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thenodnarb

have hooking bbs? Hopup might not be your problem

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I've had an inconsistent left hook for a little while now, and I thought my hopup was applying uneven pressure. So I was experimenting with no hopup by removing the the hopup spacer and testing the accuracy. To my surprise, the left hook was still present, and even exacerbated! So I started racking my brain to figure out what could cause this. Ultimately I determined that the outer barrel was not perfectly aligned with the inner barrel, so that when I installed my barrel spacers, it was forcing the inner barrel to the left by a few mm. So I elongated the outer barrel mounting screw and shifted the outer barrel to the right until the inner barrel rested centered in the outer barrel. This resulted in my outer barrel LOOKING askew, but actually being straight. I reinstalled my barrel spacers, and shot my rifle, and the hook was gone!

 

What causes this? Well, actually something Brainplay said made me think about this. Some paintball barrels curve upwards in order to apply backspin (hop). I'm not sure why but I think it may have to do with the ball rolling along the edge of the barrel. So a left curving barrel would cause hop to the left, and vice-versa. Why was my problem exacerbated by reducing hop? I believe that the hop applied by the hopup caused a backspin, which sort of competed with the hook caused by the curving barrel. What I got was some degree of backspin and sidespin which could vary from shot to shot.

 

My rifle is a KJW M700 takedown, but this principal could apply to any airsoft rifle.

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Used to be somewhat common in the old days. People would crank the outer barrel set screw that goes through the stock to the point that it would bend the outer barrel out of alignment and cause a curve.

 

On a side note, have you tried without barrel spacers at all? Bnoji tested this out a while back and saw no real advantage for having them. I had one but removed it. Currently the only contact is at the hopup chamber and the endcap. I saw no real loss but no real gain from doing it. So it's stayed "naked" since then. It sounds like the spacers might be contributing to the problem.

Edited by Brainplay

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Used to be somewhat common in the old days. People would crank the outer barrel set screw that goes through the stock to the point that it would bend the outer barrel out of alignment and cause a curve.

 

On a side note, have you tried without barrel spacers at all? Bnoji tested this out a while back and saw no real advantage for having them. I had one but removed it. Currently the only contact is at the hopup chamber and the endcap. I saw no real loss but no real gain from doing it. So it's stayed "naked" since then. It sounds like the spacers might be contributing to the problem.

 

I considered it, and even tried shooting it with the silly "free floating" idea. I don't really want to go with no barrel spacer and no end cap since I want to run a supressor. So far I'm pretty pleased with my limited test so far. I didn't have any mysteriously hooking bbs, so good deal.

I actually believe that if everything is true and straight, a rigid internal barrel is superior to a barrel that can wobble around. It's not like free floating a RS rifle, where harmonics come into play, and the barrel doesn't need support from the handguard. Our relatively flimsy inner barrels can move around too much leaving room for shots that can wander. It may be an improvement when an outer barrel is misaligned, but I think a perfectly aligned and rigid inner barrel is the best solution.

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Some things to note about the setup that I used:

 

It had an EdGI inner bull barrel (full diameter to the muzzle end), secured tightly at the muzzle side by an internal o-ring in a custom end cap. My end cap is not a slip fit like the standard Tanaka/KJW and the hopup isn't exactly "stock". I'm also running a 20" outer barrel, so an additional 4" of inner barrel length is not accounted for. This combination is actually very solid without barrel spacers.

 

We have several customer rifles in progress right now, so I can do a little more testing on this as I finish them up.

 

BTW, your mock suppressor adapter will almost definitely function as a muzzle end spacer. Most come with an internal o-ring.

 

One version:

th_M700_CQB_03.jpg

 

Another version with a 6.00mm barrel waiting to be shortened:

th_M700_Endcap.jpg

Edited by bnoji

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Is your outer barrel custom, or did you thread it for your end cap? If it's custom, what other differences are there compared to a stock barrel?

When you say your hopup isn't stock, is that in reference to the thicker barrel, necessitating a bucking or hop system that needs to accept that thicker barrel? Or is the barrel size at the hopup unit the same diameter as your average barrel and it necks up after the chamber?

 

Nice precision looking rifle.How's it shoot?

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