deerslayer Posted April 7 Report Share Posted April 7 I spent some time with two more guns doing my best to make them work well with the frt. By doing all the things I've mentioned before with semi-auto guns including opening the chamber and polishing the parts you get a pretty good running gun. But one thing that is cropping up with one of the guns is out of battery detonations. I was assuming that the cartridge was firing before the bolt completely closed but the super slow motion camera revealed what was really going on. The bolt was closing and bouncing back and then the cartridge was firing. I can't get a video of what the firing pin is doing, but as I think about it the firing pin is most likely traveling slightly behind the bolt as it goes forward. So the bolt hits, bounces, and then the firing pin hits and causes the primer to pop. Sometimes the bolt is just far enough back and the case is weak enough that it's popping the primer and bursting the case. Link to comment Share on other sites More sharing options...
Motorcar Posted April 8 Report Share Posted April 8 That is a fascinating slow motion video. Dan, have you done any slow motion of a standard chamber/fire/repeat without the FRT? The question being, with the identical gun and standard springs, is there any bolt bounce back out of the chamber like this shows? With a standard firing pin, bolt, and springs, and our human eyes, do we just not see an occasional bounce, or is this the result of the FRT rapid fire causing a back and forth harmonic with the entire gun (similar to a bump stock) that makes to bolt bounce? It would seem these semi autos just don't do well cycling that fast with the firing pin still running independently of the bolt. Takes me back to those few pre'86 NFA pins that that locked into the bolt and made it fire open bolt only. Maybe the only reliable solution long term. Link to comment Share on other sites More sharing options...
Bayrain Posted April 8 Report Share Posted April 8 Is this with the EZ spring kit as well? Link to comment Share on other sites More sharing options...
deerslayer Posted April 8 Author Report Share Posted April 8 Well, no i havent done any slow motion of factory kahr guns. They dont run well enough as supplied. This was with factory springs. Ez pull did not work well. The frt operation steals some energy from the cycling process. I did another test with a longer firing pin spring and it seemed to eliminate the problem. Ill add the video later. 1 Link to comment Share on other sites More sharing options...
deerslayer Posted April 8 Author Report Share Posted April 8 Well, no i havent done any slow motion of factory semi auto kahr guns. They dont run well enough as supplied. This was with factory springs. Ez pull did not work well. The frt operation steals some energy from the cycling process. I did another test with a longer firing pin spring and it seemed to eliminate the out of battery firing from the bolt bounce. I used an extra long spring from my ezpull kits. (I normally cut to length). The extra enrrgy forward is showing no lag in the firing pin following behind the bolt. This coupled with the factory pair of recoil springs is actually too strong for full recoil as you will see in the video. You will also notice the bolt bounces while closing on the empty chamber. I only loaded 4 rounds for these slow motion videos. https://youtube.com/shorts/AZ8zaQeHa1Y?si=RSVajSlTaSZAw9QG Link to comment Share on other sites More sharing options...
damifino Posted April 8 Report Share Posted April 8 Great video. Thanks for sharing. Link to comment Share on other sites More sharing options...
68coupe Posted April 9 Report Share Posted April 9 As with all things Kahr, some tinkering is in order. Your testing of the system is greatly appreciated. You clearly have access to a range whereyou can make changes on site. Mt "local" range sort of frowns upon taking the guns apart on the line. I only get away with it because I'm a member in good standing. However, it's a 45min drive. I have to bring EVERYTHING with me, as they don't loan tools, unless it's to make a gun safe for transport, even though I'm a member in good standing. I usually bring in way more than I actually need because of this. They don't allow high-powered rounds like .30-06, so I have to travel at least an hour to the next nearest range to fire my 03A3, Garand or OOW BAR. I can hardly believe that they let me shoot my new semi STG44. Yeah, it sux. Karl 1 Link to comment Share on other sites More sharing options...
deerslayer Posted April 9 Author Report Share Posted April 9 You're gonna like this. I have a farm to shoot at 15 miles away. But it gets better. Small town iowa (where i live) has a tree, yard waste dump a mile out of town. I shoot machine gun there all the time. Everybody target shoots there and its ok. People will say "i heard you shoot yesterday, what were you testing?" If somebody is there dropping off leaves when im there, they always get an invitation to shoot whatever it is i have in hand. I don't think there is a soul in town that doesnt know me. I went there 6 times yesterday. 2 Link to comment Share on other sites More sharing options...
68coupe Posted April 9 Report Share Posted April 9 I'm super jealous. When I go back to TX, I can shoot whatever on my brother's property, but I LIVE in FL, and have to bring everything with me... Karl Link to comment Share on other sites More sharing options...
Bayrain Posted April 10 Report Share Posted April 10 (edited) On 4/8/2026 at 6:49 PM, 68coupe said: As with all things Kahr, some tinkering is in order. Your testing of the system is greatly appreciated. You clearly have access to a range whereyou can make changes on site. Mt "local" range sort of frowns upon taking the guns apart on the line. I only get away with it because I'm a member in good standing. However, it's a 45min drive. I have to bring EVERYTHING with me, as they don't loan tools, unless it's to make a gun safe for transport, even though I'm a member in good standing. I usually bring in way more than I actually need because of this. They don't allow high-powered rounds like .30-06, so I have to travel at least an hour to the next nearest range to fire my 03A3, Garand or OOW BAR. I can hardly believe that they let me shoot my new semi STG44. Yeah, it sux. Karl Jealous I need to get a OOW BAR and a M3 grease gun. Dream unicorn gun is a Colt Monitor but I couldn't afford one without saving up for a year......or 2. On 4/8/2026 at 2:44 PM, deerslayer said: Well, no i havent done any slow motion of factory semi auto kahr guns. They dont run well enough as supplied. This was with factory springs. Ez pull did not work well. The frt operation steals some energy from the cycling process. I did another test with a longer firing pin spring and it seemed to eliminate the out of battery firing from the bolt bounce. I used an extra long spring from my ezpull kits. (I normally cut to length). The extra enrrgy forward is showing no lag in the firing pin following behind the bolt. This coupled with the factory pair of recoil springs is actually too strong for full recoil as you will see in the video. You will also notice the bolt bounces while closing on the empty chamber. I only loaded 4 rounds for these slow motion videos. https://youtube.com/shorts/AZ8zaQeHa1Y?si=RSVajSlTaSZAw9QG Good thing I kept all my original springs. Wonder how it could function with a surplus Usgi firing pin spring. I need to start ordering parts, but at least now both of my thompsons have usgi barrels. I need to find a place to get extractors. Edited April 10 by Bayrain Link to comment Share on other sites More sharing options...
deerslayer Posted April 10 Author Report Share Posted April 10 If you try to use a full length gi spring in the "firing pin" hole the total force to recoil and chamber a new round would probably be too much overcome. Link to comment Share on other sites More sharing options...
1927a1kahr Posted April 13 Report Share Posted April 13 This is why the HK designed their smg bolts with sealed chambers containing tungsten to act as a dead blow hammer. Especially on the UMP45. Link to comment Share on other sites More sharing options...
damifino Posted April 13 Report Share Posted April 13 Also the MG 42 used a spring loaded weight (bolt catch), too stop bolt bounce. Link to comment Share on other sites More sharing options...
deerslayer Posted April 14 Author Report Share Posted April 14 In a normal semi auto bounce isnt an issue. 1 Link to comment Share on other sites More sharing options...
1927a1kahr Posted April 14 Report Share Posted April 14 Yes of course but when trying to make a closed bolt semiauto into full auto it becomes a problem. Link to comment Share on other sites More sharing options...
DARIVS Posted April 15 Report Share Posted April 15 Many of the restrictions that appear silly to use are the result of the range having to deal with mishaps from ignorant, reckless or just stupid people on the line. It curtails a lot of fun activities that would be safe with responsible and knowledgable shooters. Link to comment Share on other sites More sharing options...
peter kohler Posted April 20 Report Share Posted April 20 so this frt has to be used with the factory springs? and a longer hammer spring? Link to comment Share on other sites More sharing options...
Merry Ploughboy Posted April 21 Report Share Posted April 21 5 hours ago, peter kohler said: so this frt has to be used with the factory springs? and a longer hammer spring? And a related, but perhaps academic question: I have the Howell "low pull effort" springs and buffer in my 27A1 and I believe that others do as well - how/what does this mean vis a vis the FRT? [I say "academic" because for me, to the best of my knowledge, FRT's and the like are considered unregistered machineguns under state law here, though the state AG has indicated that should the legislature and executive branches change the wording of the state machine gun law, the legality of FRT's would be reconsidered and could potentially be allowed. And in any case, I have a registered Thompson submachine gun, so a FRT 27A1 has a low level of interest even if legal to pursue.] MHO, YMMV, etc. Link to comment Share on other sites More sharing options...
deerslayer Posted April 21 Author Report Share Posted April 21 In my testing the ezpull springs dont work well with a fully loaded 30 round magazine. The kit induces a little more friction than normal. It would fire a lightly loaded magazine ok in the gun i was testing with ezpulls. The news is that a gi recoil spring cut to around 8 inches seems to have eliminated the out of battery issues some people have. 1 Link to comment Share on other sites More sharing options...
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