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223 Trim
- Thread starter cervri
- Start date
These are the 223 SAAMI specifications. The cartridge overall length ranges between a Maximum of 1.760" -0.030 so a Minimum of 1.730". The commonly seen 1.750" is the common suggested trim to length.
Load them and choot em.
Ron
Load them and choot em.
Ron
The cartridge overall length ranges between a Maximum of 1.760" -0.030 so a Minimum of 1.730".
The overall length according to SAAMI is 2.125 NIN, to 2.260" MAX. So the op is correct when he is referring to trimming the case to length and trimming.
Reloadron, when you say overall length are you talking about adding the length of the case from the case head to the case body/shoulder juncture and the distance between the two junctures and the length of the neck for an overall length. When I make references to overall I am adding everything between the top of the bullet to the case head. And then there is the other length that is measured from the bullet contact with the rifling to the case head.
F. Guffey
Last edited:
Cervri,
A lot of gas gun match shooters dump their brass after about 4 reloads to avoid the possibility of getting a head separation during a rapid fire string. The gas guns are harder on brass than bolt guns are. If you are actively shooting matches you fire enough ammo that wasting time becomes an issue, so what a number of these guys do is trim their cases about twice as far as SAAMI standards call for, knowing the amount of case growth won't exceed all that trimming in the four-reload life they allow for the case. So this lets them trim each one just once in its useful life.
This does not seem to affect their chamber wear any within the normal life of a match barrel. In theory, because you get slightly lower bullet pull from the shorter case necks you have lower start pressure and could have lower ignition consistency result. But that usually shows up only in benchrest or in long range shooting. For normal target accuracy to 600 yards with COL's short enough for magazine feeding, there seems to be no harm in it.
A lot of gas gun match shooters dump their brass after about 4 reloads to avoid the possibility of getting a head separation during a rapid fire string. The gas guns are harder on brass than bolt guns are. If you are actively shooting matches you fire enough ammo that wasting time becomes an issue, so what a number of these guys do is trim their cases about twice as far as SAAMI standards call for, knowing the amount of case growth won't exceed all that trimming in the four-reload life they allow for the case. So this lets them trim each one just once in its useful life.
This does not seem to affect their chamber wear any within the normal life of a match barrel. In theory, because you get slightly lower bullet pull from the shorter case necks you have lower start pressure and could have lower ignition consistency result. But that usually shows up only in benchrest or in long range shooting. For normal target accuracy to 600 yards with COL's short enough for magazine feeding, there seems to be no harm in it.
Fguffy, when I kake reference to the cartridge overall length I am referencing the SAAMI drawing case head to case mouth which I linked to. My link clearly shows 1.760" -.030" which is how I derived 1.730" to 1.760" for the range.
Where do we get the 1.725" dimension?
The OP only ask:
That sort of implies to me the only concern is the case and not including a bullet. Therefore, I went with the SAAMI cartridge dimensions less a bullet.
Ron
Where do we get the 1.725" dimension?
The OP only ask:
Not sure if still asleep or a senior moment but I trimmed a small batch of 223 to 1.70 this morning, so how short is too short? 1.76 looks to be max and 1.75 is the trim too length. No minimum given.
That sort of implies to me the only concern is the case and not including a bullet. Therefore, I went with the SAAMI cartridge dimensions less a bullet.
Ron
603Country
New member
I, like the OP, once made a mistake and way over trimmed some 220 Swift brass. Luckily, that brass has a long neck. Didn't matter at all to the accuracy, and I reloaded and shot that brass a bazillion times (prob less than a full bazillion, but you get the point).
"...The overall length according to SAAMI is 2.125 NIN..." That's COAL. The 1.760" -.030" is the case length. The -.030" is the tolerance. So it's 1.760" MINUS .030" for the minimum length.
Cervri's case length is 30 thou too short according to SAAMI. Very much doubt anything bad will happen anyway.
Cervri's case length is 30 thou too short according to SAAMI. Very much doubt anything bad will happen anyway.
cervri,
The 0.050 difference between the trim to length of 1.750 and your 1.700 trim is just about the breadth of 11 sheets of copy paper. Your trim length is less then 2.9% shorter than the trim to case length and 1% off the minimum SAAMI trim length.
Using a 52 grain SMK bullet seated at 2.250 OAL with H335 powder in the middle of the pressure range, the difference in a 0.05 case trim length results in a difference of only 26 fps in velocity at 3161 fps (0.07%) and would be about the same as a 0.2 grain reduction in the powder load. The pressure difference would be 1577 psi out of 44115 psi (3.7%) or less than a powder load reduction of less than 0.3 grains.
Interestingly, if you seated the bullets with case length of 1.750 out to 1.798 OAL you would get the same results as if you trimmed to 1.700. I've seated my bullets out that far in my CZ bolt action to get closer to the rifling and improve accuracy (My CZ has a very deep chamber). No one gets all that excited when you do that as long as you have enough bullet shank in the neck.
Practically, if you chronograph your loads, you should expect your best reloads to average 7 to 10 fps variation across the same set of reloads. You're only going to be offset just under 3 times that.
I've had chronograph results for some loads that averaged 25 fps variation when the loading techniques were questionable or the casings were at the end of their useful life.
Results with different powders might differ slightly.
If it were me, I would load those cases and shot them and then neck size the cases to let the necks stretch a bit.
I doubt you will see a difference in accuracy in group size for the loads with the short case length but the impact point might be slightly lower.
The 0.050 difference between the trim to length of 1.750 and your 1.700 trim is just about the breadth of 11 sheets of copy paper. Your trim length is less then 2.9% shorter than the trim to case length and 1% off the minimum SAAMI trim length.
Using a 52 grain SMK bullet seated at 2.250 OAL with H335 powder in the middle of the pressure range, the difference in a 0.05 case trim length results in a difference of only 26 fps in velocity at 3161 fps (0.07%) and would be about the same as a 0.2 grain reduction in the powder load. The pressure difference would be 1577 psi out of 44115 psi (3.7%) or less than a powder load reduction of less than 0.3 grains.
Interestingly, if you seated the bullets with case length of 1.750 out to 1.798 OAL you would get the same results as if you trimmed to 1.700. I've seated my bullets out that far in my CZ bolt action to get closer to the rifling and improve accuracy (My CZ has a very deep chamber). No one gets all that excited when you do that as long as you have enough bullet shank in the neck.
Practically, if you chronograph your loads, you should expect your best reloads to average 7 to 10 fps variation across the same set of reloads. You're only going to be offset just under 3 times that.
I've had chronograph results for some loads that averaged 25 fps variation when the loading techniques were questionable or the casings were at the end of their useful life.
Results with different powders might differ slightly.
If it were me, I would load those cases and shot them and then neck size the cases to let the necks stretch a bit.
I doubt you will see a difference in accuracy in group size for the loads with the short case length but the impact point might be slightly lower.
You are describing the length of the cartridge to 2 decimal places.Not sure if still asleep or a senior moment but I trimmed a small batch of 223 to 1.70 this morning, so how short is too short? 1.76 looks to be max and 1.75 is the trim too length. No minimum given.
Dimensions in reloading as well as machining are typically conveyed to the 3rd decimal place.
The 3 decimal places shows the level of precision that is required in the application.
I still think that they would be fine to shoot.