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Discussion Starter #1 (Edited)
As i'm sure most of you have been beat over the head with by DI proponents, i've also been told that piston guns are not as good as DI guns especially in the area of spare parts avalibility, cost, etc.

Over the last couple of days i've been involved in a thread on a training related site about the best gun for "best gun for long term disaster, piston or DI".

In that thread, most were beating the drum of DI, almost to a man (and I was willing to agree) that parts avalibility would be the most difficult aspect of trying to keep a piston gun going simply because there were so many parts avalible for DI guns and those parts would be avalible longer simply due to sheer numbers.

As the argument became a little bit heated, I finally decided to not just accept what I had been told and see for myself exactly what worked and what didn't.

What I found was quite the eye opener and made me a very happy man.

As we all know from my other posts here, I chose to buy an MR556 upper, mod it to my preferences, and use a standard AR style lower (Gen 2 Noveske Forged Flared Lower) so I could use any STANAG style magazine without worry and also not be concerned with proprietary HK lower parts.

I assumed (like a dumbass) that nearly everything in the upper was incompatible with DI parts with the exception of the extractor, ejector, cam pin and associated springs for the ejector and extractor. Because of this, I bought a spare 416 bolt (complete) and tried to figure ways to chop the end off of a standard DI bolt to make it the same length as the HK bolt, just in case I needed spares beyond that.

So, tonight, I decided to throw caution to the wind and dissassembled a brand new Noveske bolt carrier group and my MR56 bolt carrier group, then do partial swaps and worked my way up to a full swap out of the entire bolt, firing pin, cam, etc.

It turns out that standard DI bolts and ALL of their parts are direct replacements for the HK parts, either in partial or as a whole. I compared firing pin lengths and firing pin protrusion from the bolt face and found them to be the same. The firing pin spring still also fits into the full swap and works exactly as it does with the HK bolt.

In other words, everything inside both upper and lower receivers with the exception of the bolt carrier itself, is a full, and direct swap out if necessary. The bolt carrier is not an issue though as it is a major assembly of the rifle and is expected to last the life of the rifle, as are the only other incompatible parts such as the barrel, op-rod, piston, gas block.

A quick check shows that it headspaces just fine as well.

Right now my only possible concern would be the proprietary HK firing pin retaining pin. I've seen some take a hell of a beating in the past (of course this was in DI guns, so I don't really know how those forced translate into the 416 series), but even then, a field expedient replacement could easily be manufactured in a few minutes if necessary.

So, should any of you find yourself with a need of new bolt parts or even a complete bolt, take them from the guns of the dead DI koolaid drinkers lying next to you..... :18:
 

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Nice find! Also, you saved me a stack of cash as I was planning to purchase a complete spare bolt for my MR556.

I'm guessing that the same doesn't apply with my MR762 and AR10 type rifles as it seems that parts vary by manufacturer. I don't have an AR10 to compare with, so I'll probably just buy a spare bolt for it. Thanks for cutting my MR spares budget in half!
 

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Other than "fit", do you have actual confirmation that the DI bolt actually works and properly cycles in the MR/416?

And any link to this thread?...it sounds entertaining.
 

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Discussion Starter #5
Other than "fit", do you have actual confirmation that the DI bolt actually works and properly cycles in the MR/416?

And any link to this thread?...it sounds entertaining.
At this time, no.

All I did was simple parts replacement and visual inspection of critical dimensions. Live fire is planned for when the weather gets better this weekend.

Something tells me that this "coincidence" may have been intentional now that I think about it.
 

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I'm intrigued by this, so please keep us posted. I've compared small parts/springs, but never the entire bolt assembly.

But as anyone who "tinkers" with firearms knows that fit does not always equate to reliable function. Remember to bring your camera.

Also, wheres the link to that thread?
 

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Discussion Starter #7 (Edited)
Ok. Today was range day. Decided to finally get around to answering the accuracy testing questions and also do the parts compatibility testing.

For starters, it was a frustrating as **** day as the only magnifired scope I have avalible is a cheap POS bushnell that someone gave to me. Now I know why they gave it away. ****in' lump of crap.

Took 60 rounds just to get it on paper as a 4 click adjustment would send the bullet a foot and a half in 2 directions when I first started.

But, once it finally settled down and started working properly, I was able to get some groups.

Most were in the 2 inch range, which I blame myself for as I have an astigmatism (got LASIK in '05, but that didn't account for the astigmatsm and no matter what I do, crosshairs and target will never seem to focus together). That being the case, I apologize for my ****ty shooting and I'm sure someone who is much better at it would have performed to what the rifle is capable of.

In the end, I was able to finally pull out my "best" group with the 3-9x magnified scope. Too bad that group had a flyer though otherwise it would have been a great end to the accuracy portion of the test. Turns out though that I had an even better end to the day on pure accident.

So, without further adoo, here is the final target of the day. It actually has 3 seperate shot groups on it with two different sight systems and this is what lead to me having a giggle-fest as I finally put everything away before hitting the pistol range just to blow off some steam.

Here is the target with the 3 shot groups marked:



Group number one is the last group with the magnified scope. Rounds 1,2,3, and 5, are in the main group (one through the same hole) with shot number 4 being the flyer. I knew I pulled it when it happened and was a bit upset, but cest la vie.

Group number 2, on the other hand, was AFTER I removed the magnified scope and replaced my Irons and the Aimpoint PRO and was re-verifying zero of my setup with Hornady 75 grain TAP (my go-to ammo). Group 2 is 7 rounds with a 2MOA aimpoint pro and a 2.5x po-boy magnifier. This was with the same point of aim as group 1. Only difference being that Group 1 was shot with Federal 55 grain M193, and Groups 2 and 3 were shot with the Hornady 75 grain TAP.

Group three is after I raised the shot group a little to match the shot group to the offset at 100 yards that would be experienced with a 50 yard zero. Group 3 consists of 3 rounds.

All groups were shot at 100 yards off of of a bench using sandbags to support the rifle at the Poulsbo Sportsmans Club in Poulsbo WA. Keep in mind that I also hand-lapped my barrel prior to nitriding, which will effect how accurate a barrel is (makes it more accurate then stock).

Here are pics of the groups with a tape measure for reference.

Photo 1: The full size, with flyer of Group 1.




Photo 2: the main cluster of Group 1 without the flyer.




Photo 3: full length of group 2 as done with Aimpoint and 2.5x magnifier.




Photo 4: full length of Group 3 after adjusting for 50 yard zero to 100 yard zero match.




Photo 5: screwing around with the little tiny silouhette on the upper right corner of the target with the Aimpoint. Approx 1 round per 2 seconds, 10 shots.




I have no idea what the equivilent distance would be considering the little guys size, but I think that 7 shots out of 10 isn't too terribly bad. Of course this doesn't really accuratly reflect the reality of making such a long shot as there will be a hell of a lot more things effecting a bullet on such a long flight, but it's fun to do anyway.



As for the DI AR parts compatibility, I shot the entired day with the DI bolt in place. I took two videos, one showing install shortly after setting up the target, etc., and another after the last accuracy group that I shot where I was only shooting to demonstrate that the gun being fired was in fact with the AR bolt, as I took the BCG apart after shooting to prove that it is in fact a DI bolt, cam pin, firing pin, and of course, the HK firing pin spring.

I also took several before and after pictures of the bolt head itself to see how 170 rounds might affect it. My primary concern was for the bottom lugs of the bolt. Since the bolt fits into the HK carrier freely, even though it still has the gas rings, I was expecting that upon the bolt coming in contact with the top round in the magazine, it would be cammed downward as it stripped the top round from the magazine and possibly come into contact with the bottom lugs on the barrel extension, thereby being out of alignment and causing excessive wear and marring of the bolt lug edges.

Turns out I had nothing to worry about and the brand new Noveske bolt barely shows any signs of wear, much less mis-alignement strikes/wear.

The biggest difference I noticed was brass throw. The DI ejector spring is in fact weaker then the HK ejector spring, so brass was ejecting further forward as the bolt was able to travel rearward further before the brass actually struck the deflector. It still ran flawlessly though, and while deflected to a different location then normal, the ejection was still consistent.

Before pics:





After pics:






And here are the videos I shot. First one showing install, second one showing shooting and then removal for proof.

[video]http://smg.photobucket.com/albums/v186/grumpym4/?action=view&current=ARboltinstall.mp4[/video]
[video]http://smg.photobucket.com/albums/v186/grumpym4/?action=view&current=shootandprove.mp4[/video]
 

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Very interesting stuff, Grumpy. Although I don't think I will be in any rush to sell off my factory spare parts, it is good to know that this could work as a contingency.

To add to your comments on the HK ejector...although I don't really pay much attention to ejection patterns as my focus is typically downrange, I have noticed that when doing manipulation drills with brass-cased dummy rounds, the 416 kicks 'em farther across the room compared to a standard DI AR.

And regards to your groupings, were these with or without your can?
 

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Thanks for that info. That is some nice work there Grumpy. Keep us informed on what you find out through further testing. It seems to me that DI vs. Piston just comes down to personal cost/taste IMHO.
 

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Discussion Starter #11
Very interesting stuff, Grumpy. Although I don't think I will be in any rush to sell off my factory spare parts, it is good to know that this could work as a contingency.
Agreed. I'm guessing that HK parts will last a hell of a lot longer then even the best manufacture of DI parts. This test was done more as a proof of concept that DI parts could be used should you have no other choice, either due to financial reasons, or if there are no other parts avalible.

To add to your comments on the HK ejector...although I don't really pay much attention to ejection patterns as my focus is typically downrange, I have noticed that when doing manipulation drills with brass-cased dummy rounds, the 416 kicks 'em farther across the room compared to a standard DI AR.
I'm one of those throwbacks that uses ejection as a performance indicator. I find that when applied properly, it is a great diagnostic indicator.

And regards to your groupings, were these with or without your can?
Without the can. Only put the can on for screwing around at the end. Didn't want the gas blowback to affect my already crappy sight picture.

I'm sure that you could tell in the second video where I was shooting prior to removing the DI bolt, that I was blinking a lot due to the gas blowback.
 

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Very interesting stuff, Grumpy. Although I don't think I will be in any rush to sell off my factory spare parts, it is good to know that this could work as a contingency.

To add to your comments on the HK ejector...although I don't really pay much attention to ejection patterns as my focus is typically downrange, I have noticed that when doing manipulation drills with brass-cased dummy rounds, the 416 kicks 'em farther across the room compared to a standard DI AR.

And regards to your groupings, were these with or without your can?

The 416 kicks the cases further out because it has a much stiffer extractor spring.
 

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Discussion Starter #13
The 416 kicks the cases further out because it has a much stiffer extractor spring.
Incorrect.

The 416 has a much stronger ejector spring which when coupled with the high bolt speeds found in most piston guns (with the 416 being no exception) is what *can* cause thespent casings to eject in such a strong manner.

The spring that HK uses for the ejector is a very small dual wire spring that is quite a bit longer then a standard AR15 ejector spring, and is also stronger then standard as well.
 

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Discussion Starter #15
No problem. I like to know virtually every facet of my weapons so I can fully maintinence them myself rather then rely on the manufacturer. I hate sending gun through the mail and I have a very strong self reliant streak.

And if this helps others, i'm all for sharing the knowledge.
 
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