STI Open Mag Components

[Pirate]

I recently acquired my first open gun and I have four stock STI mags that I need to get up to max capacity.  Two of the mags are 170s and the other are 140s. I know I'd like to use TTI basepads as I've had good luck with those on my limited guns, but I'm not sure what size basepads I'll need.  According to the chart on the TTI site it looks like I need 4mm for the 170s and 7mm on the 140s but I'd like verification on that.  Next, what spacers/springs/followers are best with the STI tubes and what capacity are y'all getting with your setup?  Thanks in advance. 

[jcc7x7]

3mm on 170's so they fit the gauge and stay under length rule

4mm work and give a little reload cushion but most of the time your not going to reload a 170 mag

 

4mm on 140's is what most use, 7mm will work and of course will fit the gauge, some folks don't like the feel of them

with the 7mm you might get an extra round in your 140's if that is important to you.

 

I use the 4mm like on my limited mags, mostly because if I need an extra round or two I'll use the 170 mag instead.

[Pirate]

So do the 4mm pads fit the gauge with a big stick?

[Glk21C]

Reality is the actual length of the tubes vary just a little so buying one size bp because a chart tells you so is a gamble.  If you don't have one ask fellow competitors you shoot with if they have a mag length gauge you can borrow.

If you never do this and one day you are at a match and then find out the 170 mag is just a smidge too long because they were checking.....

Personally I prefer Grams BP's, springs and followers.

Good luck in the path to the dark side. ?

[cferree]

I used TTI base pads on my Limited gun, Edge, for a season and a half without issue.  I bought them for an Open gun (9 major) and had issues with the 7 mm pads with the 140's.  The mags have Grams followers & springs with SS spacers.  The spacer can slide down in the base pad causing failures to feed on the last 2-4 rounds.  I switched the 140's to Dawson pads (now marked 9 mm) and the issue went away.  I still use 4 mm pads on the 170's.  I'm going to sell/trade the 7 mm base pads when I return from a vacation.

Edited May 8, 2017 by cferree

[Jerry Anderson]

Load them up and strip one round off. they will work flawless.