What would be a better material for this?

[AndyP]

I use a fully moderated shotgun for pest control in areas where noise can be an issue. Fully licensed and legal I might add.

The moderator consists of a number of baffles like this. They are 1.5mm thick aluminium, fit inside a 50mm aluminium tube and have 17mm holes punched in for the shot to pass thru but the blast from a 20gauge shotgun soon seems to destroy them particularly in the middle part between the barrels, the weakest point I suppose.

I was looking to replace them with something more durable and was looking for suggestions. Weight is an issue and I would like to avoid adding any more weight if possible. There are about eight in the gun forward of the muzzle with spaces to seperate them.

Any ideas about materials and bright ideas about making them would also be handy, I was looking at using my lathe or mill but there may be an easier way.

Cheers
Andy

 

[Hitch]

Is changing them a pain in the backside? Why not get a boxfull lasered or cnc punched.
Dear initially, but youd have a lifetime supply...

 

[AndyP]

Changing them isn't too much trouble but the replacements are not very accurately made which means I have to chuck them in a lathe and rebore them. Be nicer to just make a set that would last.

 

[Paul.]

Andy
I Don't know about a suitable replacement material, but for accurate replacements take a good fitting one up to Premier laser at Corby, just up the road from you, they have a clever scanner that will progam the laser from a sample, alternatively draw it in autocad and send a dxf file, they will cut exactly what you draw, they would each cost pennies to make, as Hitch says a lifetimes supply for a few pounds.

 

[AndyP]

Andy
I Don't know about a suitable replacement material, but for accurate replacements take a good fitting one up to Premier laser at Corby, just up the road from you, they have a clever scanner that will progam the laser from a sample, alternatively draw it in autocad and send a dxf file, they will cut exactly what you draw, they would each cost pennies to make, as Hitch says a lifetimes supply for a few pounds.

How much do you reckon they would charge for, say 2 dozen of these?

 

[TechnicAl]

Be very careful.
I should take advice from gun manufacturers who have got tried and tested materials.
I dont know what could happen but you could have a very nasty accident.

 

[mike os]

the parts are designed to be "worn out" fairly quickly.... avoids more dangerous problems like parts failing & blocking the silencer, or deflecting shot.

(trust me I used to use one on a uzi professionally)

 

[AndyP]

Be very careful.
I should take advice from gun manufacturers who have got tried and tested materials.
I dont know what could happen but you could have a very nasty accident.

Don't worry, I have a pretty good understanding of the relevant issues.

Strange thing is that the OEM replacement baffles are all over the place which is frightening when you realise the clearance is about 0.5mm on a perfect set

Truth be told the worse that would happen is that a few pellets would catch and damage the baffles and the vast bulk of the shot would just pass thru.

Unlike a normal gun, the barrels are heavily ported into an outer tube before the baffles are reached so the pressures are all dispersed safely.

 

[AndyP]

the parts are designed to be "worn out" fairly quickly.... avoids more dangerous problems like parts failing & blocking the silencer, or deflecting shot.

(trust me I used to use one on a uzi professionally)

The latest models use a CNC'd monoblock baffle but unfortunately they also use a slightly larger tube so I can't fit one in this and there isn't enough meat on the new type to turn it down

http://www.saddleryandgunroom.co.uk/Gunroom/SG_Hushpower.htm

 

[hareng]

Stainless steel G303, 304 and 316 will last longer.
Want the best titanium but it will cost twice what the guns worth as long as it doesnt get too hot.

If the o/d needs to be accurate for alignment purposes it will need to be turned then parted off. If theres a gap over the baffle to inner bore for gases to flow may get away with a holesaw without cr drill.
If you havent a rotary table, chuck and DRO its going to be awkward. Could drill through one hole in each baffle and clamp all together with a screw. Problem is getting the bore holes in right place then drilling the other screw fixing hole.
Looks like old fashioned scribing and centre punch with inherant errors making a template.

Had to laugh the other week, firearms officer bought one in shaking his head and doing his fruit, why do people do things like this.

 

[AndyP]

Stainless steel G303, 304 and 316 will last longer.
Want the best titanium but it will cost twice what the guns worth as long as it doesnt get too hot.

If the o/d needs to be accurate for alignment purposes it will need to be turned then parted off. If theres a gap over the baffle to inner bore for gases to flow may get away with a holesaw without cr drill.
If you havent a rotary table, chuck and DRO its going to be awkward. Could drill through one hole in each baffle and clamp all together with a screw. Problem is getting the bore holes in right place then drilling the other screw fixing hole.
Looks like old fashioned scribing and centre punch with inherant errors making a template.

Had to laugh the other week, firearms officer bought one in shaking his head and doing his fruit, why do people do things like this.

I don't understand.

What's wrong with replacing worn baffles in a silencer, possibly with higher spec ones

Anyway, I shall take one of the better originals over to be copied as Paul suggested.

 

[hareng]

What's wrong with replacing worn baffles in a silencer, possibly with higher spec ones

Nothing Andy its just what its fitted to and realise it serves a purpose. Ok on rim and centrefires.

 

[sheetmetalworker]

hiya,
just a thought, i used to work for an acoustics company and made several prototype silencers for the US based parent company, rimfire, centrefire rifles etc.. not a problem, .410 / 20 gauge shotgun (like hushpowers ) etc.. were a bit of a disaster, very broadly speaking, shotgun blasts are low frequency ( up to 125 hz) 'gas blasts' ,centrefire etc. rifles mid frequency (500hz) air rifles high fequency (1k),during testing, titanium inserts (baffles) lasted quite well but shatter easily, 316 grade stainless although heavy, lasted well but the safety factor deems that are made to collapse under a misfire/rogue pellet etc...so we settled on using 16 gauge aluminium baffles, lowcost, replaceable etc...and in any case it became harder (in the us at least) to legally obtain a silencer than a firearm!! so was a commercial failure, mind you that was over ten years ago, maybe things have progressed a little better technically!!

Generally speaking , Shottie silencers arent efficient for many shots, and may be looked at as consumables,(well,used to be).

Under test conditions mineral wool (rockwool, etc?) and an internal perforated sleeve worked 30% better for a straight dB reduction and lasted/perfomed for about thirty times longer i recall! but was heavier and more expensive to make, more of a machining job than an assembly job. I have the design spec for this should anyone fancy a bash at making one.

In any case, we never got a 12 gauge as quiet as that the one that blokes got in 'old country for old men'

Not to be too nerdy, but during a very brief meeting with an old colleague he told me of an Ulster ex services firearms expert who demonstrated the best silencer he ever saw for a pistol, an unused ford escort oil filter,screwed onto the end, worked great.

 

[brightspark]

bit dificult putting a sight on one o them i take it that he used to use it at short range. just point and pull trigger . nothing 2 acurate

 

[malcolm]

For the material I think aluminium is used for weight saving. I can well see why the front of the gun would feel a bit heavy with steel of a similar thickness. There will be durability trade-offs against weight in the design.

For silencing performance - rockwool would be great for high frequencies but I can't thing of a way of stopping it from blowing out. Reflection and cancellation of sound is the way they generally try to work. I guess they are restricted on size as they all seem a bit Briggs and Stratton.

An almost totally unhelpful post there, but it's a subject I find interesting.

 

[AndyP]

For the material I think aluminium is used for weight saving. I can well see why the front of the gun would feel a bit heavy with steel of a similar thickness. There will be durability trade-offs against weight in the design.

For silencing performance - rockwool would be great for high frequencies but I can't thing of a way of stopping it from blowing out. Reflection and cancellation of sound is the way they generally try to work. I guess they are restricted on size as they all seem a bit Briggs and Stratton.

An almost totally unhelpful post there, but it's a subject I find interesting.

I have found that despite all kinds of fancy baffles and screen mesh to absorb/disperse the blast, that pure volume of expansion area seems to be the most important factor in reducing muzzle noise. If the gases haven't got a space to expand into they will just come out the muzzle as noise.

If you shoot at a solid object such as a wooded area you will get sound reflected back at you to a degree but shoot into the air and these moderated guns really are quite remarkable when you consider what they are pushing out the barrel. I think the over and under benefits from having quite a large expansion area and each barrels gases can even expand into the other barrel and its baffle area to a degree making it relatively efficient.

Aluminium is also supposed to act as a heat sink which makes the gases contract and so reduce sound. Have to do it bloody quickly to work though

 

[hareng]

Nothings changed in the US, though there are certain states that allow without the prerequisite licensing/permits which are relatively hard to obtain. Only around $150.

Without saying too much, this is firearms we are talking about here and ok in general for the owner to service/repair his own firearms. A friend or anyone else cannot by law even if currently holding a section 1 or 2 cert, it has to go via an RFD a big difference so carefull what anyone says.
Sound absorbtion ie the hair roller with J cloth wrapped round and similar arrangements may or may not work as well as deflection ro in other words sound/pressure drop by using baffles- Its in the design but must be tuned to the frequency of what its fitted to which means no changing of the loads.

 

[hareng]

Andy i think the only definitive way is to either a sound meter or get a good friend to monitor the difference in sound with and without baffles even though worn.
The sound may be loud where you are but its down range where it counts.

Malcolm most car exhausts are not free flowing, some the gases have to turn 180 degrees within the box it self and therefore create back pressure.
The performance exhausts on the other hand rely on sound absorbtion ie perforated tube with some sound absorbing material wrapped round that encased in what you visually see.

 

[scarecrow]

I wonder if the reason why they used aluminum is that there is a lot of different makes of weapons which are all slightly different even within the same brand there can be slight differences in weapons so it might just be a way of making one to fit all and let the shot do the adjusting

 

[AndyP]

Andy i think the only definitive way is to either a sound meter or get a good friend to monitor the difference in sound with and without baffles even though worn.
The sound may be loud where you are but its down range where it counts.

Malcolm most car exhausts are not free flowing, some the gases have to turn 180 degrees within the box it self and therefore create back pressure.
The performance exhausts on the other hand rely on sound absorbtion ie perforated tube with some sound absorbing material wrapped round that encased in what you visually see.

Im not too worried to be honest. I bought a replacement set of baffles from the manufacturer and they were so poor I ended up with a refund and had to machine them to fit.

What I have done now is to take some proper measurements and am having a couple of spare sets made by the company that welderpaul suggested for a £1 a baffle, about 7 per set.

I know each set will take several hundred rounds to destroy and even then it is just the narrow bit between the two holes that gets blown forward. The rest appears to come out of it relatively unscathed.

In my original post I was just wondering if there was a superior metal to make them out of but it seems that pound for pound ali is probaly the best bet.