I was trimming some lake city 5.56 cases this morning . I checked and found a variance in length most all were between 1.748 and 1.750 after sizing and trimming. I found a few that were 1.743 and 1.744. How important is it that they all be exactly the same for accuracy ? Will the shorter ones be flyers in the group ?
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trimming 5.56 cases ?
- Thread starter rebs
- Start date
I have never found that neck length affected accuracy but then I have never conducted any testing in that area. 1.748-1.750 valiance is fine. Almost impossible to have all the cases the same length. I use a RCBS trimmer and was having problems with the OAL not being consistent. The cutter appeared sharp and seemed to cut OK and it was about 20 yrs old. I got a RCBS carbide cutter and the variance is now a LOT less. The carbide cutter is well worth the cost and it should last a lifetime.
"...exactly the same for accuracy..." Not at all. All the same length is for ease of loading for the OAL.
There is no SAAMI spec for a 5.56NATO case. Use .223 Rem for it. None of 'em will be 1.anything though.
That 1.748", etc., is the distance from the case head to the beginning of the neck(as in the case body length) and that distance doesn't have anything to do with trimming.
There is no SAAMI spec for a 5.56NATO case. Use .223 Rem for it. None of 'em will be 1.anything though.
That 1.748", etc., is the distance from the case head to the beginning of the neck(as in the case body length) and that distance doesn't have anything to do with trimming.
All the same length is for ease of loading for the OAL.
I take a piece of half inch pipe 4 inches long and drop it in a piece of two inch pipe two inches long and if I measure from the bottom of the 2 inch pipe to the top of the 4 inch pipe I will get a measurement of 4 inches. I drop that same piece of half inch into a two inch piece that is only one and a half inches long, it will still measure 4 inches. That is because we are starting our measurements from the bottom of the two inch.
Same thing when using a seating die. You are starting your measurement at the case head and measuring to the metplat of the bullet. The shorter length only affects how much of the bullet is being covered by the case.
I would not sweat it if the extremes are within .005 of each other unless you are doing long range benchrest which would be about impossible with a AR
The suggested trim to length for the 223 Remington is 1.750". The Maximum cartridge length is 1.760" so the suggested trim to length is right about 0.010" below the Maximum. The minimum is 1.730" or right about 0.020" below the suggested trim to length. So really anything between 1.730" and 1.760" is fine. I seriously doubt even above or below the overall case length length dimensions will matter. As mentioned, there is no single 5.56 NATO case length specification.
Ron
Ron
Unless you are shooting for precision it is ok to shoot. My plinking ammo varies in its length, but my hunting ammo has more tight tolerances as I expect a consistency of match ammo so that my velocities and trajectories are known for various distances to necessitate corrections and adjustments accurately.
If you're not crimping with a crimp die, it doesn't matter too much. One could argue there is less neck tension with the shorter cases, which COULD affect SD and accuracy. One could argue such, but I don't buy that it has any significant effect unless you're shooting bench rest comps.
Case volume is the most important thing to be consistent for accuracy, at least in the realm of case dimensions.
Case volume is the most important thing to be consistent for accuracy, at least in the realm of case dimensions.
Rebs,
In the 1992 SAAMI standard, the length of the 223 case was 1.740" to 1.760". In the 2015 standard, it was changed to 1.730" to 1760". As a general rule, manufacturers will aim for the middle of the range to give themselves the maximum tolerance error range. By that standard, the trim-to length used to be 1.750" and is now 1.745", to match the length manufacturers are expected to target with new brass. However, I have not noticed any of the reloading manuals dialing the old trim length back to the new dimension. Nor do I know why the old dimension was changed, as no other rifle cartridge has that 0.030" wide window of case length that I am aware of.
As an aside, while the 5.56 STANAG documents are still marked as classified in the usual catalogs, it has been generally true from the 30-06 forward that military brass has only a -0.015" case length tolerance and variability window. The maximum case length is the same as the SAAMI drawing, but the mid-point and newly manufactured brass or trim-to length would be -0.0075" shorter than maximum. So if you want to use military ammunition specifications, aim at 1.7525" trim length. I am unaware of this making any functional difference over using 1.750" other than needing to be re-trimmed a little more often, but thought I would throw it out there as one of the possibilities.
The fact is a lot of M14 shooters used to trim their military 7.62 brass back about -0.040" shorter than maximum and -0.020" shorter than SAAMI minimum just so they would only have to trim it once in its reloading life. These were match shooters and they had no problem with the practice that I've ever heard of. They were not shooting the shortest bullets, though. This would have been for 168-grain MatchKings and not for 147-grain bullets, which often offer rather little seating depth of the bearing surface of the bullet when loaded to military standard overall length. But, in principle, the same should apply to 5.56/223.
Overall, I would suggest you simply pick a trim-to length you are comfortable with and stick to it. The book value of 1.750" is just fine.
In the 1992 SAAMI standard, the length of the 223 case was 1.740" to 1.760". In the 2015 standard, it was changed to 1.730" to 1760". As a general rule, manufacturers will aim for the middle of the range to give themselves the maximum tolerance error range. By that standard, the trim-to length used to be 1.750" and is now 1.745", to match the length manufacturers are expected to target with new brass. However, I have not noticed any of the reloading manuals dialing the old trim length back to the new dimension. Nor do I know why the old dimension was changed, as no other rifle cartridge has that 0.030" wide window of case length that I am aware of.
As an aside, while the 5.56 STANAG documents are still marked as classified in the usual catalogs, it has been generally true from the 30-06 forward that military brass has only a -0.015" case length tolerance and variability window. The maximum case length is the same as the SAAMI drawing, but the mid-point and newly manufactured brass or trim-to length would be -0.0075" shorter than maximum. So if you want to use military ammunition specifications, aim at 1.7525" trim length. I am unaware of this making any functional difference over using 1.750" other than needing to be re-trimmed a little more often, but thought I would throw it out there as one of the possibilities.
The fact is a lot of M14 shooters used to trim their military 7.62 brass back about -0.040" shorter than maximum and -0.020" shorter than SAAMI minimum just so they would only have to trim it once in its reloading life. These were match shooters and they had no problem with the practice that I've ever heard of. They were not shooting the shortest bullets, though. This would have been for 168-grain MatchKings and not for 147-grain bullets, which often offer rather little seating depth of the bearing surface of the bullet when loaded to military standard overall length. But, in principle, the same should apply to 5.56/223.
Overall, I would suggest you simply pick a trim-to length you are comfortable with and stick to it. The book value of 1.750" is just fine.
I was trimming some lake city 5.56 cases this morning . I checked and found a variance in length most all were between 1.748 and 1.750 after sizing and trimming. I found a few that were 1.743 and 1.744. How important is it that they all be exactly the same for accuracy ? Will the shorter ones be flyers in the group ?
How important
And then there is 'MORE IMPIORTANT': You measured the length of the case from then end of the neck to the case head before sizing. After sizing you found some of the cases shortened between .006" to .007", and I wonder how that happened.
I would start by determining the length of the chamber from the end of the neck/beginning of the throat to the bole face. So no matter 'what it should be' I know 'what it is'.
The most accurate way to trim a case and to save ware and tare on tools is with a forming die and file. It does not matter to me if the case is trimmed before sizing or after sizing, by knowing the length of the chamber from the shoulder to the case head I know how much length to trim when setting up on the shoulder for trimming.
F. Guffey
m&p45acp10+1
New member
I trim all of my AR brass a wee bit shorter. By the time it needs trimming I retire it. That way I only have to trim once. For my AR I tend to get 8 to 10 firings before they need a trim. I then put them into the I will mess with those later bin. I have paper clip tested them, and they all seem just fine. I just have so many that are already trimmed I put them in the bin marked that they are multi time fired, and need another trim.
I have not had any noticeable changes in accuracy from any of them. I run a generic load that gives me great accuracy without having to be so fussy about little things. Out of my Bolt action they give half to 3/4 MOA with a bipod, and rear sandbag.
I have not had any noticeable changes in accuracy from any of them. I run a generic load that gives me great accuracy without having to be so fussy about little things. Out of my Bolt action they give half to 3/4 MOA with a bipod, and rear sandbag.
A trim length decrease of 0.006 inches would increase the muzzle velocity by about 4 fps if you are loading heavy bullets near Pmax.
That should be within the Standard Deviation of the velocity measured by a chronograph if all the rounds were trimmed exactly to the same length. The change should be invisible to the extreme spread between the slowest and fastest bullets of a load all trimmed exactly to SAAMI length of 1.750 inches.
I doubt you would see a significant difference in POI.
That should be within the Standard Deviation of the velocity measured by a chronograph if all the rounds were trimmed exactly to the same length. The change should be invisible to the extreme spread between the slowest and fastest bullets of a load all trimmed exactly to SAAMI length of 1.750 inches.
I doubt you would see a significant difference in POI.