Lee Case Trimmer & Military (Thick-Headed) Cases

[Gary L. Griffiths]

I've been using a Lee case trimmer to trim my .223 and .308 cases. The Lee works by having a cutter with different size/length mandrels with pins to fit in the flash holes of your cases. Although it has a collet that fits the case head so you can chuck it into a drill, I find it easier to use just by grasping the case firmly and twisting the cutting head.

I recently did some correlating case weight, capacity, and length, finding all of my trimmed commercial cases well within tolerance. Results were: Federal Avg 1.7497 SD 0.0055; PMC Bronze Avg 1.7554 SD 0.0023; PPU Match Avg 1.7540 SD 0.0031; and PMC X-Tac Avg 1.7540 SD 0.0022. I then checked some unfired Lake City cases, which averaged 1.7538 with a SD of 0.0007.

This morning it occurred to me I was somewhat comparing apples with oranges; fired resized cases to unfired. I sized, trimmed and primed a like sample of Lake City cases that were twice-fired. Unsurprisingly, the cases held an average of 30.84 grs BLC(2) as opposed to 30.16 for the unfired cases. What rather shocked me, was that the trimmed cases averaged 1.7661 in length with a SD of 0.0048. The longest was 1.7735, with the shortest being 1.7590. I double-checked to see that the mandrel was solidly attached to the cutter head, which it was. Apparently the difference in case length is due to the fact that Lake City brass is about 0.01" thicker in the case head.

Since I recently ran into trouble (very high pressure indicated by velocity of 3448 fps & blown primer) apparently due to cases being over-length (Hot case was 1.7730") do I need to be concerned about using this trimmer on military cases? Specs call for case length of 1.75", not to exceed 1.76". Should I get another mandrel and trim off 0.02"?

 

[Jimro]

Were you using BLC-2, or other ball powder in the same burn range, and a light projectile (55gr or less)?

If so it was quite likely a secondary pressure spike and not case length.

Jimro

 

[Gary L. Griffiths]

No, I was using 25.4 grs of AR-Comp. I used BLC(2) to measure case capacity because it is a fine-grained ball powder. I'm not a big fan of using water to weigh cases, since I use a beam scale to weigh them.

FWIW, the load I was using is 0.2 grs shy of what Allied publishes as maximum for a Sierra 55-gr HPBT. They advised that the have not tried Armscor bullets, so that may have caused the problem. I somehow doubt that whatever difference there is between a Sierra HPBT and an Armscor FMJBT would cause a difference in pressure of that magnitude. Also, I have used that load before, with Federal and Wolf Gold cases with good results. The fired LC cases I had problems with have an average case capacity identical to the Federals.

Not to sidetrack the thread -- Wondering if the Lee type case trimmer is unacceptable for use with military cases.

 

[T. O'Heir]

Using a powder tells you nothing about case capacity for anything but that powder.
"...apparently due to cases being over-length..." Not a chance. Excessively long cases in a semi will give you feeding issues, but not pressure issues. If it did chamber the bullet would likely be pushed into the case. In any case, you absolutely must check case lengths every time when loading for a semi.

 

[243winxb]

Lee Case Trimmer

The web thickness has nothing to do with the trim length. The pin on the pilot bottoms out on the lock stud/shell holder. Some flash holes will be of a smaller size. A tight flash hole may not let the pin make contact with the stud/shell holder, resulting in a long trim length. The web is measured in this photo.

 

[Gary L. Griffiths]

Using a powder tells you nothing about case capacity for anything but that powder.

Agreed. And using water tells you nothing about case capacity for anything but water. It is useful in comparing relative case capacities. In my measuring, I found that there is really no difference in case capacity between civilian .223 cases and military 5.56mm cases.

Excessively long cases in a semi will give you feeding issues, but not pressure issues.

In that case, I'm back to square zero in trying to figure out the extremely high pressures from these loads. Pressure signs seem to roughly correspond to case length.

A tight flash hole may not let the pin make contact with the stud/shell holder, resulting in a long trim length.

Hadn't thought of that. I'm not using the shell holder to trim cases, so the pin won't bottom out on it, but a tight flash hole might keep the mandrel from bottoming out on the case head. I'll have to check relative flash hole sizes. Thanks, 243.

 

[Jimro]

Not to sidetrack the thread -- Wondering if the Lee type case trimmer is unacceptable for use with military cases.

Yes, use as directed. I've trimmed a lot of milsurp brass with Lee trimmers, in 223 and 308. I transitioned to a Possum Hollow trimmer for 223 though, and it was money well spent for convenience.

But for the primer blow out, I wouldn't blame the brass, all the St. Marks medium to medium slow burn rate powders can all exhibit that "delayed ignition leading to a pressure spike" problem. One of the reasons to use small rifle magnum primers in 223 is to ensure positive ignition. The other is to prevent out of battery ignition when the floating firing pin slams forward in an AR. The gas system can get wonky with a delayed pressure spike, or secondary pressure spke, so that the round bolt can go out of battery when the pressures are high enough to pop the primer clean out.

I would figure that what you experienced is a rare statistical event. It happens from time to time, even with factory ammo.

Jimro

 

[243winxb]

Lee Case trimmer

I'm not using the shell holder to trim cases, so the pin won't bottom out on it,

You must use it like in the photo, to get the correct trim length.

 

[Brian Pfleuger]

Hadn't thought of that. I'm not using the shell holder to trim cases, so the pin won't bottom out on it, but a tight flash hole might keep the mandrel from bottoming out on the case head. I'll have to check relative flash hole sizes. Thanks, 243.

Using it without the shell holder will result in cases MUCH shorter than typically "trim to" lengths. Usually, so short that they're essentially unusable, IME.

 

[Gary L. Griffiths]

You must use it like in the photo, to get the correct trim length.

Using it without the shell holder will result in cases MUCH shorter than typically "trim to" lengths. Usually, so short that they're essentially unusable, IME.

Both assertions are incorrect. I deprimed the cases manually and locked them into the Lee trimming base, as shown in the photo that 243winxb provided. I then re-trimmed them, noting no shavings at the time of trimming. Results were as follows (before and after re-trimming): 1.590 - 1.580; 1.7635 - 1.7640; 1.7735 - 1.7730; 1.7665 - 1.7670; 1.7680 - 1.7680. Inasmuch as my calipers only measure to 5/10,000ths of an inch, that was as close as I could get. In my estimation, there was no change other than a tiny variance no doubt caused by having the case in a slightly different position than when I originally measured it. Certainly a reduction of (at the max) 1/1000th of an inch would make no practical difference in case length.

I remain convinced that the Lee trimmer works, in the instance of the Lake City cases I tested, in any event, by cutting the case to a certain length from the interior portion of the case head. A thicker head will result in a longer case; in this instance in a case that 0.0161" longer than the maximum recommended trim-to length.

 

[Brian Pfleuger]

Both assertions are incorrect.

The Lee trimming base IS the shellholder.

as you said previously:

I'm not using the shell holder to trim cases, so the pin won't bottom out on it,

The whole point of the Lee shellholder is that the trimmer WILL bottom out on it, that's what controls trim length.

If you're using it, all is well, and it WILL bottom out on it (except for too-small flash holes).

 

[sawdustdad]

My understanding is that the trimmer mandrel pin MUST go through the flash hole and index against a solid surface supporting the case head.

I use the Lee case trimmer differently, but it works for me. I mount the mandrel in a drill, clamped at a 45 deg angle in my woodworking bench vise. I turn the drill on and lock the trigger. I put a case in the Lee case holder, slide it over the mandrel and push against the cutter to trim the case. It's easy to simply remove and replace the cases in the shell holder, and push it on the spinning mandrel. Takes less than 10 seconds/case.

 

[243winxb]

Measuring the Web

If the web is thicker than normal (defective), stopping the pin early, this would affect trim length. Pressure would be higher (less volume) for that brass. Weight of the brass would be on the heavy side. There is a homemade tool to measure web thickness. It does work, i tried it.. Link has photos http://www.ar15.com/mobile/topic.html?b=6&f=42&t=276154

I made a case web checker tool as described by Kieth_J in many posts of his.

I used a 3/16" dia rod and cut to 2 inches.

Cut a hole in the center of the end of the rod to clear the flashole burr. (drill bit)
Tool shown in caliper. Next step was to zero caliper with the 2" rod. So now I would be measuring the web only.

I sorted into 3 groups.

Under .175 = unsafe, I recycled these.

.175 to .185 = safe, but I would save these for SHTF or something.

.185 + = GTG, I will load and shoot these.

 

[Gary L. Griffiths]

If you're using it, all is well, and it WILL bottom out on it (except for too-small flash holes).

My understanding is that the trimmer mandrel pin MUST go through the flash hole and index against a solid surface supporting the case head.

Fellas, trust me on this. That ISN'T how it works. Just to make sure, I just checked the trimmer and mandrel in the cases I checked before. The pin was visibly shorter than the base of the case. I used the depth-gauge tool on my caliper and checked it -- it averages 0.02" below the base of the case. I also checked it with some commercial brass I'd resized and polished, with the same results -- 0.0195 - O.021" below the base of the case. If you have Lee trimmers, suggest you check for yourselves; it's possible I got one that was out of spec.

It works just fine on the commercial cases I have, but leaves the Lake City cases too long.

If the web is thicker than normal (defective), stopping the pin early, this would affect trim length. Pressure would be higher (less volume) for that brass. Weight of the brass would be on the heavy side.

That hasn't been my experience. The Lake City fired cases I measured averaged 30.84 grains of BLC(2) powder, exactly the same amount as Federal commercial, slightly less than PMC Bronze, and slightly more than PPU Match and PMC X-Tac. The primed case weight was 95.81 grains, the least of any of the cases I weighed. That would seem to indicate that contrary to conventional wisdom, LC cases have thicker heads but thinner walls than run-of-the-mill commercial cases.

BTW, Thanks for the reference on how to measure case head thickness, 243winxb. Will have to make me one at the earliest opportunity.

 

[sawdustdad]

Are saying that your Lee trimmer Mandrel is bottoming out inside the case before the pin comes out of the primer hole? So there is no way for the pin on the end of the mandrel to touch the case holder?

If this is the case, and you are getting correct case lengths, then you are using the wrong mandrel--perhaps a 30-06 for a .308 case? Something like that.

The mandrel pin MUST contact the case holder, or you'd experience just the problem you are having--different trim lengths based on case head thickness. Indexing the cutter relative to the case head face is the ONLY way to achieve consistent case lengths with that cutter system.

Sorry, but I ain't trustin' you on this.

 

[243winxb]

Lee case length gauge (pilot) measurements.

Mine is about 30 years old.

Hope this helps.

 

[Gary L. Griffiths]

Are saying that your Lee trimmer Mandrel is bottoming out inside the case before the pin comes out of the primer hole? So there is no way for the pin on the end of the mandrel to touch the case holder?

Exactly. It lacks 0.02" on average of being flush with the case head.

If this is the case, and you are getting correct case lengths, then you are using the wrong mandrel--perhaps a 30-06 for a .308 case? Something like that.

No, I'm using a mandrel marked ".223 REM" on .223 & 5.56mm cases. Again, works perfectly on commercial cases, leaves LC 13 cases an average of 0.0161" over max spec.

Guess I'll have to contact Lee about this. I have issues with their .308 mandrel, also -- won't fit deprimed sized cases! It's just a little too big in diameter to fit inside the case mouth. Works on unsized fired cases only.

 

[sawdustdad]

Nosler's reloading data shows .223 Remington case length at 1.760.

1.435 + .328 = 1.763.

Allowing for some error in measurements, it looks to me like the case length is indeed determined by the length of the pin + mandrel body. So the pin should bottom out on the case holder.

Interesting. You must have some cases with extraordinary head thicknesses--over .328. Wow.

 

[Bart B.]

Any case that's excessively long will cause peak pressures higher than normal. Here's how and why.

SAAMI spec .223 Rem chamber specs have a minimum length from bolt face to chamber mouth of 1.772" at maximum .254" chamber neck diameter to 1.787" at minimum .224" diameter. The case mouth's angle from max to min diameter is 45 degrees. Depending on case neck wall thickness, it will just touch that angled chamber mouth at some point when head clearance to the bolt is zero.

When the firing pin drives the primer cup in, it also drives the case forward setting its shoulder back a few thousandths if head clearance is zero. That forces the case mouth to swage down against the chamber mouth angle increasing its grip on the bullet. That means peak pressure will be higher because the bullet's release force to get it moving is now higher. Shoot some empty primed cases measuring their headspace before and after firing to see how much case shoulder setback the rifle's firing pin causes.

All of which is why chamber lengths are specified some distance longer than case lengths. For the .223 Rem, it's 1.772" minimum for the chamber and 1.760" maximum for the case; allows .012" clearance. It prevents them from pinching bullets by being driven hard into the chamber mouth angle when the firing pin smacks their primer. I've measured shoulder setback from firing pins on .222 Rem cases; I don't think the .223's much different. And was I surprised how much it was.

A .005" or so difference in case length has only a microscopic effect on accuracy. It might be noticable if you consistantly shoot your stuff no worse than 19/119ths MOA at 100 yards. It's the least critical case dimension for accuracy anyway; don't get upset if your's have a .007" spread.

 

[Brian Pfleuger]

Fellas, trust me on this. That ISN'T how it works.

It's how every single on of mine works and I have them for .22-250, 6mm Rem, .30-06, .243Win, 7mm-08 and .357sig.

In fact, accurate trimming requires that it does exactly that or you will not have a consistent length. Since the head/web thickness can vary, your case lengths will vary if that is the point that controls trimming.

The mandrel most certainly should be bottoming out on the shellholder.

You can clearly see in Lee's own picture of the device that the mandrel is nowhere near touching the inside of the case head/web and the tip is clearly touching the shellholder.

http://leeprecision.com/userfiles/images/casetrimmer.jpg