Don’t underestimate the power of your PCP!!!!

Well generally lead is really bad penetrator just too soft and deforms on impact. Also when we talk about subsonic speeds, lead and superlight projectiles they really dont go through much. I use 5/32" steelplate as my target plate and Iv shot it with 200FPE 257 for about 1000times and there is simply no way that soft lead is going through it. Is it bent yes it is are there marks sure yep is it even close letting something through.. Just no. For penetration ideally you need speed, momentum (weight of the projectile) and bullet material preferably something hard. Even light 21gr bullet shot at 3000fps dosent penetrate much since its lacking momentum on mostlikely explodes on impact or deforms so badly and dumps energy. Dont underestimate penetration of subsonic rounds yes but lol stay on facts its not like your 22 airgun is same as 338lm or 50bmg. 
 
After putting a couple of dents in my garage door, I bought one of these. It is a Chinese version of a more expensive model but works great in my basement range. I have put over 3K of pellets into it and have had no issues. Not even dented .

Highwild Bullet Trap Box for .22/.17 Caliber (Rimfire Only) | 10" X 10"

https://www.amazon.com/gp/product/B07MH44YS5/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

41CT3JOiKsL.1608901689.jpg

 
I've had the same thing happen to me shooting my.25 cal Sumatra. I was doing some cronny work with some 59 grain cast slugs. I had a cardboard box stuffed tight with rags that was at least 12 inches thick and the slugs blasted through the box and the wall of my shed. I've since went to a bin filled with rubber mulch. Luckily my wife never knew it had happened 😂 I live 1/4 of a mile from my closest niebor (sic).
 
i do agree that air rifles are very powerful. but i’m guessing that the beginning thread only happened after there was already a hole in the aluminum and plywood after a few shots. and i have a hard time believing that any air rifle would penetrate a 6” SOLID piece of plywood. not saying it didnt happen. just not in one shot through a FRESH backstop as the ones described.

good thread. some forget that the backstop needs to be reinforced after taking a few rounds, and this is a good thread to ne reminded of that.
 
I have a homemade target holder. 1/16" steel plate with 1" of duct seal plastered over it. It weighs 15 Lbs, but has stopped 1000's of .177 pellets. My gun used to put out 23 fpe but I have since slowed it down and get around 19fpe. Every year at the end of shooting season (before I pack it all up for the winter) I pick out the majority of the pellets and re-form the duct seal (it usually takes me about an hour to do this- I wear rubber gloves when I do it). Going on 4 years now and not single issue. Of course it is heavy and a bit cumbersome but I never worry about ricochets or pass thru.
 
How close are you shooting at it CharlieF? Ad description says a minimum of 30 yards. Do you get any splash back at close range?

I shoot at 15 yards and have not had any splash back issues. I use thick cardboard as a cover to mount targets on and so far any splash back has been retained by the cardboard. I would say that if you were using just paper, you would get some minimal splash back.
 
If I remember correctly, the US Military uses a 1/2 inch pine board to determine if a projectile is lethal. If the projectile can penetrate, it can be lethal to humans. Granted, a .556 generating 1100 foot pounds of energy is capable of much more damage than my lowly .22 Marauder, but both will penetrate a 1/2 inch pine board at 30 yards. The pine board will probably stop the Marauder at 50 yards, where the .556 will continue on, but up to 30 or 40 yards a 20-ish foot pound gun can still be lethal.

No, do not underestimate the power of these little rifles.
 
I built a nice little nifty 12” x 12” x 3/4” plywood trap a while back and filled it with rubber mulch. It worked great but quickly got heavy as it filled with lead. I tried to clean it out and separate the lead from the rubber which was a less than pleasurable task that I did not want to repeat.

Keep using the rubber mulch! It’s really good stuff. Use a sifter to clean out lead, it makes it super easy. Here ya go: https://youtu.be/ok2Kraq53Mg