How far does the bolt travel in a 9mm conversion?  Does it travel far enough to get held open on the last round by the factory BHO?

Also...what exactly is the spacer for...is the bolt too short?

cycled by hand the bolt does have enough space to travel past the 5.56 bho but the problem is that the mag follower is what actuates the bho feature and the 9mm is a blowback setup so i dont think it will travel that far back on its own.

spacers? did you mean the mag block? i have no spacers behind my bolt nor anywhere near it.

Which 9mm conversion?  There is Colt style or Oly style.  Colt setup will operate bolt hold if using Colt mags and the lower has the correct bolt hold or the mag adapter has the pivot.  Oly style mags have not bolt hold so won't work.

And how far the bolt travels will depend on the ammo.

Quoted: How far does the bolt travel in a 9mm conversion?  Does it travel far enough to get held open on the last round by the factory BHO? Also...what exactly is the spacer for...is the bolt too short?

Since you are making reference to the stock spacer, I presume that you are talking about Colt style systems.  Oly system is supposed to be a drop-in design with no modification to the lower assembly (if you are using the Oly Sten mag with the mag spacer weld to the mag itself) which includes the receiver extension.  In a Colt/RRA style system, the bolt should travel past the BHO even if you are not using mags that will trip the bolt latch.  If you are using a 9mm hammer, the bolt must travel at least 1.5" to cock the hammer (at least that's what it does in my system).

The spacer (or stock spacer) must be installed in a rifle length receiver extension since the 9mm buffer+CAR action spring assemble is not long enough to fill the entire length of the rifle receiver extension. BTW, the 9mm bolt and 5.56 bolt carrier are the same length.