TommyBuilt USA is an 07/SOT FFL specializing in Customization, Creation and Modification.



        1. What parts do I need for a basic conversion?

You will need a complete UMP lower (any model), a UMP stock, a UMP stock axel pin, a UMP stock-block, and a USA made UMP magazine (which also counts as your three 922R compliance parts).

        2. Can I use an empty UMP lower housing?

The UMP mag release, mag release axel pin and front pin are not the same as the USC. You cannot swap the parts over from your existing USC. Those parts are not often in stock and sold separately. This is why we recommend that you buy a complete lower that can be converted to semi-auto.

        3. Can I use a pistol brace on my USC?

All USC’s are rifles. They can only be converted to a SBR. There is no pistol brace option on a rifle of any kind.

        4. Can I add the twenty-five-round magazine?

No. There is no solution currently to convert the USC to a double-stack mag without doing a UMP lower.

        5. Can I just add a pistol grip to my USC?

No. By adding a pistol grip, you must make the firearm 922R compliant. That would require three particular parts to the platform.

        6. What 922R compliance parts are available?

Most commonly used are the USA made magazines from Those will count as all three compliance parts needed. You can also purchase the USA made trigger, barrels, bolt carriers and stocks. The current USA made sear that is available through is not compatible with the USC fire controls.

        7. I have an aftermarket UMP clone receiver. Can you remark it with HK markings?

No. Aside from trademark infringement, it is not legal to mark other manufacturers markings on a firearm without marking variants in place by the ATF.

        8. What is a rear section fuse? Is it strong?

A rear section fuse conversion is the most accurate UMP conversion. Cosmetically it appears the same as a UMP. It also functions the same as the original semi-auto USC. Although the conversions are very strong, we still recommend using a top-rail as a back-up reinforcement on any fuse job.

        9. Will a UMP carrier fit in a USC?

Not directly, UMP carriers have to be machined to fit into the USC. We do offer a service that will allow your UMP carrier to fit into the USC.

        10. Can I switch calibers on my UMP conversion?

Yes. The caliber change is just the barrel, bolt carrier and magazine. It takes just minutes to change calibers on this platform.


        1. Can I have a UMP conversion in California?

Yes. We do many conversions for Californian clients. You would be required to have a pinned stock, a grip wrap and a magazine limited to ten rounds.

        2. How is the folding stock of a UMP conversion pinned?

We replace the spring with a spacer and install the stock axel pin. It is reversible, but only allowed if you move out of the state. If you have a fuse job, or a UMP clone receiver, we use an Allen set screw through the bottom of the receiver into the stock.


         1. Can I ship a firearm directly to TommyBuilt Tactical?

Yes. We are on 07SOT manufacturer. There is no special paperwork required to ship your firearm us for service/repair. We prefer FedEx with tracking and insurance. We will only return firearms signature required.

         2. Can I ship through an FFL?

Yes. You may ship through an FFL and we will return it to that FFL when the work is completed.


        1. What is required for a G36 conversion?

You need an SL8 rifle to start (any model). You will need a G36 de-milled rear section, G36 stock, G36 stock axel pin, G36 lower, G36 lower locking pin, G36 buffer plate, G36 magwell, and G36 bolt head. There are many models of G36’s and these are the basic parts you need to start the conversion.

        2. Can I do a pistol brace on my SL8 and make it into a pistol?

No. All SL8’s are rifles. The only short barrel option is to SBR it.

        3. Can I just add a folding stock to my SL8?

No. There is no simple solution to adding a folding stock to your SL8. A full G36 conversion would be required.

        4. Can I just use double-stack magazines (either G36 or AR-15)?

Yes, but it requires conversion. That conversion requires purchasing a G36 bolt head, magwell and having the receive properly milled and filled to accept the double stack mags. This process also requires you add a total of five 922R compliance parts.

        5. Is it less expensive to convert an SL8 to a G36 or buy the T36 version?

It is typically double the cost to buy a SL8 and have it converted to a G36, then it is to buy one of our USA made versions (the T36). There is no pistol option on a SL8.

        6. Can I use .223 ammo in my G36 conversion?

Yes, but it will cause cycling issues due to its weakness.

        7. Can I use steal-case ammo in my G36 conversion?

Yes, it will function but it is not recommended.

T36 FAQ’s

        1. Can I use the T36 receiver for an XM8 build?

No. The receivers are completely different. The only option currently for an XM8 build is to start with an SL8.

        2. Can I use a German lower on the T36?

Yes, if you convert it. All German lowers are machine gun parts, including the SF marked lowers. They all have to be modified to fit and converted to semi-auto. They are not a direct fit.

        3. Can I use a German bolt carrier in the T36?

Yes, if it is converted to semi-auto. All G36 bolt carriers are machine gun carriers and will not fit in our receivers unless rendered semi-auto.

        4. Can I use a SL8 bolt carrier in the T36?

Yes. The top rear alignment pin will need to be machined off.

        5. Can I use a SL8 barrel in the T36?

Yes. A barrel install requires a G36 barrel wrench and mandrel.

        6. I have a G36 parts kit. Can I use that on a T36 receiver?

Yes. The bolt carrier and lower has to be converted to semi-auto and to fit.

        7. Can I use my suppresser on the T36?

Yes! We have not tried ALL suppressers with the T36. The Silencer Co. Saker-K model is the only one we know of that is not compatible.

        8. What thread pitch is my T36 barrel?

The standard sizes are 15mm by one right hand, which is the same as the German guns. We do offer 1/2 by 28 on certain models.

        9. Can I use AR-15 mags on the T36?

Yes. If you buy the specific AR-15 magwell, you can use AR-15 mags. Our complete guns ship with a G36-P mag or a German factory G36 mag.

       10. What ammunition should I use in my T36?

The G36 platform was designed around .556 NATO ammunition. You may find that weaker off-brand ammo may not cycle properly.

       11. Can I use .223 ammunition in my T36?

Yes, but it will cause cycling issues due to its weakness.

       12. Can I use steal case ammo in my T36?

Yes, it will function but it is not recommended.


         1. What do I need for an XM8 conversion?

You will need a SL8 rifle to start. You will need an XM8 kit from Tommybuilt Tactical, a G36 magwell and bolt head.

         2. Can I use a T36 receiver for the XM8?

No. The handguard and top rail are compatible but the rear of the gun is different. There is no way to do a proper XM8 conversion using the T36 receiver.

         3. What optic did the XM8 use?

The XM8 used an Insight ISM-V. The civilian model was discontinued many years ago and are now very difficult to find. Currently the Vortex UH-1 is the best option.


          1. Make sure you have filled out a Work Order on our website with a description of the work requested and your contact information so we can contact you when the project is ready.