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Posted: 10/29/2024 10:31:51 AM EDT
[Last Edit: 1saxman][Edited]
| I have a 10.5" 5.56 pistol, bought whole gun, and a 10.5" 7.62x39 upper. Everything works fine, but I can't help wondering if I should install a heavier spring and buffer in the lower when using the 7.62x39 upper on it. I have been concentrating on sighting both in and fixing little gremlins as they pop up, like dot sight coming loose, changing muzzle attachments, etc., so I haven't been paying attention to ejection angles and distances. Anyone have experience using these combinations? |
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I found that the H3 buffer is the sweet spot for 10.5 5.56, with a "larger" gas port. The Geissele Super 42 with H3 is IMO the best option for 10.5 5.56, but could be too much for some uppers/barrels with smaller ports. An H3 with standard carbine buffer spring runs differently than with the braided spring. The outcome could be different for your uppers, so I think it would be worth it to test a few different buffers. I know there are companies that sell adjustable buffers, or you could look into buying tungsten and/or steel weights and a couple buffers. I've found buffer weight tuning is more dependent on the size of the gas port/barrel length, gas system length, than the caliber, but 7.62x39 should be a more gassy than 5.56 all things considered. I would also test different buffer weights with and without different power or braided/flat wire buffer springs. They can impact how a weapon cycles. You could also start looking into adjustable gas blocks, gas keys, bcgs, etc. |
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Originally Posted By CharlesRyan: I found that the H3 buffer is the sweet spot for 10.5 5.56, with a "larger" gas port. The Geissele Super 42 with H3 is IMO the best option for 10.5 5.56, but could be too much for some uppers/barrels with smaller ports. An H3 with standard carbine buffer spring runs differently than with the braided spring. The outcome could be different for your uppers, so I think it would be worth it to test a few different buffers. I know there are companies that sell adjustable buffers, or you could look into buying tungsten and/or steel weights and a couple buffers. I've found buffer weight tuning is more dependent on the size of the gas port/barrel length, gas system length, than the caliber, but 7.62x39 should be a more gassy than 5.56 all things considered. I would also test different buffer weights with and without different power or braided/flat wire buffer springs. They can impact how a weapon cycles. You could also start looking into adjustable gas blocks, gas keys, bcgs, etc. The Super 42 and H3 is a great set up as well I have two of those...completely forgot |
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Thanks. The thing runs great as it is with both uppers, so I guess the only thing to look for is over-energetic ejection with the 7.62x39 upper. I did have to install a stiffer hammer spring because I got some misfires with the steel-case 7.62x39 with hard primers. Today I'll be shooting both uppers to make sure it doesn't pierce primers on the 5.56. Its not the heaviest spring available and it was listed as a 5.56 spring, not one of those listed for 7.62x39 in an AR, so it should be a good compromise. It definitely is stiffer than the one that was in it. The original ignition set was pretty bad so I put an upgrade set in. I'm pretty sure I caused the spring issue myself by second-guessing the heavier spring that came with it and installing a regular one instead. I had noticed that the hammer felt too easy to cock but it fired normally with 5.56. So when I put the 7.62x39 upper on it, I got three misfires out of about 50 shots. Dented primer but no go. I understand this is to be expected in this configuration with a weaker hammer spring. So the first thing I will do at the range is to load those three rounds and see if they fire now. I'll tell you one thing, a 7.62x39 pistol is a brutal little beast. I've also put a comp on it, and with the stiffer hammer spring slowing down the bolt carrier a little, I think it'll now be a little less so. |
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Both our pistols (10.3 and 11.5) ran fine with stock springs and buffers. But I did wind up and replace with Damage enhanced springs and Spike's T2 buffers, and there is a very noticeable difference, much smoother and softer shooting and no sproing noise from the tube. |
Smaug:"I laid low the warriors of old and their like is not in the world today". 1 dedicated marksman who held his ground and kept shooting:"Haha bow go twang!"
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You're wondering if you should go with a heavier spring and buffer? No one can tell you that. It depends on whether you need a heavier buffer and/or spring and only you will know that, since you shoot the guns. Are they exhibiting signs of too little closed bolt lock time or excessive bolt velocity? You can control the closed bolt lock time by either adjusting the weight of the buffer or the amount of gas being run through the system. Although the spring rate has little to no effect on closed bolt lock time, you can tweak the bolt velocity with differing spring weights. I like to run a bit of a heavier spring to increase feeding reliability when the rifle is dirty. Either a sprinco white hot or blue spring will do. Generally speaking and assuming proper gassing and that you are running unsuppressed, an H or H2 buffer with a sprinco white hot spring should do. My 7.62 barrel is overgassed. I run an H3 with blue spring. With the 7.62, be aware that when you break the extractor, a standard 5.56 extractor will work just fine. No need to spend the stupid price on a 7.62 extractor. When the bolt breaks, youre gonna have to decide how committed you are to 7.62x39 because its gonna keep happening. If youre committed, get a Young manufacturing bolt and you won't have the problem anymore. It is expensive though. As for the misfires, the heavier hammer spring may be masking a firing pin problem. You need a dedicated 7.62 firing pin. Theyre a little longer. I abandoned 7.62x39 in favor of 300BO. It just made everything easier. |
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Originally Posted By 1saxman: I have a 10.5" 5.56 pistol, bought whole gun, and a 10.5" 7.62x39 upper. Everything works fine, but I can't help wondering if I should install a heavier spring and buffer in the lower when using the 7.62x39 upper on it. I have been concentrating on sighting both in and fixing little gremlins as they pop up, like dot sight coming loose, changing muzzle attachments, etc., so I haven't been paying attention to ejection angles and distances. Anyone have experience using these combinations? Don't fix what ain't broke! I would leave the spring alone in favor of buffer weight changes, but if it runs let it run. |
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Originally Posted By TonyAngel: You're wondering if you should go with a heavier spring and buffer? No one can tell you that. It depends on whether you need a heavier buffer and/or spring and only you will know that, since you shoot the guns. Are they exhibiting signs of too little closed bolt lock time or excessive bolt velocity? You can control the closed bolt lock time by either adjusting the weight of the buffer or the amount of gas being run through the system. Although the spring rate has little to no effect on closed bolt lock time, you can tweak the bolt velocity with differing spring weights. I like to run a bit of a heavier spring to increase feeding reliability when the rifle is dirty. Either a sprinco white hot or blue spring will do. Generally speaking and assuming proper gassing and that you are running unsuppressed, an H or H2 buffer with a sprinco white hot spring should do. My 7.62 barrel is overgassed. I run an H3 with blue spring. With the 7.62, be aware that when you break the extractor, a standard 5.56 extractor will work just fine. No need to spend the stupid price on a 7.62 extractor. When the bolt breaks, youre gonna have to decide how committed you are to 7.62x39 because its gonna keep happening. If youre committed, get a Young manufacturing bolt and you won't have the problem anymore. It is expensive though. As for the misfires, the heavier hammer spring may be masking a firing pin problem. You need a dedicated 7.62 firing pin. Theyre a little longer. I abandoned 7.62x39 in favor of 300BO. It just made everything easier. If I break a bolt, it'll have to happen soon. I don't shoot them much after sighting in - no point to it, just blasting away. |
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Took it to the range today and everything was great until the very tip of the firing pin broke off. I just ordered some enhanced firing pins for it and my other AR in 7.62x39, a 16". I put a standard AR firing pin in it in case I just have to have it before the new pins arrive :). No more trouble with light strikes - the misfire ammo from the previous session (dented primer) fired normally today with the stronger hammer spring. Recoil impetus was much lower with the VG6 Gamma comp. Accuracy is phenomenal now that the sight is not loose and the castle nut has been torqued and thread-locked. After re-mounting and thread-locking the dot sight, I was only about 1" off. I only had to fire a few rounds to zero it at 25 yds (25-200), then the firing pin broke. Somebody said Bear Creek does not use enhanced firing pins - I guess I can believe that now. ETA: forgot to mention ejection; straight out to the right and about 10'. |
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I use an A5 length buffer tube and RB5007 for full auto 9mm / 40SW / .45ACP (All CMMG RDB), all 5.56 configurations, all 5.45x39 and 7.62x39 configurations. Warthog flat springs works in all the above although I will use the strong Tubb .308 flat spring for 7.62x39 and the belt fed Shrike as more energy is required to strip rounds off the rough commbloc feed lips w/ AK mags and stripping rounds off links. I have been running full auto 7.62x39 for over 20 years. Back in the day, I was also using extra power hammer springs till extended FP's came out. I don't use them anymore. I use a standard power hammer spring and they work fine even in full auto. Only $10 from BRA below. Both work fine for me. https://www.redxarms.com/AR15-Enhanced-Firing-Pin-For-762x39-545x39-p/5061.htm https://www.blackriflearms.com/AR-15-762x39-545x39-Enhanced-Firing-Pin_p_9.html https://c3junkie.com/?page_id=185   Full auto 7.5" 7.62x39 M16 |
| Thanks - I already had ordered a few of the BRA pins. I also had considered that with the enhanced FPs, the extra-power hammer spring might not be such a good idea. I'm glad to see you changed that on your guns, and I am going to go back to the standard hammer spring too. I use the same lower for a 5.56 pistol upper also, so that's another good reason to not have the extra-strong hammer spring in it. At least I'll try it that way and make sure the lower is good for both calibers. |
Okay, this thing is complete and proofed! Received the firing pin last evening, put it in and went to the range this morning. I expected the zero to be the same, and the first shot was dead center. I had a 20-rd mag in it so I just kept shooting, still slow and carefully at first but I ended up shooting rapid fire. Function was perfect, no misfires, mag worked fine (Duramag 20) and the primers had good dents. 18 shots were in the center 2" white dot with 2 just outside.
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| Now my focus is on the 5.56 upper - I previously zeroed it at 50 yds so it should still be good, but I installed the new V6G Gamma brake on it last night and the lower has a slightly stronger hammer spring, so I just need to check in on that zero and function. |
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The 5.56 upper is sighted in at 50 yds. Twice as hard to do than 25 yds but I got it done on a cold, wet morning. I shot up both targets and they were all I brought, so I tore up an ammo box and made some new centers. I finished the adjustments on the RH target and fired three rounds at the new square on the LH target. Results not ideal but I accepted it. The barrel is a 1:7 and I was shooting M855 (62gr) so maybe I will try it again with some 69 and 75gr. The V6G Gamma brake functioned as expected - a nice piece of equipment. Function in the shared lower was perfect. The spread on these three shots is 2" (4MOA). 
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