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STI Frame Rail Dimensions- Frame Work or fit new slide?


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I recently picked up a used STI Open gun off of the classifieds here and I am having a literal blast with it. I shot it last weekend and it held a nice group for me (considering I am a first time dot shooter) but when transitioning in dry fire I was feeling and hearing a weird slap as I stopped the gun. The slide is tight on the frame vertically while the gun is in battery but loose horizontally. Where front of the frame rail contacts the slide there is about .016 inches of play while the gun is in battery.

I pulled the slide off the frame and took my calipers to the rear rails, and the outside dimension was .746. The front rails were .748. I pulled the slide off my Limited gun that locks up like the proverbial bank vault and got a value of .750 and .751 respectively.

I still need to do more group shooting work to see if there is any apparent horizontal dispersion due to the "looseness". I found a lot of threads that said its fine if its loose, but in this case I have a frame mounted optic and am concerned it might affect accuracy after a hard transition left or right.

I am not looking to have the gun Accurailed but assuming I wanted to have this fit corrected would the best choice be to have the frame welded and frame re machined or have a new slide fit? I am not sure how "oversize" slides are to allow for fitting, or what a normal "in spec" frame rail would look like for an STI. At some point I will likely have a new slide fit, unless I can have the frame fixed- then I would eventually have the slide cut down a bit, and have a lighter comp and hybrid barrel fitted.

I may entirely be overthinking this, and I know practicing with the dot will make a bigger difference than the mechanical accuracy of the gun, so that is what I plan to do first. Should I take care of the headspace issue (between my ears) or is it something that might be worth sorting out mechanically?

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It's not as much about looseness as much as it is about consistent lockup. Does it group them well now?

I say shoot it like you stole it, and if your skills progress to where you think 1/4" at 25yds is affecting your scores, you will probably be ready for a new gun anyway.

Edited by sfinney
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Thank you all for the advice and confirmation, I feel much better about it now- I will see if maybe one of the experienced open guys around here will print a group or two with it after the match on Saturday. Although if my math is right, it's going to be considerably more than 1/4" at 25 yards. The horizontal play I measured wasn't .002, it was .016, so 8 times that much, Still 2 inches at 25 yards is within my current margin of error, my limited gun groups at 25 run around 3 inches or so. I will shoot it until I feel like it is holding me back, then either have the frame welded up, or have the frame done, slide chopped, hybrid barrel, etc. Thanks again!

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