2600+ FPS, 123 gr. bullet, 20" barrel... Problem?

[Vasux86]

I am relatively new to reloading and wanted to share a little curiosity (and maybe caution) I have about a load I developed. The rifle is a 20" Shilen barrel with a target crown; about 600 rounds through it. The most accurate load has been 123 gr. A-Max seated 2.235" COAL (.005" off the lands), 26.5 gr. AR-COMP, CCI 41, Hornady case. Below are some velocities from earlier today.

2643, 2634, 2634, 2603, 2598, 2576, 2601, 2682, 2641, 2622, 2631

Avg. velocity 2624
SD 28.7
ES 106

Both the velocity and extreme spread seem higher than should be expected with this combination of barrel length, bullet weight, and powder charge. When I did a load ladder with this bullet and powder combination, I got all the way up to 28.0 gr. without any visible signs of pressure on the brass (did not have access to chronograph during the ladder test).

By the way, I am not concerned about the velocity spread for the sake of accuracy, but I am concerned about having too high of pressure.

Does anyone have any ideas of what might be going on here? Did I possible just luck out and get a fast barrel?

[JASmith]

Checking against both Volume 2 of the 6.5 Grendel Reloading Handbook and the Ammoguide database shows that 26.5 grains is well below the heaviest AR Comp load listed.

Your velocity being well above the fastest listed in those sources suggests that something is not working the way it should.

First, have you chronographed any factory ammunition? BTW there is a good chance that factory AMAX or SST will jam in your lands if your handloads with a COAL 2.235" are just .005" off of the lands. Hence you should try cycling a live factory round or two to see if you get engraving marks o the ogive.

Have you done a ladder in overall length too?

[Vasux86]

I have not checked the velocity of any factory ammo. It's been hard to find factory ammo in stores, but I will keep an eye out for it. If I can get my hands on some, I'll try to cycle it and check the velocity.

Ladder test for COAL have been done, but without velocity data. The ladder test included 2.215"-2.245" cartridges.

When you say something is not working the way it should, what do you think could be causing this?

[37L1]

Your chrono may be off.

[Drillboss]

I am relatively new to reloading and wanted to share a little curiosity (and maybe caution) I have about a load I developed. The rifle is a 20" Shilen barrel with a target crown; about 600 rounds through it. The most accurate load has been 123 gr. A-Max seated 2.235" COAL (.005" off the lands), 26.5 gr. AR-COMP, CCI 41, Hornady case. Below are some velocities from earlier today.

2643, 2634, 2634, 2603, 2598, 2576, 2601, 2682, 2641, 2622, 2631

Avg. velocity 2624
SD 28.7
ES 106

Both the velocity and extreme spread seem higher than should be expected with this combination of barrel length, bullet weight, and powder charge. When I did a load ladder with this bullet and powder combination, I got all the way up to 28.0 gr. without any visible signs of pressure on the brass (did not have access to chronograph during the ladder test).

By the way, I am not concerned about the velocity spread for the sake of accuracy, but I am concerned about having too high of pressure.

Does anyone have any ideas of what might be going on here? Did I possible just luck out and get a fast barrel?

My load through a 20" Shilen barrel using 123 gr SST's and 26.5 gr of AR-Comp gave me 2500 fps. I was using S&B SR primers and was loaded a little longer to 2.267". I don't think I checked any factory velocities that time, but on another day, 27.8 gr of AR-Comp gave me 2538 fps and factory Hornady SST's came in at 2624 fps. On the day I clocked the 26.5 gr load, a 27.7 gr load averaged 2587 fps.

Mine were SST's versus your AMAX, but at that load I would think your pressures are fine. Agree with checking them against some factory loads.

[Squatchy]

I averaged 2488fps with factory 123gr amax through my 20" odin works barrel shooting through a crony gamma master. Not sure if that will really help much. I can offer some advice- if you are going for velocity dont use TAC. Accuracy is great though

[kmon]

How many shots through the barrel, have seen more than one barrel speed up after 200 rounds or so. Also check your power scale, make sure it is measuring what you think it is (check weights help). Same brass, different lots can have different volume leading to more of less pressure

[LRRPF52]

How many loads have you fired on the Hornady brass, and what is the length of the brass itself before you seated any bullets?

What scale are you using?

[6.5 Grendel]

My go to load for my 20" BHW barrel is 32.3 grains of Leverevelotion with a 123gr sst for avg. 2610 fps.

[PredatorDown]

I agree with others that either the chrono or scale may not be working correctly. My 22" barrel loaded with 123 amax and 27.6gr of AR-Comp gets me to 2530, with velocity backed up with drop charts to 1000+ yards.

[Vasux86]

The barrel has about 600 rounds through it. The brass has been reloaded six times, and before the fifth reload each brass was trimmed to 1.520" (+/- .0001").

My scale should be good. I use a Frankford Arsenal DS-750 electronic scale, which comes with a calibration weight that I use several times throughout each reloading session. The scale has been double-checked with a beam powder scale just to make sure it's good-to-go. Since the loads are still being developed, I weighed each charge after throwing it. So I have enough here to trust that the powder charge is accurate.

The chronograph should also be good. On a different day, I shot a different rifle over it to test it out. The velocities were right where I expected them to be. It's possible that since then something got out of wack with the sensors, but the chronograph was good at one time and was running off new batteries when the reloads were shot over it.

As you can see, many possible explanations have been eliminated. Thus leaving me with one hand on my hip and the other scratching my head.

Does anyone have any thoughts on the ES? As mentioned earlier, this seems much higher than should be expected. I wonder if it may be a clue that there truly is something wrong with the chronograph...

Later this month I am heading out on a hog hunt. May try shooting long range and checking the drop to see how it compares to what I am expecting based on velocity. Will also see if I can borrow someone else's chronograph to shoot over.

[McFireFighter]

If I missed it, sorry. How far are you placing the chronograph from the muzzle?

[McFireFighter]

http://precisionrifleblog.com/2012/07/20/chronograph-accuracy-tips-15-practical-tips-to-increase-accuracy-reliability/

[PrairieWindDynamics]

Go out to 900-1000 yards and check the drop. If you don't have the range to go out that far, you can go shorter, but the data you collect won't be as accurate. If you are wanting to find the true MV, you need to make sure your scope is tracking correctly, if you just want to make dope, you can use the error in your scope and be fine, but your MV will be off from the true velocity.

This is how all MV should be calibrated, regardless of what your chrono says at the muzzle.

The ES & SD are high because your brass is getting hard and needs annealed. I don't know why, but non of my hornady brass hardens at the same rate. Meaning some will become harder faster than others, even with the same amount of firings on the case, causing some pretty extreme spread.

[JASmith]

...The ES & SD are high because your brass is getting hard and needs annealed. I don't know why, but non of my hornady brass hardens at the same rate. Meaning some will become harder faster than others, even with the same amount of firings on the case, causing some pretty extreme spread.

I had similar experiences and am now annealing even though there are questions about how uniformly one can anneal outside a factory setting.