UHP10 and UPUR10 .308 combo set assembly notes.
The UHP10 lower builds with a standard DPMS-pattern .308 lower parts kit and takes DPMS-pattern magazines; the UPUR10 upper takes DPMS-pattern .308 barrels, bolt carrier groups, dust covers and a variety of handguards. Two things differ from an AR-15 build: the takedown pin detent spring is captured by a 4-48 set screw under the pistol grip, so the spring in your kit must be shortened to about .750 in., and the UHP10 and UPUR10 fit only each other, not other makers' .308 receivers. Have a qualified gunsmith check the headspace before the rifle is fired. This page is the sheet that ships in the box.
Parts kit, magazines and finish.
Lower parts kit
A standard DPMS-pattern .308 lower parts kit. It includes the correct takedown and pivot pins and the correctly sized bolt catch for the UHP10.
Magazines
DPMS-pattern .308 magazines only.
Finish
Type III Class 2 hard anodize. New anodizing can carry a slight film; a light oil such as Rem Oil takes it off.
Assembly is very similar to a standard AR-15 lower, with the exceptions below.
The lower, in order.
- Bolt catch pin. The threaded bolt catch pin is provided and pre-installed in its hole. Remove it with a 1/16 in. Allen wrench before installing the bolt catch assembly, then thread it back in through the bolt catch.
- Takedown pin detent spring. The UHP10 captures the takedown pin detent spring with a 4-48 set screw under the pistol grip, instead of the buffer tube end plate capturing it as on a standard AR-15. The full-length spring in a DPMS-pattern kit must be shortened to about .750 in. (3/4 in.) to work with the capture screw: too long or too short and the takedown pin detent will not function properly. The capture screw ships installed so it is not lost; remove it with a .050 in. Allen wrench before installing the detent and spring, then reinstall it.
- Tensioning screw. A lower-to-upper tensioning screw is pre-installed in the lower. The nylon-tipped screw adjusts with a 1/8 in. Allen wrench to take the play out of the upper-to-lower fit.
- Safety selector. The lower is compatible with the Battle Arms Development 45-degree safety selector. The fire marking is a quarter-radius mark that reads correctly at either the 90-degree or the 135-degree position, depending on the selector you install.
The UPUR10 upper.
- Designed for DPMS-pattern .308 barrels, bolt carrier groups and dust covers, and a variety of handguards.
- Use a lubricant when inserting the barrel into the upper. It is fine to warm the upper with a hair dryer to ease the barrel in.
- Do not exceed 70 ft-lb on the barrel nut, or the barrel nut maker's own limit if it is lower. With a CMT 308 rail the values are in the handguard install guide.
- Do not run the bolt carrier group without lubrication.
Frequently asked questions.
Does the UHP10 take a standard AR-15 lower parts kit?
No. Use a standard DPMS-pattern .308 lower parts kit. It has the correct takedown and pivot pins and the correctly sized bolt catch for the UHP10. The threaded bolt catch pin and the tensioning screw arrive installed in the lower.
Why do I have to cut the takedown pin detent spring?
On a standard AR-15 the buffer tube end plate captures the takedown pin detent spring. The UHP10 captures it with a 4-48 set screw under the pistol grip instead, and the full-length spring from a DPMS-pattern kit is too long for that. Cut it to about .750 in. (3/4 in.). Too long or too short and the takedown pin detent will not work properly.
What is the small set screw under the pistol grip?
The 4-48 capture screw for the takedown pin detent spring. It ships installed so it cannot be lost. Remove it with a .050 in. Allen wrench, install the detent and the shortened spring, then run it back in.
Will the UHP10 or UPUR10 fit another brand's .308 receiver?
No. Other manufacturers' .308 receivers vary too much, so the UHP10 lower and UPUR10 upper are only compatible with Cross Machine Tool .308 receivers. They are sold as a matched set for that reason.
Which barrels, bolt carrier groups and magazines fit?
DPMS-pattern .308 barrels, bolt carrier groups and dust covers in the upper, and DPMS-pattern .308 magazines in the lower. CMT's own AR-10 handguards are the UHPR MOD 2-HP and ARCA-HP 308 rails.
Do I really need a gunsmith to check headspace?
Yes. Headspace between the bolt and the chamber has to be inspected and, if needed, the chamber adjusted to match your bolt. Firing a rifle with wrong headspace can cause catastrophic damage to you and the rifle.
Notice.
No liability is expressed or implied for damage, injury or death resulting from the improper installation or use/misuse of Cross Machine Tool products.
Like climbing mountains, racing motorcycles or jumping from perfectly good airplanes, ownership and handling of firearms carries with it certain unavoidable risks. If you are not willing to accept the responsibility for your own actions, then firearm ownership is not for you.
- The use of non-compatible custom parts or modification of these parts will void your warranty.
- Returns will not be accepted on any non-defective part that has been installed or modified.
- Before cleaning or performing any work on your firearm, make sure that it is clear. Remove the magazine and visually inspect the chamber to ensure the firearm is completely unloaded.
- It is strongly recommended that a qualified gunsmith check the safety and function of your firearm before use.
- It is your responsibility to ensure that the firearm you are building is legal to build and possess in your city and state.
- Must be 21 years old to purchase this product.
Compatibility with other components
Due to the abundance of aftermarket components available and introduced each year, it is impossible for us to provide compatibility information for all components with our products. Some simple measurements, visual examination and some common sense can save a lot of time. Ultimately, it is your responsibility to verify that the parts you intend to use are compatible.
Questions or a warranty issue: email support@cmttac.com. You will receive a response within one business day.