M90

It says in the title that it's a "High Cycle Life" spring, this falls under the category of "Low Spring Compression" ,"Low Tension Coil" or "Low Spring Attenuation" springs, as it says on the box if you looked. This means that these springs have less coils and are shorter, but are more compressed to extend the life of said spring, but they only fit in certain gearboxes or with specific spring guides. If you don't have an Arcturus gun, or the matching gun listed in the description, then don't buy this product, if you are looking for a standard spring, then go to BrillArmory or Evike and look for a Matrix Irregular Pitch or Evike Irregular pitch instead.If anyone who left a bad review actually LOOKED at the product, you'll see in the description it says"360FPS when used with stock Arcturus AT-NY06-CB and AT-AK12 AEGs", their gearboxes are setup differently in comparison with standard V2 gearboxes, you can actually find videos and photos of the Arcturus gearboxes and compare them to standard gearboxes like G&G's.I'm leaving a 5 star review so future buyers will understand why this product has such bad reviews.

I purchased an M120 and a M130 string from Arcturus.Most "off the self" M4 airsoft rifles come with an M100 or M110 spring.The Arcturus M120 string had identical FPS as the stock string. Then the Arcturus M130 spring actually performed worse then their M120...I'm no expert, but no slutch on airsoft builds. I know what I'm doing for "the most" part.By far the most disappointing springs I've purchased.I wanted to be a believer that the comments were incorrect on performance, but they were right on this one. Don't waste your money or time.

Went from 350 to 310 FPS by switching to the 425 FPS spring.

These springs do not perform as advertised. I bought the M130 to bring my DMR build up to ideally around 330fps with 0.32’s and my rifle was shooting just north of 300. I build the entire internals and I know my compression is solid because it was shooting around 310/320 with the m120 stock spring

This is a joke! I bought this to raise my fps and it did the opposite. I have a G&G ssg1 dropped in a M4 quick change lower and the stock spring shoots at 305 fps with .30 bbs. I ordered the m130 and it send it would bring it up to 425 fps. It did the opposite and brought it down to 285 290 fps. Don't waste your money!

Installed an M110 in my KWA RM4 Ronin T10 with electric recoil. With .20g BBs and hop-up off, I was getting 30 fps lower than what was rated. Had expected the recoil system might affect it prior to ordering so was not surprised. Just wish it had a better system to identify the spring. The white was barely visible and doesn't look very durable.

horrible spring i ordered the m110 because it was supposed to be stronger then my previous spring but it was weaker making fps go down. very doodoo product!

My AEG was shooting 380fps, bought this spring to upgrade the fps to the advertised 395. Fps actually went down to 310 fps.