
not to get too off topic, but cow calling has given me the most success... I carry a handful of Wayne Carlton's fighting cow call; it's super loud so you can get some distance on it. And then I use a Primo call (IMAKDABull Crazy) for the closer up stuff... and i ALWAYS have a reed in my mouth. A reed in the mouth should be mandatory!!! it's the best insurance you could have. Also good to have a couple different brands of cow calls so you can project the sound in different directions - sounds like a few different elk talking to each other. Remember too, it's usually the cows that will pull the bull away.
Depending on the area you hunt, and the pressure it sees, the elk may just not bugle - but he'll come in quietly for investigation... In 2008 I called in a couple young bulls using only cow calls, didn't even know they were in the area. Except, I "thought" I heard a twig snap about 100 yeards off... so I blew one more cow call and waited. 15 minutes later I had 2 elk less than 15 yards from me; one is now hanging on my wall... In 2010 I had the SAME thing happen, called in 2 young bulls on the estrus call, but then I did get a 3rd bull to let off some chuckles. That was the last of the vocalizations from the 3rd bull, but he came in to 20 yards - and yes he's hanging on the wall... no bugles in either scenario.
Bottom line, I see a lot of hunters, new and experienced, leave a setup too early just because they're not getting vocalization... the elk are wise to the game - guys are educating them all summer bugling from the truck every time they see one.
Also, I've found that pressured elk tend to call back more when you are further away... So I'll use the bugle to call into big drainages or valleys to see if something sticks its head out or call back. I had one scenario where I had two elk bugling back from different areas in a valley right before dark... So, I knew where I was hunting in the morning!!! When I got in there in the morning, I positioned myself, played the wind, and gave those elk everything I had in terms of calls - couldn't get anything to respond or come in. After about an hour, I went 40 yards through some noisy brush to look into where I "thought" the elk were from the night prior. As soon as I popped my head through, a bull and a dozen cows looked at me and ran off!!!! They were sitting there the whole time!!!! and that bull didn't care less.
Anyhow, just my perspective... hope it helps! Good luck.