Chrono testing report on my new 16-er with Faxon barrel

[grayfox]

I've been doing some chrono testing on my new 16-er build, with a Faxon gunner 16" barrel. I'm liking this one, mostly looking at it for a walking-around weight rifle... but some of my chrono data has me a bit puzzled.
I'm ~100 rounds downrange with it so far.
My routine is to speed test 4-round sets of handloads or factory's and look for low std deviations, ideally in the single digits. This method has shown me several good shooting nodes over several different rifles. I use my magnetospeed.
All handloads are Hornady brass, cci450's.
Anyway, 2 or 3 factory loads seem to do well for this one:
1. Federal AE 90 gr TNT - avg 2840 sd= 7, I've done 2 4-round sets of these.
2. Hornady Black, 1 set of 5, avg 2360 sd=9.
3. Hornady 123st avg 2405 sd=9
4. The Fusion 120 is not too bad, showing 2429 and sd of 14.

And a couple of handloads also tested out well:
4. 100 gr Amax, 29.1 xbr, 2584 sd=5
5. 100 gr Amax, 33.1 cfe223, 2668 sd=3
6. 100 gr Nos BT, 29.8 xbr, 2662 sd=4.

Now the puzzling results. My other Grrrrs take 123 sst's usually 30.8-31.4 (this last one is for the howa), the ARs (18" both) use the 30.8, 2508 give or take with low sd (like 6-8 iirc). But for this 16" above 31.0 results start to scatter and definitely drop, and nowhere near what I thought I would get (2470-ish? for 16").
31.0 2433, sd=10.7
31.2 2451, sd 25.5 (!!!)
31.2 (2d set) 2447 sd=24.5 (!!!)
31.3 2437 sd=12.5
31.4 2444 sd 22

I think the gun is telling me to stay below 31.0. So that's what I will try next time. "Happy gun, happy shooter..." lol!

But the velocities do seem to be slow for this bullet. All of this is a bit of a surprise to me, I have to ponder it a bit...

[LRRPF52]

If those last speeds are with CFE223, everything looks normal in that charge weight range of 31.0-31.4gr because you aren't getting much resolution with .2 and then .1gr increments. With .1gr increments, you would need a Sartorius to kick out the loads, but you are getting some resolution still. If it were my ladder work-up, there would be at least .2gr increments (I usually do .3 and see 12-28fps average increase in speed per .3gr step).

I think these barrels are rifled with a different land/groove depth, so they might not pressure up as fast as the rifling in other barrels.

That should give you a little more room for accuracy nodes on the top end actually.

In a conventional-rifled test breech with SAAMI chamber, we hit 50,000psi at 31.9gr of CFE223 with the particular lot of powder and 123gr Hornady bullets being used for those tests.

If you look at Hornady's data, they include the 120gr GMX in their 120-123gr class of bullets, which limits the top end to 31.2gr of CFE223, but is mild for a 123gr SST or AMAX.

But when you look at their 129gr load data for the SST, Interbond, and Spire Point, the max charge weight they had was 31.7gr of CFE223.

The 129gr cup and core Hornady bullets with the same jacket construction as the 123gr SST build pressure faster than their lighter counterpoints due to case intrusion, mass, and bearing surface.

You might consider working up some more, realizing that 32.0gr is about where the cut-off would be in a conventional rifling profile and SAAMI chamber.

We should have a little bit more room to work with in the Faxon barrels.

What COL are you using?

[grayfox]

COAL of 2.240.
I did the 0.1's b/c I thought 31.4 was going to be my top end and 31.0, 31.2 (1st set) seemed a bit weak based on what I got out of my 18" ones...
Didn't realize there could be room above 31.4 for this combo, so maybe I can try that. I had noticed the 31.7 of the 129's as you say, but didn't yet make a connection to the 123's.

I normally try for 0.2 increments, I like to be just a bit smaller than 1% powder chg (0.3 for the 30 grain-ranges) so as not to miss something.

In fairness to the barrel I should also confess that I was using new brass, not 1 or 2x which is what I usually do... this chamber stretches the brass to about 1.220(up to 1.224) on the comparator, vice the 1.215 of the howa.

I'm not unhappy if the results stay down in these 2400-ish for this rifle, but would of course like to see the 123's a bit peppier. Speed is always nice (!) as long as it's safe speed.....

[VASCAR2]

Here are the velocities I got from my Faxon 16” group buy barrel with a Caldwell chronograph set at 10’ on a 70 degree day.

My velocities are in the same range as yours.

100 grain A-Max 29.0 grains H-335

2476
2464
2426
Error
2502

Avg 2467
Ext spread 76
SD


123 grain A-Max 31.0 CFEC223
2428
2416
2376
2426
2388

Avg 2406.8
SD 23.48

123 grain NCC 31.0 grn CFE 223

2445
2435
2417
2435
2448
Mm. 2436
SD 12.12

[Sticks]

If this is a GB Faxon barrel, then the rifling is not the norm. BFT modified the specs on it to make the grooves shallower than norm.

[grayfox]

Boy you guys are up early!

I got this one from JoeBob... my GB barrel is an 18" (and somewhere on the way...) and definitely waiting on it! That one should be my last build for a while.
VC2, looks like the 2 barrels are in line as you say! I'm looking at taking the cfe charges up based on '52s insights.
I suspect that I can find nodes at 2390-2400 and around 2470-2475, so will be interested if my theory bears out.
It's a good barrel I think and has some loads I'll definitely use for it, but am looking to find my load also for the 123s.

Once again the horde shines bright!!!

[LRRPF52]

What I found in my AA 16" Grendel MLGS (old school Shaw barrel) with SAAMI chamber was that I could easily get past 2500fps with CFE223 and not exceed 50ksi.

123gr AMAX
Lapua brass 1x
Rem 7 1/2 primer
2.272"-2.277" COL
60˚F
Beta Chrony Master 15ft from muzzle

31.1 2489fps
31.4 2520
31.7 2532
32.0 2555 (50,484psi) I wouldn't produce a load past this point in the AR15.
___________________
32.3 2572 (52,075psi)
32.6 2598
32.9 2612 (This is where I would stop in a bolt gun or the CMMG Anvil at 55,257psi.)
33.2 2640 slight primer cratering
33.5 2698fps slight cratering, time to stop

If I was one of the other novice hand loaders I see frequently, or in my younger years, I might excitedly declare the 32.9gr as magic with exclamations of "NO PRESSURE SIGNS!". Then my older self would tell the younger self, "See those velocity readings? There's your first excessive pressure signs.

You'll notice that between 50ksi and 55ksi with CFE223/123gr AMAX, we only have 57fps difference in speed. Is it worth the extra 5,000psi over the working pressure of the cartridge?

I'm not competing with a 16" Grendel at 1000yds, so no, it isn't. By staying at 50ksi, my brass lasts forever, I don't stress the gun, and everything just behaves very well.

With the reduced depth rifling, there will be a little more allowance for speed, so I'm interested to see where you end up at. It won't be earth-shattering, but any gains are welcome.

I have a 12" Group Buy barrel that I will find out where the same ladders are at.

[BluntForceTrauma]

For their own 65G barrels, Faxon uses standard 5R rifling.

For the group buy barrels made for us by Faxon, they use my custom rifling with reduced lands.

So the Faxon Gunner that Grayfox has, has standard rifling.

His group buy Faxon 18 from here will have my 5R-EE (Easy Engraving) rifling.

Guys who currently have group buy F12s and F20s have 5R-EE and can slowly begin experimenting with the 5R-EE rifling. (The first batch of group buy F16s has standard 5R rifling; future batches will be 5R-EE.)

[grayfox]

What BFT said. Apologies if it sounded differently.
And like I said, the barrel's doing fine by me. I do plan to try above my earlier 31.4, watching for pressure signs, next time I get it to the range, following '52s comments; it'll be with Hornady brass, as that's what I have on hand.