OK, cant find it anywhere, but I know some time ago, somebody posted an article about the barrel mods needed to correctly convert a Hudson PFC barrel to PR screen accurate.

Can anyone assist?

Keep the barrel as it is. Just remove the front sight and extend the barrel with a piece of 0.75"/19.05mm outer diameter tube. If the front sight is not a separate piece you'll have to grind/lathe the sight down so that you get a 0.75"/19.05mm barrel (in the area where the front sight was).

Cheers,
Stefan

The barrel extension is slightly larger diameter than the PR barrel. Mine was turned from aluminium rod on a lathe, bored out a 10mm hole and crowned the end. I threaded the inside of the hudson barrel and the extension screws in.

You'll probably need to replace the front ring on the barrel vent as well since everyone still copies the SD barrel (which is too narrow). It makes me cry when people remove the entire barrel of their Marui M1A1 and replace it with a skinny tube...

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Jon

'Do not go where the path may lead: go instead where there is no path and leave a trail.'

Can I confirm the barrel diameter is 19.05mm?

Because with a 10mm hole inthis, it makes a wall thickness of 5mm (ish) which seems quite large to me?

Ups, sorry 19.05/0.75" it is - forget about my 12.7mm rubbish!

With a caliber of .45 (11.43mm) you get a wall thickness of 3,81mm - not too much at all.

Cheers,
Stefan

Does anyone have a good image of the tip of this barrel?

I know on the live fire that it is not perfectly round, as it had some kind of shape to allow the use of a spanner or a grip for removal

How about Harry's site?
http://www.harryharris.com/opr09.htm
http://www.harryharris.com/opr10.htm

Cheers,
Stefan

here's a pic from the SF&FM photoshoot that isn't on Harry's site



and here's the front of one of my PR's - this one has an SD receiver and a machined steel barrel the "correct" dimensions.



I'll post a more recent pic of the Hudson barrel a bit later.

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Jon

'Do not go where the path may lead: go instead where there is no path and leave a trail.'

Yep, checked those already. and the prop store images, but nothing really shows a detail image of this.

Do we think it is just two flat sides on the barrel?

*EDIT*


..... You posted faster than me! Nice images Jon! Just what I was after! Thank you

here's a fresh pic of the front of my Hudson barrel extension - it's 18.25mm in diameter



In the SF&FM pic I posted you can see that the diameter of the front support on the barrel vent is pretty much the same diameter as the remington barrel.

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Jon

'Do not go where the path may lead: go instead where there is no path and leave a trail.'

Thanks for the pic Jon.

18.25mm is a little under Bug Stompers recommended 19.05mm.

Why did you go for 18.25mm?

because that's how big I made it based on scaling reference pics relative to the diameter of the hudson barrel.

[/i]

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Jon

'Do not go where the path may lead: go instead where there is no path and leave a trail.'

Jon,

Any chance you could post a pic of the business end?

I would like to do a comparison with the photo you posted.

Bug Stomper - Where did you get the 19,05mm figure? I realise that is the dia of the end of a Thompson, but do you know if it was the dia used for the extension??

Feel like I'm back at school and getting graded on an algebra test - "Extra points will be given for showing your working"

this is what 0.75" looks like next to a 1:1 BAPTY photo of the 10 hole Hero i.e a bit too fat



Yes that's a real SPAS cage to double check the size of the photo.

PS that's the original photo not one of the "copies" that's been circulating recently.

_________________
Jon

'Do not go where the path may lead: go instead where there is no path and leave a trail.'

Jon does that mean the copies aren't 1:1 scale? I have one but haven't checked it. Actually I'm not sure where it is!

Harry

_________________

http://www.facebook.com/TheHHACA - @TheHHACA

Harry, I guess he means this is true 1:1 scale. Reprints can distort the sizing slightly, and as we are talking mm's here, having measurements from the original is important.

Jon - You are a legend!

Nice thread guys!

Wishing I didn't sell my marui parts!.

What's the final diameter Jon?

Jon,
that's a very good point you have there! Could you please measure the thinnest point of the barrel in the photo?

The reason for me to state 0.75" was that there is no step between the muzzle adapter and the original Thompson muzzle. As you can see the slot for the front sight pin I always assumed the barrels were unmodified. If the front diameter is indeed smaller, they had to rework the barrels - not an easy thing to do and it makes a rebuild to an original Thompson more difficult.

Cheers,
Stefan

Ok, here's my comparison:


The outline you see is a CAD-Model of an actual, unmodified M1A1 barrel (with the barrel adapter attached) with dimensions taken from the real deal and cross checked with blueprints of the Thompson. As you can see - it matches perfectly to the picture of the photo. So unless they (Bapty) modified the whole length of the Thompson barrel (which I find unlikely) the front diameter is 0.75"/19.05mm.
I guess the problem arises from the perspective that's in the picture. The side wall of the SPAS cage is slightly near to the camera than the barrel. So when the side wall in the picture matches perfectly to the real deal, the barrel will show up slightly smaller in the picture.
You can see the effect at the slots of the SPAS cage too - if it would be a true isometric picture the slots of the rear wall would align perfectly with the front slots.

I hope this helps.

Cheers,
Stefan

I'm pretty sure the ruler is being held down the centerline of the barrel. The slot spacing on the SPAS is 1.5" (the length of a slot + the bit between the slot) which can be measured from the near and far sides on the print - the near slots are big, the far slots are small - split the difference and I get 1.5" (as close as I can measure).

The narrowest part of the barrel is 0.65" on the print - which is 0.01" (0.25mm) smaller than the spec but even scaling it up to account for that I still can't justify the extension being any more than 0.71"

Since the hudson barrel is slightly fatter than the print the extension I made was a bit bigger so the proportions were consistent.

I think they threaded the barrel, attached the extension then, to make it look seamless, stuck the whole thing in a lathe and skimmed a few thou off the front. And the whole barrel in the print was probably turned down slightly to remove any blueing or rust.

_________________
Jon

'Do not go where the path may lead: go instead where there is no path and leave a trail.'

Going on the assumption that they did remove rust or bluing (as the photo would indicate - the barrel is super shiny) this would account for the barrel in the photo being 0.01" (0.25mm) smaller than an actual real Thompson.

I'm going to fix my skinny barrel!

The G+P barrel is probably better than the skinny SD style.


The Marui has the sight molded on, so I need to grind it down to the .75 in ?

There's a doughnut shape on the end of the barrel. Guess I need to grind to

that point.


Maybe we can SD to do new barrel triangles....

I do have one of those posters which I received as a freebie (Thanks, Jon!) -- however, way back when we tried to do some CAD/CAM work off of it, we noticed that it was definitely not 1:1 depsite being a real photo.

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Does here anyone make the thicker barrels?

Thanks

Not that I know.


I picked up some 3/4 aluminum tube today.