What BB weight for TM Thompson!

[sir veilance]

I picked up a used TM Thompson a while back. I noticed that many places sell these on-line with a small bag of .25 gram BB's !?! Is this the weight BB this gun was designed for? Or are .20 BB's OK as well?

Thanks in advance!

[toboggan]

Really an weight above .20 are fine, ex. .20, .23, .25, but dont ude over .25, because those wont travel far, and are more than likely designed for snipers!

[sir veilance]

Thanks for the info Toboggan! That's about what I figured! I have ton's of .20's, that I use in most of my guns and bought some .25's for a Tanaka 98K that I have.

Thanks again!!

[2nd Bat]

The guns come with .25 weight BBs because (unknown by most airsofters) that in fact is the most efficient weight BB for the gun. Many people use .20 gram because they produce higher FPS readings (at the muzzle) and many people therefore assume they'll get better range with the lighter BBs. In fact the .20 gram Bbs lose inertia very quickly and beyond about 30 feet are equal to or lower FPS then the .25 (depending on the gun) By 50 feet the 20 gram BBs have noticeably lower FPS and it becomes increasingly the case unitl all weights lose inertia and simply drop from the sky. The reality is the .25 gram BBs will produce GREATER range then the .20 grams when fired from the same gun. Add to the fact that the .25 gram will penetrate brush somewhat better and are less effected by wind and overall from an AEG .25 gram is a more efficient BB. Some players like the reduced reaction time in close provided by the .20 or .23 gram BBs and for that I say it's a matter of taste.

One sure bet is do not use the super light weight .12 gram BBs as they are typically poor quality and will tend to jam inside your gun and have terrible flight characteristics. The ballistic properties of BBs is actually quite fascinating and I wish more airsofters would scientifically test their rifles both inclose and at range to learn more about the strange flight characteristics of sherical projectiles. If they did they wouldn't be wasting as many shots on long range targets and they wouldn't be as upset about people "Not calling their hits" You'd be amazed how much it can look like a hit when in fact the BB simply ran out of inertia and dropped practically like a stone. Or had so little inertia that it would be imperceptable by anything but a naked man.

Although counter intuitive I would recommend .25 gram and if upgraded .28 gram You'll get slightly more range and greater accuracy. (with properly set up hop up.)

[toboggan]

I have both .20, and .25, when its windy out, i use my .25, and on a relativley calm day, i use my .20

[biged]

I used to think you got less range with heavier bb's but apparently this is untrue... You gain a little extra distance.

When switching bb weights you must adjust your hopup for maximum range of the bb weight being used. The magnus effect...

You gain only 2-6 feet by switching from .20 to .25 bb with a stock 200 fps gun.
cybersloth.org/airsoft/trajectory/07-B-01.htm

You will gain 8-16 feet with a 400 fps gun by switching from .20 to 25's.
cybersloth.org/airsoft/trajectory/07-B-08.htm

The heavier weight bb's will fly straighter and punch through dense foliage better than lighter weight bb's.

I think this is what you were looking for 2nd bat:

The whole article on bb weight and range:
cybersloth.org/airsoft/trajectory/index.htm

///ed///

[sir veilance]

Thanks for the additional replies!

I will give the .25's a try!!

[2nd Bat]

Big Ed points out a critical element not mentioned in my diatribe. The gain in range is quite small. This is remarkably true with upgrades as well. You can spend a whole lot of money and reduce the durability of your AEG for an extra 12 feet of range. (If that) Granted there are other upsides but I wonder how many people realize how little upside there is?

As for the Tanaka gas powered bolt action rifle you will probably see increased FPS at the muzzle with BBs heavier then the 25s you're using Even possibly if you went up to .36s. (It varies from gun to gun and temperatures.) Long barreled rifles (especially gas powered) often create greater FPS with a heavier BB as the initial propulsion down the barrel is slightly slower which allows a more complete accumulation of gas (air is a gas too) so the heavier BB actually leaves the barrel faster at the muzzle. Naturally as a heavier BB it will maintain that inertia longer. The key here is that for fairness and safety players should chrono with the weight of BB they intend to use and the jouelles should be calculated accordingly to determine if they meet the game specifications. If a guy chrono'd with .20s and barely squeaked under the limitation for his style of gun (Let say the limitation was 550 FPS with .20 gram for a bolt action rifle) If he then went and fired .36 gram and they had a muzzle FPS of 586 you're talking significant increase in power and a potential safety hazard. Even if the FPS were the same the increased hitting power is significant due to the greater mass.

I didn't believe this ascertion when I first heard it until I saw it demonstrated repeatedly with a number of weapons by a California chrono expert who swore it was true to a bunch of us un unbelievers. I also scientifically tested the range ascertion regarding .25 BBs or .20 BBs with a stock AEG and was surprised they fired further out of the same gun.

Round balls are practically the worst ballistic shape for any kind of projectiles and present all kinds of challenges to range and accuracy. Hop up was probably one of the most brilliant enhancements to airsoft BB limitations. Properly adjusted hop up is still your best friend when it comes to range.