Building Supressed AR pistol, is 7.5 too short?

[LINEOFDEFENSE]

Is 7.5 too short for ar pistol? Using 765saker supressor; someone told me <10.5" will cause feed/function issues in .223? Didnt know if that was true. Found a good deal on a 7.5" in .300; but would rathet keep same .223 caliber across multiple platforms.

Totally newbie to the whole pistol ar deal; so any guidance is much appreciated. Will be mounting scope and using this for a varmint "pistol" with sig brace; if that matters.

 

[JollyMon]

You may have to play around with the buffer and spring .... Or get an adjustable gas block.... but should be fine, people suppress 7.5 barrels all the time.

 

[milton]

A lot of suppressors won't warranty 556 under a 10 inch barrel, so be sure to research the cans first. A 7.5 inch barrel can be dialed in, but they aren't as trouble free.

 

[JollyMon]

A lot of suppressors won't warranty 556 under a 10 inch barrel, so be sure to research the cans first. A 7.5 inch barrel can be dialed in, but they aren't as trouble free.

He mentioned it was the Saker 7.62, which is rated to 7" with 556.
https://s3.amazonaws.com/com.silencerco/support/barrel+restrictions.pdf

 

[wsenefeld]

Do use a carbine buffer.
Do use a light bcg.
Do use a 1:7 or 1:8 twist.

Don't use a pig tail style gas tube.
Don't use a 1:9 twist.
Don't use weak ammo.

A 7.5" 5.56 barrel with a 1:9 twist shooting weak 55gr ammo through a 5.56 suppressor WILL, at the very least, result in an endcap strike (possibly even a baffle strike). I know this from first hand experience.

 

[chef1231]

Do not be fooled by rated. I spoke with someone at Griffin armament When making my purchase for SBr suppressor. He informed me that it was rated to handle the blast of a 7 inch barrel but would not be warranty until I got to a 10.5 inch barrel. He said the 5.56 round might not stabilize in a shorter barrel and would cause Bethel strikes either way would not be warranty

 

[chef1231]

Just out of curiosity, why not just SBR it?

 

[LINEOFDEFENSE]

I will do sbr eventually, just not in the mood to mess with it now. So from what ive read, to be safe for someone like me (non mr fixit types); i should probably stay with the 10.5" length in order to have a load and go no issues pistol?

I dont want to have to "play with it" to find the right settings.

 

[M67]

Do not be fooled by rated. I spoke with someone at Griffin armament When making my purchase for SBr suppressor. He informed me that it was rated to handle the blast of a 7 inch barrel but would not be warranty until I got to a 10.5 inch barrel. He said the 5.56 round might not stabilize in a shorter barrel and would cause Bethel strikes either way would not be warranty

Then they need to make that statement clear it's not warrantied under a 10.5" barrel.

If a company states it'll take a 7.5" but is only warrantied to 10.5, then they shouldn't make any statements about using them under a 10.5"

The Saker is warrantied down to 7", and in that case I'd use it on a 7.5" and if I had an issue I'd send it in

 

[LINEOFDEFENSE]

Do use a carbine buffer.
Do use a light bcg.
Do use a 1:7 or 1:8 twist.

Don't use a pig tail style gas tube.
Don't use a 1:9 twist.
Don't use weak ammo.

A 7.5" 5.56 barrel with a 1:9 twist shooting weak 55gr ammo through a 5.56 suppressor WILL, at the very least, result in an endcap strike (possibly even a baffle strike). I know this from first hand experience.

I understand the reccomendation on twist, I was thinking 1:7 just in case. As far as light bcg any brands better than others? Also, what do you mean by pig tail style gas tube? Obviously, I know 0 about this stuff...but, I am learning

 

[wsenefeld]

These are the bcg's I'd use for a 7.5" barrel.
Light Weight AIM AR .223/5.56 NiB 9310 MPI Bolt Carrier Group

http://www.aimsurplus.com/product.a...ride+9310+MPI+Bolt+Carrier+Group&groupid=4644

A pig tail gas tube looks exactly like it sounds. A normal gas tube will go directly from the gas block to your upper receiver. A pig tail will go from your gas block, spiral around your barrel a couple times, then go to your upper receiver. It creates more of a problem and solves nothing but because it's new, a lot of suckers bought into it.

 

[trucker777]

Do use a carbine buffer.
Do use a light bcg.
Do use a 1:7 or 1:8 twist.

Don't use a pig tail style gas tube.
Don't use a 1:9 twist.
Don't use weak ammo.

A 7.5" 5.56 barrel with a 1:9 twist shooting weak 55gr ammo through a 5.56 suppressor WILL, at the very least, result in an endcap strike (possibly even a baffle strike). I know this from first hand experience.

Hi there! I am currently building an ar pistol, and I find this info in conflict with other info I have found.
First let me say I will not be using a supressor.
I was under the impression I should get a heavy bcg and buffer tube for the 10.5 barrel. I'm not saying what your saying is wrong, buy can you please elaborate on why. Much appreciated. Thank you.

 

[wsenefeld]

Hi there! I am currently building an ar pistol, and I find this info in conflict with other info I have found.
First let me say I will not be using a supressor.
I was under the impression I should get a heavy bcg and buffer tube for the 10.5 barrel. I'm not saying what your saying is wrong, buy can you please elaborate on why. Much appreciated. Thank you.

When you run an 11.5" or shorter barrel, you're obviously running with less gas. It's harder to move more weight with less gas. That gas has to get a full cycle out of the bcg and buffer. The most prominent issue with an SBR is undergassing. So which will be easier to cycle when you've got less gas available...

Heavy bcg/heavy buffer (most weight)
Light bcg/heavy buffer (varies but medium weight)
Heavy bcg/light buffer (varies again)
Light bcg/light buffer (least weight)

A light bcg/light buffer will always be the easiest to cycle. It isn't always the best choice for an AR-15, but it is the best choice for a 7.5" 5.56 AR.

If you're seeing recommendations for a heavy bcg/heavy buffer, I'd guess it's on a 16" AR with a carbine length gas system. If you see somebody recommend a heavy bcg/heavy buffer for a 7.5" 5.56 AR, don't believe anything they are saying.

 

[trucker777]

I understand the reccomendation on twist, I was thinking 1:7 just in case. As far as light bcg any brands better than others? Also, what do you mean by pig tail style gas tube? Obviously, I know 0 about this stuff...but, I am learning

When you run an 11.5" or shorter barrel, you're obviously running with less gas. It's harder to move more weight with less gas. That gas has to get a full cycle out of the bcg and buffer. The most prominent issue with an SBR is undergassing. So which will be easier to cycle when you've got less gas available...

Heavy bcg/heavy buffer (most weight)
Light bcg/heavy buffer (varies but medium weight)
Heavy bcg/light buffer (varies again)
Light bcg/light buffer (least weight)

A light bcg/light buffer will always be the easiest to cycle. It isn't always the best choice for an AR-15, but it is the best choice for a 7.5" 5.56 AR.

If you're seeing recommendations for a heavy bcg/heavy buffer, I'd guess it's on a 16" AR with a carbine length gas system. If you see somebody recommend a heavy bcg/heavy buffer for a 7.5" 5.56 AR, don't believe anything they are saying.

Fantastic info, thank you!