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I've just bought Dangermouse's SGC 9mm

he's done a fairly neat record of things he's done with the gun on his 'something black continued' thread
(http://www.full-bore.co.uk/viewtopic.ph ... &start=130)

so one thing he talked about was the thread protector on the barrel, and the thread, which seems to be 3/4 x16 tpi which seems to be a huge thread (almost 20mm dia), especially for brakes and suppressors. looking at the barrel, sgc have counterbored the end of the barrel by about an inch deep, and have taken the internal dia from 9mm out to about 16mm (5/8 for Dromia). the thread protector is a cap type, with a 9mm clearance hole drilled through the end.

does anyone know why they have done this?

i would have thought it would make more sense to leave the int dia of the barrel as is all the way to the end, and either bring the ext dia down and stick a normal suppressor thread on it, or then thread it to 3/4 UNF as before. but as it is, you can't do anything to the barrel without parting off the counterbore and then starting again on the major dia. shortening the total length of the barrel in the process (although i haven't checked barrel length yet, so i dont know if that will be an issue or not yet).

instead, they have seemed to create a small expansion chamber on the end of the barrel. if it was drilled through from the side it would be a comp.... or have they done it to increase back pressure or something?

it seems to be a ballache now to get accsessories for it.

bradaz11 wrote:
instead, they have seemed to create a small expansion chamber on the end of the barrel. if it was drilled through from the side it would be a comp.... or have they done it to increase back pressure or something?

it seems to be a ballache now to get accsessories for it.

If it has created an expansion chamber I would hazard a guess and say they have done it to improve gas pressure due to the relatively short barrel and the relatively small (case wise) round.For a comparison the short barrelled AK-74u and AK-104 carbine have a flash hider that incorporates an expansion chamber to increase gas pressure to aid cycling, although both will cycle perfectly well with the flash hider/chamber removed!.It could be to aid cycling when using subsonic ammo perhaps?, just an idea.

hmmm, ok, that was the only reason i could think of. I wonder if they are still doing it?

now, could i machine up a step down thread adapter? thread it 3/4 unf, bring it foward, and step it down to something like 1/2 x 36 to accept a new muzzle break or silencer?? as long as its all done true, and gives more clearance around the bullet than the original barrel cap / thread protector, should there be any issues??

Why not buy a piloted muzzle brake and bore and thread it to suit the original, you can also build or order a suppressor to suit as well.

what do you mean by 'piloted'?

do you mean one that has only a pilot hole on the barrel end?

Yes, you can buy muzzle brakes which come un-threaded and with a pilot bore only so you bore it to your chosen diameter and thread to suit. Alternatively just make one from scratch.

have you got any links to these? i can't seem to see any

the main issue i could see with using 3/4 as the main thread would be the with the comp having to a rather large dia

Mik at Dolphin makes muzzle brakes and can probably supply an un-threaded version, alternatively machine one from a section of old barrel, I have some here if you fancy building one yourself and need some materials.

My 9mm is away being threaded at the moment so I can fit a Mod, due to recessed crown it will be 3/4 16tpi.
Do not know why they came recessed it looks like the newer ones do not mine is early Glock mag one.


TW

ovenpaa wrote:Mik at Dolphin makes muzzle brakes and can probably supply an un-threaded version, alternatively machine one from a section of old barrel, I have some here if you fancy building one yourself and need some materials.

ah go on then! yes please :) out of interest, what are mik's prices like? are we talking £50 or £100-150 or higher?

toffe wrapper wrote:My 9mm is away being threaded at the moment so I can fit a Mod, due to recessed crown it will be 3/4 16tpi.
Do not know why they came recessed it looks like the newer ones do not mine is early Glock mag one.

ahhh ok, who are you getting the mod done by? or did you by Dangermouse's?