.204 chrono results and questions

[alltherage]

Broke out my chrono for the first time today. Tried my 2 most accurate loads of cfe223 with 32g varmageddons. Have been doing load development for a while. 31grains averaged 4200 and 31.8grains averaged 4300. Both will do 1/4" at 100 yards. I had big swings in velocity which is what concerns me. Im talking 100 fps difference between min and max. This happened with both loads. I shot another rifle in different caliber with factory ammo and didnt see the swings so it wasnt the chrono i presume. Is this acceptable because we are talking 4000fps and not 2800fps? 100fps deviation seems high but is it all relative? Is this a negative of neck sizing? My full length sizing always seems to produce more consistent neck tensions and ive only neck sized my .204

[Scott Evans]

Often times that is a symptom of a too close to maximum, slightly overpressure load for the powder. approach with caution especially in hot weather. Use a swage gauge to check primer pocket expansion.

Neck sizing with a bushing die on a batch of brass with varying neck wall thickness can also do this. While I'm not fond of Lee products overall their collet dies do a good job sizing the ID of the necks consistently in batches of brass that have varying wall thickness. They make a 204R version. PS this can also be cut down to do 20 Prac/20 Tac and a couple others.

[alltherage]

thanks. here are my 31 grain speeds: 4195,4230,4154,4195,4188,4206,4183,4130. I misspoke as I only shot 2 rounds at 31.8grains which were 4312 and 4359. close but only 2 rounds so who knows. 31.8 is hot for sure but shoots good with no significant pressure signs. These rounds were all sized with a lee collet.

[alltherage]

am using hornady brass with cci 450 mag small rifle primers. I know many aren't fond of hornady brass, not sure why this is though. If it's variation in the brass, then that could be a factor i suppose

[alltherage]

Ran these numbers and SD is 28 and some change. Coefficient of variation is around .67 percent. Guess it's not that bad although some more work to do

[Zero333]

If you're shooting this load no farther than 400 yards then I would not loose any sleep over it. I seen this before with someone 223 load. Fella had a ES of about 100 fps (10shot string) but all his groups were sub 1/2 moa at 330 yards !

[big honkin jeep]

Chrono may be saying "WTH close enough" at those speeds :)

[JASmith]

Velocity swings of 100 fps can have an effect on accuracy at longer ranges. With 1/4" in groups at 100 yards including the 100 fps velocity swings, the observable effect is on drift and drop at longer ranges.

The .204 is not likely a 500 yard, much less a 1,000 yard, rifle. So, crank up your favorite ballistics calculator and find the difference in drop at your nominal "long range" for 50 fps above and 50 fps below your nominal velocity.

With .25 in groups at 100 yards, you might be able to see the difference at 300 yards, which might take you out of "minute of mouse" but there is a high likelihood you will still be within "minute of prairie rat."

[sharpshooter]

Velocity spreads that high are usually associated with case capacity variables in cases of that size. I've seen 100fps difference in .17 Rem cases that were only 2 grs. heavier. If you weigh your brass you might find it's all over the place.

[alltherage]

that's what I think too...the powder always looks inconsistent in the case after filling. Is this a common complaint with hornady brass?