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Highest Capacity .40 STI Mag?


jimmcc

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I shoot at a local range that uses "outlaw" pistol classes. We don't have to conform to the 170 MM rule. Currently I am running a .40 STI 170 tube, ISMI 13 coil spring, Dawson +2 base, and a Dawson follower. I can get 25 rounds into it but I would like more. The tube is untuned. Anybody played with different combinations to get 30 plus? I've read other threads where SVI .40 tubes and Bolen internals and bases have gotten 28. I may try this or just call Freedom and see what they can come up with.

Thanks in advanced.

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Bolen springs and followers will give you the most capacity for a given volume of mag tube and basepad. However, I think you will be changing springs more often. So, that's just up to you. I believe I get an extra round with the Bolen guts vs the Grams. But, the Grams last longer.

Chris

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Bolen springs and followers will give you the most capacity for a given volume of mag tube and basepad. However, I think you will be changing springs more often. So, that's just up to you. I believe I get an extra round with the Bolen guts vs the Grams. But, the Grams last longer.

Chris

Yes I think you are right about capacity, but why not a hybrid system of bolen internals and the grams 11mm base? Isn't that more volume inside the mag? Or is the Bolen 7mm bigger internally?

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Hello: Bolen springs are made by ISMI and last a very long time. The Grams springs don't last that long. I have also found that the Bolen follower/spring setup will turn sideways if the mag width is not correct on the 40 STI mags. The 11mm Grams is longer than the Bolen 7mm by 4mm :devil: Grams also make a 7mm and 8mm. If you can shoot 9mm in your matches without scoring minor you may look at a Glock 34. You can get the Glock 18 33rd mags and add a Arrendondo base pad and get 37 rounds plus one to start :cheers: Hope this helps. Thanks, Eric

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That's funny, I do have the CCW coupler for 3 gun. There are a few guys running Glocks with the 33 round mags and I just wanted something close to their mags for my STI. Nothing against the Glocks because I get beat by them often, just a 2011 fan. Thanks for the responses.

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Bolen springs and followers will give you the most capacity for a given volume of mag tube and basepad. However, I think you will be changing springs more often. So, that's just up to you. I believe I get an extra round with the Bolen guts vs the Grams. But, the Grams last longer.

Chris

Yes I think you are right about capacity, but why not a hybrid system of bolen internals and the grams 11mm base? Isn't that more volume inside the mag? Or is the Bolen 7mm bigger internally?

I wasn't commenting on the basepad used. If you don't have a length restriction then just use the longest basepad available and then use Bolen spring and follower for the max capacity.

Chris

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So I am playing with the STI 170mm body ever so slightly tuned. With a Bolen 7mm pad, spring and follower I am getting 27. The ammo does show some interesting swirling indentations which do not seem to affect reliability or feeding. I had to bevel and polish the bottom edge of the body and the bottom of the creases in the sides. They were causing round 27 to slip beneath the follower. It's all working fine now. It's too long to be legal but I have yet to do any serious top end tuning. I am think a 4mm will be sufficient to make the gauge and as I am running a Para the Mag can afford to get a little fatter.

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Bolen springs and followers will give you the most capacity for a given volume of mag tube and basepad. However, I think you will be changing springs more often. So, that's just up to you. I believe I get an extra round with the Bolen guts vs the Grams. But, the Grams last longer.

Chris

This may be a taste great - less filling sort of thing but I have found that Grams springs last longer the Bolen springs also. I think Bolen springs are great for special stages that 1 round would make a huge difference. My experience has been that after 10-20 cycles loaded fully, the mags get intermittent. I like springs that will be reliable for more than 3 club matches ;)

Just my experience, YMMV

Chuck

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Bolen springs and followers will give you the most capacity for a given volume of mag tube and basepad. However, I think you will be changing springs more often. So, that's just up to you. I believe I get an extra round with the Bolen guts vs the Grams. But, the Grams last longer.

Chris

This may be a taste great - less filling sort of thing but I have found that Grams springs last longer the Bolen springs also. I think Bolen springs are great for special stages that 1 round would make a huge difference. My experience has been that after 10-20 cycles loaded fully, the mags get intermittent. I like springs that will be reliable for more than 3 club matches ;)

Just my experience, YMMV

Chuck

Thanks fellas I aprreciate the info. I guess the Grams springs are the ones to get for the reliability? and Bolen for capacity? OK.

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  • 2 weeks later...

Hello: The Grams 11mm is deeper than the Dawson +1 or the "SNL". The Grams 4mm is the same as the Dawson "SNL". The Grams 11mm will be illegal for a limited magazine since it will not fit the gauge with the current mags. It works great for the shorter Pre Ban mags. Thanks, Eric

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A thought is to try the dawson Para bases as they are looking to take a factory para mag to 140mm. Best guess is that para factory mags are about 120 when compared to a 126. Thats 20 to 21mm. You could try that.

You do realize that eventually you are going to need more coils on your springs right? Anybody know of a 15 coil STVI spring? Maybe try the glock 33 rounders?

Eric this guy isn't trying for legal. He's going for reloading sometime tomorrow.

Edited by Forrest Halley
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Eric,

From what I have seen, you are correct about the 4MM base being the same as the +1 Dawson. So an extra 7MM will help. Thank you.

Forrest,

You are exactly right about the spring. I don't know of any 15 coil springs but I do have a couple 33 round Glock mags that I can use as donors for their spring if needed. I use to shoot a Para and don't have any Dawson pads left for it, but I didn't think they would fit the bottom of an STI mag. There are several guys at my club that shoot them and I will try to put one on my tube. And I don't want to reload tomorrow, maybe next week! Thanks a million.

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Eric,

From what I have seen, you are correct about the 4MM base being the same as the +1 Dawson.

Just to be pedantic, the Dawson "+1 Plus S.N.L." is like the Grams 4mm. The regular Dawson basepad (a.k.a. "+1") is like the Grams 2.5mm.

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