Sub 300 BLK recs

[CMV]

In the very near future I will start working on a subsonic 300 BLK load and I'm not sure where to start. I intended to use the Hodgdon data with W296 and that's why I selected that powder for my standard loads - there was data for both standard velocity and subsonic published with that powder.

But further research/reading & that may not be a good choice for everything I want to do.

This is what I'm looking for out of the load:

1. Reliably cycles an AR with 16" 1:8 barrel w/o opening up gas port. Rifle has carbine gas, carbine buffer & spring, non-adjustable gas block. I want this rifle to still cycle standard loads.

2. Suppresses well. Here's where I'm a little unsure. I think I'm at odds because I want a faster powder to suppress better but a slower powder to cycle better.

3. Accurate suppressed & unsuppressed. Suppressed may be a non-issue and just "accurate" is what I'm looking for. I've seen POI shifts, but not groups opening way up just from screwing on a can (that wasn't attributed to obscuring the sights on a pistol). But I've never played with a suppressed .308 so don't know.

4. Available & moderately priced bullets. I was planning on 220 gr Sierra MK HPBT to go with the Win296 powder & Hodgdon website load data. But at ~$45/100 & rare as hen's teeth right now I'm wondering if there's a good substitute. Something like a Hornady 208 gr HPBT Match or A-Max maybe? I won't be hunting with these so don't care much about any performance characteristic beyond consistency/accuracy. I really like every Hornady bullet I've used for everything else so far and I think they're a good balance between cost & performance in general. But I'm open to whatever works.

5. ??? There's probably more that I'm not considering yet. You guys who have been through this already can fill in some blanks for me I'm sure. This will be my first attempt at a subsonic load. I guess my .45 ACP & 147 gr 9mm are subsonic, but I wasn't reducing loads to get them that way.

If anything I have on hand will work, great, but I suspect I'll be shopping. For powders I have H335, Win296, Win231, & HS-6. For bullets I have 125gr Sierra HP Match & Hornady 150 gr FMJBT

 

[Nikdfish]

H110 / W296 is a good choice for supers but probably not so good for subs. It has a fairly narrow window of function for a given round. Back down a load a bit too much & you can end up with a squib. Short of a squib you'll see non linear changes in velocity for small changes in charge. It works best in fairly hot loads. For sub workups look for some of the more common powders used in subsonic loads.

I did some loads with MBC 245 grain hardcast with H110 & AR function was not consistant for lighter loadings. Only the supersonic loads were consistantly reliable for me (which was ok as I was wanting a heavy super & ended up with a good 1300+ fps load).

Nick

 

[osage48]

I have loaded several hundred of the Hornady 208 gr BTHP match with 9.7 grs 296. These have been used in a single shot suppressed rifle. The rounds were sub-sonic and shot well. I cannot comment on how well they will perform in an AR.

 

[Lennyjoe]

http://www.300blktalk.com/forum/viewforum.php?f=141 is a good place to view loads.

I'm waiting on the suppressor to come in before I start building subs. Til then, I have Lilgun and AA 1680 in the storage unit and about 600 cases.

I've loaded some 200 gr Speer Hot Core with 11.0gr of 1680 and 125gr Speer bullets with Lilgun to ops check the rifle and they all functioned fine. Not sure on the grouping as the intent was to only ops check the action (AR).

I plan on using either 208gr A-max or 220gr SMK bullets in the near future.

 

[Lennyjoe]

BTW, there are some 245gr lead rounds guys are using for subs too.

Are you planning on supressing the rifle?

 

[Lennyjoe]

http://www.missouribullet.com/details.php?prodId=182&category=6&secondary=&keywords=

 

[CMV]

Yes the rifle will be suppressed, but not 100% of the time which is why I don't want to mess with the gas system to make it function on subs. The suppressor will help with cycling subs.

 

[paintballdude902]

Back down a load a bit too much & you can end up with a squib.

to add to this you also need to remember that if you have too little powder in a case you need to be aware of the rare but still possibility of an explosion. the primer will ignite all the powder causing allot of pressure very quickly.


just an FYI i like to throw in when people are talking about light loads

 

[Lennyjoe]

AAA 1680 seems to be the best all around for 200+ gr sub loads.

 

[CMV]

I flashover a concern with that round? A 200gr+ bullet has to fill an awful lot of that case.

Is a filler necessary as a precaution?

 

[CMV]

I don't think flashover is a concern here. I can't hear powder moving when I shake the case. That bullet really takes up a lot of volume.



Anyway, my first attempt at subs was good & bad.

Good in that:

Rifle functioned fine. Cycled well, BHO on last shot.
1090 fps avg

Bad in that:

They were WAY low at 100 yds. I was expecting a 2" holdover or so, but these were at least 7" low. Should they be that far apart?

Load is:

Hornady brass
CCI #41
10.8gr A1680
208 Gr A-Max
2.210 COAL

Velocity spread was 1060 - 1101 fps, groups were 2.5" (but probably b/c of my holdover more than anything else)

Is my expectation wrong or is this unusual?

My other load & what the scope is zeroed for is getting better. I got one 1" group at 100 yds today. Others were mostly 1.25" - 1.5" with 2 holes touching & 1 flier.

It's:

Cut down LC brass
CCI #41
18.1 gr W296
125 gr SMK HP
2.200 COAL

2160 fps avg velocity with an 80 fps spread. I'm going to get a FCD - I think that might help the consistency. I'm measuring every charge twice on 2 scales, trimming carefully, sorting by HS... Maybe trying to taper crimp is the issue? Never tried to do that before so I might be doing it wrong.