Forster case trimmer damaging my necks

[synfinatic]

Bought a Forster case trimmer many years ago and never used it. Fast forward to today and I'm trimming Lapua 6.5CM brass. Cases are getting damaged- there seems to be two rings being placed into the neck. One is clearly because the pilot was rubbing right where it goes from chamfered to full diameter which is easy to diagnose. The other ring is happening where the neck meets the shoulder... which is behind the pilot. I've no idea how that is happening. The issue is that this second ring at the shoulder is raised so the 0.005" undersized pilot will not pass.

Pretty much all the cases I trimmed are this way Anyways, I'm sizing with a Redding Type-S die and the neck bushing does not resize the entire neck. Not sure what could be causing this? I have some other untrimmed brass which I just sized and didn't trim and none of them have either ring. Was planning on polishing the pilot to prevent the first ring from happening, but no idea what I can do to stop the ring at the base of the neck from happening.

Here is a cut case with the pilot. You can clearly see the first ring lining up with the pilot chamfer and the other ring at the base of the neck:

Higher resolution of the necks showing both rings. Note the gouge in the bottom right is most likely from cutting the case with the dremel:

 

[spife7980]

First ring is the trimmer pilot, it’s why I refuse to use a forster or rcbs trimmer head.
Second ring could be a donut where thicker shoulder material has migrated up into the neck. Which is sort of tough to tell because it could be burrs from the dremel but it looks like thickness to me.

 

[Aftermath]

@spife7980 what case trimmer do you recommend?

 

[synfinatic]

First ring is the trimmer pilot, it’s why I refuse to use a forster or rcbs trimmer head.
Second ring could be a donut where thicker shoulder material has migrated up into the neck. Which is sort of tough to tell because it could be burrs from the dremel but it looks like thickness to me.

Definitely agree in the first ring.

2nd ring isn't from the dremel since nearly all my trimmed and non-dremeled cases have the same issue.

A donut seems possible (not sure if it usually forms there?) but I'm confused why none of my untrimmed Lapua cases with just as many firings have it. Not sure I can believe that is due to lot to lot variation.

 

[spife7980]

@spife7980 what case trimmer do you recommend?

I use a giraud myself, but anything powered with a three way cutter blade is groovy in my book.

Definitely agree in the first ring.

2nd ring isn't from the dremel since nearly all my trimmed and non-dremeled cases have the same issue.

A donut seems possible (not sure if it usually forms there?) but I'm confused why none of my untrimmed Lapua cases with just as many firings have it. Not sure I can believe that is due to lot to lot variation.

Are you using an expander ball or mandrel? Anything other than the trimmer pilot go in the necks before?

 

[synfinatic]

Are you using an expander ball or mandrel? Anything other than the trimmer pilot go in the necks before?

I've used the included Type-S expander ball in the past. Recently I've just stopped using it as didn't seem to help my concentricity and I didn't like how it would catch the neck on upstroke.

More recently, I've started using the LE Wilson mandrel for any cases with bent necks which is rare. So maybe it's the expander ball? Not sure what to make of the other brass which was also processed with the same die/expander ball and doesn't have the ring, but it was always processed separately (it's actually some older brass that I've mostly retired) from this group that has the ring.

Other than that, just bullets and powder.

 

[spife7980]

I've used the included Type-S expander ball in the past. Recently I've just stopped using it as didn't seem to help my concentricity and I didn't like how it would catch the neck on upstroke.

More recently, I've started using the LE Wilson mandrel for any cases with bent necks which is rare. So maybe it's the expander ball? Not sure what to make of the other brass which was also processed with the same die/expander ball and doesn't have the ring, but it was always processed separately (it's actually some older brass that I've mostly retired) from this group that has the ring.

Other than that, just bullets and powder.

Well something is rubbing on it in those thicker looking parts.

Personally I wouldnt worry about that, could very well be the bullets knocking the soot off the thicker part.

 

[synfinatic]

Personally I wouldnt worry about that, could very well be the bullets knocking the soot off the thicker part.

Yeah, I guess I'll find out next time to the range if this actually causes any problems.

Honestly, I'd like to understand what is causing it so I can stop causing it to happen or prevent it from getting worse. Not sure I buy the bullets knocking soot off.

I use a giraud myself, but anything powered with a three way cutter blade is groovy in my book.

So I was considering the Giraud and Henderson before this happened since the Forster is so slooooooowwwww. I was leaning towards the Henderson, but while researching this issue, I came across a thread from 2021 where someone reported the Henderson having a very similar issue. You probably remember the thread. Not sure if they've changed their pilots since to prevent at least this first ring from happening?

 

[spife7980]

Yeah, I guess I'll find out next time to the range if this actually causes any problems.

Honestly, I'd like to understand what is causing it so I can stop causing it to happen or prevent it from getting worse. Not sure I buy the bullets knocking soot off.


So I was considering the Giraud and Henderson before this happened since the Forster is so slooooooowwwww. I was leaning towards the Henderson, but while researching this issue, I came across a thread from 2021 where someone reported the Henderson having a very similar issue. You probably remember the thread. Not sure if they've changed their pilots since to prevent at least this first ring from happening?

Henderson used to use forster pilots/cutters.
And somethings touching that spot, what I couldn’t tell you but there are only limited options to choose from here: expander, mandrel or bullet.

 

[Rocketmandb]

Henderson uses forster pilots/cutters.

He now makes his own. I just got a Henderson and the cutters are definitely not the Forster ones.

 

[FLIGHT762]

I had a similar issue with my Forster Trimmer pilots being a bit tight. I used some 600 grit paper and took off about .001" and polished it up with some 800 grit. They worked much better after that.

I've moved on the Giraud Trimmer for 5 Rifle cartridges, but I still have two of the Forster Trimmers. I have one set up for neck turning, although I found turning didn't any noticeable better accuracy. I bought one in the 1970's and the other was given to me. I never got rid of them. They still can be used for odd jobs. I do have the Military crimp remover for one, it works pretty well.

 

[synfinatic]

Well I had 40 rounds loaded from the same lot and same number of firings, but not trimmed. So I pulled them down and inspected the necks and found no indication of either ring. Then I resized the cases (since the bullet will expand the neck) and trimmed them with the pilot that I cleaned up.

End result is I now have 40 trimmed cases without either ring that look great.

So yeah, no surprise that the first ring is gone. No idea why the ring at the base of the neck which was preventing the pilot from passing isn't there or what was causing it, other than it seems related to the pilot. Lesson learned I guess. Thanks for the help @spife7980 and @FLIGHT762