Possum hollow brass length vs traditional trimmers- which is right?

[BrokenWheel]

I have a possum hollow trimmer that trims 223 brass, using the datum line of the shoulder of the casing as its reference point. I've set it to 1.750" but some bass after trimming measures up +/- .004" (usually on the + side though). The brass are a variety of different head-stamps, but I thought using a full length re sizer die should bring them all into the same dimensions.

Currently, after the PH trimming, I finally trim the brass exactly to 1.750", using a hand crank Lyman trimmer. This last step makes processing brass more time consuming. So I thought, isn't the case length measured from the datum line a more realistic measurement since it mimics what happens in the rifle chamber? Could someone tell me which trimming procedure is correct?

If so that would save me a step...

 

[Walkalong]

Are you sizing before trimming? I use the PH for .223 and it does a great job with little variance. Around +/- .002 at most. Most cases are +/- .001. Many are dead on.

I am using power to trim with it. Maybe that makes a difference.

 

[BrokenWheel]

yes I am sizing before trimming. Odd.

 

[RVenick]

I tend to have the same results as Walkalong. It may be that you are stopping the trimmer too soon. I had 1500 rounds of LC 5.56 that needed trimmed I didn't check every case but random checks showed them to be almost dead on 1.750".

 

[rhubarb]

There is inconsistency somewhere. I have measured a batch of 100 .223 I trimmed on the Possum Hollow in a drill press that were all within -0.0/+0.0015. When I started using a drill press and running the trimmer vertically it improved slightly over using a hand-held drill in the horizontal position. Presumably the brass trimmings are less likely to stay in the trimmer and affect the length.

Could it be the sizing that is inconsistent? Differing amounts of lube? Not fully stroking the press handle? Or like RVenick says, you might be pulling them out of the trimmer a second too soon. I can feel when the cutter stops cutting.

 

[kelbro]

I would bet that these are range pick ups and have not been fired in your rifle yet. A lot of folks have the issue when sizing 223 that the shoulders are not set completely back.

 

[BrokenWheel]

Rhubarb- some great points but I am sure that I am doing everything to a "T".

Kelbro - The brass are indeed range pick ups, but I dont understand your point that they "had not been fired in my rifle yet". How will firing them in my rifle or the 223 rifle before me change anything after I FL resize them? I set the FL redding die as per the instructions- tighten the die down until the die is touching the shell plate, then 1/4 to 1/8 twist more.

 

[EddieNFL]

If you have the tool, measure the distance from case head to the datum. I'm bettin' the differences will pretty much mirror the OAL differences.

This can be caused by a few things: Differences in brass hardness (more/less springback), inconsistent case lube and/or the expander ball (if used) can drag the shoulder forward if there is not enough lube inside the neck.

 

[BrokenWheel]

Thats a good point, I am using the redding carbide button/ ball insert. Which technically says that you dont need lube with it, but interestingly Walkalong, I believe, also has the same setup so the only thing I can think of is maybe different brass case manufactures cast to different specs?

Im thinking that everyone who is getting consistent sizings may be using the same head stamp brass.

 

[Walkalong]

This can be caused by a few things: Differences in brass hardness (more/less springback), inconsistent case lube and/or the expander ball (if used) can drag the shoulder forward if there is not enough lube inside the neck.

Yep.

Remember, .001 (even .002) difference in case length is a very small amount. Certainly nothing to sweat about. You will never see it on target.

Yes, I use a carbide ball in my sizer, and yes, I was talking about mixed brass as well.