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Posted: 9/22/2023 9:56:15 PM EDT
[Last Edit: doolz][Edited]
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I grabbed a 6933 11.5 complete upper from Brownells a few weeks ago and finally got my project out to the range today. My friend noticed that the gun appeared to be "over gassed" and after he made that comment, we both then noticed that the ejections were consistent at around 2 o'clock and didn't make any contact with the deflector on the upper receiver. The spent casings were just flying out at 2 o'clock. I'm going to take her out again tomorrow and see if this continues but this isn't necessarily an "issue" per se? |
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Originally Posted By VLODPG: And what buffer are you using? JP Silent Capture |
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Originally Posted By Doberman2245: Im the armorer for a local PD in Ma. we are running 6933 EPR's with HUXWRX suppressors. I have an inventory of 17 rifles with an approximate round count of 3k per rifle. Every gas tube is shot out and the cam pin is gouging the upper receiver. Out of the 17 rifles, 3 have gone back to colt with an issued with the bolt catch, the bolt catch plunger is being retained inside the receiver because the catch peened over a crown into the receiver capturing the plunger in the receiver. Take a look at your upper receiver and see if the cam pin is hitting the upper receiver. The brass being ejected should be coming out last the 4-4:40 oclock position. I believe the gas port is over sized. Had this issue once on a S&W Sport 2. Difficult to get the plunger out, but got it eventually. Something out of spec but I never delved into it further. |
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Update: Details on the juice of the build are as follows: S&W MP15 lower Colt 6933 complete upper receiver group JP Enterprises Silent Capture Spring Gen 2 Geissele SSA-E trigger Zero failure to feeds, Zero failures to extract. I grabbed a quick 30 second video (having trouble posting for whatever reason) of some controlled fire and the spent casings are ejecting between 1-o'clock and 3-o'clock and making absolutely no contact with the shoulder. I broke down the rifle when I got home and didn't notice anything out of the ordinary in terms of build up on the BCG, gas tube, or feed ramp. Cleaned as normal... First things first I guess and that would be to replace the buffer, so I'll order the JP H2 buffer and see if the "issue" continues after that troubleshoot. |
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Originally Posted By doolz: @TGWLDR Which specific USGI spring? Originally Posted By doolz: Originally Posted By TGWLDR: First thing I'd do is throw an H2 and USGI spring in it. I've not had an issue with 11.5" Colts in this configuration. GP diameter should be .074", IIRC. @TGWLDR Which specific USGI spring? @doolz SP62373 |
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Range update from today: I swapped out the buffer system and am now running the JP SCS H2. I did no modifications to it and am running it straight out of the box from the factory. I also have the SP62373 USGI spring on order from Arms Unlimited, just waiting on it to come in. I ran a ten shot group using some M193 55 grain ammo out to a target at 100 yards with a dot and got the following:  I can't upload the video/transfer from my phone for some weird reason (probably formatting) but I did notice that the ejections were more in the area of the 2 o'clock to 4 o'clock range as opposed to consistently spitting out at 2 o'clock prior to the buffer change. No failures to feed or eject. Is this "normal" with SBR's? I'm hoping to get this figured out so I can stake the castle nut and put this project to bed. Thanks for the prior input from everyone to get me to this point. |
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Originally Posted By TGWLDR: @doolz SP62373 @OTDR @TGWLDR Might be having an abosulte rookie moment here, or just newborn dad brain... I have the SP62373 spring and it doesn't appear to be compatible with the JP Silent H2 system... Do I need a whole separate H2 buffer to run like a factory AR comes with... or did I completely miss the point with both your suggestions and won't be able to use the JP system?  |
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Originally Posted By doolz: @OTDR @TGWLDR Might be having an abosulte rookie moment here, or just newborn dad brain... I have the SP62373 spring and it doesn't appear to be compatible with the JP Silent H2 system... Do I need a whole separate H2 buffer to run like a factory AR comes with... or did I completely miss the point with both your suggestions and won't be able to use the JP system? https://i.imgur.com/y82kue6.png Conventional kit. USGI spring and carbine buffer. |
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Originally Posted By MGYSGT8541: Why did you move away from stock? This is a perfect example of changing parts out and chasing ghosts. Stay with stock. Your weapon will be more reliable. To all others, let this be a lesson to you. SBRd my lower and purchased a complete upper. The ejections were all at 12:30-1:00 when I went from the 16" to the 11.5". I then swapped out the factory buffer and spring with the JP SCS as that was highly recommended. The ejections were still the same. I then posted this thread and was advised to go with either an H2 and USGI spring or an JP SCSH2 with the heavy buffer. The recommended USGI spring was backordered so I went with the JP SCSH2. Still had a variation of ejections from 12:30-4:00 Finally got in the recommended spring and, at this point, am deciding to bail on the project for personal reasons. Wouldn't necessarily say I was "chasing ghosts" but I believe there had to be some internal changes done in order to complete an SBR transformation. |
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Originally Posted By Luvman: Sounds like the JP SCS H2 was a step in the right direction. To use the standard spring you ordered simply pick a standard carbine type H2 buffer. There's no magic to an SBR set up as long as it has a properly sized gas port which your Colt upper should have. Appreciate the response. Unfortunately, life comes at you fast. I would have loved to finish this project but family comes first. A lot of what I had for this will be thrown up in the EE. Thanks for the help everyone. Maybe I'll get another crack at this again in the future. |
