Been lurking here for a bit and picking up lots of knowlege and a bit of common sense toward 1911`s.
Question is some time back you had a good thread on Frame cracks and the flexing in the frame with points on the movement of the back of the stock recoil guide rod in relation to the frame. ( may be combining threads here ) Edit: It`s the post about 25 down called " 1911 Dust Cover Crack"
Question is I use Full length guide rods and Recoil Buffers in my Commander & Govt. Models with no problems after 10,000`s of rounds, but I use the CP Buffs, which have a slightly higher profile all round. I suspect that changes the relationship of the barrel - guide rod head - lower frame in let off and recoil.
Is that a good or bad thing long term ? and should I trim it flush ? It will, after several 100 rounds exhibit minor ware on the edges.
I tend to take both sides of the issue on shock buffs. I don't recommend them for a carry gun, but if your pistol runs okay with'em, they're fine for range use. They do reduce the shock impact, and that's always a good thing. Whether or not they'll delay or prevent cracks in the area that you mentioned... maybe. It depends more on the amount of clearance between the slide and frame than anything... and the second factor is the recoil spring rate. A lighter spring will allow more higher impact stresses, but many guns seem to do better when they're more lightly sprung. Again, we're comparing Carry vs Range use. I'm not concerned with frame impact on a gun that may have to get me out of the swamp when I'm UTMAIA. If I intend to use the gun to burn up 5 or 6 hundred rounds a week, it's more of a concern. My 5-inch carry guns are more lightly sprung(14#) than my range guns (16#) Carry Commanders wear 16 pound springs, while range Commanders are kissin' 18 pounds... but that varies from gun to gun, depending on what rate the gun will run reliably with.
The CP buffs are harder than conventional neoprene buffs, and would seem to strike a compromise between protection and durability. The dynamics involved in the frame cracking likely wouldn't be a lot different than it would be without a buffer. Again... it's more about whether the top of the dust cover/spring tunnel makes contact with the slide when it flexes... and how hard that contact is.
On the sizing of the buff... I'd say that as long as it's not causing bulges on the sides of the frame adjacent to its location, it's okay. Some drop-in guide rods can do that if the head is a few thousandths too large, but it's normally adjacent to the frame rails, right at the spring tunnel's terminal point, and is more of a tolerance stack issue betwen the tunnel and the head than a problem with specs. Easily solved by simply making a light bevel on the backside of the guide rod head to provide a little clearance in the corners. Once that clearance is established, there usually isn't a problem. This normally only causes a problem on the guide rod heads that are square on the edges. The radiused Colt and GI stub guides don't give a problem.
I Like the CP buffs and they are all I use. Like Tuner, I do not use them in my Carry Commander, nor do I like guide rods in Commander size 1911's. I have no reason for this at all so it is up to the person who carries the gun as to what they like. I like to assess the intended purpose for the gun and go from there. My Red Eye Special just came back home Friday and I remembered that I did not do the slide to frame fit that I would do on a gun that was not going to be Hard Chromed. It has never galled and is very accurate, but looser than any others I have done. I think the cracks are due to poorly built guns who have a bad fit where they smack the frame after every shot. I have never had one crack, but Tuner has seen two of the kind of guns I used to build. I wonder who built them? Every little detail has to be addressed while putting these together. If you skip one step, it may give you trouble later on.
I just bought an unfired Series I Kimber Classic and was confused as to why when I had the slide lock in place and I'd pull the slide back that the lock would not release. I found the previous owner had installed a shock buff and when I removed this the slide stop functioned properly. This thread helped me understand the reason why these would be used.