View Full Version : KAC SR-15 FTF w/ SD-3G
Charlie Don't Surf
05-27-19, 12:45
I had an extra SD3G trigger lying around so I put in my SR15 mod 0. During the last stage of the half and half drill I experienced 2 ftf with light primer hits. The rounds fired fine later. The ammo is American Eagle 55gr 5.56mm.
My diagnosis is that I’m firing too fast for KAC’s finely tuned gas system and the hammer is following the bolt. I have never had a malfunction in this rifle before. So the original KAC trigger is going back in for now.
Am I correct here, or is something else going on?
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I doubt seriously you could out run the bolt during firing and if you're actually getting hammer follow then there is something wrong with the disconnector.
How many rounds have you fired with the SD3G? The one big issue I have had with FTF, all came back to my SD3G. I have a post here about the issue. I checked everything and replaced the extractor and spring. I checked headspace and ejector. I changed ammo and tried different BCG's. I tried switching uppers with different lowers. I thought I had fixed the problem after the new extractor. However the issue arose again.(Only with the lower with the SD3G.) The only common denominator was the SD3G. I changed the hammer spring to a new one.
Since I changed the hammer spring I have not had any FTF in the last 2,000 rounds. (Both reloads and factory ammo and with different uppers.)Keep in mind that the only FTF happened with that particular lower with the SD3G trigger. Perhaps, it was a coincidence, I don't know. That particular lower with the SD3G is only used in gun game situations and I do run some drills with it. It is not my SHTF/HD gun. However, if it suffers one more FTF, I will be replacing the trigger.
YMMV, Cheers, Steve
Out of curiosity, did you swap the hammer spring out with another of the same weight, or was it a heavier spring?
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Charlie Don't Surf
05-27-19, 14:25
Out of curiosity, did you swap the hammer spring out with another of the same weight, or was it a heavier spring?
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It was the lighter geissele spring.
I've had between 100-200 with the SD3G, only problems were when I've tried to shoot fast.
Out of curiosity, did you swap the hammer spring out with another of the same weight, or was it a heavier spring?
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I called GA and asked if the SSA hammer spring was the same as the SD3G hammer spring. They said it was and that is the spring I used. They affirmed that it would work with the SD3G. I keep a few new SSA hammer springs in my parts bin.
Cheers, Steve
Is it installed correctly? I had a super tricon that would have light primer strikes every now and then, but it was so rare I thought it was just a hard primer. Turns out I made the rookie move of installing the legs wrong.
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It was the lighter geissele spring.
I've had between 100-200 with the SD3G, only problems were when I've tried to shoot fast.
Whats your fastest splits with that same (type) trigger in a different gun?
If you're getting light strikes, my money is on the hammer spring being installed backwards.
Charlie Don't Surf
05-27-19, 20:45
Is it installed correctly? I had a super tricon that would have light primer strikes every now and then, but it was so rare I thought it was just a hard primer. Turns out I made the rookie move of installing the legs wrong.
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I thought I did. I’ve put in over a dozen triggers. Since I’ve already put the KAC trigger back in, there is no way of knowing for sure if it was correct or not.
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Charlie Don't Surf
05-27-19, 20:46
Whats your fastest splits with that same (type) trigger in a different gun?
I’ll have to get back to you on that. I’m certainly not special.
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I thought I did. I’ve put in over a dozen triggers. Since I’ve already put the KAC trigger back in, there is no way of knowing for sure if it was correct or not.
Sent from my iPhone using TapatalkEasy enough to look up the correct orientation online. Check it against your install.
Charlie Don't Surf
05-28-19, 00:42
Easy enough to look up the correct orientation online. Check it against your install.
I looked at the spring position of the hammer and trigger. They are correct, so I did have it installed the right way.
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Fluke spring? Super human trigger finger? Maybe not if there's two in this thread alone. I've not heard of this issue with other GA triggers, would be interested in the corrective action if BG ever addresses it. I have SSA's and SDC's in all of my rifles and haven't encountered problems with those.
Failure2Stop
05-28-19, 07:44
I had an extra SD3G trigger lying around so I put in my SR15 mod 0. During the last stage of the half and half drill I experienced 2 ftf with light primer hits. The rounds fired fine later. The ammo is American Eagle 55gr 5.56mm.
My diagnosis is that I’m firing too fast for KAC’s finely tuned gas system and the hammer is following the bolt. I have never had a malfunction in this rifle before. So the original KAC trigger is going back in for now.
Am I correct here, or is something else going on?
I can assure you that your trigger finger is not outrunning the gun, unless something is slowing the bolt carrier return/lock.
I’ll have to get back to you on that. I’m certainly not special.
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If by not being special, you mean you are not getting .10 splits, then you are not outrunning the action. Probably closer to .08s.
tweakmeister
06-01-19, 10:43
Assuming the trigger was installed correctly and there is no binding I’m going to guess it’s an ammo issue in combination with the smaller gas port size of the mod 0.
On some of the earliest MOD O SR-15s the gas ports were smaller and were finicky with some ammo, this was corrected throughout the run of the MOD O. Some guys had the port opened up by KAC, I hope I’m remembering this right from way back when, probably not related to your issue but thought it doesn't hurt to share.
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