After 10 years of walled exclusivity, Fidelity Magellan (FUND: FMAGX) recently flung open its doors to new investors. As one of the industry's most storied mutual funds, Magellan's reopening is a pretty big event.

Just make sure you watch it from a safe distance. If you're itching to dive back into the fund, there are several good reasons to keep your wallet closed.

1. Peter Lynch, where art thou?
An actively managed fund is only as good as its manager. Magellan was a rock star after Peter Lynch came aboard 31 years ago. Unfortunately, he left 13 years later. His reputation put Magellan -- as well as Fidelity, and perhaps even the entire mutual fund industry -- on the map.

The past 18 years have been a revolving door at the helm of the iconic fund. The current manager is pretty good, but Harry Lange has only been running Magellan for a little more than two years. Let him navigate such a large asset base for a few more rocky quarters before crowning him Lynch-worthy.  

2. The weight on Magellan's shoulders
The fund's biggest gains came early in Lynch's tenure. He inherited the fund when it had just $18 million in assets, granting Lynch the luxury to be nimble. He was able to load up on small consumer-driven growth companies like La Quinta, Dunkin' Donuts, and Pier 1 (NYSE: PIR) while they were still able to move the needle.

Now that Magellan is saddled with nearly $45 billion in assets, Lange's choices are limited. Instead of small caps early in their growth cycles, Magellan's largest holdings tend to be fat caps such as Corning (NYSE: GLW) and Staples (Nasdaq: SPLS)

There's nothing wrong with a $35 billion communications-equipment maker or a $15 billion office-supply superstore chain; both are solid companies. However, investors hoping to resurrect the ghost of Magellan's heyday returns will be disappointed.

3. Around the world in 80 plays
Lange's success has come partly from global diversification. Finland's Nokia (NYSE: NOK) is the fund's largest holding. Chinese travel website (Nasdaq: CTRP) -- itself a smaller company -- is another hefty holding.

Again, there's nothing wrong with those companies. Nokia's latest line of cell phones looks strong. Ctrip will make a ton of money during the upcoming Olympic Games in Beijing. But while Fidelity's fund has performed well under Lange relative to stateside blue-chip funds, it hasn't fared quite so well against the better-performing global funds that Magellan has gradually grown to emulate.

4. Fees-a-vis
Magellan's annual expense ratio of 0.53% is attractive for a stock fund, especially one taking on a global bent, where expenses typically clock in higher. Then again, investors should expect such low fees from a slow-moving fund sitting on $45 billion in assets.

Fools, you'll find even cheaper funds with smaller asset bases out there. Compared to Vanguard's thrift funds or the growing selection of low-cost exchange-traded funds, Magellan isn't the cheapest game in town, even if it is one of the biggest.

5. Groucho Marx's sage advice
Ask yourself why Magellan is opening in the first place. I get weary when famous funds reopen, recalling comedian Groucho Marx's famous insistence that he would never join any club that would accept him as a member.

Why is Magellan soliciting fresh meat after 10 years of shooting prospective investors down? As it turns out, assets peaked at more than $100 billion eight years ago. The fund has suffered net outflows ever since.

To be fair, that decline is entirely understandable. If a fund restricts new investments, it'll be subjected to such gradual redemptions as its investors reach various stages in life. However, Magellan's laggardly performance for most of that time -- failing to beat the market in four of the past six years -- hasn't helped.

The next Magellan is not the current one
If the next Magellan is what you're after, you'd do well to search for a more nimble fund. (One good place to get started is among Amanda Kish's Motley Fool Champion Funds recommendations.)

Maybe Magellan will prove itself worthy. I just believe that even Lynch would have a hard time pounding a $45 billion behemoth into consistent market-thumping submission. For now, it's a spectator sport. I'll keep your seat warm for you until you realize that I'm right.

If you're looking for well-researched ideas for market-beating funds, check out the Champion Funds newsletter service. If you need a few weeks to kick the tires, your free 30-day trial awaits you.

Longtime Fool contributor Rick Munarriz invests mostly in stocks, but he always has a mutual fund or two in his portfolio. He does not own shares in any of the companies mentioned in this story. Ctrip is a Motley Fool Hidden Gems recommendation. Staples is a Stock Advisor pick. The Fool has a disclosure policy.