Will be following this post... I have noticed using a 80* locking piece in my mp5k suppressed results in about a 20% reduction in rate of fire. But why exactly I have no idea.

Welcome to the Forum!

 

Thanks!

Yeah, I was wondering about that as well, either reducing the rate of fire with a different locking piece, or reducing the recoil. I kind of just want to work out the system on paper based on different peak pressures + area of the cartridge case head for fun (my background is in engineering and I'm a nerd). But I also recently got a PTR 32, and with my sear it just chugs along slowly like an old WWI machine gun. Probably a 550 rpm rate of fire, maybe less?

If I could set something like that up for an MP5 for new shooters (even if that meant machining a heavier bolt carrier and a custom locking piece)... well, for me that would be a very fun project. But I'd really want to work things out on paper before doing any $$$ machining.

 

I just put my burst group in and let them pop off 3 at a time. Seems to be the best way to break in new FA shooters.

If I could set something like that up for an MP5 for new shooters

 

In a nutshell, the locking peice sets the delay holding the bolt locked until the pressures drop to acceptable/desired levels. A longer delay bleeds more energy from the system. This can slow your rate of fire. It can also lessen felt recoil. If too much delay the system may fail to cycle, too little delay and the bolt carrier has too much energy and when it impacts the buffer (at the end of its travel) the excessive rearward energy can cause the bolt to still attempt to continue rearward forcing the rollers to try to extend. This can cause the notorious roller dents at the rear of the rails. It will also produce more felt recoil.

 

Sorry in advance if this isn't the right place to post this. I am new to the forum.

Has anyone ever sat down, analyzed, and written anything in depth about the physics of locking pieces? For example, how the bolt thrust translates into some % of energy lost in the pushing up against the "uphill" section of the trunnion + locking piece angle, and then what remains as the bolt and bolt carrier launch backward into the receiver against the recoil spring?

I know there are these older posts, but I haven't seen anything that goes beyond what they discuss:

Guide to HK Locking Pieces

Guide to HK Locking Pieces Identification of HK Locking Pieces An HKPRO Special Note from HKPRO-- The following article was published in the January, 2001 issue of Small Arms Review Magazine, and is reproduced here in its entirety, with permission from the author, for the obvious...

www.hkpro.com

Technical Engineering Detail of the G3

Technical Engineering Detail of the G3 Technical Engineering Detail of the G3 The Roller Locking System in Detail The G3 Automatic rifle has often been described in numerous German and foreign military and weapons journals. Generally, the operation of the bolt system, the...

www.hkpro.com

I'm guessing the "Technical Engineering Detail of the G3" is about as good as I'm going to get?

Thanks!

Yes, the engineers /inventors have. Math, esp. trig and calculus formulas , along with physics and metallurgy, are contained in various designs, patents, inventions and improvements. You can find this information by searching all these topics combined with specific to your interest input.

 

@west

@gulfstategaurd is correct, but lets break it down in a way that's easy to understand.

Think of it like this, larger locking piece angles are like pressing the accelerator in your car to go faster. Locking pieces with larger angles stay locked for a shorter period of time and put more energy into the relatively lower mass bolt group translating into more bolt velocity as they perform their unlocking move. This results in less dwell time for the gas in the barrel as it bleeds off at a correspondingly higher pressure. This means more energy needs to be dissipated by the recoil spring and buffer thus more felt recoil.

The other side of the coin is locking pieces with lower angles are like lifting off of the accelerator so that you slow down. These types of locking pieces stay locked for a longer period of time and put more energy into the relatively more massive receiver which translates into less bolt velocity as it performs its unlocking move. This results in more dwell time for the gas in the barrel as it bleeds off at a correspondingly lower pressure. This means less energy needs to be dissipated by the recoil spring and buffer thus less felt recoil.

I went over this analogy many years ago in the following thread where another member shared a link to a weaponsguild thread post for the formula used to calculate locking piece angle.

Factors influencing lock time? (Gunsmithing/math questions)

I hope this helps and solidifies the locking piece operating principles and foundation as well as a link to the math to help you in your endeavor.

 

Thanks! That was a good thread.

That WeaponsGuild forum looks awesome, but do you or anyone else know if the link still works? I registered for the forum and it says the post "appears to be either missing or off limits to you." I spent a good twenty minutes searching for "locking piece" results to see if I could find it without much luck. There was a good thread on how to measure locking piece angles in there though.

There's so much good stuff out there in the "old Internet". I hope it doesn't get lost with time.

 

There's so much good stuff out there in the "old Internet". I hope it doesn't get lost with time.

Too late.

As I'm sure you are aware, things have been evaporating on the net since it started. I can recall material disappearing back when the net was command prompt and finding out search engines were still to come.

Systems die without backup. Rent is no longer paid on server space or domains. People pass on or pass away without anyone designated or interested in maintaining the material they left behind. Sites that were free move behind a pay wall to provide for maintenance funding or because they changed hands and someone decided they had something worth charging for.

Just look at Netflicks. The old content at one point reached archival levels. The copywrite holders decided to charge the same for material that was ancient and not being viewed as for newer content that was being watched regularly. All that old material got purged from the service and that's now a regular practice where Netflicks runs an algorithm that trims out anything that's not being accessed enough to warrant what they are being charged to provide access to it.

 

I would imagine R. Blake Stevens' Full Circle - A Treatise on Roller Locking would have what you're looking for.
It's published by Collector Grade Publications, but not sure if it's in print anymore.

Amazon.com

 

When I typed those articles, I was pretty sure there wouldn't be much interest in the science. Glad to see this thread. I have the Full Circle book. I can look for more detail in it.

 

If you don't mind, I would appreciate it. I am a nerd / engineer to fault. I would love to sit down and understand the physics / mechanics of how these guns work (calculus and higher level math required or not) without having to reverse engineer everything myself.

@drace I will have to find a copy of that book. I should have picked one up when I saw one at the Tulsa Gun Show back in 2019.

 

Here you go. Seven pages, which includes that 1970 document I transcribed back in the day.

 

Thank you! Now I just need to sit down and figure out the math with the different common locking pieces and ammo types. Then maybe I can translate that into the energy that's required to move the bolt carrier + bolt (with their weights) versus the hammer spring and recoil spring to get some sort of velocity value + "depth of stroke versus potential stroke space available in the receiver" value. It should be fun

 

Enjoy!