Crosman Nitro Fire

My nitro Fire .177 is very accurate and hits hard (especially for $79.00) for about twenty rounds, then the accuracy falls off a cliff, 3 inches at twenty yards. I clean the barrel each time this poor accuracy returns and it goes back to being dead-on, less than an inch at 20 yards I have about 300 rounds through the gun and each time I clean the barrel, the swabs or patches come out solid black. Is this normal? Shouldn't the break-in be over after 300 shots? All stock screws and scope mounts tight and loctited in!
 
Wow, that does seem a bit excessive for 20 shots... hmmm.... ok, here's a few things that I might try.

1 - Wash and lube a tin of the pellets that you're using and see if that helps. Maybe they are the culprit...

2 - Clean up the breech area for any excess lubrication. Could be getting dragged into the barrel.

3 - Use a felt pellet and some honing compound and hone the bore. Any roughness in the bore could be fouling your barrel quicker than normal.

I have a Benji Prowler that I've honed out and it tightened up the groups quite a bit. Hope you find a solution to your troubles, friend.
 
What Brian said. To me it seems like it could be the H&N’s but I’ve never experienced this before. Maybe try another pellet, JSB’s could work better. 

I have two np Titans and it took about a tin of pellets before they grouped constantly. One problem I had with the 22 cal Titan was that when the rifle warmed up from shooting it would spray the shots. But in your case if you clean the bore your accuracy returns. Maybe try another pellet when accuracy starts to fall and see if they group, they might not group at your poa but they should group.

If this fails look at your barrel lockup, there may be an issue there.

Good luck

Gary
 
https://www.amazon.com/Goodson-Lapping-Compound-400-Gr/dp/B0009RM4J4/ref=sr_1_10?keywords=lapping+compound&qid=1559518634&s=automotive&sr=1-10

They have grit up to 1200 if you'd care to go that far.

Start with the coarsest grit and push a coated felt pellet through with a push rod. Repeat, and add compound as needed. (I did ~100 passes each with 3 different grits) You will feel when its smooth to that grit.

You then need to clean the barrel thoroughly and repeat with any finer grit you choose. Just remember to clean the barrel between different grits.

Please keep us informed of any progress.