Unexpected "Crack" Sound When Shooting Air Rifle (and related issues)

I have had the Ruger Impact for about a month, and have fired 600-700 pellets through it. The last 150-200 pellets were various types, as I am searching for the "Right Pellet" for this gun (still haven't decided).The Ruger Impact is a .22 caliber spring-piston air rifle, with a rated velocity of 800 fps with lead pellets. I do not have access to a chronograph, so I don't know the actual velocities this rifle is capable of. About 2 weeks ago, I mounted a Bushnell Banner 3-9x40 scope on this rifle. So far, I have been very pleased with the scope. It has not come loose, and seems to hold zero extremely well

Yesterday, I was shooting my Ruger Impact, when I experienced my first problem/concern with this rifle. I was shooting .22 caliber Crosman Premier Hollow Point pellets, which I feel are a decent pellet for my rifle. I have been using these Crosman's since I bought the rifle, and have shot about 250 of these pellets with this rifle, primarily because I have an abundance of these pellets, and they are relatively inexpensive ($7.00 a tin of 500 at Walmart). I have shot over 2000 of these pellets through various air guns.

While taking a shot, my rifle made an unexpected "crack" sound, like a pellet when it goes supersonic, or the first shot in a new rifle that is filled with oil/lubricants. The sound certainly got my attention (an uneasy feeling). I was not able to see where the pellet hit. It appeared to have missed the target completely. Up to this point, I had fired 15-17 pellets at an 8.5" x 11" target, and all other shots were accounted for. This sound concerned me to the point where I performed an extensive visual inspection of the barrel (breech and muzzle), the compression chamber exit port, and the muzzle break/baffle assembly. Everything appears to be OK. My initial impression is that I shot the rifle without loading a pellet. However, I checked the container I use to hold my pellets, and I had the correct number, which means, I did load a pellet. The Crosman Premier Hollow Points have always had inconsistent head/skirt sizes. For this rifle, some fit very tight, some fit just right, and some fit extremely loose. As a matter of fact, I have had some of these pellets fall out the breech while closing the barrel. It is possible, that the pellet fell out of the breech, and I shot the rifle dry. I know this is not a good thing for spring piston air rifles, for a variety of reasons. I don't know what else could have caused the sound I heard.

After this occurred, the rifle started shooting very erratically. Before, I consistently shot 1/2 inch groups or better, from 10 yards. Now I am getting 3" groups, at the same distance. This event seems to have knocked my scope off zero. There is no consistency. The pellets are shooting high, low, left, right. So much so, I had to adjust my scope 30-40 clicks (up, and right), just to get close to my point of aim. Even after adjustments, I had to change pellet type to RWS Superdomes, in hopes to shoot a decent group. I put 3 superdomes in a dime sized hole, then, shot 4 went 2 inches to the left, and shot 5 went 1 inch high.At this point, I decided to quit for the day, as my concern and frustration mentally impacted my shooting.The help I seek from the forum members, is as follows:

1. What could have caused the rifle to make that supersonic sound (Crack)?
2. What damage could have been caused by shooting my rifle without a pellet?
3. How can I inspect my rifle for damage?
4. Could my scope have been damaged, and how can I check?
5. What are your recommended next steps?Any information will be helpful.

Lcheevers
 
I had similar issues with an Impact I was trying to work out for my neighbor. The CPHP pellets where the same in that one as in yours. I put 1000 pellets through that gun for the recommended break in as per the owners manual. At 50 pellets it was firing CPHP at around 820fps, at 1000 it was firing CPHP at 500fps.

Later, I bought myself another RWS34 clone, a Remington Express. This rifle also had the same problems but more pronounced. At 50 pellets it was 750fps and at 500 pellets it was 300fps. I returned the Remington, my neighbor had to keep the Impact since she couldn't return it.

Both rifles would give the occasional Crack that you describe and a wisp of smoke. I believe they had faulty piston seals that was allowing oil from the spring to leak into the compression chamber causing dieseling. Both of these rifles originate in China and I believe from the same factory, from the matching builds and tool marks.

I suggest you run it over a chrono or try using the smart phone app Chrono Connect, to check your velocities.

I can't speak to the scope issue as I have no experience with the Banner series and don't even know if it is springer rated.
 
Definitely check the screws as William Leven suggests. It is possible that some factory lube has just taken a while to find it's way into the chamber. It might explain the crack, and dieseling could explain the erratic groups. In the shots after the crack, did you notice any smoke from the muzzle or the breach? I would suggest running some patches through your barrel, and see if any oily, sooty residue comes out on the patch. If so, your gun is likely dieseling, or at the least has a fouled barrel from dieseling. Sometimes a good barrel cleaning is all you need to restore accuracy. How does the gun sound when fired? Have you gotten more cracks? What about the mechanical/spring noise/twang, has it changed at all? 
 
Thanks for your responses guys. I do appreciate it. I was out and about late last night and did not have time to respond. Since you all took your time to help me, I will do my best to provide responses to your questions/recommendations. 

I will say, that I did return the rifle last night. Oddly enough, I exchanged it for another Ruger Impact, which I will explain later. Call me a gluten for punishment, but I really like the feel and shootability of this rifle. 

I did go out and shoot the rifle yesterday when I got home from work. I shot from 10 meters. 5 rounds each using CPHP’s (2.5” group), RWS Superdomes (2” group), and RWS Superpoints (1.5” group), with the scope on. I then removed the scope and repeated the test with open sights with similar results. It wasn’t just the group size that concerned me, it was the patterns. I would get 2 or 3 shots very close (< ½”) and the others would go high, low, left, right. Absolutely no consistency.

The stock screws were tight before and after “the shot”. I also removed the action from the stock to inspect and checked the barrel hinge screw/bolt, which was a little loose. I performed a visual inspection of the wooden stock, and it appears to be sloid and undamaged.

I did get smoke from both the muzzle and the breech after “the shot”. It was light smoke, but it was there. I did notice some oil/lube on the breech area.

I haven’t heard anymore “cracks”, but I do think the gun does sound different when it shoots. However, I’m not sure. Mentally, I think there is something wrong with it now. I do notice a more pronounced “twang” when it fires, which I did not hear before. Additionally, the gun seems to jump more, but again, that could be me.

Smoke and Dieseling – When I first bought this rifle, I cleaned the barrel the best I could with 20-25 patches before shooting it the first time. Even after the cleaning, the first shot had that distinctive “crack”, and quite a bit of smoke. The rifle smoked with every shot for the first 50 shots or so, then started to settle down. Even after 500-600 shots, I would still get some smoke every 8-10 shots, or when I change pellet types. Even now, I will periodically find lube/oil on the breech area of the barrel. Not much, but it is noticeable. I suspect some lube has entered the compression chamber as you all have mentioned.

More to follow
 
One of the things I wanted to mention to you all, is that I am by no means an expert, when it comes to air rifles, and especially break barrels. I do consider myself a very competent rifle shot with powder burners. With that said, I have learned an enormous amount of information about these break barrel air rifles, and pistols, over the last year or so, and really enjoy getting better. I am competent enough to know when a rifle isn't shooting properly, but do not have enough knowledge to know why. That's where you guys come in :) 

And before I forget, here is a list of all of the pellets I tested in the Ruger Impact: CPHP (14.3 gr); CPUM (14.3 gr); RWS Superdome (14.5 gr), RWS Superpoint (14.5 gr); JSB Exact Jumbo Heavy 5.52mm (18.13 gr); H&N Baracuda Match 5.52mm (21.14 gr); H&N Field Target Trophy 5.53mm (14.66 gr); Air Arms Falcon 5.52mm (13.43 gr); Gamo Match Pellets; Ruger Superpoint (17 gr). None of these pellets stood out. So far the best have been (in order) RWS Superpoint, RWS Superdome, CPHP, AA Falcon. 

After I purchased my first break barrel air rifle (1 year ago), I learned several things. One of those things is how powerful these air rifles can be, and that they can shake the bejesus out of the gun, loosening screws, destroying scopes, even make your shoulder sore when holding loosely (artillery hold). I have conditioned myself to check the stock screws, and the optics (scope, red dot, etc) before every shooting session. 

So why did I buy another Ruger Impact? Well, there are a couple of reasons. Let me give you some background. 

The first break barrel I purchased was for the purpose of target shooting and pest control (rats, squirrels, and an occasional rabbit, possum, or raccoon. I had no intention of spending a lot of money on my first break barrel. I purchased a Ruger Air Hawk (.177) from Walmart for $80. I thought it was a heck of a deal, and it was. After struggling to shoot this rifle with any accuracy, I did my internet research, and learned about the artillery hold, pellet selection, and a host of other things. I was able to quickly determine the best pellets for this gun which are Crosman Premier Lights (7.9 gr) and Crosman Premier Ultra Magnums (10.5 gr). I prefer the magnums as they pack more punch. I added a BSA red dot sight, and was quickly shooting nickel sized groups at 25 yards, which is very acceptable to me. I currently have shot over 2000 rounds through this rifle, and have taken 3 squirrels and a dozen rats, with humane kills. 

I bought the Ruger Impact because I wanted a .22 caliber air rifle. I wanted extra power for shooting larger pests like possums and raccoons. Since I had such good luck with the Ruger Air Hawk (both distributed by Umarex), I figured I couldn’t go wrong. Beside, like so many of us “plinkers”, I really couldn’t justify spending $300-$400 on an RWS 34. Hopefully, I will have better luck with this rifle.

What are your recommendations when a person buys a brand new air rifle? I think the first step is to clean the barrel, and clean up as much excess oil/lube as I can. I know that Bill stated a 1000 shot break in period, but I did not see any mention of the break in period in the Ruger Impact Owner’s Manual. What are your recommendations for breaking in a new air rifle? I was thinking of shooting a tin of 500 CPHP’s with open sights, before settling in to test pellets. What else should I do? 

Lcheevers
 
Sorry. I have one more bit of discussion specifically for Bill. It seems we have a few things in common. 

About 3 months ago, I wondered into a local pawn shop. The guy had 3 Remington Express, .22 cal, synthetic stock rifles new in the box. I opened the box and everything appeared to be factory packaged. I bought one for $60.

I took it home, cleaned the barrel and other areas I could reach, tightened the stock screws, and commenced to shooting (open sights). I shot 250 of the Daisy Precision Max pellets, and 250 of the CPHP’s. They were all over the place. I bought some premium pellets (JSB, H&N, Air Arms), but still couldn’t shoot a group less than 1.5” from 10 meters. This rifle bounced all over the place when shooting. Occasionally, I would get that “crack” sound when shooting.

I performed a physical inspection of everything I could without complete disassembly. I even communicated with some experts. They all agreed I got a lemon. I took it back to the pawn shop, exchanged it for another. This gun performed a little better, but still shoots erratically.

Lcheevers
 
Lcheevers,

I think the Ruger Impacts and Remington Express rifles coming out of China in the last year have suffered from faulty parts and workmanship. I also suspect that contributed to Remington going with Crosman for the newest series of their air rifles. I came to these conclusions because both of these rifles suffer from similar issues and my research and limited springer experience point to a bad piston seal in both of the rifles I had.
 
One thing that hasn't been mentioned is that if your rifle is dieseling the carbon can foul the bore, destroying accuracy. I had a Mendoza RM200 which was a pretty accurate little gun, except that it was over lubed from the factory and dieseled like mad for the first 1000 shots or so. I had to pull patches every 100 shots while it settled down or it would spray pellets. Try pulling some patches and see if that helps.
 
lcheevers said: "Beside, like so many of us “plinkers”, I really couldn’t justify spending $300-$400 on an RWS 34. Hopefully, I will have better luck with this rifle."

I am one of those who was totally in line with this philosophy. My preferred flavor of airgun is The Crosman product. Not because I think they build a super high quality product but because their guns are inexpensive, and they are easy to get parts for. I also like to tinker, and these guns lend themselves well to the tinkerer. For very little money and some of my time I can have a cool, hard hitting, accurate, and fairly easy to shoot gun. All that said, I bought a Diana 460 Magnum last year for $350.00 as a refurb from Airgun Depot. It is a really hard hitting, beautiful, VERY accurate, and easy to shoot gun OUT OF THE BOX. I have not done a thing to it but add a scope and shoot it. So am I still interested in Crosman guns? Of course! But I now totally understand spending a bit more for a better gun, and won't hesitate to do so in the future when I want to buy myself something niiiice!