Yes. You can get replacement springs for airsoft sniper rifles.
No
Airsoft sniper rifles can range in price from $100 to $250, depending on the model. Specific prices can be found by visiting websites such as EBay or EastCoastAirSoft.
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Springs in airsoft are never "modded" they are upgraded. An overall good brand for springs is guarder. Their springs usually run from $15 to $35 dollars. Madbull makes decent AEG springs for the money if you sniper takes an AEG spring (like the A&K SVD).
Airsoft sniper rifles can be bought for as little as $50 and as much as $300. The average price seems to be around the $150 mark but could be purchased cheaper as used on ebay.
Sounds like you are looking more towards BB guns. Check out the BB (not airsoft) rifles instead.
Yes. Otherwise, it would be a little annoying having to shove the BB's in manually.
No they don't. If you know what your doing then buy a different sniper spring or get a professional to do it for you. But it has to be a spring from another sniper not just from an other AEG. But remember not all Sniper springs will fit so beware of that. To find out which ones fit and which ones don't go into a Airsoft shop and they will do it for you.
no, metall bbs will break your gun, and are too small to fire properly. Do not attempt this.
Most of the guns listed here will shoot around 400 fps or above. http://www.6mmbb.com/servlet/the-Airsoft-Sniper-Rifles/Categories Expensive guns are around $300-$800.
No it depends, you need to check the rail size of your rifle, then the sort of rail that the scope can attach to. These are some standard airsoft scopes, check your gun rail size first though!
There really is no answer to that question, because it is based on opinion and personal preference. An airsoft sniper rifle and an airsoft aeg are two different things, and since aegs can be full or semi auto, and sniper rifle are only bolt action or spring, there really is no comparison. Sniper rifles are more powerful, but aegs have a much higher rate of fire. It all depends on what you want to use and what you like better.