Handguard length vs gas system length

[mercervillerental]

I'm in the process of building my second upper so apologies if this is a somewhat naive question.

I don't know if I fully understand the distinction between hand guard overall/total length vs hand guard gas system length. What I've read so far leads me to believe the handguard gas system length measurement is basically guaranteeing that if I buy a hand guard for a carbine length gas system that it will fully cover the gas block in a carbine length config. Is that accurate?

I ask because I'm looking at hand guards for a new pistol build and I'm *assuming* that if I have a pistol length gas system I can still buy a "carbine length" hand guard. Is that accurate as well?

 

[Steel head]

I like the hand guard to fully cover the gas block.
Example- on a SPR barrel(18” with rifle length gas) a 15” hand guard is nice.
Same barrel length with a mid gas port could be Ok with a 13-14” hand guard.
With a carbine gas port a 12” would cover it.

 

[stilesg57]

For drop in, it’s distance to the FSB (carbine, mid or rifle). They fit by category; don’t worry about inches.

For free float, don’t pay any attention to the designation as a manufacturer can call anything a “carbine” or “rifle” or whatever length handgurard. They’re for rough lengths only. Go by measured inches, and follow Steel head’s measurements above. Also recommend covering the gas block at the least.

 

[mercervillerental]

What is the minimum length to cover the gas block in a pistol length system?

 

[Steel head]

I should add I usually like 2-3” of barrel sticking out so even if a 18” had a carbine gas system I’d still run a 14-15” guard.
A 16” middy barrel looks great with a 13-14”

 

[Steel head]

I know nothing about pistol lengths.

 

[stilesg57]

Since I happen to have all 4 here in the room with me and a tape measure...

Pistol: 6”
Carbine: 9”
Middy: 11”
Rifle: 14”

Handguards of at least that length will completely (but just barely) cover your typical lo pro gas block.

Note: this isn’t about looks or preferences, just the minimum needed to cover a standard lo pro gas block. For example, I like more HG real estate so I’d put a 15” on anything with a 16” barrel or longer.

 

[Steel head]

Since I happen to have all 4 here in the room with me and a tape measure...

Pistol: 6”
Carbine: 9”
Middy: 11”
Rifle: 14”

Handguards of at least that length will completely (but just barely) cover your typical lo pro gas block.

Note: this isn’t about looks or preferences, just the minimum needed to cover a standard lo pro gas block.

There you go.

 

[mercervillerental]

Since I happen to have all 4 here in the room with me and a tape measure...

Pistol: 6”
Carbine: 9”
Middy: 11”
Rifle: 14”

Handguards of at least that length will completely (but just barely) cover your typical lo pro gas block.

Note: this isn’t about looks or preferences, just the minimum needed to cover a standard lo pro gas block. For example, I like more HG real estate so I’d put a 15” on anything with a 16” barrel or longer.

Nailed it - Thank you!