PRS Trainer Load Development - .223 Rem, Origin, Bartlein, Razor Gen III, MPA Matrix Pro

[stevieb92]

Hey all,
I thought I would share some load development results from my PRS Trainer rifle. It is based on a Zermatt Origin, wearing a 26 inch Bartlein heavy palma barrel chambered by Southern Precision Rifles in .223 Rem (Wylde chamber), topped with a Vortex Razor Gen III, and sitting in a MPA Matrix Pro chassis. I'm planning to shoot this rifle in TAC division PRS matches in the local area and use it for centerfire PRS training. Initially, I used a load of 24.0 gr of Varget with a Hornady 75 ELD-M and in Starline brass lit by a CCI 400 srp. During the initial shots, I did a very short shoot/clean cycle and then began shooting it with this load. It provided decent results and I noticed the muzzle velocity climbing. During the last 30 shots or so, it has stabilized so I figured it was time for load development. That put me right at 200 rounds down the barrel.

Anyway, on to the meat of the story. My goal was roughly a half minute and single digit SDs. Shouldn't be that hard, right? I loaded a test using charge weights varying from 23.4 up to 25.2 in 0.2 gr increments. Then I shot them round robin style. I waited about 2 minutes between shots and at least 5 minutes in between shot strings. The results are below. I'd say that I am happy and will pick the 24.2 charge and load some of those up and do some shooting to confirm it's a good load. My reasons for picking the 24.2 was two parts. The charges were dispensed using an ATV4 on an A&D fx-120i. First, obviously the group size is small enough for my purposes and second, the point of impact between the charge directly below and above it appear to have the same elevation on the target. Lastly, the SD for the 24.2 was 10, so it was close enough to single digits and with some work I could possibly get it smaller. On to the data and pics...

Charge / Avg Vel / ES / SD / MOA
23.4 / 2738 / 25 / 11 / .56
23.6 / 2748 / 23 / 9 / .95
23.8 / 2795 / 65 / 25 / .34
24.0 / 2841 / 54 / 22 / .70
24.2 / 2853 / 24 / 10 / .36
24.4 / 2892 / 43 / 19 / .82
24.6 / 2904 / 43 / 16 / .83
24.8 / 2928 / 50 / 18 / .56
25.0 / 2944 / 39 / 15 / .90
25.2 / 2958 / 25 / 11 / .48

The primers looked a little flat on the corners in the 25.2 charge, but the bolt lift was the same as each other charge weight. It looked like there might be a good spot there around 25.2, but I have no reason to hot rod this, so I'll stick with 24.2 and call it done. Thanks for reading.

 

[Ned Ludd]

Looks good! Based on your velocity data, I'd guess 24.0 to 24.2 gr were hitting the same node, whereas the velocity increases markedly at 24.4 gr (+40 fps). I'd bet that 24.0, 24.1, and 24.2 gr would all perform similarly. Because the 24.4 gr velocity increased markedly, it is likely that 24.2 gr load is at the upper edge of the "window". Knowing this, you could easily drop the load a tenth or two in hotter temps, if necessary. FWIW, given the [much] larger ES/SD values at 24.0 and 24.4 gr, I suspect the much lower ES/SD for 24.2 gr is an anomaly caused by small sample size. I wouldn't be surprised if you see that increase on subsequent outings. Regardless, I wouldn't spend a huge amount of time (or barrel life) trying to obtain ES values under 20 fps or single-digit SDs. It is very difficult to accomplish that feat with any consistency using the relatively small .223 Rem case.

Thanks for posting!

 

[Zero333]

You might also try the Horn. 75 gr BTHP. And the 77 SMK is always worth a try. I found the Hornady BTHP Match bullets to shoot better than their ELD-M counterparts. At least in my 223, 243 and 308 rifles

 

[Cfshooter]

5 looks like a good spot to me! I agree with Ned, don’t chase single digit SD, just worry about the target, espy with 223.

 

[stevieb92]

Looks good! Based on your velocity data, I'd guess 24.0 to 24.2 gr were hitting the same node, whereas the velocity increases markedly at 24.4 gr (+40 fps). I'd bet that 24.0, 24.1, and 24.2 gr would all perform similarly. Because the 24.4 gr velocity increased markedly, it is likely that 24.2 gr load is at the upper edge of the "window". Knowing this, you could easily drop the load a tenth or two in hotter temps, if necessary. FWIW, given the [much] larger ES/SD values at 24.0 and 24.4 gr, I suspect the much lower ES/SD for 24.2 gr is an anomaly caused by small sample size. I wouldn't be surprised if you see that increase on subsequent outings. Regardless, I wouldn't spend a huge amount of time (or barrel life) trying to obtain ES values under 20 fps or single-digit SDs. It is very difficult to accomplish that feat with any consistency using the relatively small .223 Rem case.

Thanks for posting!

Thanks for the reply! I agree, I'm not going to chase for single digit sd. This isn't a bench rest rifle, so the load at 24.2 should work just fine for PRS. Or on second thought, maybe I will split the difference between 24.0 and 24.2 and pick 24.1? lol

 

[stevieb92]

You might also try the Horn. 75 gr BTHP. And the 77 SMK is always worth a try. I found the Hornady BTHP Match bullets to shoot better than their ELD-M counterparts. At least in my 223, 243 and 308 rifles

I have a bunch of the 75 bthp and 77 smk, so maybe I will play around with them a bit.