Case length after trimming

M

Machineguntony

New member
I measured some of my fired 223'brass, and they're all 1.74 a 1.76.

After trimming, I have brass that is 1.73.

Most books say to trim to 1.75.

Will there be any downside to using brass trimmed to 1.73? Is 1.73 acceptable?

I was trimming on a Dillon RT 1500.
 
Since the case doesn't headspace on the mouth, slightly shorter won't matter for feeding and firing.

Can make a difference when seating and crimping bullets, though.

"Trim to" case length is almost always either 0.01" or 0.005" less than max case length, depending on the specs for the round being trimmed.

9mm and .45ACP trim to length is 0.003" less than max length, in the Lyman books. With cases headspacing on the case mouth, it can be critical. With rimmed cases, and bottlenecked cases, not so much...

Check your trimmer, reset it if needed, and figure out if it was something with it, or something you did (besides incorrect length setting) that caused the short cases.

Good Luck!
 
Kinda confused by your measurements. You said your untrimmed cases were running 1.74" to 1.76". That's twenty thousandths of an inch variation. You're trimming to 1.73", that's another ten thousandths of an inch. I think you'd know if you were cutting off .030" of the case mouth( almost 1/32"). Remeasure? ;)
 
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You're trimming when you don't need to trim. Those 1.740" are already 10 thou short of the Trim-to of 1.750". Max case length is 1.760". If the cases measure between the 1.750" and 1.760" you don't need to trim.
Like 44 AMP says, you'll have some seating and crimping issues, but nothing bad will happen.
Sounds like your trimmer isn't set up right too.
 
223 brass must not grow very much when shot.

These casing have been on 22 firings. I've reloaded them 22 times. The longest cases are at 1.76, the shortest untrimmed are around 1.74. The difference is because there are some cases which have been fired only a few times (I pick up range brass and toss it in with this batch).

I wanted to trim them because I bought a new RT1500 case trimmer. Usually I don't trim. I'm trying to see how many firings I can get out of this batch.

Based on everyone's advice, I moved it to 1.74 trimmed length. My Lyman book says 1.75, but I just pulled a factory new case, and it reads 1.74. I checked the caliper, and it's working fine.

308 brass grows a lot, btw. That's why I bought this trimmer.
 
Machineguntony,

I assume that you are loading .223s by the SAAMI recommended case length of 1.750.
To give you an idea of the effect of varying case length on a .223 round, I ran a load for my two .223 rifles (A Les Baer Super Varmint 18 inch barrel and a CZ 527 Varmint 24 inch barrel bolt action) so you can see the difference.

A case length variation of 0.02 inches will have a fairly small impact on muzzle velocity and just a slightly larger impact on pressure.

I ran CFE223 powder loaded at 27.1 grains with an OAL of 2.250 (SAMMI recommended OAL) and only varied the case length. I used QuickLoad to give the following results. It is a pretty good way to see effects of varying one part of a loading setup.

Les Baer 18 inch barrel
Case ----- Muzzle vel -------------- Pressure
1.750 ---- 2960 fps --------------- 47543
1.740 ---- 2954 fps (99.80%)---- 47144 (99.16%)
1.730 ---- 2948 fps (99.59%)---- 46735 (98.30%)

CZ 527 24 inch barrel bolt action
Case----- Muzzle vel -------------- Pressure
1.750----- 3177 fps ---------------- 47547
1.740----- 3171 fps (99.81%) ---- 47147 (99.16%)
1.730----- 3168 fps (99.62%) ---- 46743 (98.31%)

If you get really anal about accuracy like I do when loading for really accurate rifles, just keep the case length under 1.760 and keep loading.
Trim when you get close to the 1.760 mark.
 
Max case length is good to watch. Chambers vary. If you fudge a little, then fudge a little more because the last fudge factor was ok, you may eventually end up w/ a neck just long enough to get pinched at the end of the neck increasing pressure that could be destructive. You can learn your chamber a bit more by measureing several once fired. If you intermix manufactures brass, they can vary as well as springback , etc varies. But at least you get an idea about your chamber.
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As you know, once you trim your brass (always after the sizing operation), watch how much you chamfer/debur to prevent too much thinning at the end or you may end up causing premature splitting at the end.
 
I'd be more worried about the cases being reloaded 22 times already. Personally, I would chuck them in the scrap bucket a while ago....223 brass is easy and cheap to get right now. The two thou extra length is no big deal, even when crimping. If you were really worried you might be ale to get back a thou or two just by resizing again.
 
Does your measuring tool only go as small as one hundredth of an inch? (.01)
"Normally", measurements are taken in thousandths of an inch (.001) and are much more accurate (.010" is much more accurate than .01"). While the tolerance of the case length is mebbe .010" you are measuring in .010" jumps, not very accurate (and a bit confusing)...:o
 
Just a side note that really doesn't apply to your question but might for the next: If you reload cannalured and crimp for that, the shorter your neck, the shorter oal you will have if you crimp them in the cannalure. Crimping for the cannalure also shortens a tad bit more as it typically snugs the bullet in a bit further. You then need to determine the variations that go along with that. re: AR-15 If you decide to use taper crimp, pending how short you have the case, you will lose some of that neck tension that holds them. Measure and record the bullets as they are placed in your magazine. Make the very last round a dummy round. Fire one round, then measure the next one in the mag (remember there is one in the chamber). If ok, fire two more and repeat measurement. If not ok, unchamber the bullet and measure it. Make sure you measure the very last dummy round "AFTER" it has been chambered and save for pulling the bullet. If none of them walked, and the bullet inspection of that last round is good, you will know a little bit more of that taper setting.
 
RickD1225 caught it. 1.730-1.760" is the current SAAMI case spec, so the OP's numbers are not out of line with normal practice. It used to be SAAMI used 1.740-1.760", but they widened it at the last revision. The military (NATO) speck is 1.745-1.760", IIRC.


Rimfire5 said:
I assume that you are loading .223s by the SAAMI recommended case length of 1.750.
Click to expand...

That's actually a load manual recommended trim-to length. It was chosen because it fell in the middle of the obsolete 1.740-1.760" SAAMI standard span, and therefore allowed the most error in either direction for the sloppy trimmer. If it were revised based on the current SAAMI standard, it would be a trim-to length of 1.745" to get in the middle of the error tolerance range.
 
Les Baer 18 inch barrel
Case ----- Muzzle vel -------------- Pressure
1.750 ---- 2960 fps --------------- 47543
1.740 ---- 2954 fps (99.80%)---- 47144 (99.16%)
1.730 ---- 2948 fps (99.59%)---- 46735 (98.30%)

CZ 527 24 inch barrel bolt action
Case----- Muzzle vel -------------- Pressure
1.750----- 3177 fps ---------------- 47547
1.740----- 3171 fps (99.81%) ---- 47147 (99.16%)
1.730----- 3168 fps (99.62%) ---- 46743 (98.31%)

Is that right Rimfire5? I guess I would have assumed less case volume with the same amount of powder would have increased pressure and Muzzle velocity not decreased it.
 
A couple of decades ago, I was trimming cases for my 220. I trimmed them way way too short, probably the biggest part of 1/8 of an inch. Well, those were the only 220 cases I had, so I loaded and shot them. Shot them for a few years. No problem. And I didn't crimp them.
 
datum214

You would think that but those are the results from QuickLoad.
The loads are well within the 55,000 PSI Pmax rating for .223 SAAMI rounds.

I've noticed the same type of results with other powders as well in that range for .223s.
 
I measured some of my fired 223'brass, and they're all 1.74 a 1.76.

After trimming, I have brass that is 1.73.
Click to expand...


.030" from 100 cases is about 3 inches of trimming, when forming casaes I trim .100" plus from each case; that works out to be 10 inches. There are times I trim 30 inches of brass from 100 cases. When I trim that much brass I use the man tool; the hack saw.

F. Guffey
 
datum214

I thought about it a bit more and realized that since the overall length was kept constant, the bullet had less of the body in the neck while the volume behind the bullet base remained the same.

That would mean that there was slightly less neck to hold the bullet so that could result in a marginally quicker release from the neck and hence a slightly lower pressure and velocity.

If you kept the case trim length constant and reduced the OAL by the same amount, you would see the increase in pressure that you predicted. It wouldn't be huge but it would increase as the volume behind the bullet was reduced.
 
That would mean that there was slightly less neck to hold the bullet so that could result in a marginally quicker release from the neck and hence a slightly lower pressure and velocity.
Click to expand...

I believe it is impossible to micro manage the bullet and case neck release. As R. Lee suggest; you will not believe how fast the case neck expands when releasing the bullet. There are those that believe the neck expands before the bullet moves; if I was guessing I was guess that is fast.

And there are those that believe everything moves in slow motion. When describing the sequences of events they start with; the firing pin strikes the primer and then everything is driven forward and hits the shoulder of the chamber. Again, things happen fast in my chambers, my killer firing pins crush the primer before the case, and powder and bullet know their little buddy, the primer, has been crushed.

F. Guffey
 
F. Guffey said:
I believe it is impossible to micro manage the bullet and case neck release. As R. Lee suggest; you will not believe how fast the case neck expands when releasing the bullet. There are those that believe the neck expands before the bullet moves; if I was guessing I was guess that is fast.

And there are those that believe everything moves in slow motion. When describing the sequences of events they start with; the firing pin strikes the primer and then everything is driven forward and hits the shoulder of the chamber. Again, things happen fast in my chambers, my killer firing pins crush the primer before the case, and powder and bullet know their little buddy, the primer, has been crushed.

F. Guffey
Click to expand...
I've never heard of cartridge components being personified. Now I feel bad for the little guys.

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