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Posted: 8/16/2026 1:43:54 PM EDT
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I built a 635 replica using a H&R 635 complete lower, a H&R 635 upper, RRA CL 10" barrel with sight tower, KAK bolt, KAK K-SPEC Enhanced AR15 PCC 9.5 oz Buffer w/ their flatwire spring. I even bought the tungsten bolt weight, just in case. The FRT is/was a new in the package FRT-15L3 I snagged at an estate sale for pennies. The first attempt to use the FRT was without the tungsten bolt weight, it was completely unsuccessful. Yesterday after a wipe down, proper lube, and the tungsten bolt weight, it worked well, but not perfect. The first two magazines, I got my first and only bolt bounce -dead hammer failures at about halfway through each magazine. The third, forth and fifth mags were plagued with multiple bolt bounce-dead hammer. The last mag was a replication of the first two mags. I would appreciate your thoughts on what I can do to improve the performance. I have read some folks are adding washers inside the buffer tube, prior to the buffer spring being installed. I have some springco blue (enhanced power) and red (extra power) springs laying around, any thoughts on those? I also read that a slightly longer pin may help. As far as ammo: I prefer to shoot this rifle with 147gr ammo, factory or handloads. Right now I am mostly shooting Winchester 115gr, because I got it for a steal. The failures have occured with both weights of ammo. |
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I don't have experience with that buffer, but looking at its spec sheet, you should be all right on that end. Now about the buffer spring. This is a common misconception, that a stronger spring will help prevent bolt bounce. The opposite is true. Stronger, stiffer springs make bolt bounce worse. They increase bolt speed. I can't give you any recommendations at this time. I would expect your parts list to work properly. |
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I use a WOT trigger (RB clone) in my DOE build. I use a kynshot 5007 buffer, everything else is standard. The hydraulic prevents bolt bounce and gives a nice ROF. Hydraulic buffers were used on factory Colt SMGs as well. You have a lot of variables from standard spec in your setup. I'd start by eliminating variables, maybe the flat spring first, and see what effect it has. |
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I have a 10 ounce buffer… put in thinner spacers between weights to give more movement. Regular carbine spring. Works ok on my 10.5” and DOE (not H&R, normal barrel without threads) with FRT. Same with my Angstadt Vanquish 10.5” with FRT. Both are RB L3s. The C3 does not work with the 9mms. Use the same buffer in my AR-40 (without FRT), which is an Aero receiver set and Angstadt bolt. |
| The problem may be firing pin inertia (see this long but very helpful article). Try replacing the current firing pin spring with an extra power spring. This simple $3 part cured intermittent FTF on my blowback 9mm PCC and did the same for a couple of friends. If you have a titanium firing pin, you can try that instead, but the spring is a cheaper and more robust solution. |
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Originally Posted By ELittlefield: Now about the buffer spring. This is a common misconception, that a stronger spring will help prevent bolt bounce. The opposite is true. Stronger, stiffer springs make bolt bounce worse. They increase bolt speed. Thoughts on me snipping buffer the spring? Say maybe 2 coils at a time? If that doesnt work I can always pick up a Springco reduced power (white) spring. I still have the original buffer spring that came with the lower, an email to both PSA and KAK is probably in order. Speaking of the PSA buffer spring, it came with a little plastic doodad that sat at the back of the buffer tube. The original 5.4 ounce buffer that came with it is on. my desk. Its sealed, so I dont know if its tungsten powder or solid steel (it looks like KAK is the manufacturer). I dont hate the idea below about the stronger firing pin spring. I read the article he linked to a few days ago. I feel like I am on the edge of complete reliability. |
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Originally Posted By FAIL-SAFE: Thoughts on me snipping buffer the spring? Say maybe 2 coils at a time? If that doesnt work I can always pick up a Springco reduced power (white) spring. I still have the original buffer spring that came with the lower, an email to both PSA and KAK is probably in order. Speaking of the PSA buffer spring, it came with a little plastic doodad that sat at the back of the buffer tube. The original 5.4 ounce buffer that came with it is on. my desk. Its sealed, so I dont know if its tungsten powder or solid steel (it looks like KAK is the manufacturer). I dont hate the idea below about the stronger firing pin spring. I read the article he linked to a few days ago. I feel like I am on the edge of complete reliability. Originally Posted By FAIL-SAFE: Originally Posted By ELittlefield: Now about the buffer spring. This is a common misconception, that a stronger spring will help prevent bolt bounce. The opposite is true. Stronger, stiffer springs make bolt bounce worse. They increase bolt speed. Thoughts on me snipping buffer the spring? Say maybe 2 coils at a time? If that doesnt work I can always pick up a Springco reduced power (white) spring. I still have the original buffer spring that came with the lower, an email to both PSA and KAK is probably in order. Speaking of the PSA buffer spring, it came with a little plastic doodad that sat at the back of the buffer tube. The original 5.4 ounce buffer that came with it is on. my desk. Its sealed, so I dont know if its tungsten powder or solid steel (it looks like KAK is the manufacturer). I dont hate the idea below about the stronger firing pin spring. I read the article he linked to a few days ago. I feel like I am on the edge of complete reliability. I think that would be worth a try. |
I don't see no Americans. I see trespassers.
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Originally Posted By FAIL-SAFE: Thoughts on me snipping buffer the spring? Say maybe 2 coils at a time? If that doesnt work I can always pick up a Springco reduced power (white) spring. I still have the original buffer spring that came with the lower, an email to both PSA and KAK is probably in order. Speaking of the PSA buffer spring, it came with a little plastic doodad that sat at the back of the buffer tube. The original 5.4 ounce buffer that came with it is on. my desk. Its sealed, so I dont know if its tungsten powder or solid steel (it looks like KAK is the manufacturer). I dont hate the idea below about the stronger firing pin spring. I read the article he linked to a few days ago. I feel like I am on the edge of complete reliability. The Sprinco Yellow carbine buffer spring is reduced power. I’d recommend that instead of cutting a regular spring - shortening a spring is not the same as reducing its weight rating, and you don’t want to flirt with premature bolt opening in an unlocked blowback gun. The plastic spacer that came with the gun originally just shortens up the bolt stroke, which confers some minor benefits (reduced impact on the bolt catch, faster feeling recoil stroke) but you don’t need it with the longer buffer you are using now. I sent you an IM about the FP spring. |
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