MAX 10-15/11-15 Caliber Mod Thread
- Thread starter techspy
- Start date
Bolt bounce is a thing. The round should be going off in lock up though and not the "bounce". An issue I had with a M16 set up in 7.62x39 and wolf/tula ammo having deep seated primers. This would lead light firing pin strikes and sometimes delayed firing. Never had a case let go, but had a few with the shoulder blown forward quit a ways. Upped the length of the FP by 10k. Problems went away
This is when he gets up to make content for his "only fans" page
SecondAmend
Well-known member
- Joined
- Apr 3, 2007
- Messages
- 1,752
To perhaps dispel your misbelief in bolt bounce in a rotating bolt firearm system, I respectfully suggest that you read "The Black Rifle". In particular, the section where the development of the multipiece recoil buffer for the M16 is discussed.
MHO, YMMV, etc. Be well.
A&S Conversions
UZI Talk Life Member
This is exactly what I think happened. Steel cased Eastern Block ammo is notoriously known for hard primers. With the M16, an enhanced firing pin (with greater protrusion) and a stronger hammer spring is recommended. The barrel extension (the threaded on part at the chamber end of the barrel) and the bolt carrier are hardened steel. What happens when you put a quality ball peen hammer in a vice and strike the flat face with the flat face of another quality ball peen hammer? You can feel the striking hammer "bounce" back.
As "Eric" points out in the enhanced video, the bolt carrier collides with the barrel extension and bounces back. Just as like the factory system, the primer should be ignited as the bolt is still going forward, which would absorb some of the recoil of the round going off. With a standard hammer spring and standard firing pin, in the M16, I would get strikes to the primer that looked like the round should have gone off but didn't. Most of those rounds would go off if struck a second time. After installation of an enhanced firing pin and extra power hammer spring, those issues pretty much disappeared. The M16 auto sear should time the hammer to strike the firing pin just as the round is fully chambered. But this is a mechanical system. There will be some variation. If the hammer is a fraction of a second slow, the carrier will bounce off the barrel extension so the carrier would be recoiling back. That is the whole point of the buffer system of the M16.
Secondly, there is also the issue of the amount of gas, to the system. This is a minor issue, but might have contributed. Semi auto function doesn't require quite as much gas to function. I had taken a 16" M4 style 7.62x39 Blackthorn chrome lined barrel to be shortened at the point of the step down for attaching a grenade launcher. I went to the range with some tools, cordless drill and numbered drill bits. I opened up the port one size (approximately 0.002 to 0.003 inches) at a time. I did this at the static range. My "frankenmags" didn't have a provision to activate the bolt catch. I opened up the port until it ran in semi and packed up. When I tried the upper in full auto, it would run a few rounds and stop.I had to open up the gas port one more size to get reliable full auto function. I am about six and a half feet tall. At the time I weighed 275 lbs. I let a friend try this upper. He was around five and a half feet tall and weighed around 150 lbs. The upper would run for him in semi, but not in auto. He just didn't have quite enough mass for the rifle to function in auto. I have found that the same gas adjustments to a 7.62x39 barrel tend to have bigger reactions than that same adjustment in a 5.56X45 barrel. Why, I think that the smaller bore of 5.56 has a smaller volume makes for less of a pressure change at the gas port. So the same size hole at the gas port puts a smaller volume of gas in the system of a 7.62x39 than a 5.56X45.
Personal, I think with the Lage extra power spring and the enhanced 7.62x39 firing pin that you already have would rectify the problem that you have. I might also give the upper one more click of extra gas for automatic function. It might just be that the initial strike of the primer was not quite hard enough for ignition. The carrier striking the barrel extension, might have been that little extra push into the primer for the primer to activate. But because of the delay and the carrier bouncing off the barrel extension, caused the round to have the OOB. Good luck with the caliber change. We are all lucky to have Richard in our community. Thank you Richard.
Scott
SecondAmend
Well-known member
- Joined
- Apr 3, 2007
- Messages
- 1,752
I may have missed seeing it mentioned in the discussion, but in the H & K MP5, the bolt bounce of its delaying (i.e., ROF reducing) roller on ramps, off-axis lost motion bolt/carrier system, the bolt bounce is quelled via tungsten granules inside of a cavity the bolt. See, for example, the H & K patent: U.S. patent no. 3283435. Note - the U.S. PTO website does not have the figures sheet, but the description should be sufficiently informative. The use of tungsten powder in aftermarket AR-15/M16 buffers to quell bolt bounce is, of course, well known; as is its generally higher cost vis a vis a standard three steel rod sections plus intermediary resilient pads buffer.
MHO, YMMV, etc. Be well.
Thanks Richard! So far I have managed to get the gouges filled back in but once I get this running correctly I will likely take you up on that and get a nice clean upper again. The extra power spring may be a good option as well. I actually did email yesterday inquiring about a new left side receiver half and bolt but haven't heard back. I will give you guys a call tomorrow in case my emails aren't going through.
Enhanced firing pin and roller cam pin installed and ready to test again. I also have brass Belom ammo. I left a couple VMs with Lage about the hi power spring and still haven't heard back :dunno I suppose it shouldn't be needed with the Belom anyway. I also opened up the gas port in the barrel so I will have a bit of headroom if needed. Testing again this coming weekend.
Attachments
Please Visit our Sister Sites Below
Please consider becoming an UZI Talk Supporter