GB Mod

[sccritterkiller 473]

After opening up the ports on my gun it still wasn't able to do universal drum dumsp..I thought that opening up the ports would fix the issue but once I got to looking at things I had two of the ports somewhat covered by the GB....

So here is my question.....Too much, not enough, or fuck it looks good from my house shoot the shit out of it!

The front port hole still concerns me but I didn't know if you can file past the ridge.

Edited March 25, 2013 by sccritterkiller

[Cobra 76 two 2,677]

NO DON'T get into that area. In fact IMHO you already took away far too much. That whole "D" mod thing is something that should be taken down IMO. You don't need to remove any material from the GB except for increasing the bevel form the BOTTOM side, to give the ports breathing room.

[sccritterkiller 473]

So did I screw it up???..Most of that front hole was blocked by the GB. I did all that from the bottom side coming in from the hole below....took a while...

Edited March 25, 2013 by sccritterkiller

[dubya 198]

I was thinking of doing the same eventually. So you want to angle the OUTSIDE rather than inside like in this picture?

[Cobra 76 two 2,677]

The idea is to channel the force of the gas backwards at an angle, for one. So removing anything at all from the surface you can see on the inside of the gas block (where the puck is and the gasses are trapped while expanding against it), which is at all forward of the blocked port you want uncovered, is counter productive. The ports themselves are slanted backwards for two reasons. One is to keep the edges of them from shaving off pieces of wad and sucking them into the gas chamber. The other is to apply as much rearward pressure as possible to the puck (piston). I even angle mine back a little more if I have to drill them. Now all that material that was removed in those front two corners that make the 90 degree parts of the "D", did nothing at all to help uncover anything, nor direct more pressure rearward. IMO it also takes away mass, therefore enlarging the area the gasses have to expand in, possibly decreasing pressure developed on the piston, instead of the opposite effect that is the whole reason for uncovering the ports. There are plenty of photos on here somewhere, in the numerous threads posted on this topic. I know I have posted several myself. With the GB off the barrel, upside down where you can look at the wider, bottom side of the beveled, (cone shaped) port of the gas block. The idea IMO is to ONLY remove the smallest amount of material absolutely necessary, and do it as close as possible to the direct path of the gas flow from the port itself.... therefore increasing the "jet" action so to speak.

Think of a media blaster, or pressure washer..... What happens when you decrease the size of the opening of the tip?

[Cobra 76 two 2,677]

To the OP, I am not trying to sound like a smartass or talk down to ya on what you did. On the contrary I'm only hoping others will see my post from now on and stop following what I seriously consider to be a bogus tutorial that is causing people to hack up the GBs, without even getting as much positive effect as they could, or should be getting by performing this action. You have to be really careful what you tell folks to do on this forum. Some people following these "tutorials" have never even used a drill before, and suddenly they feel so empowered they start trying complex changes to the dynamics of a semi auto military shotgun. Sorry but that ain't cool.

And if I remember correctly, that original thread shows pics of the OP actually cutting clean through into the recessed part around the base of the threads.... another boo boo.

[sccritterkiller 473]

I didn't think it was a good idea to go into the recess, that's why I stopped and posted a pick....I was under the impression that removing an obstruction from the port was the goal.....win some loose some I guess....So I guess now I need to find a new GB???

 

Wasn't really going for the D shape...just tryimg to uncover the ports...I under stand the nozzel analogy.

Edited March 25, 2013 by sccritterkiller

[Cobra 76 two 2,677]

I wouldn't go that far before first exploring other options to reduce friction, and amount of gas needed to operate the system. As long as your ports are of sufficient size, and your bolt, carrier, hammer, rails, feed ramp, barrel hood, etc.... are not adding any unnecessary friction the action, the gun should still run low brass. It would just be more efficient IMO with a circular port that a D shaped one.

[sccritterkiller 473]

It will run federal low brass just not universal....I have polished all the internals, hammer, rails, carrier bottom, carrier groves..I opened up the ports to .078, it's a 4 port gun....still wouldn't run universal...removing the obstruction was the last resort....believe me...I have better things to do than spend a couple of hours with a needle file...

 

 

Before this I couldn't see the port on the ejection side or the one closest to the muzzle....I could barely get a bread tie wire into them..

Edited March 25, 2013 by sccritterkiller

[filthygovemploye 64]

just need less agressive tooling homes!!! naw its all good. so does it run? or did i miss that?

[mikeNM 8]

Naturly,I ported the gun (4x.092"...did the gas port "D" mod....I don't remember any FTF's...Shoot competiton gun.... Never real dirty (I use "Frog Lube" and no other product).... The gun, run's fine for my use....all shells work...

[sccritterkiller 473]

It will be this weekend before I have a chance to test it out.

Edited March 25, 2013 by sccritterkiller

[sapper1371usmc 107]

You wont need a new gas block. Its good you didnt go into that recessed area. You might not have needed to make the opening that large, but it wont affect anything. And just because you cant see the ports when looking into the gas block, doesnt necessarily mean theyre covered up. When you remove the gas block, as long as the ports are within the carbon/paint overspray oval circle left on the barrel, then your good to go.

 

And you might need to increase the ports up to the next size. While 4ports at .078 is all that is needed for some guns, others might require a little more oomph. Some even run 4 at .093.

[sccritterkiller 473]

You wont need a new gas block. Its good you didnt go into that recessed area. You might not have needed to make the opening that large, but it wont affect anything. And just because you cant see the ports when looking into the gas block, doesnt necessarily mean theyre covered up. When you remove the gas block, as long as the ports are within the carbon/paint overspray oval circle left on the barrel, then your good to go.

 

And you might need to increase the ports up to the next size. While 4ports at .078 is all that is needed for some guns, others might require a little more oomph. Some even run 4 at .093.

 

You can see oval circle shifted down to left here...

 

Edited March 25, 2013 by sccritterkiller

[TYBOY 33]

OP,

 

I did not see anything in your post about the hammer reprofile. This is a big part of reducing the friction.

[sccritterkiller 473]

OP,

 

I did not see anything in your post about the hammer reprofile. This is a big part of reducing the friction.

 

Started with a tromix fcg and polished/profiled it from there. Also running a JTE mainspring.

[Maxwelhse 1,285]

Go shoot it and let us know how it turned out...

 

Personally, as misguided as this might be, if it was MY gun and it still didn't fire the ammo I wanted it to run, I would open the gas ports up another notch or two.

 

Is it boom-boom-bang (or such) that posted all the info about recoil springs? Open it up until it runs and if you want to run some nasty slugs, beef your springs up some before hand.

 

I absolutely encourage constructive debate on that thought. I'm not an expert.

Edited March 26, 2013 by Maxwelhse

[dubya 198]

Wouldn't it be better to add another SMALL port than opening up the existing ports even more? It seems to me the bigger the ports the more crap (plastic) can get in and clog stuff up. But I'm a S12 noob so I am only guessing.

Edited March 26, 2013 by dubya

[sapper1371usmc 107]

The way his ports are situated, it doesnt appear to be enough room to add another port without opening up the gas block even more. Going up just one size,more than likely will not create a whole lot more debris in the gas block, any more than 5 ports at .078 would.

[sapper1371usmc 107]

You wont need a new gas block. Its good you didnt go into that recessed area. You might not have needed to make the opening that large, but it wont affect anything. And just because you cant see the ports when looking into the gas block, doesnt necessarily mean theyre covered up. When you remove the gas block, as long as the ports are within the carbon/paint overspray oval circle left on the barrel, then your good to go.

 

And you might need to increase the ports up to the next size. While 4ports at .078 is all that is needed for some guns, others might require a little more oomph. Some even run 4 at .093.

 

You can see oval circle shifted down to left here...

 

Judging by your picture, only the top and right port appeared to be right on the verge of being slightly blocked so only a slight bevel would have been needed. If the paint overspray could get to it, then the gas can escape, no need to open the gas block more than needed. Too late on your particular gas block, but hopefully others can benefit.

[Cobra 76 two 2,677]

OP,

 

I did not see anything in your post about the hammer reprofile. This is a big part of reducing the friction.

 

Started with a tromix fcg and polished/profiled it from there. Also running a JTE mainspring.

If you didn't take much off the hammer face, you might still be getting lots of resistance there.

[gunfun 3,931]

You can see oval circle shifted down to left here...

 

 

 

It looks to me like your ports weren't covered in the first place. ports come in 2 flavors: Blocked and Unblocked. There is no such thing as "more unblocked". I am not an engineer, but I once did a bunch of reading on fluid dynamics, and followed through a series of tests designed to prove or debunk some claims made about directed gas jets inside what amounts to a piston. Those tests were extremely conclusive, that the jet effect is very minimal, and made no measurable difference compared to the standard measurements of pressure on surface area and volume.

 

That aside, I have to agree with Cobra on this. You want to do the least you can to your gas block/ ports to achieve reliability. This is why I advocate lots of tiny ports increasing in incremental steps until you get what you want.

[gunfun 3,931]

edit. I missed sapper's post so I duplicated his.

[TYBOY 33]

If it were my gun this it what I would do:

 

1. Make sure all friction is reduced.

a. Hammer reprofile (ensure you have done enough).

b. Reprofile bottom of carrier.

 

2. Check amount of puck play with bolt closed.

3. Slowly open ports (or add a small port) until cycling of cheap stuff achieved.

 

My oprod was not going in GB very far. Puck had a pretty big "running start" before striking it. I installed a Tom Cole op rod and pinned it so there was very little axial play in the puck with bolt closed. This seemed to make a big difference in my gun during my "Vodka to Raped Ape" transformation. Mine was originally a 3 port. Now it is a 4 port with slightly larger holes than yours. I also did the D Mod and went a little further than you did into the foward recess (i was a little pissed after I found out this was too far).

 

These are the steps I would take if doing another S12. These are only my opinions and Im sure others will differ.

 

 

Good luck

 

 

Fordguy

Edited March 26, 2013 by FORDGUY

[evlblkwpnz 3,418]

NO DON'T get into that area. In fact IMHO you already took away far too much. That whole "D" mod thing is something that should be taken down IMO. You don't need to remove any material from the GB except for increasing the bevel form the BOTTOM side, to give the ports breathing room.

I agree 100% . Ripped the words right off of my tongue.... but, of course, I will elaborate

 

I never disturb the interior of the gas block, for multiple reasons, which I do not care to discuss. Work should only be done on the underside of the port orifice. As long as the ports are not sealed off or partially sealed off by the gas block, they will function. Pressure is how the gas affects the puck. The gas impulse is too short for aerodynamics to be beneficial. Pressure merely needs to enter the system for a split second.

 

Scritter, take a pic of the puck now and after firing the next 500 rounds. If you have a mic, record the diameter as well.

 

You can see oval circle shifted down to left here...

 

 

 

It looks to me like your ports weren't covered in the first place. ports come in 2 flavors: Blocked and Unblocked. There is no such thing as "more unblocked". I am not an engineer, but I once did a bunch of reading on fluid dynamics, and followed through a series of tests designed to prove or debunk some claims made about directed gas jets inside what amounts to a piston. Those tests were extremely conclusive, that the jet effect is very minimal, and made no measurable difference compared to the standard measurements of pressure on surface area and volume.

 

That aside, I have to agree with Cobra on this. You want to do the least you can to your gas block/ ports to achieve reliability. This is why I advocate lots of tiny ports increasing in incremental steps until you get what you want.

Very well stated.

 

You wont need a new gas block. Its good you didnt go into that recessed area. You might not have needed to make the opening that large, but it wont affect anything. And just because you cant see the ports when looking into the gas block, doesnt necessarily mean theyre covered up. When you remove the gas block, as long as the ports are within the carbon/paint overspray oval circle left on the barrel, then your good to go.

 

And you might need to increase the ports up to the next size. While 4ports at .078 is all that is needed for some guns, others might require a little more oomph. Some even run 4 at .093.

 

You can see oval circle shifted down to left here...

 

Judging by your picture, only the top and right port appeared to be right on the verge of being slightly blocked so only a slight bevel would have been needed. If the paint overspray could get to it, then the gas can escape, no need to open the gas block more than needed. Too late on your particular gas block, but hopefully others can benefit.

I was thinking the same thing about benefit to others.

[evlblkwpnz 3,418]

The way his ports are situated, it doesnt appear to be enough room to add another port without opening up the gas block even more. Going up just one size,more than likely will not create a whole lot more debris in the gas block, any more than 5 ports at .078 would.

Larger ports allow larger debris to enter the system. I have tried 5 @ .078" and 4 @ .093" on many different S12s. Smaller ports foul the gas block much less until the weapon is allowed to get extremely hot (like 100+ round dump hot). When shot cups/wads are liquifying on the way through the bore, then port sizing does not matter, the debris sprays in. For regular use, smaller ports are superior when reduced fouling during normal use is the goal.

[sapper1371usmc 107]

The way his ports are situated, it doesnt appear to be enough room to add another port without opening up the gas block even more. Going up just one size,more than likely will not create a whole lot more debris in the gas block, any more than 5 ports at .078 would.

Larger ports allow larger debris to enter the system. I have tried 5 @ .078" and 4 @ .093" on many different S12s. Smaller ports foul the gas block much less until the weapon is allowed to get extremely hot (like 100+ round dump hot). When shot cups/wads are liquifying on the way through the bore, then port sizing does not matter, the debris sprays in. For regular use, smaller ports are superior when reduced fouling during normal use is the goal.

I usually go along with that same line of thought, however, the OP doesnt appear to have enough room to drill a fifth port, and by increasing the 4 ports he already has, I was talking about only going up to a #46 drill bit which would only open up the ports to .081. While larger and probably going to increase the fouling some, It wont be an extravagant amount more than what it currently does.

[evlblkwpnz 3,418]

By increasing the bevel to the rear, room can be created for a fifth port. Forward is not a good idea.

 

Agreed, .080"ish ports are about perfect, IMO.

 

 

With certain ammunition, the difference in fouling between that of small and large ports can be fairly extreme until the weapon is crazy hot. After that it doesn't matter what size the ports are, especially with Federal Multi-Purpose.

Edited March 26, 2013 by evlblkwpnz

[sccritterkiller 473]

OP,

 

I did not see anything in your post about the hammer reprofile. This is a big part of reducing the friction.

 

Started with a tromix fcg and polished/profiled it from there. Also running a JTE mainspring.

If you didn't take much off the hammer face, you might still be getting lots of resistance there.

Before I go ape shit on the hammer...

I think there isn't a whole lot more to take off...with the carrier over the hammer the hammer wing is barely below the disco....maybe a 1/16th..closer to 1/32...I would post a pic but my gallery is not letting me upload.....

[gunfun 3,931]

That sounds like a stopping point.