Henderson Trimmer Upgrade (Inside Neck Reamer)

nick50471

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Jan 30, 2025
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15
Location
rudd, IA
I've been using a trimmer from Henderson Precision for awhile. The repeatability and speed is amazing.
After talking to Todd Henderson I developed a reamer to clean up and true the case neck.
I've made a couple different types. First I modified a LE Wilson neck reamer to fit into a blank Henderson cutter head. That reamer was for .243 cases. The Wilson reamer is .2455 - .246. I used this after firing. While it did a great job cleaning up the neck and removing doughnut the real winner was improved ES and SD from better seating pressure consistency.
That pushed me to try reaming after sizing. I bought a .242 reamer and ground it to fit into another blank cutter head.
This is where things got interesting… ES, SD improved significantly. Even on rifles with really good numbers.
Now I made a reamer to replace the pilot in the cutter head. Now I can inside neck ream, trim, chamfer and deburr in one step.
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Looks good ! looking forward to try mine out. What is the ID measurementof the neck that you recommend for your reamers?

The Pilot Replacement Reamers are .001" under bullet size.
I have been running bushings .002"-.003" with Peterson, ADG and Lapua brass. This seems to work well.
I've ran 6BR, 6GT, 6CM, 6Dasher, 6ARC, 243AI and 6.5CM so far. Working on a 6.5-284 at the moment.
Will be testing other calibers when batch #1 comes in.
In my 6ARC gas gun I run a much tighter interference fit and the inside reamer removed too much material. I run .005" bushing. I run a stand alone reamer for my gas gun.
 
I've been using a trimmer from Henderson Precision for awhile. The repeatability and speed is amazing.
After talking to Todd Henderson I developed a reamer to clean up and true the case neck.
I've made a couple different types. First I modified a LE Wilson neck reamer to fit into a blank Henderson cutter head. That reamer was for .243 cases. The Wilson reamer is .2455 - .246. I used this after firing. While it did a great job cleaning up the neck and removing doughnut the real winner was improved ES and SD from better seating pressure consistency.
That pushed me to try reaming after sizing. I bought a .242 reamer and ground it to fit into another blank cutter head.
This is where things got interesting… ES, SD improved significantly. Even on rifles with really good numbers.
Now I made a reamer to replace the pilot in the cutter head. Now I can inside neck ream, trim, chamfer and deburr in one step.
View attachment 640680

View attachment 640679
When you write about improve ESs and SDs, do you have any numbers? I have been using a mandrel die and turning necks. I am finding the improvements better, but not to where i want to be.
 
When you write about improve ESs and SDs, do you have any numbers? I have been using a mandrel die and turning necks. I am finding the improvements better, but not to where i want to be.
The testing I've done so far is as follows;
Load 10 rounds normal process
Load 10 rounds inside neck ream before sizing (.246)
Load 10 rounds inside neck ream after sizing (.242)
Shoot the 10 round samples over chrono. Ideally tried to keep environment the same wanted fair test.

So far only one test has not shown improvement. That test was 6CM with mixed Federal brass. I could tell when prepping the brass we would have issues. No two pieces were the same. Lot integrity matters.

The others varied but all showed improvement. The most improved in terms of ES/SD was another 6CM pushing 109 Bergers and virgin Lapua brass. Control is 44/14.5 and before sizing 27/9.8 after sizing 22/8.4
No prior OCW work was done on this rifle/cartridge

My 6.5CM that I have done load work on was improved as well. Peterson brass several firings. 140 Berger Hybrid, 41.3 H4350, Fed 210M. My control is 14/5.0 and after sizing 11/3.6

We all know that the neck thickness in cases isn't perfect. Even in really good brass the neck wall thickness will vary slightly from case to case and even around the mouth of a case.

This isn't turning…it's a reamer with several long straight edges that will true the ID of the neck. Yes some material will be removed in doing this. However the entire neck is supported by the reamer and diameter is consistent. Like a mandrel with teeth.

In large lots you will find your outliers. In both cases above when loading lots of 100 rounds I found about 5-10 cases that the reamer passes over and does nothing. I run these through the FLS die again but with the bushing flipped over. This gives another .0005" and does the trick.
I have also found again about 5-10 that excessive material is removed. This I believe is on me and not paying attention to properly starting the case over the reamer. I toss these into a fouler/burner container.

I have tested several other rifles, cartridges, dies, bushings and brass. The ES/SD improvement has varied.

I am currently in the process of making my first batch of Pilot Replacement Reamers. They are spoken for. Once they get out in the wild and more feedback is given I'll make another batch.
 
This is interesting. Have you measured any of the necks before and after to see if this helps with consistent neck wall thickness? In theory, you are pushing any inconsistencies to the inside of the neck with the bushing die and then reaming them out vs neck turning.
 
I have measured necks to check material removal. This depends greatly on what neck bushing is used. I have settled on Wilson bushings that are .002"-.003" under. This gives the reamer just enough to do its job. Typically reducing neck wall thickness by .0005" - .0007".
With a tighter bushing you will remove more material.
I have not tried to remove an excessive amount on purpose.

I understand what you're after and can say that my current design with a straight reamer isn't ideal for that. You would want to use a slightly tapered reamer. Ah…the wheels of innovation.
 

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