Tip for the day

[bigtoe01]

Do NOT under any circumstances feel that fitting a silencer will not cause POI issues on a new gun, even when the gun is a Diana and the silencer is a HW.

150 pellets tonight thru my new 280k 0.177 (new to me) pellet testing only to find all the inaccuracy issues were silencer related and yet nothing was clipping.

No silencer = 1 hole at 25 yards and ragged hole at 30 yards
With silencer 10 mm groups 25 yards and hopeless at 30 yards...really head scratching.

As I said, no clipping. Right now im baffled as to what the issue is with the mod fitted.

[wonky donky]

I had the same problem many years ago when I fitted one of John Bowketts long silencers to a Titan MC010. The rifle was fine without or standard or short length silencer. it turned out to be the bore relation.

Also when testing a couple of Steyr 10mtr match rifles from a test rig, indoors, I found if the barrel weight was moved forward by the permitted 50mm the groups would open up quite dramatically. I put this also down to bore relationship because the rifles were unaffected when I tested my 50mm sight extensions which fit into the barrel sleeve.

[haloutdoors]

Hello Tony, just a thought as I've just been reading JT articles on barrel harmonics. Could it be that the silencer is buggering up the natural barrel vibrations. My Webley Vulcan was greatly effected bu a lump of lead flashing wrapped around the barrel in various places. It was always useless with H&N preferring AA fields but after reading JT's article I decided to try putting weight on it and it transformed the groups with H&N. just a thought.

Are you going to keep the tip of the day going throughout the Christmas period? I'm sure it would be greatly appreciated by the membership.
ATB. Hal.

[benchstop]

Do NOT under any circumstances feel that fitting a silencer will not cause POI issues on a new gun, even when the gun is a Diana and the silencer is a HW.

150 pellets tonight thru my new 280k 0.177 (new to me) pellet testing only to find all the inaccuracy issues were silencer related and yet nothing was clipping.

No silencer = 1 hole at 25 yards and ragged hole at 30 yards
With silencer 10 mm groups 25 yards and hopeless at 30 yards...really head scratching.

As I said, no clipping. Right now im baffled as to what the issue is with the mod fitted.

Nothing worse than being 'baffled' about a silencer issue.

rgds Mike

[u.k.neil]

Could be slight eccentricity problems between barrel bore and baffle/end cap bores. If the pellet is leaving the end of the mod towards one side of the end cap then there could be a pressure differential from one side of the pellet to the other and destabilising its flight. I have had this before and it was down to the bore of the rifle not being concentric to the barrel o/dia. This was on a supposedly good barrel as well.

Neil

[Biker_Bob]

+1 vote for barrel harmonics.
Have you seen that Youtube high frame rate video of a springer firing? It's frightening, the barrel lashes about all over the place.
Try the trick of wrapping a band of lead around the barrel 1/2 way along, then move it fore and aft to see if makes a difference.

[bigtoe01]

Could be slight eccentricity problems between barrel bore and baffle/end cap bores. If the pellet is leaving the end of the mod towards one side of the end cap then there could be a pressure differential from one side of the pellet to the other and destabilising its flight. I have had this before and it was down to the bore of the rifle not being concentric to the barrel o/dia. This was on a supposedly good barrel as well.

Neil

Neil its true...looked at that last night....we are talking Diana here, NOT HW....had 4 HW100 barrels and none of them were screw cut correctly from the facotry so ended up fitting BSA (learnt my lesson)

Barrel is clean also, although i will reclean it again today and check the crowning...as i said however, bare barrel, tight groups so i doubt im missing anything. Silencer came off my MFR, on the mfr it allows 5mm groups off a bag at 40yards

[bigtoe01]

+1 vote for barrel harmonics.
Have you seen that Youtube high frame rate video of a springer firing? It's frightening, the barrel lashes about all over the place.
Try the trick of wrapping a band of lead around the barrel 1/2 way along, then move it fore and aft to see if makes a difference.

yep thats what im thinking, so decided over Xmas I will machine up a slim silencer/weight and do some testing

[bigtoe01]

Are you going to keep the tip of the day going throughout the Christmas period? I'm sure it would be greatly appreciated by the membership.
ATB. Hal.

you like the idea...its something XTX does on his FB page, so I would be nicking his idea really so maybe not...I will ask Darrin

[junglie]

Could be slight eccentricity problems between barrel bore and baffle/end cap bores. If the pellet is leaving the end of the mod towards one side of the end cap then there could be a pressure differential from one side of the pellet to the other and destabilising its flight. I have had this before and it was down to the bore of the rifle not being concentric to the barrel o/dia. This was on a supposedly good barrel as well.

Neil

I've had this too, usually shows up rotating the barrel, with silencer fitted, on a flat surface with a light shining down the bore from the breech.

[Gwylan]

I've had this too, usually shows up rotating the barrel,, with silencer fitted on a flat surface with a light shining down the bore from the breech.

Me to, but if it's true, then probably harmonics. In theory, adding mass to the muzzle end will lower the frequency, and increase the amplitude of vibration, making the effect slightly greater.

Gus

[Arai]

I've got 2 HW silencers here Bigtoe, one in its box and one on my own .177 Diana 280K, (which is very accurate with or without moderator) - you're welcome to test either.

[BTDT]

Me to, but if it's true, then probably harmonics. In theory, adding mass to the muzzle end will lower the frequency, and increase the amplitude of vibration, making the effect slightly greater.

Gus

Would increasing the amplitude, but decreasing the frequency, significantly alter the muzzle first mode vibration velocity, Gus?

For anyone interested in barrel vibrations, Mike Wright's article on tuning barrels was in the May 2011 edition of Airgun World.

[alex.mc]

Bernoulli effect! The pellet doesn't have to clip the silencer, just pass very close to it. The pellet will tend to be drawn slightly towards the nearby object(the silencer) and away from it's previous trajectory. It won't be consistent either as all sorts of things will affect it each shot.

I had this on my X2 when I first got it. It wouldn't group for toffee! After a few magazines wondering what the hell was happening, I took off the silencer and shroud and peered down the barrel, nothing untoward! Fired a few pellets..... single hole groups at 20 yards rather than the 10 inch spread of before. Shroud back on... still good. Silencer back on and it was all over the place.
I found the silencer to be slightly bent at it's base. Just enough to send the pellet perilously close to one side, but not actually clip it. I shimmed it with a piece of paper, checked it, and it was as good as gold!

[Gwylan]

Would increasing the amplitude, but decreasing the frequency, significantly alter the muzzle first mode vibration velocity, Gus?

For anyone interested in barrel vibrations, Mike Wright's article on tuning barrels was in the May 2011 edition of Airgun World.

You and the Prof are the experts...! I'll look up your articles again, I seem to recall lumps of lead and jubilee clips? I was spouting theory based on tuning concertina reeds, obviously not the same as rifle barrels.

Gus