Thread: 1st Shots from 300BLK AR.

Here are my first 1/2 dozen shots from my new 300BLK AR. The top 3 loose ones are factory Remington UMC 115 grn ammo and the lower clover leaf is my reloads using 125grn TARGEX HP Match and 17.1 grains of Hodgdons H110.
Shot at 50m off bags so I'm happy with the reloads, it's just under MOA. I bought the factory stuff so I had some control cases to double check my case sizing.

I'm using a JP silent captured buffer and spring and it's cycling fine with factory and 125 grain reloads. I shot some 220 grain Match Kings with 9 grains of H110 and the group was also a clover leaf but the gun did not cycle. I'll try the subs again when my can arrives as I think it will cycle ok with back-pressure. I will get the chrony out next time too.



Ray.

I doubt if you will get any joy with the 220s using H110, its simply too fast - need to slow down to 2207/H4198 - 10gr ish

Originally Posted by Spanners

I doubt if you will get any joy with the 220s using H110, its simply too fast - need to slow down to 2207/H4198 - 10gr ish

Spanners, do you mean with cycling using 220's and H110? I'll see what I have kicking around that's a bit slower burning.

Yip.
Let me know what you have and I'll check my data

Originally Posted by Spanners

Yip.
Let me know what you have and I'll check my data

I've got some 2209 and 2213SC which will probably be too slow, and some W748. I have a 30 year old tin of W680 which might be close but it's really too old to try... Might have to spring for some 2207.

Yip all too slow
10gr of 07 should have you going pretty good.
As always (with subs) start HIGH and work DOWN - start 11ish

Also whats you port size and position?

Originally Posted by Spanners

Yip all too slow
10gr of 07 should have you going pretty good.
As always (with subs) start HIGH and work DOWN - start 11ish

Also whats you port size and position?

Thanks, I'll try that. It's carbine length gas and the port is 0.105" ish.

Cheers, Ray.

0.105 is on the small size
0.110-0.120 is preferable, but some 2207 should sort you out

Nice! How you finding the JP silent captured spring?

Originally Posted by Grue

Nice! How you finding the JP silent captured spring?

Well, it's a bit quieter than a standard buffer and spring for sure, I'll know better when I have my can fitted. I've only bought the silent jobbie to use on this gun. I'll keep running the JP LMOS buffer and spring on my JP15 supermatch.

I chrony'd my reloads today, the 125 TARGEX are only going 2000 fps and I need them up around 2200 so I've gone up to 17.5 grns of H110.
The 220 subs were doing 1000 fps but not cycling so I got some AR2207 and have done some loads at 9.6, 10, 10.5 and 11 grains which I will try in reverse order tomorrow (Thanks Spanners).

Ray.

Your 125 load is pretty anaemic
150gr will uses ~17gr H110
110 loads are up at 20gr

Ok, I was working from the Hodgdon tables which suggested 16.7 to 17.8 (Max) with 125's. I've no doubt you're right, but I'll crack these off now anyway and then do some up towards 19.

Thanks, Ray.

Righteo, the 17.5 grains of H110 pushed the velocity up to 2100 so I'll go another 1/2 grain and recheck. The 2207 did a better job with the sub-sonics, all shots fully extracted and ejected but only a couple managed to catch and feed a new round. The velocity was still under 1050 fps so I can afford to try a bit more powder. My can is due later this week though, so I will not make any more changes until I've tried the current load with the can. As fallback plans, I can ease the gas port out to 0.110", and/or try lighter spring on the JP silent buffer, I think 1911 springs will fit and they are available in several tensions.

Ray.

Not just a pretty face

If you get to your speed for subs and still not functioning 100%, yes can open up the port a touch
Should be able to get lockback

Try a std spring and buffer - if its good there, then you can tune your JP setup
No point in opening up gasport if the buffer is whats changing things up.

I have recently fitted the new jp silent buffer to my gun
It replaced a jp lmos buffer and polished spring
Gun needed one and a half full turns more gas from the gas block to lock back on empty mag, so seems to require more effort.

Using TT2 on my mobele