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Posted: 8/8/2015 10:22:06 AM EDT
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Well everyone this is a new one to me. I thought I had seen about everything on an Ar that could go wrong-surprise. I had put together another lower, everything looks, feels good and function checks. Go shoot, after about 10 rounds-light primer strikes and no bang. This is a 545 and I thought light spring, the upper had worked fine on another lower with the regular hammer spring, but oh well, go to change hammer spring and the left side of spring (looking from back to front of rifle) is bent up around 45 degrees, the other side looks fine, Change spring and do a couple of dry fires, trigger feels lighter, pull spring and it is bent also, do this about 4 times with new and used springs-same result, left side is bent up. I change the complete trigger group with another I have laying around, all good. I start checking the hammer and FINALLY notice the outside of the left side where the pins go though looks smaller, check with mike and left side measures .255 and right side measures .300, check other hammers and all have around .298 to .300 outside diameter. This was a new one to me. The lower kit was from CMMG, I only say this in case someone else runs into light hammer strikes, I have had good luck with CMMG in past so I chalk this up as a fluke, but it is something else to check if all else fails. Live and learn. |
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Quoted:
Well everyone this is a new one to me. I thought I had seen about everything on an Ar that could go wrong-surprise. I had put together another lower, everything looks, feels good and function checks. Go shoot, after about 10 rounds-light primer strikes and no bang. This is a 545 and I thought light spring, the upper had worked fine on another lower with the regular hammer spring, but oh well, go to change hammer spring and the left side of spring (looking from back to front of rifle) is bent up around 45 degrees, the other side looks fine, Change spring and do a couple of dry fires, trigger feels lighter, pull spring and it is bent also, do this about 4 times with new and used springs-same result, left side is bent up. I change the complete trigger group with another I have laying around, all good. I start checking the hammer and FINALLY notice the outside of the left side where the pins go though looks smaller, check with mike and left side measures .255 and right side measures .300, check other hammers and all have around .298 to .300 outside diameter. This was a new one to me. The lower kit was from CMMG, I only say this in case someone else runs into light hammer strikes, I have had good luck with CMMG in past so I chalk this up as a fluke, but it is something else to check if all else fails. Live and learn. So taking it that the hammer is rubbing down one side of the inside of the carrier as it makes is way to the FP, and this side hammer binding to the inside of the carrier is slowing the hammer down to cause the problem? |
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Any chance of posting a pic of the hammer & spring?
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
| It is not rubbing anywhere, it is the outside diameter that is off. Yes, it looks like the burst hammers with one side smaller diameter than the other. I will try to get a picture. The hammer looks like your regular semi-auto hammer except for the od on the left side. I am guessing the smaller od lets the spring compress around it and changes the id of the spring making a smaller loop and that lets the leg of the spring raise up instead of being vertical like the other one, kinda like the old trick of bending the hammer spring legs up to lighten pull. Since the id of both sides is the same the hammer is in the correct position, it just bends the leg of the spring and in turn lightens the hammer strike. I tried this hammer in my 556's and it will work, just not in my 545 where I need the full power. |
Could it be a burst hammer that has the auto sear tail (tab that catches on the auto sear) removed? Also what type of bolt carrier do you have, is it milled out on the bottom so that the firing pin is exposed, or is it solid steel that shrouds the firing pin?
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
| It reminds me of the burst hammer without the tail, it does not look like the tail was removed, it appears to have been made this way. I have several different bolt carriers, full and semi both. The springs will deform when the trigger group is installed and the hammer is cocked by hand a couple of times, it does not have to be assembled with the upper. It does not make any difference if if the hammer is used in any other lower either, tried 4 different tried and true lowers, each time this hammer is used it will bend the left leg up, I have bent 8 springs so far just checking it out. I was in error when I said this was CMMG, I looked back at the invoice and it was a Brownells lower parts kit on this particular build, I contacted them and they are sending a replacement hammer, they advised the replacement would be a Hi Standard. I have not had much luck posting pictures, I would be glad to send pictures via e-mail to anyone that wants them and if you can post them that would be great. The upper I was using at the time will run on any of my other lowers without problems. I have narrowed the problem down to the hammer itself. |
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Sorry I misunderstood you earlier, it is the enclosed shroud,solid steel regular bolt carrier, I e-mailed some pictures to a member who said he would be able to post them. They should show the only difference is the OD on each side where the pin goes threw and how the pin is retained by the little spring (not a very technical term) it is different from my other hammers. The replacement works great. I have measured this hammer to death and can only find the OD where the spring goes over each side is different than a "normal" semi-auto hammer. Thanks everyone. |
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Quoted:
Sorry I misunderstood you earlier, it is the enclosed shroud,solid steel regular bolt carrier, I e-mailed some pictures to a member who said he would be able to post them. They should show the only difference is the ID on each side where the pin goes threw and how the pin is retained by the little spring (not a very technical term) it is different from my other hammers. The replacement works great. I have measured this hammer to death and can only find the ID where the spring goes over each side is different than a "normal" semi-auto hammer. Thanks everyone. That looks like a standard semi hammer made from an A2 hammer blank. What you are actually measuring in the pics shown is the OD of the axle boss, not the ID. Please measure the actual ID. If the inner diameters match the hammer is fine. |
| My mistake. Yes it is the OD that is off, the ID is correct, This hammer will cause the spring leg to bend every time after cocking the hammer 2 or more times, which in turn causes less spring tension. The hammer will work (with reduced tension and slight reduction of trigger pull, yes I measured it) with 556, 300 AAC or my Grendel with brass casings. It will not work reliably with 545, 762 x 39 or Grendel with Wolf steel case. I have tried the hammer in 8 different tried and true lowers with multiple uppers in each caliber, it will not work reliably as stated above. I have had 8 different springs bent, all the same, I have tried this in multiple lowers that I know are good, results are the same, it ends up with a reduction of the "power" of the hammer, causing failure to fire. It is the same as the old trick of bending or clipping one leg of the spring to lighten the trigger pull, will not work where full or extra power is needed such as steel case ammo-of any brand, I have several different brands. Every combo of lower, upper, bolt carrier and bolt with this hammer will produce the exact same result, spring will bend. The bend occurs on the small side. |
| Many thanks for posting the pictures for me. Just for grins and giggles I made a small bushing to go over the small side of the hammer and get it close to the .300 OD, no longer bends the spring, I believe this eliminates any other variable that could have been with this hammer, it doesn't bend the spring and it will function 100% with steel case ammo. |
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Saw one of these in kits being sold at a local show today so I got one to see what all was wrong with the hammer.
Made like a three shot burst but the large side is bigger than a standard hammer should be. As mentioned by another poster the spring is bending. Bend looks to be caused as the spring is totally wrapped/tightened around the hammer and keeps getting bent more as the hammer finishes being cocked. Just want to add the kit I bought with that style hammer was just generic not a name branded. I checked and found kits boxed similar to the one I got with the hammer in it on Amazon for about $37. So no surprise. |
| Just a quick follow up. I was looking in my spare parts box and found another hammer spring bent just like the one above, I was a little puzzled where it came from. I started looking at my different ARs and finally found one with the spring bent. I pulled the hammer and it is just like the previous one, one side has smaller OD. I finally remembered I built it around two years ago and had been running some drills in a light rain and when done decided to detail clean and dry it. I notice at that time the spring was bent but did not think that much about it since the gun was running fine for over 1,000 rounds, it is a 556 nothing special. I changed the spring and went on about my business, now with over another 2,000 rounds though it it has never failed to fire or function. I put my 545 upper on it and instant fail to fire about 60% of the time in 30 rounds. Back to 556 upper and 0 malfunctions. My conclusion is the 545 steel case needs all of the spring power and 556 doesn't so the problems I had may not show up for anyone else. Just something else I will check more closely on future builds. Thanks all. |
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