ARH Springs n' Seals (gamo accu)
I have to buy some new seals for my np2 so I figured I'd get a back up spring and seals for my accu. I've seen where people say the "euro Terantula 32coil...) is the spring to get, then other say it won't fit during compression that you have to use the MarlinXL or the E3650... I also read somewhere that crosman makes better seals and the person was getting inconsistent velocities with the ARH seals. Does any one have experience or advice? I don't care about power, just accuracy out to 50.
For now I'd rather not make any changes unless I thought something was wrong or being damaged. I bought it slight used from Skip. I chronyd it (new chrono and first time i ever used one so could be wrong)and I was getting some pretty high spreads, like almost 100fps variance but I didn't do more then about 7 shots. This gun is accurate though. Today I shot several half inch 50 yard groups with JSB exact and the heavies which is becoming pretty frequent with this gun. I just don't understand if the velocity is changing so much, how the heck is the accuracy there... I'm even afraid to install the Charlie the tuna trigget Skip included with the gun lol
I don't know anything about that gun, but I do like JM springs. I would say to just measure things yourself. Take it apart first and see how much "stack" room you have. It is probably maxed out stock. Get a $15 dial caliper and measure your spring coil wire diameter and multiply it by the number of coils to see what room you have. Match the JM spring to the outside diameter of your guide and close to the stock wire thickness.
You said you aren't interested in max power, so maybe the precut JM top hat may work with your setup. A top hat is a MAJOR reducer of twang and if it fits is a good option. Look how things fit because sometimes one may have to shorten the stock spring guide slightly to fit a top hat. It is really quite simple and obvious once you know what you are looking at.
If this uses a Diana type seal, I have not found a great difference in the various ones. A spread of 100fps points to issues. Breech seal, cut piston seal are good starting points. As an aside, that is accuracy I can really only dream of, as 2" at 50 yards is most common.
I got in in front of the chrony again today. I think I was putting it too close (rookie mistake) and the weather conditions were wrong. Today with CP box 10.5 I got 761, 755, 753, 746, 748. I mostly tested my NP2... I think I will take your advice and do the measuring myself and just wait to order for this gun. The accuracy with this gun blows my mind. It's not uncommon though for me to pull off groups like that with the JSB Exact and JSB exact heavy. Today I shot a group with dozens of shots because I wanted to see it's consistency (I was out of exacts, they came in when I was out today) with cp 10.5 I had around an inch at 25 yards, shooting in a laid back kneeling position from inside my mini-van. I've been mostly tripod shooting it to see what it's capable of and shooting a ton of different pellets through it. I keep all my targets and record them. For instance last 2 at 20 jsb hvy was .437 and .256 then hn ftt .437 .406 .437 .625 .362 and at 50 hn ftt averages 1.2 cp 10.5 averages 2' and the exacts all depend on me but range from 2.125 max and .5 at least with most around .7
I've never had any problems with JM/ARH piston seals. What I have seen a lot of are cases where people just shoved the piston and seal down the receiver tube during installation, and a sharp edge on the cocking slot caught the seal and scraped it up, sometimes causing a sealing problem if the scrape was bad enough. You should always install a seal carefully to avoid this problem.
Now, something I could see happening where some problem/inconsistency arose with a JM seal but not another seal (whether Crosman or not), is if the alternate-choice seal was made of a very stiff material I've seen that isn't as prone to getting scraped up as some others like the ARH Apex seals and several manufacturer's factory seals that are very-flexible. That flexibility makes them easy to work with. The ARH apex seals are similar in flexibility and durability to the OEM seals that RWS/Diana uses in many of their models like the 34 and 48 and they work as well as the seals in those rifles.
But, if you're not too good at avoiding scrapes, ARH makes some of the seals made from more-scrape-resistant material, too. If you'll notice on the JM site, he offers some seals made of his "Tesla" material, and that material is almost impossible to scrape. In fact, it's so tough that sizing the material can be a bit of a challenge unless your technique and sizing tools are the right ones. The same tough material makes-up not only the ARH seals with the "Tesla" name, but also what I've been sent from ARH when I bought the Hornet seal for the R9/HW95. Maybe that stiff material is what the Crosman seals are made of and is part of the reason some have reported more consistent results when using them.
But, whether your piston seal is made of the stiffer material or a more flexible one, I still suggest that you always be careful not to scrape-up a piston seal during (re)installation.
There's a good test you can do after you've installed the piston to make sure everything is OK with a piston seal. That is, before you install the spring, pull the piston back in the receiver tube, put your finger over the transfer port, and try to push the piston toward the port. If you have a good seal, the piston will move a small amount then stop on the trapped air inside the receiver. However, if you can feel or hear a hiss and the piston continues to move toward the transfer port, the seal was either sized down too far or it's damaged and it needs replaced.
I'll let others comment on the spring questions.
Safe and Happy Shooting!
Ed, the Airgun TuneMeister
I wondered why I haven't read more warning about that online... I think I am the one who damaged the seal when I put it back in after applying the moly. I can't remember for sure but I could swear I looked and didn't see anything wrong at first then the next time I pulled it out there were tons of gashes, and those sharp edges are very sharp and jagged. Will keep that trick in mind next time I pull one apart, thank you.