure-your-chamber-length-with-home-made-modified-case/


I hate trimming, chamfering & deburring, hence why I rather let them grow !!!

To give you an idea of why knowing the chambers neck length is very beneficial...
A batch of 300 pcs of 308win I've reloaded 27 times and only trimmed them twice.
Second time I trimmed them was after the 22nd sizing cycle. So it'll be shot 30x+ times before being trimmed a third time.



Treat that trigger like itís your first date, not like youíve been married to it for 20 years.

Edited by - Zero333 on May 28 2017 20:35:33
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Shastaboat
Advanced Member



USA
9125 Posts

Posted - May 29 2017 :  10:16:23  Show Profile Send Shastaboat a Private Message  Reply with Quote
I have to use a uniform trim length when using my progressive Lee Pro 1000 press or the second powder station will roll the case neck closed. Uniform trimming is also suggested when shooting cast rifle bullets to insure a uniform flare and if attempting to wring the utmost accuracy consistency is always the game. That excess length that is cut into the weapon's neck is a safety factor.
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Ireload2
Senior Member

USA
286 Posts

Posted - May 30 2017 :  16:34:27  Show Profile Send Ireload2 a Private Message  Reply with Quote
When shooting cast bullets that gap ahead of the case mouth is a cavity that permits the lead bullet to expand and leave a ring of lead in your chamber. BPCR shooters religiously try to avoid that gap.

The Lee Pro 1000 is primarily a pistol loading press and is not very relevant to a discussion for reloading rifle ammo.
Why? Because no one really trims pistol cases...

If you can't measures or refuse to measure things just because what you do is good enough don't begrudge those that chose a process involving more knowledge.

quote:
Originally posted by Shastaboat

I have to use a uniform trim length when using my progressive Lee Pro 1000 press or the second powder station will roll the case neck closed. Uniform trimming is also suggested when shooting cast rifle bullets to insure a uniform flare and if attempting to wring the utmost accuracy consistency is always the game. That excess length that is cut into the weapon's neck is a safety factor.


Edited by - Ireload2 on May 30 2017 16:41:15
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Shastaboat
Advanced Member



USA
9125 Posts

Posted - May 31 2017 :  15:35:50  Show Profile Send Shastaboat a Private Message  Reply with Quote
Just because someone is an AH doesn't mean everyone is an AH.
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KB0VSO
Average Member

USA
125 Posts

Posted - Jun 16 2017 :  20:31:11  Show Profile Send KB0VSO a Private Message  Reply with Quote
The 12th trimmer I purchased was a Lee Deluxe Quick Trim Case Trimmer.
my brass(.243) is all trimmed within a tenth of an inch and now my Winchester brass
weight is also within a tenth or two of a grain . Now any difference in the weight of the cartage is due to the primer and the bullet. Winchester primers and Sierra Bullets.
No way am I going to weight sort my primers and bullets.


Larry
Way Up North in Minnesota, USA
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Ireload2
Senior Member

USA
286 Posts

Posted - Jun 19 2017 :  19:54:32  Show Profile Send Ireload2 a Private Message  Reply with Quote
Did you ever realize that cases get shorter when fired?
Try measuring a few before being fired and after being fired. That precious gap that you seem be petrified of closing gets larger when a case is fired.
Rather than rely on a age old attitude it is possible to learn something new just by putting out a little bit of effort to measure the length of a chamber. You will find they are usually measurable longer than your cartridge cases.

BPCR shooters put out a lot of effort make sure their cases are long enough to fill that gap and even resort to case stretching processes to get longer brass.

Perhaps if you would spend some of your time on other forums you would find a larger world with a greater breadth of experience. Once properly enlightened with the knowledge of the rest of mankind you would not have to resort to two letter acronyms.

quote:
Originally posted by Shastaboat

Just because someone is an AH doesn't mean everyone is an AH.


Edited by - Ireload2 on Jun 19 2017 20:01:10
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Shastaboat
Advanced Member



USA
9125 Posts

Posted - Jun 19 2017 :  20:32:02  Show Profile Send Shastaboat a Private Message  Reply with Quote
The only time my fired brass shortens is if I'm firing a standard case in an Ackley Improved chamber. The Improved chambers seem to eliminate the lengthening of cases when fired. All other standard caliber chambers I have lengthen brass when fired. It is a safety issue to let brass flow and grow to the point that it has no place to expand in the case neck area.
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Zero333
Advanced Member



Canada
812 Posts

Posted - Jun 20 2017 :  08:16:55  Show Profile Send Zero333 a Private Message  Reply with Quote
Brass under pressure in a chamber is like a water balloon. By squeezing the balloon on opposite sides it will not grow but it will rather displace it's shape.

If a piece of brass has lot of wiggle room at the walls of the chamber, it will blow out towards the walls and towards the shoulder of the chamber, thus displacing the brass in the neck a little bit back. Thus the neck ends up being shorter after being fired.


Treat that trigger like itís your first date, not like youíve been married to it for 20 years.

Edited by - Zero333 on Jun 20 2017 08:17:30
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Ireload2
Senior Member

USA
286 Posts

Posted - Jul 08 2017 :  01:12:21  Show Profile Send Ireload2 a Private Message  Reply with Quote
Every time you fire a FL sized case in a rifle chamber that is larger than the loaded round the case will expand to fit the chamber and will get shorter in the process.
Every thing about the design of cartridge case fit is aimed at insuring function of the ammo in a large number of rifles. Those rifles chambers vary. My rifes do not vary since I measure them and know what the chamber measures. You have to play it safe because you do not know the length of your chambers and you do not put out the effort to find out.
I will repeat - If you fire a FL sized case in a chamber and then measure that case you will find it is shorter. It will get longer only when you FL size it. It is is clear that you never measure your brass as it comes out of your rifle.

I will repeat again that the entire community of BPCR shooters work to get rid of that gap at the end of the case so that their soft cast bullets do not expand into that gap and leave a lead ring in the chamber.

Brass does not flow as you describe it.
When fired the diameter of the case is stretched by expansion of the diameter. If you are setting back the shoulder because you miss set the die you can get stretching but that is considered poor technique.
The expanded case gets longer primarily when you resize it.
You effectively squeeze in the diameter and the brass cannot compress so it begins to slide up the neck of the die. That is when your cases get longer.


quote:
Originally posted by Shastaboat

The only time my fired brass shortens is if I'm firing a standard case in an Ackley Improved chamber. The Improved chambers seem to eliminate the lengthening of cases when fired. All other standard caliber chambers I have lengthen brass when fired. It is a safety issue to let brass flow and grow to the point that it has no place to expand in the case neck area.


Edited by - Ireload2 on Jul 08 2017 01:14:11
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Shastaboat
Advanced Member



USA
9125 Posts

Posted - Jul 08 2017 :  08:50:29  Show Profile Send Shastaboat a Private Message  Reply with Quote
I finally will agree with Ireload2 on one statement.

Quote: "I will repeat again that the entire community of BPCR shooters work to get rid of that gap at the end of the case so that their soft cast bullets do not expand into that gap and leave a lead ring in the chamber."

Here is the catch. "BPCR" means Black Powder Cast Rifle". We all know that BPCR shoots at a much lower pressure than Jacketed full power hunting rounds. Also he is doing all his shooting at paper targets I presume and is not considering the field conditions that hunters may encounter. Maybe if he fired a few .270 Win at 60K psi or other non Ackley Improved slightly tapered bottleneck cartridge at max velocity, even 30-30 he might experience case stretch.
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rg1
Average Member

151 Posts

Posted - Jul 08 2017 :  17:48:41  Show Profile Send rg1 a Private Message  Reply with Quote
Grease your stop and oil your cutter shaft. Makes the finish cut easier and more uniform.
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