Straight Wall Case Trim Question

[Zen Archery]

I’m a novice with straight wall cases and need wisdom from those more experienced. This is for 350 Legend.
A). How much trim (if any) should I allow between case and throat?
My most accurate load has the case hard pressed into throat at 1.705. But that added a lot of pressure. Cycling was also problematic in gas gun. 1.700 was old SAAMI spec. is kissing throat. Accuracy was over 1.25”. 1.695 allows room for stretch but accuracy is between 1.10-1.25.” With cheap Nosler 9mm Bullets.

B). Do you anneal straight wall cases since they don’t have a shoulder?

 

[Unclenick]

Interesting. If you look at the current SAAMI drawing, the case is given as 1.710" with a tolerance of -0.010". Trim-to length is always set in the middle of the range, so 1.705" would be normal.

This case, like other rimless straight wall cases, is supposed to headspace on the case mouth, so the chamber minimum length equals the case maximum length. If you have a shorter chamber than that, it could be a problem even with commercial ammunition, in which case a chamber cast might be in order.

But before you go there, you need to keep in mind one other thing about cases that headspace on the case mouth, and that is that you absolutely must not crimp the bullet enough to reduce the case mouth diameter below the minimum given in the drawing. For the 350 Legend, the case mouth outside diameter must be 0.3720"-0.3780" on the finished cartridge right at the case mouth, with 0.3760" being average. If you got high pressure it would only be because the mouth was too narrow and was jamming into the freebore, or else the bullet stuck out so far it jammed past the freebore and into the throat, which will raise pressure about 20%.

So, if you have high pressure signs, something isn't fitting correctly.

 

[Zen Archery]

Thanks for reply. This is an old barrel when original SAAMI Specs was 1.700”. They changed specs in the past 2 years so I am having to rely on the old 1.700”. So my question is should it be pushed into throat, just touching, or have .005” free bore?

 

[tangolima]

Touching will leave zero head clearance. Best for brass life and perhaps accuracy. Not the best for reliability though. I will trim it shorter by 0.002" to 0.003", especially for hunting. 0.005" may be better for semi auto.

I did similar thing for .30 carbine. For crimping, make sure cylindrical, not roll, crimp.

-TL

Sent from my SM-N960U using Tapatalk

 

[Unclenick]

If the case mouth size is correct, it should not be possible to push the case into the freebore (the short smoothbore section between the chamber and throat). If you can push a case mouth into it, the finished cartridge case mouth diameter is too small. That is usually from over-crimping, though overly enthusiastic case mouth chamfering can do it, too. This is an unsafe situation for any cartridge that headspaces on the case's mouth. No case neck should ever get into the freebore or throat because it prevents the normal release of the bullet, so pressures get way too high.

 

[noylj]

At the freebore start, there is an edge that is the head space location. Best accuracy for me has always been a case that just touches this edge. If the case neck actuallu goes into throat/freebore, there won’t be room for bullet to exit without dangerous pressure or a throat so worn the barrel needs to be rechambered.
Generally, straight wall cases don’t stretch, since there is no shoulder to cause stretching, but some rifle rounds loaded to high pressures can stretch a straightwall case.
Go look at the headspace dimension for an accurate bottleneck rifle round and you’ll see that the dimension is often only 0.003” minimum length from contacting the edge where headspace is determined.

 

[Unclenick]

It's not shoulders that cause stretching. It's pressure sticking the sides of the case to the sides of the chamber while there is head clearance between the breech face and case head.

 

[Recycled bullet]

Also being run through a full length sizer: extruded by the expander ball being pulled through the neck grows the brass.

 

[tangolima]

No need to trim handgun brass. It won't stretch. It is practically true. Handgun brass are straight-wall, almost. The statement somehow becomes straight-wall don't stretch, which is questionable.

Straight-hall brass do stretch if there is enough pressure. I trim .30 carbine brass. Occasionally silver of brass comes off.

In order to minimize stretching, trim to have zero head clearance (touching). But tolerance may lead to difficulty in chambering. A bit of clearance (0.002" to 0.005") improves reliability. It is a compromise.

-TL

Sent from my SM-N960U using Tapatalk

 

[tangolima]

Also being run through a full length sizer: extruded by the expander ball being pulled through the neck grows the brass.

Don't know about .350 legend, but all the straight-wall full length sizing dies I have don't have expander balls.

-TL

Sent from my SM-N960U using Tapatalk

 

[Recycled bullet]

Yeah I don't know specifically about it either.

I think it would be fun to handload for given the commonality of components i.e. 9*19 or resized 38 special bullets for plinking.

I just assumed it is similar to other rifle rounds and gets full length resized on exterior body and interior neck dimensions to give good

neck tension and dimensional uniformity and so it will fit chambers and feed from magazines to operate the semi auto rifles with out telescoping.

I notice the length of my 308 brass increases more with the expander installed.

 

[RoyceP]

No need to trim handgun brass. It won't stretch. It is practically true. Handgun brass are straight-wall, almost. The statement somehow becomes straight-wall don't stretch, which is questionable.

Straight-hall brass do stretch if there is enough pressure. I trim .30 carbine brass. Occasionally silver of brass comes off.

In order to minimize stretching, trim to have zero head clearance (touching). But tolerance may lead to difficulty in chambering. A bit of clearance (0.002" to 0.005") improves reliability. It is a compromise.

-TL

Sent from my SM-N960U using Tapatalk

I got a bunch of mixed headstamp "range brass" at a gun show in Belton, TX. They were in 45 Colt caliber. I had to trim a lot of the Remington cases because they were too long. By the extractor marks I think they were shot in a lever action rifle several times previously, so revolver no, but straight walled and fit my revolver yes.

 

[Unclenick]

Generally speaking, 45 Colt pressures should be too low to get the brass to stick to a chamber wall and stretch back at the head. But in a carbine, the owner could have loaded them close to 454 Casull pressures. No way to know if you weren't there.

 

[RoyceP]

Generally speaking, 45 Colt pressures should be too low to get the brass to stick to a chamber wall and stretch back at the head. But in a carbine, the owner could have loaded them close to 454 Casull pressures. No way to know if you weren't there.

I guess it could have been a Thompson Contender too but as you say no way to know. It was like 2 cents a case so I am not complaining about having to trim 50 of them.

 

[Unclenick]

Understood. You are still getting your two cents worth!