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FFT vs. Carrier Comp...it's the little things...


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I am comparing the Carrier Comp and FFT magazine-tube package. This first section will focus on the lesser, but arguably trickier component...the spring.


The magazine spring is very important to the operation of the M4 Benelli, as you may well know. However, it's a bit more finicky than most realize. It mustn't just push a shell out onto the carrier...it must do it QUICKLY and with authority.


If you are firing heavy loads, such as 12-pellet 2.75" shells, or are firing 3" slugs, etc. the weapon will recoil briskly. When only 1 shell is in the magazine, this recoil tends to cause the non-fixed mounted shell to compress the magazine spring during recoil, attempting to remain at rest in the magazine tube, while the M4 recoils "around it". If the magazine spring permits this, a failure to feed malfunction will occur.


Yet, if the spring is made of too many coils, it will limit the loading of 7 rounds to 6. Herein lies the trick...getting a strong spring of the correct length.


Both FFT and Carrier Comp source their springs from Wolff, so I feel it safe to presume that both springs are of the same quality material and construction.


However, they differ greatly, as we are about to find out.



Static length. The FFT spring is 29.25" in length, while the Carrier Comp spring is 33":



Wire diameter. The FFT spring is 0.039" in diameter, while the CC spring is 0.041".



Solid height. The FFT spring consists of 48 coils, and the CC spring, 49 coils. The theoretical solid-height of the FFT spring is 1.872", assuming all coils stack directly upon each other. That of the CC spring, is 2.009". A capacity difference of 0.137", or roughly the thickness of 2 quarters stacked atop each other. Neither spring uses a "beehive" profile which would allow stacking without adding to solid-height. I do not feel that 0.137" difference in height is important, but with some brands of shells, it could indeed be a make/break proposition. If your favorite brand ALMOST makes it with the CC spring, it is likely to work with the FFT spring, however, there are functional trade-offs, as you will see in the next post.

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The bathroom scale is a very poor tool of measurement for this next, but my MK1 palm agrees with the scale. The CC spring applied much more tension. I used a full-length FFT magazine-tube, with an FFT follower and Federal TruBall DP 2.75" slug shell simulating the "last shot in the magazine". The follower and slug were oriented operationally, and my hand functioned as a magazine-retaining spring/cap. I attempted to "settle" the needle on the scale as accurately as possible. The difference in percentage of force shown is about how it "felt" to my hand, which the CC spring created a much more enduring mark on.


FFT spring "last round tension":




CC spring "last round tension":




Difference 1.5#, or roughly 25%.


Again, this was a very poor tool for the job, but the difference felt by hand is easily 25%.

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PiP suggestion: flatwire 17-7 spring. This will offer more consistent tension through the springs distance of travel and have a significantly shorter solid height for compatibility with any 2.75" shells and 7 round capacity. 17-7 offers excellent spring properties and effective corrosion resistance. Since nothing is in the ID of the spring, flatwire could be made very thin as material can be displaced to the inside without contact with moving parts. Further, spring resonance will be reduced and stability enhanced. Spring life will be significantly increased. "Last shot" spring tension can be higher with flatwire design without increasing last round loaded tension.


A flatwire spring made of 17-7 would be optimal for this application, keeping feeding tension on rounds more consistent, allowing easier loading of last rounds, increasing spring life greatly, and offering higher corrosion resistance.


A flatwire spring could be produced that would retrofit across the spectrum of shotguns in 12ga with 6-9 round capacity and be sold to 870, 590, FN slp, Beretta 1301, versa max, and other customers, defraying production cost via bulk order and sales. The main allure would be to the tactical and competition crowd as it would offer higher capacity on the longer 2.75 inch shells as well as reduced loading effort without any sacrifice of reliability.


Who ever does this...send me half a dozen as a thank - you for my suggestion and we can call it close enough to even ;)

Edited by Unobtanium
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Good write-up UBT. I agree 100% with your logic AND spring choice as well. When I decided to try and make mine a full time 10 shot, it was Kip's spring that made the whole thing come together perfectly although I have a "Dave's Metal Works" tube and a 1 of a kind extension cap for it.


I tried several springs that I had built up over time and bought a couple of others that were "OK" but when my springs arrived from Carrier Comp, I knew Kip's was going to be the very last spring I'd ever buy for my M4. Everything fell right in to place and even with a full 8 rounds in the magazine, I never have any issues and can blast off pretty much any ammo out there - I can even run 7 in the tube of all of the oddly sized ammo.


I was never much worried about weight so I never really saw the logic (for my needs) in throwing that kind of cash for titanium but for me, money is always a factor so one of Kip's tubes, although I'm sure they are spectacular, just wasn't in the cards and I am more than happy with what I have.


I don't have any use for "show weapons" and I build my weapons to work for "me" and not to fit any molds other than what I know I need and my own personal strengths and/or weaknesses so whatever I own, although it may not have the most "popular" choices of parts, works for my needs and will always be something I can depend on.


Thanks for the write up. Those are good words up there.

Edited by Sharkey
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