300BLK subs & barrel length

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CMV

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I have a 16" barrel now. If I go to a 7.5" or 9" barrel will I need to increase my charge weight to keep same velocity? I got them to ~1050fps and would want to stay in that velocity neighborhood with the shorter barrel. No idea since this is the only 300BLK I've ever had.

Would be going from carbine gas to pistol gas, 16" to 7.5" or 9" barrel. Loads are A1680 with 240gr MBC or 220gr SMKs.
 
I think it was the 2018 Hodgdon annual manual that did some test in the 300 BO with long and short barrels. The subsonic loads varied by just a fraction of weight. I'm sure they tested using CFE-BLK.
 
I recently worked up some sub-sonic loads for my two 300 BO firearms. This is the results of my last round of chrono measurements in both my 16-inch Ballistic Advantage barrel to the 9-inch AAC barrel.

My reloads:
Barry 220 gr (10.1 gr IMR 4227) 1040/983.8 fps
Maker 200 gr (10.2 gr A-1680) 999.6/907.8 fps
Maker 220 gr( 10.4 gr A-1680) 1066/977.2 fps
Factory:
Rem L300AAC4 220 gr 1144/1057 fps
Hornady Sub-X 190 gr 1117/1056 fps

For me I have not bother with working up a load specific from my short gun. I simply recalculated my ballistic table for the slower muzzle velocity and ballistic reticle my 9-inch pistol has.
 
Mine is going to be a replacement - no more 16". Its upper is getting torn down, getting the pistol length barrel & gas, & will be be a 2nd upper for my SBR. So will need my sub loads to be appropriate for it. Looks like very generically you are -100fps w/ the pistol-length barrel. To me, that's enough to rework the load to get it back in the 1050 neighborhood.....

The good news is I only have a very small amount of 300BLK subs loaded up so not pulling anything or wasting much
 
The average lost is 76 fps. If I was switching all my 300 BO to short barrels I would probably re-work my loads but I like my 16-inch gun and plan on keeping it and don't want separate ammo for each gun.

With a 50 yard zero I was reliably hitting a 6-inch plate at 150 yards and a steel IPSC at 200 yards with my 9-inch pistol and the 3X optics on it so I was pretty happy with what I have worked up.
 
Here a link to a video from MrGunsandGear on the MV and ME for different 300BLK barrel lengths and (boxed) loads. It will give you an idea how much loss you will get between a 16" barrel and shorter ones.
The ammo he was using was boxed ammo (supers and subs).



My thoughts on increasing the charge to get the same MV from your SBR... go for it. One of the main reasons for hand loading is to customize the ammo for YOUR rifle.

If you had a carbine 300BLK and an SBR 300BLK it would be a different story. You might want to have a common round that was subsonic in both short and long barrel lengths.
 
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I have a 16" barrel now. If I go to a 7.5" or 9" barrel will I need to increase my charge weight to keep same velocity? I got them to ~1050fps and would want to stay in that velocity neighborhood with the shorter barrel. No idea since this is the only 300BLK I've ever had.

I would say to keep the same velocity you will need to increase the charge weight. And depending on your variables (Ex. are you already at a maximum charge?), you may be over pressured trying to maintain that same velocity.

http://www.hodgdonreloading.com/rel...-barreled-rifle-require-different-reload-data
 
Went with 7.5" barrel, straight (not pigtail type) pistol gas tube, and basic low profile non-adjustable gas block.

So this is what I'm thinking for first load to chrony & test for accy. Let me know if good/bad if you run a barrel that short. Will be 100% suppressed.

LC reformed brass
CCI #41
11.0gr A1680
MBC 245gr (~240gr actual) hitek coated cast
2.122 COAL

This is a bump up from 10.6gr I was loading for 16" carbine gas upper and slightly shorter OAL was at 2.200. Didn't really have feed issues at that length, but seems long for that blunt profile. But googling around seems a lot of guys settle around 2.120" length for those big MBC bullets.

Loaded 15 of the above to test. Always hate this part.....want more if it works well to get optic squared away & verify elevation at distances. Want fewer if it sucks & need to pull them down :)
 
11 grains with that weight should keep you below supersonic.

Nice. Hopefully I won't need too many tweaks. I know lot here enjoy working up loads, experimenting, trying new things. That's great & I'm really glad people enjoy loading as hobby or recreational activity. Sadly that isn't me :) More of a chore, so when something "just works" I'm thrilled.

Hopefully enough time & decent weather this weekend to go try it all out. I've had this 300BLK rifle put up for a while so almost like a new toy. And I guess with the shorter barrel it kind of is :)
 
Went with 7.5" barrel, straight (not pigtail type) pistol gas tube, and basic low profile non-adjustable gas block.

So this is what I'm thinking for first load to chrony & test for accy. Let me know if good/bad if you run a barrel that short. Will be 100% suppressed.

LC reformed brass
CCI #41
11.0gr A1680
MBC 245gr (~240gr actual) hitek coated cast
2.122 COAL

This is a bump up from 10.6gr I was loading for 16" carbine gas upper and slightly shorter OAL was at 2.200. Didn't really have feed issues at that length, but seems long for that blunt profile. But googling around seems a lot of guys settle around 2.120" length for those big MBC bullets.

Loaded 15 of the above to test. Always hate this part.....want more if it works well to get optic squared away & verify elevation at distances. Want fewer if it sucks & need to pull them down :)
I bought a couple boxes of those bullets recently. I haven't loaded any yet. Though I don't have access to AA1680, I'm curious how the bullets will turn out for you. My barrel is either a 7.5" or 8.5".
 
I bought a couple boxes of those bullets recently. I haven't loaded any yet. Though I don't have access to AA1680, I'm curious how the bullets will turn out for you. My barrel is either a 7.5" or 8.5".

They were OK in my 16" & this one is same twist rate so assuming they will be fine in the shorter barrel. Sure hope so - lot cheaper option than the 220 SMKs I started out with. Aren't crazy accurate but good enough for what they are.

I'm sure lots of other stuff besides A1680 is good. Honestly I just went with H110/W296 & A1680 when I got into 300BLK because that's what most here & on 300BLK talk were doing at the time

Oh....I have an envelope from you arriving in my mailbox today :) If I get off work early enough I might be able to catch mailman to get your box in today's mail...
 
With the pistol powders used with the 300, your looking at +/- 100 FPS from 16” to 9”, the same load will be “ in the neighborhood” unless you live in a small neighborhood.
 
They were OK in my 16" & this one is same twist rate so assuming they will be fine in the shorter barrel. Sure hope so - lot cheaper option than the 220 SMKs I started out with. Aren't crazy accurate but good enough for what they are.

I'm sure lots of other stuff besides A1680 is good. Honestly I just went with H110/W296 & A1680 when I got into 300BLK because that's what most here & on 300BLK talk were doing at the time

Oh....I have an envelope from you arriving in my mailbox today :) If I get off work early enough I might be able to catch mailman to get your box in today's mail...
Right now I have 2400, 300-MP, and a couple others on hand, which should work. But I recently wounded my chronogragh. Fortunately, we're not close on max chamber pressures. :)

Okay, thanks for the heads up. I think we're good!:thumbup:
 
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