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View Full Version : 16" vs 20" chrono results


Airacuda
April 26, 2012, 20:04
Homelandprotector posted up in another thread about 223/556 burning all the propellant by 16" and anything more slowing the bullet. I didn't think much of that Ideer.
So today at the range I took my trusty A3 out and fired 5 types of ammo thru the 16 and 20" barrels.:aug: Some I fired 8 each thru both,
and some more expensive...like the Hornady Superformance only 3 each. I then got the average by adding all and dividing by rounds fired.Following results are the averages.

PMC X-Tac Penetrator 62gn. 16"=2959* 20"=2945

Fed Am Eagle Tactical AE223 55gn. 16"=2920 20"=2949*

Silver Bear 62gn soft pt. 16"=2849* 20"=2830

Fed Am Eagle 50 gn Hp. 16"=3052 20"=3084*

Hornady superformance Varmit 53 gn Red tip. 16"=3235 20"=3273*

The asteric is the winner. As you can see not much seperates them.
The 62 grain ammo is faster in the 16's and the light ammo is faster in the 20's. I don't see enough difference to buy a 20" barrel if you already own an A3 with a 16". Accuracy was no noticeable difference. I was shooting a metal silhouette Life size at 200 yards thru the chrono and did not re zero for the 20" barrel. It was dead on changing from one to the other.
Finally the Fed AE223 and X-Tac had 100fps difference from the fastest round to the slowest. The Silver bear was more consistent with 50fps gap. Hornady 40fps gap, and the 50 gn Am Eagle Hp's were as close as the Hornady exept for 2 out of 12 that went 120 fps faster.

Anyway..I guess there may be something to only needing a 16" barrel. I stand Corrected.:bow:

Blain
April 27, 2012, 07:46
There is something wrong there.....the 20" will always be ~ 150fps better than the 16". This has been proven through countless examples. Either your Chrony is messed up, or your 20" is. Those results are too low for a typical 20".

Airacuda
April 27, 2012, 10:26
I'm not a chrono expert,and this one is plastic. However when the anal guy with the 50 Cal comes back out. I'll run some through his for comparison. Since he killed his with my Imbel,he has a brand new one. The 20" is from my A1 which has 90 rounds through it.
I will invertigate further and post up.

Wil-C
April 28, 2012, 21:35
those speeds, or that much lack of a differential between a 16" & a 20" barrel doesn't sound right.
I ran some handloads through a 16" that in the reloading manual were developed through a 20". I ran consistently 100-150 fps below the specified velocity the book cited for that load.

Airacuda
May 09, 2012, 19:28
Got a friend with a good chrono coming out Friday. Should have some results That evening.

paulb2112
May 10, 2012, 19:37
Who has all that hi-tech stuff out there in the boonies?
What are you guys shootin at, cow pies?:biggrin:
Hey Max. Youre not going to recognize your old friend next time you see it.

Airacuda
May 12, 2012, 14:22
Well, here's what I got. Like it or not. I took my A3 back out with the 16 and 20" barrel again and ran some rounds through a members chrono. A member who is in my opinion a Rocket scientist of reloading.
His chrono is right on the same page as ours. He looked at my previous data and the rounds I put through his. We also put 4 rounds down our Ranges 24" barrel AR before the hammer spring failed to hit any more primers. Those 4 rounds were 2990,3112,3152, and 3030. For a 3071 average. Thats only 122 fps faster average than my 20"barrel and 151 faster than the 16" using the 55 gn federal ball ammo. So that kills the "All the powder is gone in 16" thing".
After checking my numbers and my barrels, this is what the Reloading guy said. My 16" is very Good. Good in that the bullet when chambered has already engaged the rifling on both the 62 gn bullets.. This causes higher pressures and better speed. My 20" barrel was made in 1989. It, like the current AR's( 2 we checked), Do not.
So, as talked about in another thread here, my 16" has 100 to 150 fps faster speed than an equal length barrel AR.Now we know why.
My 20" 1989 Steyr barrel has a similar size throat(I mean the depth till the rifling is engaged by the bullet) to the AR's,so it does not have the initial pressure spike and therefore is probably 100 to 150fps slower at 16" just like an AR. The extra 4" brings it up to close, give or take with bullet weight. So my chrono is not broke neither is my barrel,though it could use some new tech.
Chrono guy used a dusty substance to put on the rounds and chamber them to see the where the rifling engaged the rounds on my barrels and 2 16" AR's That my Steyr had been known to be faster than on a previous chrono fun day.
So Take it for what it's worth and toss it in the trash if you like. I can't make this stuff up. I just like to shoot. Not do chrono crap.
Thanks for my friends bringing out their AR's and Chrono/Reloading Guru for his input and letting us fire his .50 Barret. We had a blast! And I got paid to be there.:p
Oh yeah, he gave an example to get the gear in my head working. Crimping a reloaded bullet,or not crimping. The crimped bullet will have a higher initial pressure and more speed than uncrimped.Therefore will take less powder to achieve the same speed.
Just remembered that little tidbit and figured I would toss it out there.