300 AAC not cycling subs

fireguyty

fireguyty

Sergeant
Full Member
Minuteman
Jul 24, 2010
839
13
47
Las Vegas
#1
Guys,
I built a rifle with the following specs:

Rifle:
9" 1-8" twist Delta Company 300 AAC blackout
Donor Bushmaster bolt carrier group
Pistol length standard gas system with standard gas block
Sun Devil upper and lower
DPMS lower parts kit
Donor Bushmaster carbine buffer and tube
Giessele (sp?) DMR high-speed trigger

Sub load:
Resized and trimmed LC 223 brass
CCI 400
9.4 H110
208 a-max at mag length

Suppressor:
338 Ti SAS QD over muzzle break

It runs great with 135 supersonics and same powder at a higher charge. Even locks the bolt back. When I put subs through it, it short strokes. I am 95% sure that I need a different weight buffer, but don't pretend to know what the weight is from the factory carbine Bushmaster tube, spring, and buffer that I stole for this build, or what I should use to solve this problem........or if that is the problem.

Any suggestions would be appreciated.

Ty
 
#3
Re: 300 AAC not cycling subs

This is exactly why I'm trying to get the information out there in other threads and I'm met with stiff ridicule just for trying to make others aware.

Neither the AAC nor Noveske (probably others too) barrels below 10" will cycle subsonic rounds w/o the suppressor attached. There's not enough pressure. You could open of the gas port but then you'll over-gas if you ever shoot supersonic ammo suppressed.
 
#5
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jer</div><div class="ubbcode-body">
Neither the AAC nor Noveske (probably others too) barrels below 10" will cycle subsonic rounds w/o the suppressor attached. There's not enough pressure. You could open of the gas port but then you'll over-gas if you ever shoot supersonic ammo suppressed. </div></div>
I am running suppressed.
 
#6
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Force_Multiplier</div><div class="ubbcode-body">I had the same problem w/ short stroking subs w/ H110... with AA1680, not a problem</div></div>

I have some of this powder, and will try it. Thanks!
 
#7
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jer</div><div class="ubbcode-body">
Neither the AAC nor Noveske (probably others too) barrels below 10" will cycle subsonic rounds w/o the suppressor attached. There's not enough pressure. You could open of the gas port but then you'll over-gas if you ever shoot supersonic ammo suppressed. </div></div>
I am running suppressed.

</div></div>

Ah... I see. Welp, just ignore me then. Nothing to see here. lol
 
#12
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body">300 BLK will not cycle with H110. (Not Enough Gas)
AA1680 is what you need.</div></div>
H110 cycles perfectly for me subsonic, but I have a 16" barrel.

However, one thing I have noticed using H110 and a Chrony is that the velocity changes dramatically if the cartridge warms up in the chamber. First shots and rapid shots are at least 100fps slower than rounds that sit in a warm chamber for several seconds or longer.
 
#13
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bedlam</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body">300 BLK will not cycle with H110. (Not Enough Gas)
AA1680 is what you need.</div></div>
H110 cycles perfectly for me subsonic, but I have a 16" barrel.

However, one thing I have noticed using H110 and a Chrony is that the velocity changes dramatically if the cartridge warms up in the chamber. First shots and rapid shots are at least 100fps slower than rounds that sit in a warm chamber for several seconds or longer.
</div></div>
The 16" barrel is why it is working.
H110 will do some crazy stuff under adverse temperatures.
Worse so in sub-zero conditions.
For this reason, as well as others, I use N110 instead.
 
#14
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body">Guys,
I built a rifle with the following specs:

Rifle:
9" 1-8" twist Delta Company 300 AAC blackout
Donor Bushmaster bolt carrier group
Pistol length standard gas system with standard gas block
Sun Devil upper and lower
DPMS lower parts kit
Donor Bushmaster carbine buffer and tube
Giessele (sp?) DMR high-speed trigger

Sub load:
Resized and trimmed LC 223 brass
CCI 400
9.4 H110
208 a-max at mag length

Suppressor:
338 Ti SAS QD over muzzle break

It runs great with 135 supersonics and same powder at a higher charge. Even locks the bolt back. When I put subs through it, it short strokes. I am 95% sure that I need a different weight buffer, but don't pretend to know what the weight is from the factory carbine Bushmaster tube, spring, and buffer that I stole for this build, or what I should use to solve this problem........or if that is the problem.

Any suggestions would be appreciated.

Ty </div></div>

I've also got a DCA 9" barrel. I shoot 208 A-max's subsonic, and have a DPMS heavy buffer. With AA1680, they will cycle, but will not lock the bolt back after the last shot. This is unsuppressed. I figure if I either put a lighter buffer in or put a suppressor on, they would lock the bolt back. 1680 has not been very consistent for me. I'm looking to try H4198 next. It is a bit slower, so it should cycle better unsuppressed, and it's also an Extreme powder, so should be more stable.

-Dan
 
#15
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ddavis</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body">Guys,
I built a rifle with the following specs:

Rifle:
9" 1-8" twist Delta Company 300 AAC blackout
Donor Bushmaster bolt carrier group
Pistol length standard gas system with standard gas block
Sun Devil upper and lower
DPMS lower parts kit
Donor Bushmaster carbine buffer and tube
Giessele (sp?) DMR high-speed trigger

Sub load:
Resized and trimmed LC 223 brass
CCI 400
9.4 H110
208 a-max at mag length

Suppressor:
338 Ti SAS QD over muzzle break

It runs great with 135 supersonics and same powder at a higher charge. Even locks the bolt back. When I put subs through it, it short strokes. I am 95% sure that I need a different weight buffer, but don't pretend to know what the weight is from the factory carbine Bushmaster tube, spring, and buffer that I stole for this build, or what I should use to solve this problem........or if that is the problem.

Any suggestions would be appreciated.

Ty </div></div>

I've also got a DCA 9" barrel. I shoot 208 A-max's subsonic, and have a DPMS heavy buffer. With AA1680, they will cycle, but will not lock the bolt back after the last shot. This is unsuppressed. I figure if I either put a lighter buffer in or put a suppressor on, they would lock the bolt back. 1680 has not been very consistent for me. I'm looking to try H4198 next. It is a bit slower, so it should cycle better unsuppressed, and it's also an Extreme powder, so should be more stable.

-Dan</div></div>

I appreciate the response.

Could you share a starting point for H4198 with the 208 please?
 
#16
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body"> <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bedlam</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body">300 BLK will not cycle with H110. (Not Enough Gas)
AA1680 is what you need.</div></div>
H110 cycles perfectly for me subsonic, but I have a 16" barrel.

However, one thing I have noticed using H110 and a Chrony is that the velocity changes dramatically if the cartridge warms up in the chamber. First shots and rapid shots are at least 100fps slower than rounds that sit in a warm chamber for several seconds or longer.
</div></div>
The 16" barrel is why it is working.
H110 will do some crazy stuff under adverse temperatures.
Worse so in sub-zero conditions.
For this reason, as well as others, I use N110 instead. </div></div>

+1 H110 is uber temp sensitive. VV N110 all the time.
 
#17
Re: 300 AAC not cycling subs

How about Lil'gun? it's a great powder for the lighter bullets. Don't know about heavies thouigh

have you run some factory remington?

When I get my Core15 upper (they guarantee their uppers will work with Remington 220gr ammo unsupressed as that's what they test with) I will buy 2 boxes of 220gr and 2 boxes of regular supersonic ammo and will run the supersonic ones to break her in a little, then I will test the 220gr ones. if I can't get over 90% success, I will send it for repair work.

unforuntely you built yours from scratch so...

that's one of the reasons I will be buying a completed upper, and a company that guarantees both loads unsuppresed will work.
 
#18
Re: 300 AAC not cycling subs

Lil-Gun has shown good results for some folks over on "Quaterbore", but there have been reports of it damaging RCBS Chargemasters.
Whatever solvent is used in it apparently eats plastics.

It is on my list to test out, but need to test AA9 first.
AA9 & LilGun are very similar in burn rate.
 
#19
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ddavis</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fireguyty</div><div class="ubbcode-body">Guys,
I built a rifle with the following specs:

Rifle:
9" 1-8" twist Delta Company 300 AAC blackout
Donor Bushmaster bolt carrier group
Pistol length standard gas system with standard gas block
Sun Devil upper and lower
DPMS lower parts kit
Donor Bushmaster carbine buffer and tube
Giessele (sp?) DMR high-speed trigger

Sub load:
Resized and trimmed LC 223 brass
CCI 400
9.4 H110
208 a-max at mag length

Suppressor:
338 Ti SAS QD over muzzle break

It runs great with 135 supersonics and same powder at a higher charge. Even locks the bolt back. When I put subs through it, it short strokes. I am 95% sure that I need a different weight buffer, but don't pretend to know what the weight is from the factory carbine Bushmaster tube, spring, and buffer that I stole for this build, or what I should use to solve this problem........or if that is the problem.

Any suggestions would be appreciated.

Ty </div></div>

I've also got a DCA 9" barrel. I shoot 208 A-max's subsonic, and have a DPMS heavy buffer. With AA1680, they will cycle, but will not lock the bolt back after the last shot. This is unsuppressed. I figure if I either put a lighter buffer in or put a suppressor on, they would lock the bolt back. 1680 has not been very consistent for me. I'm looking to try H4198 next. It is a bit slower, so it should cycle better unsuppressed, and it's also an Extreme powder, so should be more stable.

-Dan</div></div>

I appreciate the response.

Could you share a starting point for H4198 with the 208 please? </div></div>

I don't even own any H4198 yet, but when I get around to it, I will start with 12 grains and go from there, based on the burn rate and my experiences with other powders.
-Dan
 
#20
Re: 300 AAC not cycling subs

It looks like LWRC fixed this issue with a two position gas block. I would try a BCM extractor upgrade kit. they are $12 for a three pack. I change mine out about every thousand rounds.
 
#21
Re: 300 AAC not cycling subs

Check your gas port diameter. If its not .118 its too small.
H-110 is useless. 1680 isnt much better.
VVN-110 is good powder for subs in the 300 Whisper as well as for running the 125's fast.... and burns considerably cleaner than that other crap.

Its been said before....the faster the powder, the lighter the charge, the less significant the sound signature.
 
#23
Re: 300 AAC not cycling subs

Lil'gun damaged chargemasters? wow... never heard that, I'll have to check it out. if anything I'll just use it, then empty the container
 
#24
Re: 300 AAC not cycling subs

Here is my set up:
>8" Noveske
>SDN-6
>Standard buffer
>208 AMAX
>11.3gr AA1680
>New 300BLK brass
>CCI 400 Primer

I started my load at 10.6gr and worked up to 11.3gr. According to the chrono I'm around 1005fps-1015fps. On my next outing I'm going to load some 11.4gr, 11.5gr, and 11.6gr and see if I can push them a little harder without going super sonic.

Suppressed it cycled all of the loads. I have not shot it unsuppressed. During part of my load development I didn't have the bolt catch installed so I can't tell you whether or not charges 10.6gr-11.0gr held the bolt back. Charges 11.1gr-11.3gr did.

Temperature and humidity during my development were 41deg and 40%.
 
#25
Re: 300 AAC not cycling subs

You want to start HIGH and work your way down. This lessens the chance of sticking a bullet in the barrel. Lower velocity is quieter. I try to stay right around 1000 fps.
 
#26
Re: 300 AAC not cycling subs

Great point. AAC recommended 11.0gr of AA1680 as a starting point when I did my load development back in January but did not say which way to go so I reduced my load by 5% and started there. Their web site now says to start at 11.2gr and work your way down as you stated.

My mind may be playing tricks on me, however, I distinctly remember having a phone conversation with them regarding starting points for my charges prior to my load development. In that conversation the individual did not/would not give me any other recommendation other than to start at 11.0gr and adjust from there. Again, not being specific in any direction up or down.

I'm not knocking them for this. They make guns and gun components, not load data.

The speed of sound is 1051fps + temperature in ferinheight, roughly, so as long as the bullet doesn't top 1051fps + temp in deg. F it should not be noticeably louder.

I want to push mine harder to test for any effect on accuracy.
 
#28
Re: 300 AAC not cycling subs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: taseal</div><div class="ubbcode-body">Lil'gun damaged chargemasters? wow... never heard that, I'll have to check it out. if anything I'll just use it, then empty the container</div></div>
Robert Silvers reported that Lil-Gun completely destroyed his Charge Master.
(I have not tried to replicate the problem.)
wink.gif

In case you didn't know, Mr. Silvers is the person that headed up the 300 BLK project at AAC.
 
You must log in or register to reply here.

Similar threads

darkfader
300 Blackout AR Malfunctions
Replies
21
Views
743
TonyAngel
T
Kangbeef
300 blk subs with light bullets experience
Replies
2
Views
250
roostercogburn98
roostercogburn98
WeR0206
Heads up, make sure to have a spare gas key, screws, and sealant on hand if getting short stroking etc.
Replies
20
Views
627
TonyAngel
T
gigabels
Upgrading AR's to BRT EZ gas tubes & VLTOR A5 at the same time - should I tune the buffer first?
Replies
10
Views
1K
Cascade Hemi
C
C
16” .308 Buffer Assembly Recommendations
Replies
45
Views
5K
BAMAboy18
BAMAboy18
Top Bottom
Back
Home
Forums
Merch
Alerts