please help

[BASE JUMPER 18]

like you no i had my shroud cut down but i dont think its anything to do with that i thought it was down to them clipping the silencer but adi threaded my barrel and crowned it for me so my daystate silencer screws directly on my barrel now i think its just down to me finding that right pellet as the groupings are not bad just need to find out why im getting FLYERS davy has gave me a good suggestion to try tomorrow to eliminate the theory of the silencer clipping so im trying that tomoz but if it was clipping the silencer surely the targets would look like i have shot a shotgun at them im only doing this at 30 yards because that is all my garden will allow but im not going to re-zero my scope no more between change of brands i should still see groupings then when i FINALY find that magical pellet i can zero my scope accordingly

[craig33 10]

change the probe seal mate it might look ok but can cause the odd flyer if not sealing right or worn also could be the reg i have de regged them in the past and all were quite a lot better.

also check the barrel is tight give the grub screws a nip up

is it leaking at all might be worth checking arround the filler nipple and bottle and joint on the middle of the block as this can cause inaccuracy probs

craig

[BASE JUMPER 18]

change the probe seal mate it might look ok but can cause the odd flyer if not sealing right or worn also could be the reg i have de regged them in the past and all were quite a lot better.

also check the barrel is tight give the grub screws a nip up

is it leaking at all might be worth checking arround the filler nipple and bottle and joint on the middle of the block as this can cause inaccuracy probs

craig

 

nice one for the heads up its the newer version air ranger august 2008 model so it is not regged like the earlier versions ill have a look at the seal but i have checked the shroud and barrel and they are fine

[zini 1,939]

In a ballistics term the reason is called Barrel droop.

 

No barrel is truly straight and everyone is different slightly.

 

Droop means that a barrel will have a very very very slight curve downwards usually in it which you will not be able to tell or see with the human eye.

 

When you zero without a silencer fitted you compensate for this slight droop.

 

When you extend a barrel with a silencer you add to the droop curve slightly via weight and untrue threading and change in how you hold and shoot the rifle which usually means a lower impact point on your target.

[andyfr1968 772]

In a ballistics term the reason is called Barrel droop.

 

No barrel is truly straight and everyone is different slightly.

 

Droop means that a barrel will have a very very very slight curve downwards usually in it which you will not be able to tell or see with the human eye.

 

When you zero without a silencer fitted you compensate for this slight droop.

 

When you extend a barrel with a silencer you add to the droop curve slightly via weight and untrue threading and change in how you hold and shoot the rifle which usually means a lower impact point on your target.

 

You'd need a bloody weighty moderator to make any kind of bend on a gun's barrel, Si.

 

It's to do with the fireing cycle and the gun barrel's relative position dureing the lock time

[rossy08 33]

well Andie theres pleanty of stuff to go at there matey. i regards to the h+m feild target pellets, they have always been good, rember stupid stu's rapid years ago he used them, and now my mate carl gets very very good results with them in his rapid. ran around 50 through my 410 at his house and they are just as good as the aa's in my rifle. i think but not shure, but think sam uses them in his air wolf, ill ask when i see him next.

 

talk with ya later on the blower mate.

 

atb pal

[zini 1,939]

Hi Andy,

 

Sorry I didn’t really explain my thinking properly buddy, sorry

 

No it doesn't bend the barrel mate LOL, i didnt mean that as that would need to be a very heavy silencer and I don’t think many could carry a rifle that heavy :showoff: .

 

Not all rifles have a floating barrel as you know buddy and some have a really good barrel fixing clamp so don’t feel this effect as much.

 

The added weight and the not 100% tolerant screw cut on the silencer side wall or adaptor due to machining (being off concentric) both externally and internally, the precise angle and tightness of the barrel fitted to the breech all can get effected by weight and added length changing things harmonically when the firing process begins.

 

We are only talking micro millimetres of change here lads not tonnes of change and you wont see it with the human eye.

 

This all enhances a more parabolic shape to the barrel and adds to droop.

 

Also with a silencer fitted the rifle barrel does not raise up in the same manner on firing that a rifle does without a muzzle weight (silencer) fitted, adding to a lower POI.

 

Remember that even the movement of a PCP due to hammer movement on firing means that a PCP is not fully recoilless and a change in weight and shape will effect POI and how the rifle reacts to being shot.

 

This will be enhanced more with a longer silencer where the pellet is still in the barrel / silencer when the shooter moves the rifle due to not fully following through. (due to lock time like you said buddy).

 

This then usually gives a change slightly left or right to (due to human error) as well as down due to the extra weight (small or not).

 

Not all rifles do this as I found out when fitting a SAK some time ago to my r10, there was no change either way, maybe I was lucky I’m not sure bud.

 

There is also a possibility of clipping too, but in this case I think it's not the factor mate .

 

I'm sure there are other factors involved too lads which we have not looked at here also at play.

 

To cut a long story short guys, fit the silencer and then zero with it on so you get no weight change, no change in rifle shape or change in harmonics as it fires.

 

Si.

 

Here are some others with the same problem,

 

Question.

 

Hi,

Do all silencers change the POI when they are fitted ? I tried to zero in my taipan rifle & found when my silencer is fitted the POI drops & moves right, is this a normal thing ? It still groups well but its moving the poi with the silencer. There was loads of play in the thread on both barrel & silencer so i machined off the thread & re-faced the barrel then machined out the silencer for a nice tight fit on the barrel, secured it with a grub screw.

tested it with & without silencer & with the silencer on it still moves to the right & little down

next step is to pull the silencer apart & check the internals. I know the silencer is fitting perfectly straight now but why the change in POI

any ideas?

 

Answer.

 

The extra weight at the end of the barrel is causing the poi to drop.

 

The left and right shift is way to long winded, to write about.

 

Answer.

 

Like the man said, heavy mods do make the barrel bend down slightly and the extra weight can also reduce muzzle flip/recoil so POI may be lower ( this does not indicate reduced power) but it might help when it come to accuracy. To ensure that the pellets fly striaght down the mod I stick a piece of masking tape over the end of the mod then take a shot, check the exit hole to see if it runs true.

 

Answer.

 

Depending on how your barrel is supported your POI will change accordingly because of the weightof the silencer, reduction in muzzle flip especially on a free floating barrel.

 

Answer.

 

Barrel harmonics has something to do with it. The weight of the silencer has a lot to do with it too. Hang a 22oz weight on the barrel and the POI will shift even if the bullet doesn't pass through the weight. A barrel deflection of only 0.0067" on a 24" barrel will cause a 1MOA shift at 100yds.

 

Don't buy the hype of companies who claim their silencers offer "no POI shift" or "the lowest POI shift." Every rifle reacts differently to a silencer, there is no way to predict it accurately. What's more important is that the groups stay tight, and that the shift is repeatable (ie, the same 2MOA shift every time you install the can). That way you just add a certain number of clicks whenever you install the can, and you're back to a perfect zero.

Edited January 3, 2011 by zini

[BASE JUMPER 18]

Nice 1 Zini that made a very interesting read like you said personally I don't think it's the silencer as this screws directly on to the barrel but I'll have a look at that today and my silencer is made out of carbon fibre

[jasper65 6]

when i FINALY find that magical pellet i can zero my scope accordingly

 

Don't think you read through what I put in the last post! OK you have eliminated the shroud being shortend and also silencer clipping so like you said it could well be down to the Pellet choice.

 

I mentioned before I shot through virtually every viable recommended pellet through My .177 Air Ranger and came up with H&N Field Target Trophy 8.66 Grain Pellets. its entirely up to you if you try them but personaly I would give them a go if you're getting the problems you say you are......

[zini 1,939]

No problems Base Jumper buddy

 

Si

[zini 1,939]

Hi Base J

 

A few more here,

 

1 Barrel harmonics can be tuned. The Browning A-Bolt full bore rifle has an option using the B.O.S.S. system. It has either a weight or muzzle brake with weight that can be adjusted along a scale to tune the frequency that the barrel vibrates at when a shot is fired. It can reduce or increase the group size.

 

If any of us had the inclination (and were a good enough shot to benefit from it), we could knock up some sort of barrel tuner (.22 bench rest shooters have made them). Thicker barrels dampen the vibration and are less affected. I recall that one of the Webley PCP's had it's barrel thickness increased (to 14mm i think) a few years ago due to accuracy problems. Pencil thin barrels are very 'whippy' and benefit from support like clamps or brackets. then again, if you give a barrel a knock it affects POI or accuracy anyway.

2. A silencer usually makes the POI drop due to the physical weight esp on a free floating barrel. However, it may also shift the POI to left or right of the vertical centre line. Adding weight and the volume of the silencer chamber can also change the harmonics of the barrel which can change the POI or more likely the tightness of the group. No precise science here.

Si

[mikeyblue 28]

Hi Si,

 

The modification re. barrel tuner has been done with air rifles. There is a bloke on the FT and HFT circuits who uses a Barrel Harmoniser! From what Ive seen its a little weight at the end of the barrel on a screw thread. So he can adjust the way his barrel reacts during the firing cycle. Very clever.

 

Mikey.

[BASE JUMPER 18]

right just been out side having a play the pic below had a 10 shot mag at the target and it was bench rested the scope is zeroed the cross hairs never moved of the bulls eye but ignore the mark next to the number 5 thats a nail mark and it was at 30 yards tried davys idea about moving the silencer quarter then half turn on the treads to see if the silencer was clipping and they still grouped, looking at the pic i think i just need a different brand of pellets that group tighter than jsb i do have some air arms on the way from the pellet swap thread so when they arrive ill try them but looking at the other pics i would say the accupells group tighter in the pic that says silencer on but between me and you i hate accupell

 

[matt_hooks 188]

In a ballistics term the reason is called Barrel droop.

 

No barrel is truly straight and everyone is different slightly.

 

Droop means that a barrel will have a very very very slight curve downwards usually in it which you will not be able to tell or see with the human eye.

 

When you zero without a silencer fitted you compensate for this slight droop.

 

When you extend a barrel with a silencer you add to the droop curve slightly via weight and untrue threading and change in how you hold and shoot the rifle which usually means a lower impact point on your target.

 

You'd need a bloody weighty moderator to make any kind of bend on a gun's barrel, Si.

 

It's to do with the fireing cycle and the gun barrel's relative position dureing the lock time

 

Not as heavy as you might think Andy. With a modern fully floating barrel, the weight of an added moderator, cantilevered over the length of the barrel, can cause apreciable droop in the lighter weight barrels usually fitted to air guns. Remember, even a half millimeter change in the curve of the barrel can cause a considerable change to the POI.

 

The recoil cycle on a PCP is so slight that they're not really bound by the same rules as proper recoiling rifles, in terms of lock time, barrel harmonics etc. I would suggest that the most likely error is to do with the floppy organic bit on the end of the butt! Paralax is a killer, and with high mag scopes, if you don't get exactly the same position each time it can cause quite a change in POI. Remember, a tiny change in position at the blunt end can cause a big change of POI!

 

I was brought up using match diopter sights, with no magnification, and with those if you don't get everything right, target central in foresight, foresight central in rearsight, then it's the difference between a v bull and dropping a few points. This is magnified by a high magnification telescopic sight!

[mikeyblue 28]

Hi Base Jumper,

 

Im not sure whether the AA Field will help your cause much pal as they are near identical pellets to the JSB's, made in the same factory, same machines etc. As Jasper said its worth trying the H&N Field Target Trophies as they work well in his Ranger. Got to be worth a go!

 

Hope you get sorted.

 

Mikey

Edited January 3, 2011 by mikeyblue