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Posted: 8/10/2026 7:52:19 AM EDT
[Last Edit: bmarshall1][Edited]
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I am working to adapt a SS or Trigger Kicker to my Extar EP9. *TLDR: how important is the timing of a blowback 9 in firing on closed or nearly closed bolt? **Is the firing pin dropping as the bolt is within 1/8 in from closed good enough...1/16in?, this is with hand cycling and zero bolt speed, I assume the bolt velocity at actual firing speed may have it closing at the right time Bonus points if anyone can tell me whether a SS or TK would be easier to tune, they both require the same exact bolt modification |
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Originally Posted By USMC2111: You're more likely to deal with bolt bounce with either a SS or TK. I ended up using a Maxim Defense bearing delay buffer to both slow the ROF and stop bolt bounce. I had a couple of partial OOB cases pop from bolt bounce. The Maxim RDB buffer is NOT rated for FA or FRT rates of fire. I tried it anyway. I had to remove the tungsten bolt weight and for me the resultant rate of fire (wicked fast) in combination with the 9mm non locking bolt and the warning against the rates of fire I was playing with collectively convinced me OOB Detonations would likely follow. My choice was to pull it, replace the bolt weight and enjoy any of three buffer solutions I deemed offered more resistance from OOB Detonation conditions. If you can get the buffer length, @blowback9s Gentle Recoil System has become my preference. I also have success using 10+oz/aluminum body/tungsten deadblow weight buffers. Finally, I have a Tromix 9mm (9.5oz?) on deck with full confidence it will run. Finally, I am wondering why/how a TK or SS might increase bolt bounce over any other assisted reset solution. IME, bolt bounce is a potential issue with any form of increased rate of fire. And, bounce increases with bolt velocity, so mass (bolt plus buffer) and spring rate are the variables you have to work with. |
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I think the Trigger Kicker is the easiest to tune, based on my experiences with SEVERAL FRT's in 9mm blowback AR's. The Triggered Company Disruptor works very well too, but is more expensive. The TK gives you ONLY safe or full Active Reset, while other types add semi only modes. Both of those required NO TUNING for me, they just dropped in and ran! However, ALL BLOWBACK AR9's will require you to deal with bolt bounce, and to use a bolt that either does not have a weight that extends forward from the rear trip surface, or a weight that is ground for clearance. It's not all that critical, and fairly easy to accomplish. The easiest deadblow buffer I have used is the KAK 10 oz. buffer with a Tubbs 300 Blackout lightweight flat wire spring. (A standard carbine spring works too, but with a faster rate of fire.) Although I haven't used one, I fully expect this Tromix 9mm Buffer 9.5oz 4" Extended buffer to work very well, based on my experience with the H3 Tromix buffers. (They are GREAT, BTW!) Depending upon your particular firearm, you may have difficulty getting those long buffers in and out of the buffer tube, because the TK or whatever type of actuator your trigger has is high enough that the buffer has to be removed or installed BEFORE the FRT is installed. I have seen some that have this issue, and some do not. It isn't too hard to overcome, but I thought I would mention it in case you have to deal with it. |
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| I have one with an AS Designs SS that works flawlessly. As mentioned, the bolt will need to be milled for the trip surface. I went with 1.640 from the back surface of bolt. That gave me a let off at about 1/4" from bolt close when manually cycling. Starting with that I figured I was still material safe on the bolt to mill back further if needed but it worked great. The Upper will also need to be cleared out in the area between the two pin lug reinforcements to clear the rearward travel of the SS finger. The good news about "bolt bounce" issues is that they are non-existent with the factory EP9 (proprietary solid buffer). I've confirmed this with 980fps video. Absolutely no bolt bounce. Zero, nada, none. I've concluded that it's an attribute of the lower density poly construction along with lower overall weight vs bolt weight that goes unappreciated. Using the factory buffer lets you keep the recoil damping system of the factory design. |
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Originally Posted By Marvinla: The good news about "bolt bounce" issues is that they are non-existent with the factory EP9 (proprietary solid buffer). I've confirmed this with 980fps video. Absolutely no bolt bounce. Zero, nada, none. I've concluded that it's an attribute of the lower density poly construction along with lower overall weight vs bolt weight that goes unappreciated. Using the factory buffer lets you keep the recoil damping system of the factory design. @Marvinla I'd be very interested in seeing your video showing no bolt bounce with a solid buffer. (I assume the buffer is made of some type of metal - searched for it on Extar's web site and couldn't find the buffer) I'm not implying that I don't believe you, I would just love to see it for myself! I love learning...! |
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Originally Posted By Ken6PPC: @Marvinla I'd be very interested in seeing your video showing no bolt bounce with a solid buffer. (I assume the buffer is made of some type of metal - searched for it on Extar's web site and couldn't find the buffer) I'm not implying that I don't believe you, I would just love to see it for myself! I love learning...! @Ken6PPC Not a team member so can't upload or I'm maybe just not savvy enough. I'll see if i can find a buddy with a youtube or hosting account to do a link for me. I realize bolt bounce with solid buffers is a given generic AR9 problem, but it's not an EP9 problem (solid 8oz buffer and 16.5oz bolt). They're pretty far departed from being an AR9 in quite a few ways. |
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Originally Posted By Ken6PPC: @Marvinla I'd be very interested in seeing your video showing no bolt bounce with a solid buffer. (I assume the buffer is made of some type of metal - searched for it on Extar's web site and couldn't find the buffer) I'm not implying that I don't believe you, I would just love to see it for myself! I love learning...! Originally Posted By Ken6PPC: Originally Posted By Marvinla: The good news about "bolt bounce" issues is that they are non-existent with the factory EP9 (proprietary solid buffer). I've confirmed this with 980fps video. Absolutely no bolt bounce. Zero, nada, none. I've concluded that it's an attribute of the lower density poly construction along with lower overall weight vs bolt weight that goes unappreciated. Using the factory buffer lets you keep the recoil damping system of the factory design. @Marvinla I'd be very interested in seeing your video showing no bolt bounce with a solid buffer. (I assume the buffer is made of some type of metal - searched for it on Extar's web site and couldn't find the buffer) I'm not implying that I don't believe you, I would just love to see it for myself! I love learning...! I *had it running with a TK but in my effort for perfection I ground just a millimeter to far and now it no longer trips (that's my fault). the cool thing was it ran slooooooow. Like I could single or double tap. Listening to videos online I was somewhere between 475 and 500 rpm, it just chugged along. I already did the relief cut in the upper for the SS but need to modify the bolt to give a vertical surface for the TK or SS to interface with; currently mine is still angled b/c I used a 3 inch grinding wheel so as the bolt closes it pushes down as well as back on the SS or TK. I do believe the bolt is solid, one thing I did was order the carbine bolt and associated bolt mass key. Together, if I recall along with the buffer you're at about 21-22 ounces of weight, roughly what everyone says is good for a 9mm blowback. One nice thing is the way the bolt mass key fits into the bolt, if you remove the spring it act as a dead blow weight and will eliminate any bolt bounce. |
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@bmarshall1 The carbine buffer and pistol buffer are the same, but if you have the carbine bolt with the top weight, you're at around 29oz total mass. I have to say I cringe at seeing what some people have done to EP9 bolts with dremels and such, but then I'm spoiled having a well equipped machine shop at home. You're trying to duplicate the trip configuration of an AR15 carrier. Pretty challenging by hand. The dimension you're after is 90 degree flat surface 1.625-1.640 from end of bolt, at least 3/16 up from where extreme bottom of bolt would be in that area. As mentioned, there is no bolt bounce at all with or without the weight. Spring loaded forward as they come will give you maximum blowback delay efficiency. |
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Originally Posted By Marvinla: @bmarshall1 The carbine buffer and pistol buffer are the same, but if you have the carbine bolt with the top weight, you're at around 29oz total mass. I have to say I cringe at seeing what some people have done to EP9 bolts with dremels and such, but then I'm spoiled having a well equipped machine shop at home. You're trying to duplicate the trip configuration of an AR15 carrier. Pretty challenging by hand. You are correct on all accounts. I said buffer when I meant bolt and I am guilty of mutilating my Extar bolt (not as bad as some though), I need someone with a machine shop that would take the time to relieve it a bit, let me hand cycle, relieve a bit more until it's at the right spot. And yes, I think the TK may be a bit easier to adapt, zero moving parts. Maybe I'll print a new TK and adjust the dimensions a bit to make up for the extra clearance I ground on the bolt |
| OK, I just had a great idea. Since I cut the bolt too far back, technically a TK with a deeper (wider?) finger should work. Set the TK on its base in the orientation it would be used, draw a line from the very top of the tip to the base, add a few millimeters of depth until the timing is correct. Easy peasy! |
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Trying to tune the following setup: Aero EPC-9 TK Aero 9mm specific trigger (MIL-Spec style) Aero 7.7 oz EPC-9 buffer and spring Faxon BCG with removable weight (with relief in weight for the TK) 5.5" barrel 147g subs do not cycle the bolt enough to load another round, or lock back on a single loaded round/empty mag. 124g +P cycles next round, but exceptional light-strike on the primer, dead trigger, and hammer is in the fired position when action is opened with the round still in the chamber. 115g about the same as the 124g. Wondering if there is actually too much weight with the buffer / bcg / spring and short barrel configuration to properly cycle. I do have another bolt and 8.5" barrel I can test, but ran out of daylight. Remove the weight in the BCG? |
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Originally Posted By CycloSteve: Trying to tune the following setup: Aero EPC-9 TK Aero 9mm specific trigger (MIL-Spec style) Aero 7.7 oz EPC-9 buffer and spring Faxon BCG with removable weight (with relief in weight for the TK) 5.5" barrel 147g subs do not cycle the bolt enough to load another round, or lock back on a single loaded round/empty mag. 124g +P cycles next round, but exceptional light-strike on the primer, dead trigger, and hammer is in the fired position when action is opened with the round still in the chamber. 115g about the same as the 124g. Wondering if there is actually too much weight with the buffer / bcg / spring and short barrel configuration to properly cycle. I do have another bolt and 8.5" barrel I can test, but ran out of daylight. Remove the weight in the BCG? Nope- Not enough weight is my guess, though you did not post how much the faxon bolt weighs. I did not find the Aero EPC-9 buffer to be workable with a Super Safety. Kak 10 oz buffer was needed. Also- I think that older style Aero buffer 7.7 oz buffer is solid, and it would also have a .308 style spring. (Aero has since changed those to a better design). Both of those are problems for frt use, and even the newer parts probably won’t cut it. Get the heavier KAK or Tromix 9mm buffer, and throw in a regular carbine buffer and see what happens. @CycloSteve |
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