He's running an older 10" Geissele rail and what the article says is a 10.5" barrel.

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If I mounted a Ferfrans CRD to a 10.3" barrel and a 9.5" Geissele, could I get it about as close to the rail collar as in the photo?

IM him and ask him?
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Let me crunch the numbers here...

10.5 - 10.0 = 0.5

10.3 - 9.5 = 0.8

delta of 0.5 and 0.8 is 0.3

So in conclusion, your planned setup would have an additional 0.3 inches of gap between the end of the rail and the rear of the CRD.

I ran those same numbers, thanks for confirming. I don't see how it'd be possible to get it closer and still be able to mount it to the brake but, the guy did it.

https://www.ar15.com/forums/t_3_4/657643_My_stamp_arrived_today__I_was_finally_able_to_make_my_pistol_a_rifle_.html

Depends on the brake probably. I'd also imagine different manufactures may measure their handguard length slightly differently.

This is my 10.5" Barrel 10" Handguard setup. I made the brake but it matches the basic dimensions of a YHM mount. There's about a .150" spacer behind the brake for clearance and timing reasons. Is your question about how the brake is torqued on without being able to reach the flats? I just use a bar through the ports.

Just make sure you find a true 10" rail since they round up or down about 1/4" or more each way. Most MFR websites list actual specs

This was my 8" SLR rail and a 8.5" barrel, I was underwhelmed by the CRD and sold it

you have to subtract the depth of the threading correct?

So a 10.5" barrel on a 10" handguard would put the rear of the muzzle device about flush with the end of the rail if you subtract a 1/2" of threads.

Forgive my ignorance if I am way off here.

Correct........need to subtract .5" for the barrel threads.

This would bring the device to rail gap to .3".......which would mimic the OP's posted pic.

Your in bold is correct, and is in fact what we see in the OP's image.

The OP is asking about a 10.3" barrel and 9.5" rail.  You can do the math your way and reach the same conclusion: 10.3 - 0.5 = 9.8"  Comparing 9.8" and the 9.5" rail gives you about 0.3" of barrel after the rail ends and before the muzzle threads begin.

Let me throw another measurement into the mix.

The barrel length is measured from the bolt face to the end of the barrel (with no device attached).  On a non-blow back operated AR (i.e. with a rotating bolt and locking lugs) the bolt face is about .3" behind the face of the upper receiver when the bolt is in battery.

In other words, if your barrel was 10.5" long and hand guard was an honest 10" long and was flush with the face of the receiver, there would be only .2" of barrel extending past the end of the hand guard.

It gets even better in a blow back operated ARs as they don't have locking lugs and don't have a barrel extension.  Thus the bolt face is slightly aft of where the end of the bolt carrier is in a lugged bolt AR.

In this case, the barrel on this 10.5" RRA 9mm is actually 11.125" long.  The hand guard butts up against the upper receiver and it is an honest 10" in length. However, because the bolt face is much farther behind the face of the receiver in a blow back operated AR, there is only a half inch of barrel extending past the hand guard.

It's notable that RRA calls this a 10 1/2" barrel as the equivalent length in front of the receiver is the same as a 10 1/2" .223 barrel, rather than the 11 1/8" barrel that it really is.


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get actual rail length not what they imply

Half the time they say its a cetain length yet its .5" longer

aero is notorious for this