Need case length opinions

[6savage1]

I'm about to start reloading for my 300wm that I'm building. I bought 100rds of new Hornady brass and measured them out. They were all from 2.6095-2.6150", but the majority were from 2.6125-2.6135". I know the trim to length in the book is 2.610". I guess the question I have is, is it worth trimming them to as close as 2.610" as i can? This is my first precision rifle I'm building and I plan on taking it as far over 1000yds as I can so I'm trying to be as precise as I can without getting too OCD lol.

 

[DarnYankeeUSMC]

They are new out of the bag? Nothing done to them? Is this your first excursion into reloading? Do you have any reloading books? Have you ever read what the procedure is for new brass?

I run new brass thru the press with my full length die. Then thru my trimmer, I use a three way trimmer head that trims, chamfers and de-burrs. They should perform pretty close to all of my other brass.

 

[Victor N TN]

New brass out of the bag will measure different from brass fired in your rifle.

Buy yourself a Lyman's Handloading Manual. I think it's up to 49th edition. Best money you can spend. They aren't trying to sell you bullets or powder. The most used book in my collection.

Good luck.
Victor

 

[kansas]

I'm kind of anal about trimming brass. For new brass I neck size it and make sure it chambers before I spend a lot of time prepping it then usually trim it a couple of thousandths long. The reason I trim it a little longer than the trim to length his because I trim it after each firing. Some pieces of brass stretch more than others so that way I can keep all the case lengths more uniform. I know that's overkill but seems to work for me. If new brass will chamber then there isn't any need to full length size them. Neck size them, trim them and load them. For neck sizing I like the Lee collet die. Cheap and keeps run out low.

 

[BuzzBoss915]

I see this as a very minor issue.

I would full length resize, trim to whatever length that appeals to you and kinda forget about it for the next several reloadings. The design is one that I have never had very much of a problem, at least so far as gaining in overall length.

The reason, (in my opinion) is the short neck, in the first place, and also the aggressive shoulder angle. There really isn't too much brass to stretch. I load 220Swift and 270Winchester which have less shoulder angle and consequently, trimming to length is needed frequently; depending on how hot the load is. But, 300WM is not a case that requires very much trimming, in my experience. I suppose there could be an issue with neck tension for super precision accuracy, but otherwise, neck length in this particular cartridge is not critical. BB

 

[witchhunter]

Measure your chamber and cut em .002 shorter. each time they are fired. This will stop the carbon ring from forming too bad in the front of your chamber.

 

[ZiaHunter]

Most manuals recommend trim to lengths .010 less than SAMMI specs. In your case I wouldn't trim to length until after being fire formed. The 300 WM neck length is less than the caliber and you certainly don't want to be trimming the necks anymore than absolutely necessary and most chambers have generous neck clearance. The 300 WM is a little more tricky to load due to the belt and best to size the case so it headspaces off the shoulder and not the belt. This requires setting up your dies with a comparator. There were some very good threads posted on this site on setting up dies for belted magnums. The best reference I found for loading belted magnums is the Precision Shooting Loading Guide edited by David Brennan. It has a chapter on belted magnums which is excellent. Unfortunately it is out of print.

 

[ArmyJerry]

Get a routine that works for your rifle and stick with it, I suggest doing everything required for a piece of fired brass, except cleaning. Run it through a sizer them trim and measure, if you have a trimmer that indexes off the shoulder then the brass should all me within a couple thou. Get into a routine, once you start getting consistent good groups you will go full OCD, its inevitable so come to grips with that now, its a sickness.

 

[6savage1]

Hey thanks for the feedback and I'm interested to here more opinions as well. And just for the record, this is not my first time reloading, I've been reloading for a couple years now, just the first rifle I'm trying to get the utmost precision out of so that I can eliminate the rifle, for the most part, as the problem if things aren't going as well as i think they should be (its something I'm doing wrong instead lol). And yes this is all brand new brass right out of the box from Hornady. It's also the first time I've ever bought brand new brass.

 

[Lakeray]

Then full length size it AND then measure. What I would do is make any that are over max, load and fire. Then when you resize them, trim all to almost min length.

 

[Powermac]

Okay, your shooting a caliber with a notoriously short neck, using heavy bullets and slow burning powder.
Forget about reloading manuals and recommended trim lengths, 99,9% chance it will not match your rifle any way.
Remember that recommended trim length might or might not have been optimal for the rifle used for those load work ups, and not yours.
If your going to use the energy and time to discuss the subject, then i assume you want the proper way of doing it.


Go to Sinclair and order a chamber length gauge in 30. costs you 5 dollars
Only need to use the gauge once per rifle barrel, and it is no doubt worth the investment.
Trim a fireformed case short at lleast .125" with light neck tension. Then drop the gage in the case, and close the bolt over the case, and take the measurement of YOUR rifles correct trim length. Do this several times to check the accuracy, write down the correct length in your reloading log and use it until the barrel is toast.

I personally keep my brass .003" shorter then the chamber neck, and trim every firing when the brass has come to length. But to go this close is potentially dangerous if you do not know what your doing.
You will need to monitor case growth a bit and be aware that unfired, once fired and annealed cases tends to stretch a bit more then work hardened brass.

Doing this little extra step in your reloading is not very time consuming,it ensures consistency and has a few benefits that makes it worth it.

Most importantly you greatly eliminate the forming of a carbon ring, and reduce throat wear.
To put it simply when the round is fired, the closer the sholuder of the case is to the chamber neck, the faster the brass will seal the chamber and eliminate backflow into unsealed chamber clearances.
The slower the powder burns the longer it takes the brass to seal the chamber in general at a proportional rate.
While the length of the case neck largely impacts the amount of backflow and how fast the chamber is sealed at a disproportional rate.
If you look at the picture it is quite obvious that if the brass would be longer, the backflow would have much less room in your chamber, and a steeper angle to overcome before it moves back into any unsealed clearances.

Now this can also have a small benefit to your es/sd simply because having all your brass trimmed to the same exact length will make neck tension more uniform, and in theory the pressure curve should be more consistent.

And by having a longer neck you get a bit more distance to use for compensating for throat erosion.

 

[ZiaHunter]

All good advice and I might add additional words of wisdom from someone who shoots 300 WM on a regular basis through a precision rifle. Take a look at the Larry Willis Collet Resizing Die which sizes the case in the area down to the belt and I use it after every resizing in addition to annealing after every firing.

 

[6savage1]

That makes a lot of sense. Thanks I'll do that