11 inch barrel and carbine gas

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offsidewing
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11 inch barrel and carbine gas

Post by offsidewing » Thu Nov 19, 2020 6:38 pm

So, this is an idea I hatched back during lockdown in April. I own a 7, 9, and 12 inch barreled uppers with pistol gas in 300BLK. I wanted to try carbine length gas on a shorter barrel just to see if I could make it work for a rifle that would always wear a silencer. I pestered dellet in a couple PMs to bounce ideas of off him and I decided to give it a try.

So I ordered an 11 inch SS barrel from X-caliber and a Radian builder kit. Both had an 8-10 week lead time. The guys over at X-Caliber were hesistant to do carbine length on a short barrel. I told them I knew the risks and it was on me if the barrel didn't work out. They did a carbine port drilled to .105" at my request. I figured I could open the gas port a bit if I need to. I had the barrel in June. The Radian Builder kit, well I FINALLY got that last week. Yeah, 26 weeks.

So, i have the 11 inch barrel in a 10 inch radian builder kit. The barrel was head spaced to a RCA bolt, and I put that bolt in an unfired AAC NiB BCG I have been holding onto for a while. I'm running a milspec carbine spring and carbine weight buffer. PWS enchanced bufffer tudpbe. Aero precision .750 gas block and Aero melonite carbine gas tube.

I had two previous range sessions to "break in" the barrel and today was my first attempt to dial in the gas. I used 125gr Speer TNT loaded over 17 grains of Viht N110 (1.535 CBTO) and 125 TNT over 18.1 grains of H110 (1.505 CTBO). Also used 220SMK tucked into 10.4 grains of Viht N120 for a subsonic loading.

Results Unsuppressed:

H110 rounds - BHO every round with the H110 loads. Bolt is all the way back, cycles great, this is what I hoped for. Loaded one round into a mag 20 times. These chrono at 2000 FPS from my 9 inch SBR.

Viht N110 rounds - the bolt would lock back, but not all the way back. The bolt head was visible thru the ejection port. This was consistent in every shot. Loaded one round into a mag 25 times. I love how accurate this powder is and want to get this powder dialed in with the barrel.

Didn't bother with subs unsuppressed with this set up.

Results suppressed:

AAC SDN-6 retro fitted with a SiCo plan B and a Q trash panda.

SDN-6 - both loadings of supers were BHO every shot every mag. A little less gas to my face than I am used to on pistol tubes. The subsonic load wouldn't lock the bolt all the way back on Magpul 300blk mags, but it would with 300blk lancers.

Trash Panda - both 125 loads would BHO all the way back. Very little gas in the face. I love the trash panda. The 220 subs would not lock back all the way back on any mag. The bolt was still showing through the gas port.

I brought along a control rifle with a 7 inch 1:5 barrel with pistol gas. Every round was BHO with suppressor, supers were BHO every round, every mag unsuppressed.

After all this I am thinking of opening the gas port a tiny bit more. I'd like to BHO unsuppessed with my N110 loads. N110 is clean and accurate and without trying 300-MP, my favorite powder for accuracy. I might try a load with little less case fill with N110 first before I open the gas port. I can probably come up with an N120 subsonic load that will BHO suppressed with this barrel using the Trash Panda.

So far the carbine gas has mitigated some of the recoil inpulse on supers, and subs are quiet albeit a little under gassed. The barrel is very accurate, it has exceeded my expectations only shooting it to 25 yards so far.

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dellet
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Re: 11 inch barrel and carbine gas

Post by dellet » Thu Nov 19, 2020 7:02 pm

offsidewing wrote:
Thu Nov 19, 2020 6:38 pm
So, this is an idea I hatched back during lockdown in April. I own a 7, 9, and 12 inch barreled uppers with pistol gas in 300BLK. I wanted to try carbine length gas on a shorter barrel just to see if I could make it work for a rifle that would always wear a silencer. I pestered dellet in a couple PMs to bounce ideas of off him and I decided to give it a try.

So I ordered an 11 inch SS barrel from X-caliber and a Radian builder kit. Both had an 8-10 week lead time. The guys over at X-Caliber were hesistant to do carbine length on a short barrel. I told them I knew the risks and it was on me if the barrel didn't work out. They did a carbine port drilled to .105" at my request. I figured I could open the gas port a bit if I need to. I had the barrel in June. The Radian Builder kit, well I FINALLY got that last week. Yeah, 26 weeks.

So, i have the 11 inch barrel in a 10 inch radian builder kit. The barrel was head spaced to a RCA bolt, and I put that bolt in an unfired AAC NiB BCG I have been holding onto for a while. I'm running a milspec carbine spring and carbine weight buffer. PWS enchanced bufffer tudpbe. Aero precision .750 gas block and Aero melonite carbine gas tube.

I had two previous range sessions to "break in" the barrel and today was my first attempt to dial in the gas. I used 125gr Speer TNT loaded over 17 grains of Viht N110 (1.535 CBTO) and 125 TNT over 18.1 grains of H110 (1.505 CTBO). Also used 220SMK tucked into 10.4 grains of Viht N120 for a subsonic loading.

Results Unsuppressed:

H110 rounds - BHO every round with the H110 loads. Bolt is all the way back, cycles great, this is what I hoped for. Loaded one round into a mag 20 times. These chrono at 2000 FPS from my 9 inch SBR.

Viht N110 rounds - the bolt would lock back, but not all the way back. The bolt head was visible thru the ejection port. This was consistent in every shot. Loaded one round into a mag 25 times. I love how accurate this powder is and want to get this powder dialed in with the barrel.

Didn't bother with subs unsuppressed with this set up.

Results suppressed:

AAC SDN-6 retro fitted with a SiCo plan B and a Q trash panda.

SDN-6 - both loadings of supers were BHO every shot every mag. A little less gas to my face than I am used to on pistol tubes. The subsonic load wouldn't lock the bolt all the way back on Magpul 300blk mags, but it would with 300blk lancers.

Trash Panda - both 125 loads would BHO all the way back. Very little gas in the face. I love the trash panda. The 220 subs would not lock back all the way back on any mag. The bolt was still showing through the gas port.

I brought along a control rifle with a 7 inch 1:5 barrel with pistol gas. Every round was BHO with suppressor, supers were BHO every round, every mag unsuppressed.

After all this I am thinking of opening the gas port a tiny bit more. I'd like to BHO unsuppessed with my N110 loads. N110 is clean and accurate and without trying 300-MP, my favorite powder for accuracy. I might try a load with little less case fill with N110 first before I open the gas port. I can probably come up with an N120 subsonic load that will BHO suppressed with this barrel using the Trash Panda.

So far the carbine gas has mitigated some of the recoil inpulse on supers, and subs are quiet albeit a little under gassed. The barrel is very accurate, it has exceeded my expectations only shooting it to 25 yards so far.
8) :P 8) :P

Make sure it's well broke in before you drill and don't forget that moving the bullet out on the sub loads can be very helpful.
300 Blackout, not just for sub-sonics.

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offsidewing
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Re: 11 inch barrel and carbine gas

Post by offsidewing » Thu Nov 19, 2020 8:32 pm

dellet wrote:
Thu Nov 19, 2020 7:02 pm


Make sure it's well broke in before you drill and don't forget that moving the bullet out on the sub loads can be very helpful.
Hmmmm. I've been seating the subs so that they are sitting right on the N120. With the N120, are you suggesting moving the base of the bullet away from the powder?

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Re: 11 inch barrel and carbine gas

Post by dellet » Fri Nov 20, 2020 12:36 am

There’s a lot going on with your set up and it can teach you a lot if you let it. Doing what “can’t be done with this cartridge” changed a lot about what I thought I knew about loading.

For me developing a sub load, accuracy is almost an afterthought. It is the absolute last thing I work on. But often the things I do work on generally improve accuracy.

The load has to function, once it functions, it has to stay subsonic. If it does both of those then I work on accuracy.

Sounds like the bolt is catching on the carrier instead of the bolt face, you’re very close to success. Both your sub and super loads will react the same way, it’s just more noticeable and easier to see changes with the subs.

With your N110 load dropping the charge to create less pressure/more gas, is no different than moving the bullet out. Except that it allows room for more powder later if you want it. Adding powder also creates more gas. So it leads to this endless circle of adjustment. No one pays attention to 25 fps velocity change with supers, but with subs it can make or brake the whole project. So if you can move the bullet out .010”, velocity drops, peak pressure drops, gas increases it might just move the carrier back enough to catch the bolt face. If not, add .1 grain of powder and check again. In that load you’re trying to get full function without excess pressure.

It works exactly the same with the sub load and N120. When I work up a sub load that is on the edge I find the least amount powder needed to cycle the action and lock back, then start adjusting seated depth to dial in velocity and ES/SD numbers. If I find a fill ratio that has good numbers, then I adjust the load keeping that ratio to get the velocity I want.

With supers nobody worries about excessive velocity, only excessive pressure. With subs everyone worries about excessive velocity, but never thinks about pressure. When you finally stop and figure out that pressure is what causes velocity it opens new doors and thinking when it comes to trouble shooting a load to get it to function.

You might very well end up opening up that port, but that’s the easy way out. You really should not have any trouble with supers without a suppressor. But if you can leave that as a last resort I think you will learn a lot about manipulating the burn rate and pressure curves of powders.

Glad to see someone else give that configuration a try. My 10” carbine gassed barrel has become a favorite.
300 Blackout, not just for sub-sonics.

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offsidewing
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Re: 11 inch barrel and carbine gas

Post by offsidewing » Fri Nov 20, 2020 9:40 pm

As always Dellet, thanks for the perspective. And yes, at this point I feel opening the port is the easy way out. I'd like to try some load development first as I'm *this* close to making it work as is.

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dellet
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Re: 11 inch barrel and carbine gas

Post by dellet » Sat Nov 21, 2020 12:23 pm

offsidewing wrote:
Fri Nov 20, 2020 9:40 pm
As always Dellet, thanks for the perspective. And yes, at this point I feel opening the port is the easy way out. I'd like to try some load development first as I'm *this* close to making it work as is.
The first couple loads are extremely frustrating, then you start seeing patterns.

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300 Blackout, not just for sub-sonics.

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offsidewing
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Re: 11 inch barrel and carbine gas

Post by offsidewing » Sat Nov 21, 2020 4:07 pm

I loaded up 4 strings of ten rounds at increased CBTO/lower case capacity with the Speer 125 TNT and N110. I am encouraged for sure. Off to the indoor range in about an hour.

The getting the 125 SMK to work with my current charge of N110 will make me explore the importance of case capacity/construction more than I have before. This endeavor may give me an excuse, err... reason, to try out the 125 TMK.

I also have a new appreciation for bearing surface calculations.

The Forster seating die made this a breeze today.

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offsidewing
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Re: 11 inch barrel and carbine gas

Post by offsidewing » Sat Nov 21, 2020 8:26 pm

Very acceptable results. I started by moving CBTO out .100 and worked back in .025 increments with the same 17gr charge of N110. From .075 to .100 out, I had BHO on every shot unsuppressed. No warning signs of pressure. At .050 increase and less, I ran into inconsistent BHO issues with Magpul 300blk mags.

So I am very pleased that I can get Viht N110 and the 125gr TNT bullets to safely work in the carbine gas. Next step is chrono and group sizes. But before that, I need to work out suppressed subs.

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Re: 11 inch barrel and carbine gas

Post by dellet » Sat Nov 21, 2020 8:36 pm

Kind of counter intuitive until you stop and think about what’s actually happening with the burn rate.

Might end up needing to cut gas off instead of drilling :lol:

Keep good notes
300 Blackout, not just for sub-sonics.

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