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rsterne · Moderator

I just made a muzzle brake for my 2260 PCP.... Since airguns don't have any significant recoil, but do have a bit of muzzle flip, I decided to vent it on the top only.... Immediately in front of the barrel it has a 3/8" diameter chamber 1" long with three milled slots facing upwards only.... the slots were made with a 3/16" mill and are 3/8" long (ie the same as the diameter of the chamber).... In front of that, the diameter is 1/4" for an additional 1/2" of length....

I can't try it outside right now, and inside I'm limited to only 7 yards.... At that distance the gun puts 5 shots into a single hole about the size of a pencil.... either with or without the muzzle brake.... What I find interesting is the POI.... it's 3/16" lower with the brake installed.... Shocked

What I'm curious about is if that is due to the reduced muzzle flip.... or if the brake is actually bending the flexible Crosman 24" barrel down during the shot.... I notice a difference in the sound because it's venting upwards and reflecting off the ceiling (I expected that).... but what I didn't expect is that the gun vibrates as it the end of the barrel it getting tapped by a hammer.... Shocked

Honest to god, it rings like a bell, but without the sound (too low a frequency to hear, I guess).... You can feel the vibrations decaying for nearly a second after the shot.... I initially thought the pellet was hitting the brake the vibrations were so strong.... The exit hole is well centered, of course.... and I checked it out with a jewellers loupe and there is no sign of even a slight touch by the pellet....

Has anyone else experienced this phenomenon?.... any comments Joe?....

Bob

fritz · Silver Status Member

I would think POI might be higher if the barrel isn't bending. This is because the top side is a low pressure zone as the air escapes. So the high pressure will want to reach equilibrium and expand, to push the pellet up.

It is very likely the brake bends the barrel ever so slightly.

AirGunEric · Site Admin

It appears that you have created less of a "brake" and more of an air stripper based on your description.

The problem may be that with slots on only one side of it, the harmonics are not balanced. Why not try putting some slots in the opposing side and see what occurs?

Air stripper: http://www.airgunhome.com/agforum/viewtopic.php?t=385

rsterne · Moderator

rsterne · Moderator

AirGunEric · Site Admin

rsterne · Moderator

AirGunEric · Site Admin

Interesting, and quite possibly it's own debate. The "brakes" used on airguns have often not had any holes and still been called "brakes" (Beeman had a couple units, no holes, that were sold as "brakes"). It does make sense that if the concept is braking air that it should have holes. I suspect what we have here is one of those situations where terminology has spread too far and includes just about everything within a certain umbrella.

In any event- you did find previously a muzzle weight eliminated muzzle flip, apparently a singular-direction vent system is now causing harmonic problems- I think you had the answer to your original issue (weight will eliminate flip), but nonetheless an analysis of why so much vibration is present would be interesting- even if you don't achieve a complete elimination of the muzzle flip using this method on an airgun. Perhaps enlarging the holes and seeing what happens would be an interesting step forward in this experiment(?)

Alstone · Moderator & Site Supporter

A difficult one Bob, you would think that the poi would move up under normal circumstances as the barrel should have no part in the action, because the pellet has already left it and the only force to move the pellet is the higher air pressure under it. Unless there is some blow by and air is exiting the barrel ahead of the pellet, and the anti flip is causing the barrel to drop?

The only other thing I can think of is that the high pressure air passing the slots is in fact drawing air in and pushing the pellet down? Are the slots angled back or straight up?

You could try putting some tape over the slots and trying it again, if the problem goes away then it’s the slots, if not then the brake.

Other wise I haven’t a clue. Laughing

Al

rsterne · Moderator

I don't think the weight on my 1750 changed the POI from what I remember.... It did make the gun more balanced and the added mass allowed me to get better groups offhand (more inertia, less wiggling around).... There would be less muzzle flip because of that increased mass I guess....

In theory, some of the air would be vented before the pellet clears the front of the muzzle brake.... but you are talking a travel of only 1.5" from the time the pellet exits the barrel until it clears the brake.... At 940 fps, that is only 0.00013 sec.... During that time, the pellet could be influenced by the air inside the brake.... while without the brake, that air would be escaping around the skirt of the pellet past the barrel crown.... I suppose that flow difference could reult in a POI change....

I think I'll try taping over the slots and see what happens to the POI.... good experiment, Al.... Wink

The slots are straight up, at 90* to the bore....

Bob

donec · Senior Member

Is the design of the brake such that you could mount it with the hole pointing down? If so you could see if it caused a rise in POI. If it did wouldn't that say the change in POI was due to the air currents created by the break and the hole?

rsterne · Moderator

Well, the good news is that the group size doesn't change much in any version I tried.... The bad news is that venting the brake on one side makes that skinny Crosman barrel ring like a low frequency bell.... Shocked

I tried taping up the holes and the vibration (ringing) went away as you would expect.... I also tried turning the brake upside down and when taped it worked exactly the same as right side up.... In both cases, the POI was 0.20" below the POI with the barrel bare.... I can only assume that the internal chamber in the brake is disturbing the way the pellet exits the barrel, regardless of the orientation....

I also tried removing the tape with the brake upside down.... The ringing returned, and the amount of upwards force is significant as the gun moved on the sandbags.... It literallys take the weight off the front support when you fire the gun.... The gun doesn't jump into the air, but I would estimate the upwards force is at least a pound!.... Shocked

With the brake upside down, the POI moved upwards 0.06" with the ports untaped.... With it right side up, however, it also was slightly higher than when untaped.... That's the only POI change that doesn't make sense....

I have made another "brake" (actually just a small weight) to finish off the end of the barrel.... It is shorter, and the opening is 5/16" diameter (larger than the crown on the barrel) and only 0.040" long to the beginning of the countersink ( the front is flared).... Basically, it just looks pretty, and shouldn't affect the pellet at all.... This proved to be the case as the POI returned to the bare barrel location with the new "brake" fitted.... Wink

Bob

AirGunEric · Site Admin

So, where's the pictures to see the cosmetics?

...must have pictures...