case trimming

[jaybic]

Hey all,

I am still in the learning process with my first .243 AI and I have a question about case trimming. I see it a lot that case trimming is supposed to be virtually eliminated with this round but I find that I am still trimming. I started with 100 brand new Lapua cases, trimmed them all to the shortest one...about 2.016....(which is a good bit shorter that the standard .243 "trim to" length....2.035 if I remember correctly) and fire formed them. Upon measuring them afterward, they call came out varying different lengths so here is my question.

do I trim them back yet again to the shortest one for consistencies sake? do I just leave them be and shoot them until they "grow" into my chamber dimensions? If so, will then then stop being different at that point? Am I doing something wrong?

I just seems that for a round that is supposed to virtually eliminate case trimming, I am not see it or I am screwing it up some how....

Thanks ladies and gents and any ideas/advice is surely appreciated.

Have a great day!

Jamie

 

[Marble]

With my AI iwill put them in the trimmer only to really square up the neck. The case doesn't grow much.

 

[J E Custom]

Once they are fire formed "I" would re-trim them just to make them all the same/uniform.

It does not have to be done, but it helps with SDs most of the time.

As Marble said the AIs don't grow very much (Unless you over size or bump the shoulder each
time you re load them).

J E CUSTOM

 

[FearNoWind]

ALL BRASS WILL "GROW" - over time. However, if you're running case lengths as you describe, I doubt that you'll get enough life out of them to see them exceed Saami spec. length.
All of my load data lists AI case length at 2.710 ... (Saami spec.)
Run a casting of your chamber and see what the specs are before you decide trim lengths. Also, if you're running them short, be sure to watch the lead on the chamber and keep it clear of accumulated carbon - it'll fill up fast and you'll eventually find it difficult (if not impossible) to chamber a spec. round.

 

[Mikecr]

You might pick up one of these chamber gages to see where you're at: Sinclair Chamber Length Gage | Sinclair Intl
With this, you trim a neck down short, hand seat the gauge long, chamber the round, extract & measure to get chamber length.

I think you'll find that you should not have trimmed them all to the shortest case. That just makes no sense, and the necks likely pull back from chamber end further with shoulder improving..
Provided all new cases fit your chamber, you should fully fireform cases into stable AI dimension, and then square them up to the mean avg(which should be most by far). This would be 3-5 firings before any trimming.

With that cartridge/it's slower powders, the closer you are to chamber end, the faster the neck sealing(which is good). Close(and rational) while watched is 5-10thou clearance. A couple thou one way or another makes no difference here. But when you're ~50thou +/-10thou away, you're probably accepting higher ES/SD muzzle velocities.

 

[Marble]

I've also noticed with my AI reloading that the necks are the first thing to go. It will usually split during resizing. If I split one, then I anneal them. Unless my primer pockets are too big and I toss the entire shell.

 

[walkingjay]

I don't shoot a 243 ackley, I shoot a 284 ackley, I trim when I must (very seldom), or just to square brass, Main reason for trimming is so that you do not pinch the neck between bullet and chamber throat, when that occurs chamber pressures skyrocket.

That all said I use a Lee collet die and neck size only. from conversations with an individual at Lee Engineering, their collet dies do not touch the shoulder of the brass, and since the generic Ackley Improved calibers I know of have the same Head space as the parent cartridge, the collet dies work well. The conversation I had with Lee was to specifically determine if I could use the standard 284 collet die on my 284 Ackley improved.


the collet dies really reduce case stretch, because the squeeze the case neck against a precision madrell. no pushing or pulling on the overall case. and no sizing lube required.

 

[Marble]

I don't shoot a 243 ackley, I shoot a 284 ackley, I trim when I must (very seldom), or just to square brass, Main reason for trimming is so that you do not pinch the neck between bullet and chamber throat, when that occurs chamber pressures skyrocket.

That all said I use a Lee collet die and neck size only. from conversations with an individual at Lee Engineering, their collet dies do not touch the shoulder of the brass, and since the generic Ackley Improved calibers I know of have the same Head space as the parent cartridge, the collet dies work well. The conversation I had with Lee was to specifically determine if I could use the standard 284 collet die on my 284 Ackley improved.


the collet dies really reduce case stretch, because the squeeze the case neck against a precision madrell. no pushing or pulling on the overall case. and no sizing lube required.

I may switch to this since the AI ends up being a pain in the butt. I hate having to fire form etc.

 

[Kennibear]

Most AI cartridges shorten up on the first fire forming. The cases will be variable in length at that time even if you trimmed them uniformly before hand. I would recommend fire forming all AI cases before doing any case work.

+1 on the Lee collet die. Brilliant engineering from an all American mind!

KB