FPS out of 223

#s per inch vary but seems reasonable to me.

And unless your chrono is not telling the truth it is what it is.
Different powder might be better or worse.
Might help others eval if you gave use the load info.

That’s a bigger spread than I would expect, but not out of the realm of reality. Generally, I expect about 40-45fps per inch for 223rem, but you have 260fps for 4”. One of the barrels is slow or the other is fast, or both. Doesn’t really matter in the scheme of things.

You also didn't mention the bullet weight... that can have a significant impact on velocity, particularly out of the 16"

There's are lots of minor contributing factors other than barrel length, but: Ballistics by the Inch.

Looking at me notes...

Factory 5.56mm 55grn NATO ammos give me 3100 and 3200fps, 16" and 20" respectively, 62grn NATO 3000 and 3100fps. Factory .223 55grn ammos can be a mixed bag... PMC FMJ gave me 2800fps out of a 16", but Federal 55grn HP popped out at 2950fps from the same barrel.

The velocity difference seems a little abnormally large to me. I normally load for around 3000fps from my 16" and that gives me about 3150 from the 20" with either hornady 55gr FMJ or soft points. Granted, all barrels are different and can give different velocities, but 260 seems a little extreme.

Were both groups shot on the same day in the same weather conditions? Was the ammo allowed to fully stabilize with the outside temperature? Those things can add in some variation that may account for it.

gifbohane said:

The 20 inch barrel was fired on a very hot day the 16 much less hot.

Thank you all for the responses.

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That'll do it.

Varminterror said:

That’s a bigger spread than I would expect, but not out of the realm of reality. Generally, I expect about 40-45fps per inch for 223rem, but you have 260fps for 4”. One of the barrels is slow or the other is fast, or both. Doesn’t really matter in the scheme of things.

Click to expand...

I have a 22" 22-250 that is faster than a 26" one. It's an anomaly. But it showed me each does whatever it wants.

Not only all of the above
But what's the twist rate?
That will have an effect too.

If you match the right bullet for your AR's twist rate you get better stabilization, therefore better accuracy.
It's a wordy 17 page doc, but has illustrations.
http://www.ammoland.com/2017/02/ar-..._6f6fac3eaa-b97fed8334-21019609#axzz4ZMPFZMyg

Fired from different firearms on different days with unknown ES/SD or sample size, I don’t find the numbers shocking at all.

I do not know what "ES-SD" means?

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They are measures of how consistent the ammunition is, in a given firearm.

ES = extreme spread of muzzle velocity. The highest muzzle velocity minus the lowest muzzle velocity. SD = standard deviation of a set of muzzle velocities. This describes the expected spread of muzzle velocity - above or below the true mean of muzzle velocity based on a set of recorded muzzle velocities.

For temperature sensitivity you can put some rounds in the sun and others in the cooler, there is also position sensitivity but you won’t have that issue with the load posted above.

Four inches of barrel isn't going to make 260 fps difference. I've seen as much as 130 fps difference between barrels of the same length. Around 50-100 fps from equal length barrels isn't uncommon. I've seen 20" barrels shoot faster than 24" barrels.

For each one degree of temperature expect 1-3 fps velocity change.

You have a combination of a lot of factors working here

Agree with the others, too many variables and not enough data for a meaningful comparison / experiment.

gifbohane said:

Interesting that heat index matters.

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H335 is a ball powder... it is not known as a 'temperature stable' powder. Some load data (Speer comes to mind...) recommends a Magnum primer with H335 to ensure a good ignition in temperature extremes. I have noted some velocity differences in different temperatures, but I don't shoot in really cold weather anymore, but I've noted the same temp differences with factory ammo as well... so it is not unusual.

gifbohane asked:
I have 2 AR's one has a barrel length of 16 inches and my loads get 2715 FPS out of it. Used for hunting.
Second one with a barrel at 20 inches with the same reloads gets 2975 FPS out of it. Used for plinking.
All chronoed.
This seems to make sense but wanted to run it by you all.

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These figures are consistent with what I typically get.

I’m reading this thread and the OP numbers don’t seem quite right to me . I shoot that weight bullet using that powder in A.R. 15 rifles with barrel lengths of 16 inch 18 inch and 20 inch . Only going off memory because I don’t have my notes in front of me but I want to say 25 g of H335 gets me about 2960 FPS out of my 16 inch barrels . I don’t think I’ve ever shot a 55 grain bullet using H335 at any charge weight that resulted in less than 2800 ft./s from a 16” barrel. I’m getting ready to go to bed now but I’ll check my notes in the morning and update

http://www.accuratereloading.com/223sb.html velocity change as 1" of barrel is removed fron 22 inch to 10 inch. 3 Different powders.

2766 fps from a Colt 14.5" barrel M16A1 in 1979. My load was IMR 4198-21.5 grs. Hornady 55gr fmjbt bullets. LC brass.

NOTE: IMR 4198 will not produce maximum velociities in this cartridge.

gifbohane said:

METAL-

I am loading and testing with 24.5 grains not 25 grains.

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I understand that and is why I added at no charge weight that I've tried have I had a velocity lower then 2800fps from a 16" barrel

Example :

16" AR with mid gas
Win 55gr FMJ-BT
H-335 powder
CCI#400 primers
LC-mixed brass
COAL-2.240

Average FPS from 5 shots fired
24gr - 2803 , 24.5-2872 , 25gr-2936 , 25.5gr-3006 , 26gr-3112

As you can see it's pretty consistent that every .5gr increment the velocity goes up about the same amount . This is why I figured your 24.5gr load only getting mid 2700's and my 25gr load getting mid 2900's seemed inconsistent then what I'd expect . Meaning if we were going off your velocity my 25gr should be 2850-ish and if we were going off my velocities your 24.5gr should be 2860-ish . This also would seem to indicate that your 20" velocity is slow as well . That said , it could be mine are all fast but I'm to special for that to happen lol

I'll add that I ran a duplicate load development as above but switched out the standard #400 primers to magnum #450 primers . 24.5gr got be 2875fps and 25gr was 2910fps . The test was to see what the two different types of primers would be and the results were similar but way worse ES/SD with the mag primers .

There was a study that said the 5.56/.223 round does tend to lose 25 fps for each inch of barrel loss, and my very unofficial testing using the original data from the 24 inch test barrels and my 16 inch AR barrel seems to roughly support it.