Trimming brass for uniformity

[CanusLatransSnpr]

I asked this question on another thread but, haven't been able to get an answer so here it goes again.

I have new Norma .243 Win. brass that I want to trim to uniform length but, it is shorter than what I perceive to be min trim length. Max trim length on .243 Win. brass is 2.045" and from what I've read min trim length is .010" shorter or, 2.035" min trim length. My new Norma brass measures from 2.032-2.0335 in length and I was wondering if I could trim all the brass to 2.032" and get away with it? Has anyone else trimmed to shorter than min trim length and gotten away with it?

Thanks,
Mike

 

[chuckbuster243]

I have the same problem with 6.5 Grendel. That brass usally runs around 5-10 thou shorter than trim length. I trim to the shortest and roll on. I dont think its a problem. It will only help uniformity and consistency. But you may run into carbon rings in the chamber. I try to keep my brass all the same length and as long as I can without issues. But I cant always do that. Matt

 

[CanusLatransSnpr]

Thanks Matt! I wasn't sure if it was a good idea or not but, then again it's already short so what's the difference?

Mike

 

[Shynloco]

Mike,
You may have already done this, but have you already fireformed the brass? The reason I ask is that it "MAY" grow in length from full length sizing and your minimum length issue might be solved quickly, not that it's anything to worry about in the first place. It's the maximum length that creates problems in the chamber. Just a thought.

Alex

 

[brian427cobra]

Unless you chambered your rifle and own the reamer 2.045 is just a number with no merit, Sinclair sells a Chamber Length Gauge, it's a small soft steel plug that goes in a modified case, chamber it and measure, trim back .010 from that number, by using this tool you know exactly what your max length is, and at what point trimming is required, I doubt very seriously that trim length has any measurable effect on accuracy except competition BR.

 

[Steve Blair]

Unless you chambered your rifle and own the reamer 2.045 is just a number with no merit, Sinclair sells a Chamber Length Gauge, it's a small soft steel plug that goes in a modified case, chamber it and measure, trim back .010 from that number, by using this tool you know exactly what your max length is, and at what point trimming is required, I doubt very seriously that trim length has any measurable effect on accuracy except competition BR.

+1 Here is an assortment of chamber lengths, measured with the Sinclair tool, in my .308 rifles. Other calibers are similarly over "max" length. [br]
2.035
2.036
2.035
2.034
2.038
2.039
2.040

 

[Shynloco]

.....trim length has any measurable effect on accuracy except competition BR.

Good point! And that is exactly my frame of reference in my comment.

Alex

 

[gotcha]

These guys have hit the nail square on the head If you trim 1st then F/F, your trim length will vary all over the place due to a number of factors..... +1 on the Sinclair chamber length gauge. It eliminates guess work & they're inexpensive.

 

[jonbearman]

I think you should measure and if all undersized just load and fireform and when you are done ,then trimm to all the same length period.Some guys shoot 2-3 times to get the case to settle down and then trim and chamfer etc.Tyhe .243 loves to grow a bit initially anyways so you are safe.

 

[CanusLatransSnpr]

Thanks to everyone for chiming in on this one! I guess I should have mentioned that this brass is going to be fireformed into .243 A.I.? I was just trying to get a good starting point and keep things as "similar" as possible but, if I won't see any noticable accuracy advantage then you guys just saved me a bunch of work! As far as brass work after fireforming goes, I'm kinda torn between neck sizing until bolt lift gets sticky or full length every time? Both have their pros and cons the way I see it. I'm going with bushing dies either way!

Thanks,
Mike

 

[mac86951]

Like some others have mentioned, I would fire-form and continue sizing/shooting until trimming is needed.

For the bolt-gun, neck-size until you need to trim, then FL size before trimming. The first firing after FL sizing, the brass is working to fit the chamber, then after that by neck-sizing only you'll be closely matching the brass to chamber fit.

-Mac

 

[CanusLatransSnpr]

Like some others have mentioned, I would fire-form and continue sizing/shooting until trimming is needed.

For the bolt-gun, neck-size until you need to trim, then FL size before trimming. The first firing after FL sizing, the brass is working to fit the chamber, then after that by neck-sizing only you'll be closely matching the brass to chamber fit.

-Mac

That's how I feel about it too Mac! I'm thinking the Redding Type S neck sizing die set is the way to go and then upgrade to the micrometer seater top and stem!

Thanks,
Mike

 

[gotcha]

On F/F to AI configuration your cases are going to SHRINK in length. My .257AI cases shrunk on average .010" Caused by the smaller brass conforming to the larger AI chamber. So, don't think about trimming 'til you've F/F'd. Good news is that The AI's almost never need trimming after forming. One of the benefits of the AI case. If you're starting w/ low charges & working up to max. Your cases will need F/F at least twice, maybe three times before cases take the full size of the chamber.