Tag Archives: H&K

Two Great Videos Explaining How Roller Delayed Blow Back Actions Work

I’m a fan of the Roller Delayed Blow Back firearms for a while and have had opportunities to own and shoot ones from HK, POF, and PTR. I knew the rollers were locking the bolt head in place but never really understood the details of the action. I’ve tracked down two great videos to help show you what is going on.

This is a PTR PDWR in .308 – basically a cut down HK-91 style pistol with a SB Tactical SOB Brace and a Vortex Optic.

Forgotten Weapons

In this short video, Ian @ Forgotten Weapons does a great job explaining just how this system works.


This is one of MouseGunner’s cool x-ray renderings where he shows the MP5’s action at work. He’s done this for other weapons as well and watching the weapon operate really helps.

I hope this helps you out. Be sure to subscribe to both guys’ channels – Forgotten Weapons and MouseGunner.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com.

HK SP5K Photo Shoot In The Leaves

Okay, I liked the leaves, the lighting and thought it would be a great chance to get some photos of the HK SP5K pistol with the SB Tactical SBTK5A brace and the Vortex Optics Crossfire red dot that is on an American Defense AD-T1-L STD quick release mount.  As you can see above, I’m still using the Uncle Mike’s case.

So those are a few from the batch.  Looking forward to taking it to the range some day.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com.

Amazon product links at are the bottom of the post.

Basic SubGun Case for HK SP5K with Brace

As I wrapped up my changes on the SP5K, I realized I needed a case to put it in.  It just so happened that I had an Uncle Mike’s “Tactical Submachine Gun Case” that I had never used and it turns out the SP5K with the SB Tactical SB5KA brace and Vortex Crossfire red dot could slide right in without the magazine installed.

This is the front of the bag – six magazine pouches, one large flat pouch to the front and the rear mounted carry handle is visible.
This is the back – you can see the shoulder strap and the carry handle at the top.

The case has a zipper at the rear of the bag and the SP5K simply slides in.  This is one thing I dislike – it does not open and lie flat.  Some folks may find this a plus but I prefer bags that open.

The exterior dimensions are 24.5x14x2 and I’d knock off about half and inch all the way around for the interior dimensions.  It does have some padding but not a ton.

Another dislike I have is the way it holds the MP5 magazines.  They slide down in the little pouches and I can’t pull them out.  I need to push at the bottom to get them to slide up.

I pushed the magazines up so you can see them in this photo.  Notice where the bulges indicating the actual lower part of the magazine in each pouch.  In practice, the mags slide all the way down and are hard to get out.  You have to press from the bottom.

On the topic of pouches, the front pouch just forward of the magazines is very tight.  The bulge you see sticking out is a Mag Lula loader.  While it can hold the loader, it’s really better suited for thinner items.

Okay, rounding out my complaints, the carry handle at the rear makes for an odd front-loaded unbalanced load.  I don’t know why they didn’t center it.


It’s a decent entry bag for only $27.95 with Prime shipping on Amazon.  Sure there are things I don’t like about it but does the job.   I will be investigating other cases but this case is a solid performer at the price.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com.

Picking an Optic for HK SP5K

In past posts, I have written about buying the SP5K, selecting a brace and the forearm.  Next up is the optic.  It should come as no surprise that my go to brand is Vortex Optics.

I’m a creature of habit.  Vortex products are solid and have a no-nonsense – “if it breaks we will fix it” – warranty.  Vortex does not sponsor me so I have no reason to stick with them other than they deliver.

I knew right way this was going to be a close-in weapon with distances being typically 25 yards or less but maybe stretching out to 50 yards.  It is hard to beat a red dot at those distances for rapid target acquisition.  That narrowed my options down quite a bit.

A second big deal for me is to have a wide field of view but also a relatively small dot size.  This combination rules out a lot of the micro dots that are out there as they are both tiny and have a 4 MOA dot size – that means the red dot will cover 4″ and 100 yards or about 2″ at 50.  The micro dots are okay and I rather like them on pistols but I wanted something a tad finer on this more controllable and accurate weapon.

The Vortex Crossfire Red Dot

All paths lead me to the current Vortex Optics Crossfire red dot. It has a 2 MOA dot size, is only 2.5″ long and only weighs 5.2oz.  It also has a battery life of 7,000 hours at an output setting of 5.  Note the optic has 11 levels so when you have it turned up for bright light settings, you will drain the battery faster – always keep a spare battery in the case.  I’ve had a couple of range sessions get messed up to do dead/dying batteries and no spares.

American Defense AD-T1-L STD Mount

The only shortcoming, if I can even call it that, with the Crossfire is its base.  Vortex did their homework and include both a short base and base that can lower 1/3 co-witness with AR iron sights.  The problem is that they are screwed onto the picatinny rail.  If you need to get the optic off fast, that’s not going to happen as you will need a torx driver.

I do have good news – the Crossfire has the same base geometry as the Aimpoint T-1/H-1 optics.  That’s the key right there – there are a lot of mounting options out there and after some digging, I have been using mounts from American Defense for over a year and they are rock solid.

By the way, make sure you get the right mount – American Defense makes there base for a variety of optics.  I am using the AD-T1-L STD.

Assembling the Optic on the Mount

The good news is that this is really easy.  Undo the four screws on the bottom of the Crossfire to remove the Vortex mount.  Put the American Defense mount underneath it, add a bit of Blue Loc-Tite thread locker and reinstall the screws.

Use the small Torx wrench that Vortex supplies with the Crossfire to remove the four screws so you can the swap the bases.
Here you can see the bottom of the Crossfire and how the American Defense mount will align.
You can see the Blue Loc-Tite and the installed screws.  I like to put the Loc-Tite in the holes and then install the screws.  I wiped the residue away with a paper towel after I took this photo.

The Result

The result turned out really nice.  The optic is just the right height that it is relatively close to the bore and I can get a good consistent cheek weld.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com.

Deciding on the Forearm for my HK SP5K

In my last post, I went over the options I considered for the brace on my HK SP5K.  In this post, I’ll review the three handguards I looked at – the original forearm, a US-made polymer unit with an integral hand stop and a low-profile aluminum unit.

I really have two places I shop for HK and related parts – HKparts.net and RobertRTG.  So I went and checked out what they had plus I did google searches on “SP5K photos” and “MP5K photos” to see what others were using.  I’m a visual guy and can scan a ton of photos very fast and then click to read the articles.

Removing the handguard is pretty much like all other HKs – pop the pin and pull down.  You can see just how short that barrel is due to HK having to comply with German export laws for the pistol to be deemed “sporting purpose.”  This also means you need to carefully think how to keep your fingers, notably your thumb, out of the way.  You could argue training and holding the mag well but… there is a risk no matter what.

After researching for a bit, I got it down to the following three options that I could afford to try out:

Option 1:  The Original Forearm

The unit that comes with the SP5K has two things going for it – the hand stop and the muzzle guard.  The little indentations you see on the sides are actually thumb rests.  From a safety perspective, this seemed like the best but I wasn’t sure about how the muzzle protector would hold up over time.

Note the thumb rest of the muzzle guard area of the original SP5K handguard.  The hand stop is well forward giving you plenty of grip options also.
See, the actual end of the muzzle is located way down in the guard.  I can’t help but wonder how the polymer will hold up over time.  I’m betting HK thought about that is why they made the guard so much wider than the muzzle to allow most of the blast cone to pass by without contacting the polymer.  I haven’t heard of folks having problems so HK must have designed it correctly.

Option 2:  A US-made Polymer Handguard Sold by HKParts.net

The second option I decided to try was a US made “Reverse stretch forearm with hand stop” that was made for HKparts.net.  It was very well, fit my SP5K great and had great room for my hand but the problem was my thumb.  It wanted to go in front of the muzzle.

To be clear, it is an excellent handguard.  I blame the German politicians for the abrupt barrel.  If I had a muzzle device out front, this would have made an excellent forearm.

Option 3:  HKParts.net’s Own Low-Profile M-Lok Unit

So this brings us to the last option.  I tend to like the flexibility that rails bring and decided to try another HKParts.net model – their Low Profile Forearm M-LOK.  I ordered an Ergo hand stop/barricade stop to mount on it as well. 

I removed all of the screws to install the unit just in case some wiggling was needed. I think it could have fit without my doing this but I was trying to save the finish.
I knew I was in trouble.  It was going to be way too short and the Ergo hand stop was going to be pushed back into a slot and not going to be able to protrude without some machining.
The Ergo hand stop / barricade stop was well made.  No complaints at all with that part.  It installed just like any M-LOK component does.
Here you can see that the Ergo’s position is constrained by the M-LOK design.
Houston, we have a problem.  I wear XL-sized gloves found the resulting set up way too awkward.  I thought about drilling and tapping the handguard to move the Ergo forward but then I would still have my thumb flopping around.

Bottom line, this just was not going to work as much as I wanted it to.  Blasted politicians.

So What Did I Do?

After trying all three out, I decided to actually stay with the original forearm.  Some day in the future, I will spend the money to have a B&T barrel installed with a tri-lug adapter.  I really like the B&T brake that I run on my POF-5 and will then decide on which of the handguards I want to use.  So, the brace and handguard were both selected, in the next blog post, I’ll discuss the optic I went with and why.

Here she is for the moment.  Note I added a QD Swivel to the mounting point on the brace. 

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com.