Recently had the need to have an AR15. Palmetto Arms 16" barrel Carbine Length tube.

I built the above for hog hunting on a friends ranches where shooting one or 2 hogs with your bolt action does not do enough damage.
If I can just learn to shoot the Ar as well as my 7mm.

I did a Velocity check and wondered about the differences 223 vs 5.56. I understand that the 556 can take more barrel pressure but seems if you shoot a
55 gr bullet and the factory lists the same velocity at the barrel then they should be the close to the same Vel at 15-20 feet at the machine with individual brands possibly a little different. Even funnier since Lake City makes the Frontier and Eagle brands.

These are 5 shot groups shot two weeks ago 97 degrees and the gun was cooled after each group.

What have you found when you checked your ammo?

Factory Measured
Brand Wt gr type listed actual
Hornady 55 SP 3240 2916
Monarch 55 SP 3248 2882
Frontier 55 SP 3240 2836

5.56
Eagle 193 55 FMJ 3165 3075
Frontier 193 55 FMJ 3240 3045


Eagle 855 62 FMJ 3020 2988

Just cannot figure out why Lake City does not make a 5.56 with a spire point because if you look LC makes both the Frontier (Hornady) brand using Hornady bullets AND American Eagle (Federal) brands for their cheaper budget line.

Could be the box of Hornady hunting bullets head stamped Hornady made down the road at their place is special other than just in price and 80 ft/sec. At Academy the FMJ bullets run less than 7$ a box and the sp bullets run less than 10$ with the Hornady box running about 20$. That is a lot of difference for under 100 ft/second.

Manufacturers use a 24" pipe to market the velocity of their 223's and a powder used to match that barrel length. You have a 16" pipe. 8" is a lot to give up regarding velocity.
Federal is providing 223 ammo designed to perform better in a short barrel for both 223 and 308. It is in their Fusion offering. Probably using faster burning powders.

I am impressed with the velocity that I got with the 16" barrel with carbine tube.

What I do not understand if if both say the same vel on the box that why the consistent 100+ feet per second difference in the sp and the fmj at 15 feet?

look at the eagle 55 fmj box 3165 crony 3075 the fastest of the 55gr bullets.

Just interesting that most use 3240 at the vel for 223 and 5.56 with 55gr but look at the real differences. I used 5 shot groups but if one was really fast or slow I took it out of the average.

What it shows me with the grouping that there is no need to go buy expensive sp rounds if you get 1- 1.5 inch 5 shot gropes and I prefer sp Hornady bullets but Eagle or the Eagle 62gr 855s would be the round other than they do not shoot as well as the 55's in my ar for longer shots and heavier bullets.

Can't directly read pressures off a chronograph. That said, friend in the industry told me most makers got tired of worrying about sustained use of factual 5.56 through a .223 throat. So for some (unknown to me) years .223-stamped AR-15 barrels have had 5.56 chambers.

Also suspect most commercially mfg "M193" and "M855" is loaded to some lower pressure spec.

Still have alot of old ammo, tho. My '80s SA M193 averages 3390-ish fps through 20" M16A1 uppers (1:12). Individual rounds break 3400 fps.

I feel lucky the little Palmetto 5.56 16" barrel will shoot the 55gr rounds as fast as it does. Wish the 62 gr would do as well.

Still cannot fig out WHY the velocity difference between the 55 grain FMJ and 55 grain Spire points if both are listed at 3240 by the factory and we get that much differences in velocities between the fmj and sp. THEN on top of that the American Eagle is that much faster that the other FMJ's and is listed at only 3165 fps by the factory compared to 3240 fps most use.

Noticed on the Hornaday site they now list Frontier as their new house brand while both Frontier and American Eagle (Federal) are loaded by Lake City.

Now if they would start loading the spire points in 5.56 in the house brands.

quote:

Originally posted by JimTx:
I feel lucky the little Palmetto 5.56 16" barrel will shoot the 55gr rounds as fast as it does. Wish the 62 gr would do as well.

Still cannot fig out WHY the velocity difference between the 55 grain FMJ and 55 grain Spire points if both are listed at 3240 by the factory and we get that much differences in velocities between the fmj and sp. THEN on top of that the American Eagle is that much faster that the other FMJ's and is listed at only 3165 fps by the factory compared to 3240 fps most use.

Noticed on the Hornaday site they now list Frontier as their new house brand while both Frontier and American Eagle (Federal) are loaded by Lake City.

Now if they would start loading the spire points in 5.56 in the house brands.

Some of the velocity difference between the two 55 grain bullets, one being a FMJ and the other a spire point is because of the difference in bearing band surface area. That's why reloading books tell you never use data from one bullet manufacturer for loading a bullet from another manufacturer even if they are both the same weight and type, that is soft point, hollow point, etc.

5.56 loads are proofed on a 20 inch barrel and 223 loads are proofed on a 24 inch barrel. That's why it appears the 223 equals the 5.56 even though the 5.56 is loaded to a much higher pressure. Also the 5.56 has a longer and fatter throat then a 223. That and the higher pressure of the 5.56 is why you shouldn't shoot them in a 223. In some instances the 5.56 bullet is up against or jammed in the 223 leade in or rifling thus really raising the pressure. Most the time you get away with it. It's the reverse with the 308 and 7.62 NATO. In this case the 308 is loaded to a much higher pressure.