Case trimming necessity?

[sic65stang]

I understand the importance of case trimming for accuracy, but I have a question about its necessity in mass reloading quantity. When the case is loaded into the chamber everything should line up close to perfect. The theory I have read is that the case can get jammed into where the bullet is supposed to be and can cause excess pressure as the bullet leaves the neck of the case. Could this even happen? It looks like the case could not even expand enough in the chamber when fired to get too long. Secondly would the case even chamber if the neck was too long? It seems it would hit the shoulder (noted by the arrow) and not even be fireable. Could the round even go off it it was not fully locked into the chamber? I am interested to hear what you all have to say about this.

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[chavezz556]

Re: Case trimming necessity?

If the brass has not been shot out of my gun I always trim the case ....

 

[sic65stang]

Re: Case trimming necessity?

I understand that, and do that, however I am trying to understand how the cases would ever need to be trimmed. It seems that the heat and pressure exerted on a case in a given chamber could only possibly extend to match that chamber, not longer.

 

[aloreman]

Re: Case trimming necessity?

Necks will stretch in the die as well. Take a peice of brass measure it run it thru a die a few times and measure it again

 

[LstManOut]

Re: Case trimming necessity?

Sic,
Sinclair has caliber diameter specific case length gages, I bought three (.22, 6mm and .30 cal) for the same reason you are describing.....well worth the small price they charge and are reusable.

Cull out a piece of junk unprimed brass that didn't make the cut (I used a piece that was way out of weight spec), full length size it and trim it way back. Insert the Sinclair case length gage into the trimmed case and slowly close the bolt. Extract the round and measure...this is <span style="text-decoration: underline">your</span> actual case length, not a saami swag.

To get the gage out, use your inertial bullet puller...hate to take a pair of pliers to it.

I still trim brass to uniform the length but I trim to my rifle's measurement.

LMO

 

[Conqueror]

Re: Case trimming necessity?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sic65stang</div><div class="ubbcode-body">I understand that, and do that, however I am trying to understand how the cases would ever need to be trimmed. It seems that the heat and pressure exerted on a case in a given chamber could only possibly extend to match that chamber, not longer. </div></div>
As noted above, the stretching is mostly from resizing, not from firing. When the neck is squeezed back down to factory dimensions, it grows in length. You ABSOLUTELY need to resize rifle brass, eventually.

 

[gunsnjeeps]

Re: Case trimming necessity?

The area you indicate with the green arrow can and will act as a crimp die if you jam a case neck into it. Even a semi auto bolt provides enough force to resize a case. If you have an AR and some brass you have fired in it measure the datum line on the shoulder then let the bolt slam home on it. It will be shorter now from the bolt closing on it. If you have a neck long enough to get to the end of the chamber it will crimp into the bullet.

You can either trim to SAAMI minimum or to a point that you are happy with between min and max or determine the max for your chamber and keep them shorter than that. Trimming will need to be done sometime.

Personally, I trim all my cases after sizing because the cases I've measured have been any where from min to max after firing.

 

[TexIndian]

Re: Case trimming necessity?

Sic, your concern about the neck being too long is well taken. The whole purpose of those 'max length' numbers printed in every reloading manual is safety, not accuracy. Even the slightest bit of inward pinching on the bullet could cause huge pressure spikes.

I suppose you could get a case that was so long that you would notice the extra pressure needed to force it into battery. But the length doesn't have to be so extreme in order for pressure problems to arise. As noted above, even a semi-auto has enough oomph to cause the bolt to close on a case that was slightly over-length. And a bolt gun has tremendous camming force that could accomplish the same thing without you even noticing.

Most guns in my experience have some extra room built in the chamber - longer than the SAAMI standards. Using the little gizmos from Sinclair will tell you how much. They only cost about $7, iirc.

 

[Jeffvn]

Re: Case trimming necessity?

If the necks gets too long, they can fire fine and then jam and make it very difficult to extract the case from the chamber after its fired. Voice of experience from my F-Class rig.

JeffVN

 

[Mike Sobr]

Re: Case trimming necessity?

If you oversize your brass in the die it grows even more by spurting the neck out the front of the die like squeezing one end of a balloon.
On a good fitting chamber and die it's common to go 20 rounds without ever trimming since the die only pushes the brass back less than .001 but on sloppy chambered factory barrells the brass is allowed to grow more and then needs to be squeezed back down like squeezing toothpaste and it is forced out the neck.

 

[Aimsmall55]

Re: Case trimming necessity?

I think the op needs to understand that if you do not trim, eventually your neck will stretch so long and will act like it's crimped around the bullet. If you are loading hot this is potentially very dangerous for the rifle and more importantly the shooter. While there are many different opinions on this topic, if you feel like your rifle shoots better with longer case necks, just get a caliper and trim to the max length allowed. I.e. A .308 is 2.005 to 2.015. If you don't, that's your choice but take a hammer with you bc your bolt will eventually have to be beaten open sooner or later. Just be careful. I have seen and heard about too many hot rods out there that ignored the "respect" that needs to be shown while reloading and they are either blind or maimed all bc they were not careful

 

[boltgunluvr]

Re: Case trimming necessity?

If anyone believes in self-preservation, by all means, trim when necessary.

 

[boltgunluvr]

Re: Case trimming necessity?

And for the record, I HATE trimming. It is very necessary!