How Critical is Overall Length?

[horseman2]

Just how critical is the overall length.
For a 300 WM, max is 2.620, and then trim to 2.610.
I get set up, and trim the first one to specs and set my Forster using the first one as the standard. The next one trims to 2.608 but they are all over the map. Some times the brass would curl under the guide so I ended up triming then champhering the inside of the neck until I got close to 2.610.
I eventually continued this process measuring after each step.
The diameter of the base appears somewhat critical. As the collett turns further, the shell pushes further into cutter. I tried to keep them from 2.611 to 2.609 but it is a lot of pi$$ing around.
I had never paid this much attention before so I now wonder just how critical everyone else is to overall length.
It was also interesting that the OAL would increase by about a thou after champhering.

 

[mooncoon]

I don't think small differences such as you describe would make all that much difference unless maybe if you were looking for ultimate accuracy. Why not sort out 5 or 10 of the shortest shells and the same of the longest shells and see if you get a difference at the range.

cheers mooncoon

 

[slushee]

Trimming brass isn't that difficult. The human hair is about 0.003 thick. If you trim your brass and chamfer it and get a +/- 0.003 tolerance, your okay

by the way, i've only ever heard of using OAL and COAL (over all length and cartridge over all length) when refering to the final cartridge AFTER the bullet was seated.

The measurment your refering to should be refered to as the TRIM TO Length .. not trying to be an a$$, just I read your post first and then typed up this long bullet seating thing, only to re read it and realize you were refering to trimming the brass

I personally trim the brass using a lee lock stud, cutter and cartridge length guide, then chamfer the inside and then the outside. I always measure my brass at this point and if its within 0.003 or 0.004 ofmy trim to length, then I move onto the next one. Sometimes you are right that chamfering the outside will curl the brass back into the neck, so I will just lightly touch the chamfer tool back inside when this happens.

To sum it all up, your doing everything right, and dont worry about a + or - of 0.003 or 0.004 unless your in benchrest competitions.

 

[Onagoth]

x2,

I usually allow variances in my TRIM to length, but always seat my bullets to the same COAL.

I haven't found that the small differences in case length really affect me, but then again, I am not gunnin for 0.1" groups.

 

[roberti11]

Just how critical is the overall length.
For a 300 WM, max is 2.620, and then trim to 2.610.
I get set up, and trim the first one to specs and set my Forster using the first one as the standard. The next one trims to 2.608 but they are all over the map. Some times the brass would curl under the guide so I ended up triming then champhering the inside of the neck until I got close to 2.610.
I eventually continued this process measuring after each step.
The diameter of the base appears somewhat critical. As the collett turns further, the shell pushes further into cutter. I tried to keep them from 2.611 to 2.609 but it is a lot of pi$$ing around.
I had never paid this much attention before so I now wonder just how critical everyone else is to overall length.
It was also interesting that the OAL would increase by about a thou after champhering.

I am a bit confused by your comment that the 'diameter of hte base is critical' The base of all the cartridges in a given calibre should be 'exactly' the same. I have the feeling that you have the wrong, collet or that you are not seating the base squarely in the collet. Once the collet is tightened the brass will never move.
It is best to place the case mouth onto the pilot first, and then align the base of the case into the collet to ensure the case is straight before tightening the collet.
If you have the incorrect sized collet then often it will hold a bit, but then move when you try to trim.

 

[horseman2]

The bases were measuring around .525 for Federal, and .528 for Winchester so the collett moves forward further for the smaller diameter.
The collett is the #1 for Forster. I have used it for .223, 30-06, 338 and 300 WM. There are four steps in this collett and and do not know which other case head size it would accommodate. I was looking for the Trim to Length term but "Vera" was telling me Breakfast was ready, and get ready for work - our priorities are different at times.

 

[cosmic]

Well - I dont think you have to worry. FWIW - The Lee system is very repeatable, if not labor intensive. If your using your seating die to crimp, then variations in case length will affect the amount of crimp action.

 

[martinbns]

I used to mess around with a lyman universal trimmer and tear my hair out over small differences and then discovered lee trimmers and my cordless drill. Very consistent, quick, almost no setup and easy. Only trouble is no wildcats.

 

[slushee]

Only trouble is no wildcats.

A little off topic, but I was thinking, you could mix and match the shell holder that holds your wildcat, then find a guage that had the right diameter to fit into the mouth, and just shorten the little pin that bottoms out on the lock stud thinger. This would solve at least some of the wildcats, cept maybe the ones that need a longer pin vs a shorter pin.

I bet if you went to a CNC shop with the dimensions it would only end up costing you 10-15$

Just thinking out loud..

 

[horseman2]

Thank you for your comments. This morning I pulled the collet, and I could not believe the collect of brass, $hit and corruption collected over 40 years.
Now it adjusts consistently and the product is bang on. Much like pulling the decapping rod on your dies . . . lubing the inside of the neck frees up pieces of brass and black crap.

 

[Gun5tuff]

I used to mess around with a lyman universal trimmer and tear my hair out over small differences and then discovered lee trimmers and my cordless drill. Very consistent, quick, almost no setup and easy. Only trouble is no wildcats.

X2. I have two different trimmers that would be very tedious to set up. The variation in brass length would really annoy me. The Lee system as described above is fast to set up, and gives repeatable lengths. The other advantage while rotating your brass is the ability to polish it with fine steel wool and do the chamfering. As an aside, the 300H&H trimmer is the one to use for Rem. 300 Ultramag.

 

[martinbns]

A little off topic, but I was thinking, you could mix and match the shell holder that holds your wildcat, then find a guage that had the right diameter to fit into the mouth, and just shorten the little pin that bottoms out on the lock stud thinger. This would solve at least some of the wildcats, cept maybe the ones that need a longer pin vs a shorter pin.

I bet if you went to a CNC shop with the dimensions it would only end up costing you 10-15$

Just thinking out loud..

Actually that's how I trim the brass for my 7mm SAUM, Lee never made a trimmer I so I bought a 7-08 trimmer and just use a magnum shellholder.

It's a great system.