Trim Length Question

T

Tony Shankle

Guest
I would really appreciate hearing your opinions on the ideal trim length/clearance for accuracy. Let's say we order a 243 AI reamer and the print says the case length is 2.0450"... what in your opinion is the ideal length and/or clearance needed? In short, the ideal trim length and why?
 
I try to set me necks .004-.006 shorter than the chamber because I think it helps me to control the carbon ring.

To do this one MUST own and understand how to use good resizing dies. If your cases "grow" or increase in length as you resize then you'd better trim to 20 or 30 thou under your chamber length lest you blow own face off.

Or throw your brass in the trash after 3-4 firings as the loading manuals advocate.

Safety First...... ALWAYS!!

Do you know the length of your chamber neck?

If so, how?

You mention an AI'd round..... you probably know that they pull back precipitously upon firing??? Perty hard to close the gap with an AI.

al
 
rescue me Al

You are correct, I usually have more of a problem from "pull back" on this round than trimming. When I have this pull back I just trim them so that all match and keep going...is that the correct thing to do?

I always have a resize reamer made for my dies and I don't get much "growth" from that part of the process.

I will walk into the loaded question of "how long is my chamber neck" by answering that the neck length on the reamer is .2531". I have no idea how to measure the chamber neck inside the barrel but shouldn't it be the same as the reamer?

So is .004 to .006 the answer???

I will pm you a copy of my reamer print if I can figure out how.

Thanks!
 
you got mail

Al,

I send you an email with my print.

Tony
 
Tony ...

Tony Shankle said:
I would really appreciate hearing your opinions on the ideal trim length/clearance for accuracy. Let's say we order a 243 AI reamer and the print says the case length is 2.0450"... what in your opinion is the ideal length and/or clearance needed? In short, the ideal trim length and why?
Click to expand...

Here's a similar question I once asked and the answers I receive from two smart gentlemen whose names you might recognize.

Chamber Length Safety Zone

Q: How many thousandths shy of actual chamber length does one establish as a safety zone, before assigning a trim "from" length, once measurements have established a rifle's true chamber length ??? Art

Mike Bryant

A: I use .010" for each increment. For instance, if the chamber length is 1.570" from the base to the end of the neck on the chamber, then the maximum case length would be 1.560" with a trim length of 1.550". Don't let the cases get over 1.560" and you'll be in good shape.

Jackie Schmidt

A: I use a .010" window. 6mmPPC chambers have been shortened to 1.510". Since shooters fire cases to expand them, the cases come out close to 1.500". I trim them back to 1.490."
 
chamber lengths

I've always used the Sinclair chamber length gauges, (cost $6.95 each & reusable), recording the actual lengths of each rifles chamber. Case overall length then is kept .005" to .010" shorter. When having a chambering reamer made (Pacific), chamber length is always one of the dimensions specified. As alinwa said, a ring of carbon will buildup if there is a "large" gap in front of the case mouth. Not too different than firing 22 RF shorts in a long rifle chamber.
 
A lot of good info

Thank you all for the information.

I must admit I didn't think I would see that much variation in the answers. I see .004 to .020 spread in what you think is best.

My print says 2.045" and since I trim (at least a trim check) with every firing why wouldn't I just trim to 2.040"? What would be the downside?
 
Nothing, you just need to be short of the O/A length on the print. If you are right on or short, you are OK. If you stay close to your print dimension. Make sure you keep a close eye on the O/A length.
Butch
 
Yup Tony, your oal is 2.045 from the print.........

And your actual neck length is .2531

So you could work from oal as you stated (altho how you'll get an AI that long is my question!) and by the same token take your caliper and eyeball the neck itself on some fired cases. Just put the point of the inside tool into the junction of neck/shoulder and run 'er out and eyeball the length.... you can easy see anything over .002 of variation.

I'll bet that your Ackley has "tens of thousandths" of room :) in other words I betcha' it's .020 or more SHORT already, in which case if you're as anal as I'm you'll still trim them all to the same length anyways.

For general information, to all who're reading this, remember to pop out your primers before measuring for case oal because most primers crater some which screws up your measure.....

hth


al
 
Thanks Al,

But, take a look at that print again,it is not an AI. It is one of mine and from past experience it doesn't leave you short for long! No where near as bad as an AI plus lots of other good points but I wont get into that here! :D

Tony
 
Tony Shankle said:
Thanks Al,

But, take a look at that print again,it is not an AI. It is one of mine and from past experience it doesn't leave you short for long! No where near as bad as an AI plus lots of other good points but I wont get into that here! :D

Tony
Click to expand...


Ahhh,

yeahh, I didn't even look except to see the pertinent measurements.

al
 
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