It will make it but the concern should be windage, there is a bunch of blow in that neck of the woods. Also run your loads over a chronograph to verify the variations of velocity, one load that does well is a duplex.

A good friend takes his granddaughter's every year and they shoot a 38-55 with a 15 twist.  They both do pretty well but like it's been mentioned, you'll need good windage if the breeze comes up but then so does everybody else. The biggest problem with a 38-55 is that if the grounds are wet the bullet is swallowed up and you don't see the misses and it's tough to get on the target if you can't see the misses. She'll still have fun no matter what and it's a great shoot. Good bullet design is important.  Smokeless and duplex are both allowed at the Q.

I've shot the 38-55 with 300 grain bullets to 1000 yards in gong matches. The biggest problem is it's darn hard to see the misses compared to a 40 or larger, so getting the sights adjusted for the wind and mirage can be a problem if your spotter isn't on top of his/her game. They also don't get to the extended ranges with a lot of umph so may not reliably set off the radio or flasher system.
Yes you can use duplex at the Quigley, you can use any of the so called substitute powders, you can run straight black or you can run smokeless, they do have a rule agains using wads with powders like 5744 and the like. 
You can view the rules on the Quigley match web site.

I was able to test some 38-55 loads using IMR3031 and a 330 gr. bullet at 600 yards. This gave reasonably good results, but more testing will be required. The rifle has a mid-range tang sight and I’ll need to determine if it has enough come-uppens for 800.
I agree, the 38 cal slugs will have a disadvantage over the larger calibers, but I still need something compatible with the wife.
The whole adventure might just be a chance to have phun, so the ability to hit at 800 maybe acidamic.
Thanks for your input.
Mike.

Mike, You will need about 38-40 minutes from your 600 yd setting to make it to the buffalo.  That's what my 38-50 needs with a 330 gr bullet and bp.

Quote:
Mike, Ranch13 summarized the capability of the 38-55 caliber, shooting long distance.  With many sighters I have hit a 1000yd gong target with a 320gr bullet and 48gr of Swiss FFFg. If you expect repeated accuracy at 800-1000yds - Forget it

My daughter and her husband stopped at the Quigley this year on the way back from Yellowstone. They wanted to find out what it is all about.  Here is a picture of her shooting my 38-50 Hepburn with 56 grains of black powder. I'm guessing probably around 1250-1275 fps. I don't have a crony, never used one. It was the first gong target that she ever shot at and she hit the buffalo 4 out of 7 times. You should be able to do 50% with a 38-55 with a little bit of experience. She went four for four on the diamond and three out of four on the number five target which I consider to be very difficult. Like I mentioned earlier, all bets are off if the grounds are wet or it's very windy.