Trimming Brass

[Wayne123]

I'm a new reloader and am wondering when is it time to trim brass?  If the cases get to long, will they not chamber?  Thanks for the help.

[nodlenor]

Get a Lee trimmer to fit the cartrige you are loading and you can't go wrong. They don't cost much and are very easy to use, that is if you are only loading a box or so at a time. If you load more than that you might want to get a power trimmer. If you load close to max then you will have to trim more often than if you use a milder load. Check everytime you reload. That works better than finding out the hard way that they were too long. A case that is too long can cause higher pressures and therefor problems that you don't want.

[davem270win]

You should routinely check your cases for length after every resizing. A random sample is good. Use a calipers, which you should have if you reload (you also need to check max OAL after seating the bullet). As long as your cases are below max length, you should be fine. Once your cases reach max length, trim.
How fast they get to max length depends on a variety of factors, so there is no predicting when until you have some experience.

[aldar]

another thing to remember is that a straight walled case stretches a lot less than a shouldered case. I have both and can see the difference. A .243 stretches alot more than 45-70 or 30-30. I trim all my shouldered cases each time but just measure the others to see where their at before trimming.

[charles p]

If you are shooting a semi-auto, case length is critical - at least is was in mine.  Not too good in a bolt either.  A bolt is strong enough to deform the case.

[Wayne123]

I am working on the second loading of new Winchester brass in .30-06 shooting from a Ruger No.1.  When new, I resized and trimmed all cases.  On the second loading, I measured the length of the brass and trimmed all cases.  If the cases were allowed to go over the max by .005-.010", what would happen?

[Grumulkin]

If they're too long, it will cause difficulty chambering rounds and likely high pressure.  Just how far over maximum they can be depends on the dimensions of the chamber in your gun.

[Cheesehead]

I believe when all brass is trimmed to the same required length it creates consistency which increases accuracy.

Cheese

[Graybeard]

If the cases were allowed to go over the max by .005-.010", what would happen?

One possible scenario is you lose some fingers or vision in one or both eyes.

Think of it this way. The chamber is cut such that there is room for the case to fit in at max SAAMI over all length. At that length it fits just perfectly to the end of a cut out space made for it. When it grows longer it no longer stops at the end of that area cutout for it. Then it kinda over laps into a smaller area. That smaller area is not made to allow the case to expand as it needs to in order to release the bullet smoothly.

The result is that there is a major binding and pressure builds far higher than intended prior to bullet release. Those pressures might do little other than push the bullet a bit faster and case case life to suffer. But they might also build to a level that causes things to come from together to apart and then bad things happen such as you have to buy a new rifle to replace the one you just trashed and some times the parts of it flying off cause lose of vision in one or both eyes and things like fingers have to be taken off as there aren't enough of them left to repair and save.

Yeah that's a rare and severe end result but yes on occasion it does happen. Normally it's less severe and you just get early case failure, reduced accuracy and perhaps a few blown primers. But NOTHING good ever comes of it and lots of bad can.

[Wayne123]

Thanks Greybeard, that is what I was looking for.  Neither the Lyman or Speer manuals state the reasons for trimming, just that it is required as the cases stretch. 

[dw06]

All good answers, but Mr Graybeard nailed it!!

[Dave in WV]

Good answers here. As posted some cartridges "grow" more or quicker than others and it also depends on each firearm's chamber dimensions. Other factors are max loads vs. moderate loads and the brand of the cases.

[Darrell Davis]

Great Graybeard,

I was wondering if someone was going to get to the real meat and potatoes of the issue, Extreme and dangerious pressures. Thanks.

For a new reloader, and maybe a few of you oldies, there is another area where tight necks can cause problems and or distroy guns and body parts.

This is in forming cases from larger cases. Example 30/06 or 308 to .243.

When this is done, the end result can be extreme pressures because of over size brass and the lack of expansion room for safe release of the bullet from the case neck.

In this case, it is not due to an overly long case jamming into the chamber throat, providing of course you have done your job and checked and/or trimmed as needed, but rather a problem of neck thickness.

I made 243s from 308s for quite a long time with never a problem. However, I was with a friend one time when the bolt of his Sako fell onto the shooting mat in pieces when he cycled the bolt.

The extractor and some other parts, probably a spring or? - happened years ago - fell out, along with the primer.

After that shot, the primer could be placed back in the primer pocket of that case and rattled around there had been so much expansion.

Back in those days, we really didn't know the reason for the extreme pressures, we just knew something was wrong.

It was years later, when another friend brought me an artical about a nice 243 - model 70 being blown up/distroyed by just such a thing - 308 cases formed to 243.

The problem?  The case neck thickness.

When the case neck is reduced in dia. that brass must go some where, and it goes into an overly thick neck which may or may not cause a problem.

This will all depend on the thickness of the brass before forming and the tolarence of the neck portion of your 243 chamber.

The solution, ream or turn the neck of the formed 243 case before the first firing.

I choose to turn my necks, feeling that the neck will remain more in line with the case rather then be reamed off center to the case body.

You would be amaised at just how many NEW, factory cases have off center necks, but they sure show up when a new factory case neck is turned.  It is not unusual to have a third of the outside case neck never be touched by the cutter.

Anyway, don't forget to reduce that neck thickness on those formed cases, as it is every bit as important as keeping neck length correct.

Keep em coming!

CDOC

[Cheesehead]

Darrel,

That is useful information. I have considered changing 243 and 7-08 into 308 since I have a large amount of this brass. Could there be issues from upsizing?

Cheese

[HL]

when sizing down brass, I always turn the necks down and check those as I do the length of cases after firing.

I do this with my 7-30 brasss formed from 375 winchester and 300 savage from 308.

[Gatofeo]

An excellent answer (and warning) from Graybeard, and a lesson that is frequently ignored.
It amazes me how many reloaders today feel that case trimming is merely incidental and not crucial.
It's not, as Graybeard has explained.
A few years ago, a co-worker approached me because his .308 reloads were difficult to chamber. Once-fired, they were difficult to extract with his bolt action.
He checked the recommended loads and everything was well within specs. His rifle had only recently begun to demonstrate this hard-chambering/hard-extraction problem.
I asked him how often he checked and trimmed his cases.
His answer was classic: "You have to do that every time you reload?"
Well, he went back and pulled the bullets on his reloads. Sure enough, the cases were well over maximum length.
He trimmed the cases, replaced the powder, seated the bullets and -- voila! no problems!
He learned his lesson and now checks case length after every firing. Luckily, neither gun nor shooter were damaged by his dismissive attitude toward case trimming.
I check every case -- including handgun cases -- for case length before reloading. Sure it's a pain in the patoot, but it's far less of a pain than tapping a white cane to determine what obstacles may lie in your path.

[Cheesehead]

I am all about trimming brass lately. I just bought an RCBS power trimmer. It is so very nice.

Cheese

[epanzella]

Just fired some warm 30-06 loads in Lapua brass. They grew .006 with one firing and needed to be trimmed.

[Tom W.]

The case trimmer is the most hated thing on my bench, but I use it every time I re-size brass.Kinda anal, but it keeps the fingers attached....

If I reform brass, I don't have any problems with neck thickness when going up. Going down a caliber ( or two)  is a bit different....