popple holes on trubor barrel

[kewi]

i'm having my first open gun built. need opinions on popple holes (size, number of holes, angle). it's chambered in 38 super with a trubor barrel and steel grips. i've read somewhere in the forums that popple holes on a trubor is a neccessity, is this true?

[zzt]

It depends.  If the smith is using a Trubore blank, he can cut any comp configuration he wants.  If it has the standard STI S2 comp it WILL need help.  Since you are running 38S, you will generate more gas than the comp can handle.  Some will be jetting out the front, increasing felt recoil.  So, IMO, Poppels are necessary.

 

There is enough room at the rear of the comp to put two 3/16" poppels in a V2 configuration.  Since 38S is not capacity limited, I'd put one or two more 3?16" in the barrel.  The idea is to get the gun running flat while fully working the comp.  Almost no gas should jet out the front.  Whether you want the 3rd or 4th poppel will depend entirely on your load.  If you are using 3N38 or slower, I think you'll want at least the 3rd.  Try it and see if you like it.  Do the white no-shoot test.  If you are getting a lot of spatter, you need another poppel.

[kewi]

thank you for the suggestion. was really hoping you'd chime in. i've been lurking the forum for a while since i decided to switch to open. and your suggestions with regards to open have been very helpful for those of us new to open. when you say put 2 popple holes on the comp itself do you mean these parts? it was a trubor blank. sorry cant post a clearer pic since it's still with the smith at the moment.

[zzt]

No.  That is not an STI S2 comp cut.  It will be much more efficient.  There is no room for poppels in that comp, so all of them will have to go in the barrel.  You have four chambers and eight ports.  That comp will exhaust a LOT of gas.  With four baffles to push against it should be soft.

 

If it were my gun, here is what I would do.   I'd have your smith mill the slide for poppels, but no put any in.  Then I would test.  The powders I would use are 3N38, SWMP or AA7.  If you make major with 3N38 and no gas is jetting out the front, try a slower powder.  AA7 id probly the fastest of the two remaining.  SWMP is the same stuff made overseas.  It is not as consistent lot to lot as AA7.  When you get to the point there is just a little spatter out the front, you are good to go.  That will be the softest load you can shoot in that gun.

 

Now you have to decide whether is is flat enough for you.  If not, add poppels.  I'd start with two 3/16".  You will have to increase your powder charge to reach your previous PF.  That's good.  The poppels will rob gas from the comp making the gun hit your hand harder.  The increase powder charge will give some of it back.

 

At this point you should be playing with recoil spring, mainspring and firing pin stop radius combos to tune the gun.  Proper tuning will make the gun run flatter.  In fact, you should do this before you decide to add poppels.  If you don't, you run the risk of 'flattening' a gun that might have run flatter if tuned properly.  If you decide you need poppels, retuning will be necessary after they are installed. 

[kewi]

guess i'll try it out first without the popples. if i do however find it necessary to put popple holes, what configuration will you think is best for this comp setup? shall i have it in a v2 configuration or just 2 on top of the barrel?

[donnyglock]

You’re going to want holes in a 38sc. 

[caspian guy]

Even in 9 I'd start with 1 hole at least.. In 38sc I would have 2 3/16s holes

[testosterone]

9.2 of 3n38 with a 124 in 38 sc in a trubor s2 with 3 holes is magical...

[zzt]

5 hours ago, kewi said:

guess i'll try it out first without the popples. if i do however find it necessary to put popple holes, what configuration will you think is best for this comp setup? shall i have it in a v2 configuration or just 2 on top of the barrel?

 

I don't think a V2 in the barrel does you any good.  I'd rather have them point straight up, or slightly forward.

 

Here is a picture of my comp.  It is a custom cut by Aircooled6racer (Eric).  It sends six vortexes out to the sides, so I had two 3/16" poppels added behind the first chamber in a V2.  That way all the gas goes out to the sides somewhat and nothing occludes your view for the next shot.  I run 9 major, so I needed the two 3/16" poppels to flatten the gun out.  My load is 10.2gr SWMP under a 115 HAP.  It does not fully work the comp.

 

 

 

 

[kewi]

thanks for sharing your opinions guys. im assuming having the popples angled forward is so that the gases wont hit you so in the face? or is there any other purpose to it, like does it flatten the gun more if it's slightly angled forward compared to straight up? sorry for the noob question, i just want to have my gun setup right the first time since there's no going back if somehow i settle on putting the holes..

[zzt]

Angled forward is to keep the lens of your dot cleaner.  I prefer straight up.  All of my mounts have a blast shield, as does yours.

[kewi]

thank you very much sir. i'll do everything as you suggested. your wisdom is of great help to someone like me who's new to open.