That has to be the best explanation of this roller system I have ever seen. Saving this one to watch over and over the more I become familiar with my PTR 9kt. I've got to change out my locking piece and possibly install new rollers if the gap is off.
Excellent Video, James. This is a confusing topic for a lot of people and it is great to have It Explained so concisely and with cutaway models to facilitate learning for those unfamiliar with the system.
Continued learning on the platform for me. Thank you for the deep dive into bolt gap and and how to adjust when needed. Very informative and well made video. Thank you!
Just purchased a factory new MAC 5. I am a FFL and it came right from my jobber who just got a batch in from MAC/SDS Imports. Firearm has not been fired, totally clean. Bolt gap was 0. No gap whatsoever.
James, love your stuff but I do believe you have the effects of too small or large of a bolt gap reversed in this video. The smaller the bolt gap the larger the delay with zero bolt gap being full lock. The larger the gap the less delay and closer to straight blowback you get. In the video you say the opposite at multiple points. Please correct me if I am indeed wrong. Thanks
This is an overall great video but may I make a recommendation that I am sure someone else may have mentioned, I would have left the cutaway on the table in frame while explaining the mechanics of the bolt and rollers and locking piece, etc. but other than that thank you for this information!
I‘ve put around 500 rounds through my HK SP5 so far (mostly suppressed) before I even became aware of this bolt gap metric. Just measured it and got a tight fit on the 0.40mm feeler. Is that considered normal break-in or cause for concern? Thanks very much for sharing!
That is fine and you’ll probably never shoot enough to have it ever be a concern, that is unless you start attending our Teufelshund Tactical MP5 Operator Courses.
@@teufelshundtactical thanks so much for your response. It‘s priceless to be able to connect with experts around the world regarding such extremely technical details. Would love to attend one day when I visit the US. Beste Grüße aus Deutschland 😄 keep on posting your awesome content!
Very comprehensive. Thanks for taking the time to make the video. So on a new build, if the barrel is not pressed in far enough or pressed into the trunion too far - what would we see in either situation? Pressed in too far would result in too little a gap and not pressed far enough would result in a larger gap?
How much force should be used on the feeler gauge when checking bolt gap? When it just falls in place with no force? Sorry and thank you for your time.
Hi James, do you know if the HK locking pieces in the HK91 are the same as the ones in the 770 / SL7? I have not been able to find an answer to this anywhere, hoping you can help. Really appreciate your videoes👍
I understand there's an acceptable range but just curious why a new HK SP5 not be shipped with a factory .45 mm gap. What would cause it be be lower....materials, manufacturing process? Mine SP5 has .35 mm. out of box. My MKE AP5-M had .33 mm.
Every SP5 I have inspected, either on my workbench or when teaching a training course, has been .45mm. I can’t see what you’re seeing but first guess is you’re doing it wrong.
I was always under impression an undersized bolt gap casued too much delay and essentaiily locks the action making it single shot and a too large of gap had too little delay and caused excessive bolt speed and recoil.
Awesome information. I just bought a MAC 5 and I'm wondering if anyone could tell me if I need to change the locking piece if I'm going to run it suppressed with a brace
@teufelshundtactical The MAC 5 is a Turkish clone like the century arms. I believe they are made in the same facility. I've been reading into the platform and people are recommending you change the locking piece to 90-100 if you run it suppressed to mitigate roller dents. I have no clue though. Bolt gap measures .33mm
@@teufelshundtactical Yea I watched it, mine is barely at the acceptable range so I guess what would you do in my situation to address bolt gap at the lowest end of tolerances ?
Thank you for explaining this so clearly! Just one additional question however: If the acceptable range begins at 0.25mm, wouldn’t any feeler gauge beneath that width also fit into the bolt gap? My Z5-P with the RCM 80° locking piece won’t accept anything past 0.35mm, but 0.25mm and under slips right in.
@@teufelshundtactical Good copy! So would you say that if a 0.25mm gauge fits with mild-to-moderate play after switching out a locking piece, the bolt gap might be undersized? In which case you lose the “roller delayed” part of the blowback operation?
I've recently been having pretty extreme failure to eject with my zenith. Put a new ejector lever. New extractor spring(2 times now) searching for possible causes
James what kind of finish is that on the bolt carrier shown?? I know it differs from the MKE as they are black and the HK cocking tube support and Bolt carrier seem to have that same off black mayby even greenish color to them.I have a brand new Zenth Z5p i have just never fired as i have quite a few other weapons i had to break in first and ammo has been tight the last couple of years. EVERYTHING is perfectly straight and the welds are even better than the sp5,,only the paint has bubbled just above the trunion weld and i scratched it lightly and the paint came right off exposing the parkerizing. I figured no big deal and then i noticed it up at the back of the cocking handle slot as well where the perfect welds are and the paint just flaked off about the size of the top of a plastic pushpin that we use to mount things to walls. Not big,,jus very dissapointing. I Do Not want to turn the gun in as everything is soo straight and the welds are soo perfect that with my exposure to mayby 20 or so MKE and HK MP5's and K models by Zenith and Century i have not seen one as perfect as this one so i dont wanna turn it in so even though its never been fired,,iv decided to have it blasted with Aluminum Oxide and have it refinished. Iv been looking at the RDTS 3 step finish that seems to be used on a lot of high dollar class 3 MP5's. They appear to have that same greenish BCG and charging tube support color when finished. Can you recomend someone or mayby let me know if you have any experience with RDTS?? It sounds like they have the actual NAVY Ocean Environment coating that was applied to Navy Seal's weapon of all types in the past. Im on in $1700 on this gun,,i have not SBR this one yet because of this paint issue. Your the Master in this area and you KNOW the diff in the MKE finishes and the HK finishes. Any help would be great. An SP5K is going for 5 grand as of today. Im sure i can keep my all in under 3500 if i play my cards correct. Any help or advice would be GREATLY APPRECIATED. Thanks James,,Kirk🙏🤙
I found an HK91-G3 LOCKING PIECE from rtg parts. Says the locking piece is very important for managing proper bolt gap. It's only 13 dollars... is this what I need for my hk51? I still don't understand why I need this bolt gap LP and a 17/36 LP for shooting suppressed? Is the bolt gap LP just for you testing and then removed before shooting? Or does it stay in along with the 17/36?
I don’t know what you are talking about. The locking piece is one of the components of the bolt group. Bolt gap is the measurement of space taken between the bolt carrier and bolt to inspect if your weapon is in the correct spec range. This is done with a feeler gauge. H&K made a bunch of locking pieces for different models and variants. H&K never made a HK51, so there is no specific locking piece for it.
I'm currently trying to barrel a trunnion for a homebuild mp5k style gun. Do you think that 0.45mm is the best gap to set the barrel for pinning at so that when the barrel settles from use into its final position that it will be in the middle? I guess is it better to pin it at the higher range rather then the lower range
James would you mind helping me out... do you go all the way down to the locking piece with the feeler gauge or just the initial gap between the carrier and bolt? My bolt gap reading is too large initially but if I push it down to the locking piece it tells me that the gap isn't too large.. im right under the max specs if i go to the locking piece with the feeler gauge. If i don't go to the locking piece my gap is way too large.
Teufelshund, do you know where there might be cutaway bolts for sale? Specifically for the HK91? I have a much beloved pre-ban HK91 and this would make an excellent addition to my gun room. Thank you.
Hello, I have a rifle bolt gap that is in spec but the rifle is single shotting, it worked fine before but now it does this? What else could it be? Thank you in advance.
