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Discussion Starter #1
I am close to finishing a PSG1 / MSG-90 hybrid and noticed that titanium 23T and 30T locking pieces and a complete PSG1 bolt head are still available. I am using a PTR SS 20" heavy barrel (the face has no relief cuts, it's just like any 91 barrel.)

I guess my questions are:

1) Is there any advantage to running this bolt head?
2) Is the PSG1 bolt head and rollers compatible with a standard trunnion? (My trunnion does have an extension welded).
3) Whats the difference between the 23T and the 40T, other than the 5 degree shoulder difference? Why would you use one or the other?
4) Does the PSG1 bolt head require an extractor relief cut on the bolt face? I can't remember and am confused, I thought I saw relief cuts on the faces of real PSG1 barrels?

Any info is appreciated.
 

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1. From what I understand, the new version bolt head has a more consistent lock up.
2. I think it is, but I'm not positive. I wish I would have just checked when I had a MSG bolt head.
3.Nothing, perhaps for running the the MSG suppressed?
4.Yes.
 

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It sounds like HKaltwasser answered most of your questions. I never looked into it too much because I could not afford to use a PSG1/MSG90 bolt group. If it were me I think I would give Ghilliebear a call he would know everything about it in detail and he is always very helpful.

Also check your mail I sent you a PM.
 

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Discussion Starter #4
Thank for the information guys. I will call Ghilli and ask.

I did find a picture of a RCM Schnieder PSG-1 barrel, and breechface is smooth. That makes it even more confusing, I build alot of AK's so maybe I am just imagining that relief cut, but given the size of the extractor on the PSG1 bolt I can't see it not requiring one.
 

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Thank for the information guys. I will call Ghilli and ask.

I did find a picture of a RCM Schnieder PSG-1 barrel, and breechface is smooth. That makes it even more confusing, I build alot of AK's so maybe I am just imagining that relief cut, but given the size of the extractor on the PSG1 bolt I can't see it not requiring one.
Here is a link to a Urbach US made PSG1 barrel.

PSG1 Barrel NIW
Description
With Camber/Extractor lockup and cut out
NEW perfect for your PSG1 Conversion, Urbach made

MSG90A1 Barrel w/Step
Description
NEW ready to go w/Flutes and Step in the barrel get the lastest barrel for you correct MSG90 A1 conversion. Urbach mfg.
 

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RCM is currently making a run of PSG1 Barrels. Some will be from the Schneider blanks with the P5 polygon rifle form. VERY HIGH END. Some from the Lothar Walther blanks I have. Along with the longer Trunnions. We never included the face cut for the extractor due to no one wanting them. I would need a print or sample to go off of to consider it.
 

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If I can figure out how to post pics, I'll post a picture of the extractor cut out on my rifle. It's got an Hk factory msg90 barrel on it.
 

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Discussion Starter #10
Seems as if most of the PSG1 barrel I can see that are available don't have the relief cut. I wonder if there is really any benefit from the half moons, maybe it was more of a marketing thing where HK wanted to prove to customers that the rifle wasn't just a G3? It's a PITA to accommodate just the bolt head and locking piece ($800ish) and that's without the real bolt carrier and forward assists (another $1200, plus labor to weld).

You also need to run the original PSG1 extractor with the PSG1 bolt head, which isn't much of a problem if you saved the one that came with the trigger pack. Otherwise, you would need to buy one ($60-80), and I don't know if it even would work in a regular 91 trigger pack.

I've already given up on the idea.

The only thing that still floats in my head: could I use the half moon rollers and the titanium lockpiece with a standard bolt head? Would that even work?
 

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I'm pretty sure you can use the locking piece, but the half moon rollers won't work with a standard bolt. The windows that they sit in are smaller on the psg1/msg bolt.
 

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Here is the route I'm going. MOAX is selling 91 Bolt carriers that are notched for forward assist at 180.00, T-Dog has forward assist housings for sell at 100.00, the pusher can be had at 160.00. Moax is also offering to Nitride the carriers for free, at least he was. I will post the links if you're interested.



Seems as if most of the PSG1 barrel I can see that are available don't have the relief cut. I wonder if there is really any benefit from the half moons, maybe it was more of a marketing thing where HK wanted to prove to customers that the rifle wasn't just a G3? It's a PITA to accommodate just the bolt head and locking piece ($800ish) and that's without the real bolt carrier and forward assists (another $1200, plus labor to weld).

You also need to run the original PSG1 extractor with the PSG1 bolt head, which isn't much of a problem if you saved the one that came with the trigger pack. Otherwise, you would need to buy one ($60-80), and I don't know if it even would work in a regular 91 trigger pack.

I've already given up on the idea.

The only thing that still floats in my head: could I use the half moon rollers and the titanium lockpiece with a standard bolt head? Would that even work?
 

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My forward assist from Tdog just arrived, now trying to connive the funds for eith one of MOAX modified carriers or determine specs to get one of mine milled
 

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I just got mine a few days ago too. I don't have specs for you, but here's another option. I just emailed these guys a couple of weeks ago, but I have no idea about their work. 99.00 to have it welded. HK PSG1 Build Services and PSG-1 Clone Builds For Sale

Never mind, I remembered it wrong, they want 199.00 to do notches, thought it was 99.00 too.......really MOAX's carriers are a bargain.


My forward assist from Tdog just arrived, now trying to connive the funds for eith one of MOAX modified carriers or determine specs to get one of mine milled
 

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Moax Rocks! So does RCM!

the difference of 5 degrees is timing slower lock up or speed it up, Longer barrel slower lock up is what some agree upon.

A couple things your going to wish to investigate is the cocking tube. Will you be using the revised A1 which has the notch in the down position? either one you should insure that your clearance with the PSG1 hand guard and the rubber grip portion of the extended charging handle dosent drag on the hand guard, I've had to mill a small portion of the hand guard to facilitate this issue.

Proper timing and/or placement of the PSG-1 / A1 cocking tube is an issue and really needs to be addressed when installing and welding it to the receiver. Some tubes may require a .7 spacer added to the end cap detent. Correct it before welding.

The Trunnion issue is something that your going to need to think about? The trunnion extension that some have used is??? I like the full size PSG1 trunnion due to the fact that the newer barrels that have been made have more surface area at the barrel area.....I look at it as structural stability and more barrel gripped at the bullet entrance / length is better

Wilson 20 inch barrel doesn't have the extra length added that the newer barrels have so trunnion extension is fine.

Your T-Rails that your using? The thinner ones can be a real pain when welding any small contaminant or improper start can blow a small hole in the top portion of the t-rail. I like Carlos but also like to add the factory holes to weld to the trunnion and receiver.
 

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Discussion Starter #17
Thanks for the info on the key degree difference.

I went with the rails sold by RTG, they were great, well machined and thick enough.

I used a standard 91 RCM trunion and machined my own barrel extension. The 20" PTR barrel does not have the extra length added to the barrel shank to seat it in a real PSG1 trunion. In fact the PTR barrel begins it's flutes at that area, so there was no way to bed it at all. I ended up just making my own, which essentially free floats the barrel and just acts as a structural addition for the hand guard. I also welded the trunion extension to the cocking tube, which makes the cocking tube much stronger and makes the front end almost deflection free.

I got so sick and tired of the PSG1 and MSG-90 handguards I went with my own custom system. Basically, my opinion is the factory HK PSG1 and MSG-90 system is garbage. It's full of deflection issues, and when the load the bipod it really shows. My goal was to eliminate all deflection and make a modern front end with tons of Keymod options. I also identified that the flex in the hanguard is magnified by mounting anything under the handguard, so I devised a bipod system to mount closer to the top of the hanguard that is hard mounted to the cocking tube. I used a combination of 3D printed stainless steel and nylon and so far it's the best precision HK forend that I have encountered.

Also, the MSG-90 front sight is laughable, mounting a half-cut triple ring on the cocking tube without reinforcing the cocking tube means every time you load the bipod you get POA change.

I'll have a full build thread up soon explaining and showing everything I learned.



 

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I've been out of the HK loop for a long time and see a lot of new things going on here. Is the shell deflector a stock item or your own design?
Edit to add: I really look forward to the bent cocking handle design you come up with to work with that scope!
 

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Holecreek

Nice to see you! One of the best and technical savvy experts. A Expert Toolmaker. Hope to see your designs input more often.

Discogod! Nice set up and great weapons design I hope we se other builds of yours in the future
 

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Looks great man!

The problem I have, is even using the the 1,200 meter irons sights with the MSG90 buttstock. You can't even get your line of sight low enough. I think they'll only work with a regular stock. I see what you're saying with the forearm mount and possible flex with the bipod. Luckily, I like my bipod mounted further back towards the trunnion and where flex isn't a problem.

Look forward to the full write up.
 
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