Feats interacting with better weapons...

[Boren]

So I started up a game where I advanced the Tech level a bit, to around US Civil War starting base, now I fully expected the PCs to take full advantage of this new setting, however one thing I did not take not of was a little feat I hadn't read before I started this

Clustered Shots...

See while I fully expected to have the PCs putting out enough lead to re sink the Titanic the downside was always going to be that DR was applied to each bullet individually and not as a big lump sum of damage this would help balance out the inevitable advance to full auto capacity that I knew they would make over the course of the game.
However this one feat completely negates that and in this particular setting has swelled in power to the point where I have to nerf it.

I'm tossing around several ideas right now such as making it into a feat chain similar to the Vital Strike chain or some other method, however I thought I would take this here to the boards to see if any one could perhaps come up with something I hadn't, fresh eyes on the problem if you will. So with that, anyone have some good ideas?

[My Self]

Clustered Shots is a feat you should be 100% OK dropping, especially if everybody has firearms. At high levels, it's very powerful if you can put out a lot of shots. If you're only playing at low-isn levels, you should be fine keeping it as-is, since high levels of DR are rare and you only have so many feats to spend.

If you want, you could rule that Clustered Shots only applies within a very short distance to your opponent, maybe 10 or 30 feet or so. This ensures that they need to put themselves in danger to be able to benefit from this.

[Claxon]

Just talk to your players and explain the situation. Tell them they can replace it with any other feat they qualify for, but you want to remove Clustered Shots from the game.

[Boomerang Nebula]

Or an alternative: declare that the recoil of the weapon when fired on full auto prevents clustered shots from working, which means they have two options:

1) Fire single shots only (semi-auto), they get the benefit of clustered shots against DR but they are limited to their normal number of iterative attacks.

2) Fire full auto, receive more attacks but get no benefit from clustered shots.