Added a buffer to a HK MP5 A2 stock

Clicker

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I never understood why the A3 stocks are buffered but not the A2 version. I have a several MP5 hosts and prefer the fixed A2 stocks when shooting but didn't like spending the coin on the buffered version offered by one of the HK smiths out there.

Given I have several stocks to try my hand at modifying I set out to see what I could fab up on my own. I robbed a 1/2" thick buffer out of a Blackthorne folding stock and began. The Blackthorne is a US made version of the B&T sidefolder.

The toughest part is removing the back plate from the stock and then putting it back into the stock. These steps require spreading the "ears" of the stock. Welded a 4mm socket head machine screw onto the plate. Next I machined a plastic spacer to fill the recessed area of the plate so the buffer would sit on a level surface. Finished it in black Cerakote (thanks to my B.I.L.) to prevent rust.

Here are a few pic's!

Back plate with spacer, this is not the actual machine screw I used. You can see the 4 dings where the carrier has hit the plate. The spacer disc has not had the notches cut to clear the rails in this photo.
IMG_0795.JPG

Buffer mocked up and bolted to the back plate, side view to show buffer thickness.
IMG_0799.JPG

Complete and reassembled. The notch was poorly cut my me to clear the BHO on the .40/10mm guns.
IMG_0801.JPG

Plan to test fire it later this week but the same buffer ran fine in the Blackthorne stock so I feel pretty confident that it will run in the 9mm gun. The real test will be the 10mm.
 
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Interesting. Let us know how it goes.
 
If your bolt carrier is hitting the back plate on a MP5A2 stock. You needed to replace to recoil spring sometime ago.
HK does not use a buffer in at MP5 A2 stock for a reason.
FWIW: Phil
 
Phil the recoil spring was no doubt worn out when that damaged occurred. I'm hoping that the buffer helps to soak up a little bit of recoil in the 10mm gun and prevent roller marks in the process, I guess I'll see after some range time.

On the other hand can you shed light or speculate on why HK never buffered the A2 stocks yet did so for the A3's?
 
Clicker: I did not catch that you had a 10mm weapon. Raleigh PD and Central Prison had some of the 10mm MP5s back in the late 80's early to mid 90's.
Since there was a wide variety of ammo and loads for that round. HK had two different locking pieces for that weapon. HI-impulse and LO-impulse (HI or LO was marked on the locking piece) for use depending on the particular ammo you were using.
When you say "roller marks" that sounds like roller dents at the rear of the receiver. If a high pressure load is used, especially with the LO impulse locking piece the weapon will over function and the bolt carrier group would crash into the backing plate...like your has done. This would force the bolt head to impact the locking rollers, forcing them outwards and damaging/denting the receiver. Starting as small dents towards the rear of the receiver. Central Prison had a couple of theirs with pretty severe dents that were actually causing malfunctions and would sometimes actual lock the bolt carrier group to the rear, when the locking rollers would actually lock in the dents they had put in the receiver.
Can you send me a pic or two of the rear of your receiver? [email protected].
As to why HK did not buffer the MP5A2 buttstocks. My educated guess from dealing with HK and several armorer courses (first time 1988) and talking with their armorers and engineers, is that they originally developed the MP5 to be used with 124 gr NATO ball 9mm ammo. About the only 9mm available at that time (mid 1960's) I think they set up the angles on the locking piece, the spring weight length of the stroke of the bolt carrier group etc for that ammo and decided it was not needed. They did have a true buffer system in the G3 rifles.
On the A3 stocks, and again, educated guess. With the pretty solid lock up of the metal rails of the A3 stocks being in contact with our cheek bones, they needed/wanted some buffering action to absorb some of the impact being transmitted back to the cheek bone. With relatively light 9mm loads, you will notice that the bolt carrier rarely actually impacts the A3 buffer during firing. Heavier loads will show some impact.
Thanks, HTH: Phil
 
Phil I appreciate you taking the time to post that information.

To put all my cards on the table I do own the following MP5 type hosts for my FA pack - SP89, MKE full size MP5 clone and a Dakota Tactical MP5 in 10mm. The only gun that currently shows any roller marks is the 9mm MKE but they're very slight, it is a SBR with a German barrel installed by Gerard Miller plus a refinish at that time. As you pointed out those marks are probably the result of a worn recoil spring which has been replaced. I suspect this occurred after running hundreds of rounds of my 125 grain LRN reloads clocking 1300 FPS. While the load was published it was max and I've since reduced it a bit.

The 10mm has been a problem child in terms of the roller damage but it was with an older Coharie gun not my new Dakota Tactical. I can't send any pictures of the Coharie and it's roller marks as I recently sold the gun. The Coharie not only developed marks near the rear of it's receiver it also had some just behind the ejection port. My guess is those mid section marks may have been due to jams where the BCG over rode the ejector lever and halted bolt travel causing the rollers to extend. I'm spitballing here just trying to figure it out. BTW a friend of mine with a 10mm Coharie has identical roller marks.

I do have all 3 LP's for the 40 cal guns - HI, LO and the discontinued #26. I generally start with the HI LP and work down from there.

Give me a day or two and I'll email you some pictures & thanks again for help.
 
Update: Shooting the full size 9mm MP5 the carrier doesn't touch the 1/2" thick buffer. We've shot high velocity and subsonic, suppressed and unsuppressed, doesn't matter the carrier never travels that far.

Now the 10mm is a different beast, it does push the carrier far enough to impact the buffer, it's not hitting it too hard as the impact marks are very faint but they're there. The buffer is not torn or deformed, you can simply see the marks left by the carrier legs. We only shot about 120 rounds, a mix of both 200 grain subs and some supersonic ammo, not sure the weight of the supers, both suppressed and unsuppressed all with the HI LP. I'll probably try a 3/8" thick buffer next and see if the carrier still makes contact.
 
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