So I recently sold my FN FNC and worked a deal on a registered Fleming sear in a SEF pack.

I have a SP5 already and just purchased a 4 position ambi/0,1,3,F trigger pack with housing and selector levers. Housing will be clipped and pinned before receiving.
From what I've read, that's all that will need to be done to the trigger pack for sear install and install into SP5. Am I understanding that correctly?

The last thing I should need is a auto spec carrier?

Anyone run a B&T side folding stock? How do you like it?

thanks in advance!

Congrats on the sear. Can't answer any about the four way pack but I can comment on the stock.
I had the B&T stock on a K version and found it too short for my taste. I went back to the triangle folding stock (Choate) and the fit was better.

Many sear owners get a "retimed" hammer for their packs, but I'm not sure that it's absolutely necessary. It will cause the rate of fire to be like a factory HK, and your hammer will rest farther back when fully cocked (like a factory HK pack).

I have the short B&T stock on a K and I like it. It weighs less than the Choate folder as well.

B&T offers a longer stock for the full size MP5.

I didn’t like the B&T slider for FA fire from my SP5K. It just didn’t feel solid enough and the metal forks made for an uncomfortable cheek weld in FA. I switched back to the B&T adjustable folder. That’s my favorite stock and what I went with in my 94, and both my K guns. I also have one on my APC 9 pro SD. Definitely the most comfortable stock for actual shooting.

I hate to be the bearer of bad news but unfortunately I have some not so great news for you regarding your plan installing a Fleming conversion sear into a 0-1-3-F "burst" trigger pack and then an using it with an SP5.

First lets start with the Fleming conversion sear that's currently in the S-E-F trigger pack.

- The first issue is that your S-E-F trigger pack with the conversion sear "as is" won't properly fit into an "Ambi" grip frame and Ambi selectors if your plan is to just move the trigger pack from the S-E-F grip frame to a 0-1-3-F burst grip frame.  The selector axle on the S-E-F is completely different in shape and size (smaller) than an ambi pack.

- If you plan to move the conversion sear itself from the S-E-F trigger pack into a 0-1-3-F burst trigger pack the next issue is that it is not legal to permanently remove the HK conversion sear from the existing trigger pack and move it into another trigger pack.   The issue is that you are only allowed to have "1" conversion sear prepped trigger pack as a trigger pack prepped to use a conversion sear will still allow full auto fire with the sear removed from the pack.   If you want to move the sear from the current S-E-F pack to a Burst pack you need to first bring the S-E-F pack back to full semi-auto spec after removing the sear which means welding the semi-auto stop pin back into the pack.   The other option is to remove the HK conversion sear from the S-E-F trigger pack and then destroy the old S-E-F trigger frame. Once the S-E-F is back to S-E or destroyed you can prep and install your sear into another trigger pack.

- The conversion sear also won't just drop into a factory 0-1-3-F burst pack.   The HK conversion sears have a  different shape/geometry than a factory HK full auto friction sear. The HK conversion sears are designed to pivot on the semi-auto elbow spring pin which is farther pack in the pack than a factory full auto sear pin hole.    Traditionally to install a conversion sear into a full auto pack you need to first cut away the factory full auto sear pin hole, next drill the semi-auto elbow spring pin hole, then install the conversion sear along with a semi elbow spring and ideally pair it with a retimed conversion sear hammer.

The burst trigger group presents a whole other set of problems to install a conversion sear vs. a non-burst trigger group.   The issue is that unlike the non-burst trigger groups you can't just cut away the factory full auto sear pin holes and drill a semi-auto elbow spring pin hole as the burst mech guts (shifter and eccentric cam) are in the way of where the conversion sear would normally go.   So for a HK conversion sear install into a burst pack you have to first weld up the factory full auto trigger pin holes and then a new conversion sear pin hole is drilled slightly off center of the original factory full auto sear pin hole.   This modification is intended so that a factory full auto sear will no longer properly function in the burst pack making the next modification step legal to perform.  Next, you then need to mill away the front of the trigger frame so that it will clear the semi-auto shelf on the semi-auto host gun.  You will also need a special HK Conversion Sear "Burst" hammer that has a much larger (front to back) sear trip ledge on it to reach out farther across the internals of the pack and engage the conversion sear as the conversion sear is now installed  much farther forward in the pack than originally intended at the original elbow spring location.  Unless you have access to a blast cabinet, TIG welder, park tank, and are comfortable taking apart a burst pack, installing a conversion sear into a 0-1-3-F back is probably best left to the handful of HK gunsmiths who know how to do this.

In regards to the SP5, it won't work with conversion sear out of the box as it has a full auto carrier block welded into the gun.  This prevents an SP5 from having a full auto carrier installed which is a requirement to use a HK Conversion Sear pack.

So you have a couple options.

1. You can contact TSC machine and get a SP5 "full auto" carrier that has a removable sear trip ramp.  The pros to this is that it requires no modification to the SP5 host gun. The downside is that you have to use an allen wrench and remove and reinstall the sear trip on the carrier whenever you want to remove/reinstall the carrier from the SP5 host.  These SP5 conversion carriers are debated online as to their legality being a machinegun conversion part unto themselves.

2. You can send the SP5 to Michael's Machines, have him weld on a full sized wrap around semi-auto shelf and then cut out the full auto carrier block.  This mod is highly debated online as to whether its "legal" or not to remove the full auto carrier block once a full semi shelf is installed.

What you can't do is take a dremel tool and cut out the full auto carrier block "as is" since an SP5 will allow you to install a factory full auto trigger pack as the shelf on the SP5 isn't big/deep enough to prevent the installation of a factory full auto pack.    So either the SP5 needs either  the full auto carrier block or the full sized 9x style shelf to stay as a legal semi-auto.

I know this probably isn't what you want to hear but hopefully it gets you going in the right direction.   Nothing you want to do is insurmountable but its also probably not something most end users can do themselves either.

The H&K SP5 has a “full auto carrier block” welded into the rear of the receiver, which prevents the installation of a full auto bolt carrier. The last I heard, most H&K gunsmiths will NOT remove the full auto carrier block, due to concerns that removing the block is/might be illegal.

There were rumors that some H&K gunsmith(s) had created an MP5 bolt carrier with a removable full auto trip, which could be attached to an SP5, once the carrier was installed into the weapon (forward of the block). However, concerns that this modified MP5 bolt carrier was a “full auto conversion device”, and therefore would be a (Post Sample) machine gun all by itself, seems to have killed off this modified bolt carrier.

One modification which would seem to make the SP5 into a workable sear host would be to have its “funky” pinned shelf corrected into a standard “early/HK94” style shelf, which would then (PRESUMABLY) allow you to legally remove the full auto carrier block.

ETA: It appears that member jbntex types MUCH faster than I do...

Thanks for the helpful info everyone. So I’m purchasing a full auto carrier. Now will I require a retimed hammer for a ambi/burst pack? If so is it the same for sef or burst pack?

A burst hammer for use with a conversion sear is completely different than a retimed hammer for a SEF.  Even the factory full auto burst hammer and factory full auto SEF hammer are different as the burst hammer is cut so that the eccentric cam will fit.

A retimed hammer for a sear in an SEF is completely optional part/mod.  HK conversion sears were designed to work in an SEF pack using a standard full auto hammer.

You can't install a conversion sear into a burst pack without a specialized/proprietary "conversion sear" burst hammer which is a unique part all its own.

Do you have @jbntex on ignore? Cause you are clearly missing important info.

I figured I would just be polite and assume he purchased another non-full-auto carrier blocked host.  If not it would become quickly evident that the full auto carrier won't drop into the SP5.

Not sure how the burst pack plans will go given there are maybe dozen (at best) HK gunsmiths that can install a conversion sear into a burst pack and the number of end users who have all the tools and knowledge is probably an even smaller pool.   Based on the posts I see online, it seems that probably 90%+ of burst pack owners have not or can not disassemble & reassemble a burst pack.

However, if he does plan to take a run at self installation of a conversion sear into a burst pack, the proper burst hammer for a conversion sear is a completely different part than either the factory burst hammer, a factory 0-1-A ambi / SEF full auto hammer, or a "retimed" conversion sear 0-1-A ambi / SEF hammer.

I should have cleared up that I will be sending everything off to a smith to get it up and running once my sear transfers.

On another note. What is a good clone to get that is pretty much sear pack ready?

Zenith/MKE (now Century/MKE) or PTR?

The MKE firearms have a carrier block, similar to the one in the SP5, so they can’t *LEGALLY* be used with a Registered Sear without first reworking the firearm’s “shelf” (major gunsmithing task: cutting, welding, etc.), as was outlined above.

From what I’ve read here on arfcom, the PTR clones will work with a Registered Sear in a “plug-and-play” manner, just as with an HK94.