looking at the troy alpha rail in 13 in with sight and it says its not compatible with rifle or intermediate length gas systems is intermediate length same as mid length

Yes.

If you use a FSB the rail will only work with a rifle system or a dissy.

Now a lo pro gas block will work fine

No.

Intermediate is a separate and distinct gas system length... also known as the "Vltor Intermediate", it was intended for 18" barrels to help with some function issues with 18" rifle gas configurations in very cold climates.  It is quite a bit longer than the Armalite developed midlength in common use, and slightly longer than KAC's unique gas system length used on their E3 16" rifles.

Noveske and MSTN offer barrels in the Intermediate length, as well as custom barrels.

With regards to the product in question, I would surmise that the folding front sight assembly takes up space under the handguard that would be required for a gas block at the proscribed rifle or intermediate positions.  Since midlength is not mentioned, it should work as apparently the gas block would be far enough to the rear to clear the front sight.

The intermediate length is very close to the KAC system used on the SR15E3, within a few tenths of an inch. I have a custom 16" Noveske barrel with an intermediate length gas system.

An intermediate gas system places the gas port 11.5" from the standing face of the receiver. IIRC, a midlength is something like 9 3/4".

The Troy TRX rail, w/o the built in front sight, will work with an intermediate length gas system.

would the 13 inch troy TRX be long enough to cover a low profile gas block on the intermediate length system

Gamma is correct.

Yes.



I used that rail on my rifle before replacing it with a DD RIS-II.

Barrel is a 16" Noveske with an intermediate gas system.

thanks i wanted to make sure before i ordered i had measured it but wanted a second opinion

MSTN posted this a long time ago, I edited it to put the labels in and add the approximate length of the KAC gas system.

Nicely done, Gamma.

Yes it was...., Thank you Gamma762.