BUMPER to BUMPER: Anything Can Go Wrong With Any Part of Your AR-15
As a builder/armorer of AR-15s, there is one truth that one must acknowledge: a string of builds will almost never go smoothly. Pretty much every part of an AR-15 is susceptible to issues and you won’t become an AR aficionado until you’ve experienced them. But maybe we can give some of you newcomers a head start. Here is a go list of some of the issues that may be encountered on the workbench. We’ll start from the muzzle device on back to the buttstock and everything in between.
The Upper Half
MUZZLE BRAKE/FLASH HIDER/THREAD PROTECTOR – Make sure the muzzle device you are installing is of the correct thread pattern. If it is not, you’ll know within the first few turns. You can count the threads and the length if you’re not sure. Remember there are different thread pitches for different calibers.
Also be aware that airsoft “copies” often have a reverse thread direction even though the dimensions are correct. These commonly get sold at gun shows as real gun parts and never discovered until the parts are taken home and on the workbench. Though some airsoft style parts might be of excellent quality, they are not built to withstand the rigors of real firearms.
Be sure to index properly. The logo usually goes down because the vents are on the top. It’s a common mistake to think the logo is supposed to show on top. Remember that if a bottom is closed it is to prevent the blast from kicking up dust whilst shooting in the prone position. The logo is there simply because it is the largest and most convenient spot to print a logo.
Don’t forget to check the diameter of the muzzle opening. If it’s not big enough to accommodate the caliber you are shooting… well that’s going to be a big problem. If you’re assembling a 9mm build, you’ll want to make sure the muzzle device’s opening can accommodate a 9mm bullet or more. Even though 9mm ARs have a standard ½” x 36 tpi thread pitch, a few manufacturers still use the ½” x 28 tpi sizing that is standard for the 5.56mm NATO cartridge.
The ¾” flats on the side of the muzzle device are used for mounting by turning the muzzle device on with a ¾” open ended wrench. These flats on many devices will index up and down or left and right to aid in indexing the vents properly. But this is not always the case. For instance, on Yankee Hill’s Phantom muzzle devices, the flats do not index exactly straight. On other muzzle devices like Smith Enterprises’ Vortex Flash Hider, the vents are not direction dependent and thus do not require indexing. The Vortex in fact does not even require a crush washer or shims for installation.
CRUSH WASHERS/PEEL WASHERS/SHIMS – Do your best not to use thread locker on the muzzle device. Crush washers are a better choice especially on devices that need to be indexed. Proper amounts of torque are really the best way to keep your brake/hider in place. BUT, be sure to follow manufacturer’s instructions. Remember not to reuse crush washers on the same barrel and muzzle device combo. At a cost of less than 2 or 3 dollars, it’s a good idea to have an extra crush washer on hand just in case you need to make impromptu changes or repairs.
Peel washers (or laminated shims) are generally no longer used. A crush washer is much easier to work with and easier to find.
Shims are specified by certain manufacturers for use with their muzzle devices and are usually included with the muzzle devices that need them. This is especially so with muzzle devices designed to be suppressor adapters. It can be frustrating to fit a muzzle device with a shim kit. Remember to start with the smallest shim size first and work your way up the various thicknesses and combinations. Be patient and find just the right shims to fit your muzzle device.
Some manufacturers specify the use of Rocksett as a threadlocker for your muzzle device. Rocksett is similar to Loc-tite except it is much less sensitive to heat and won’t soften as the barrel heats up. Don’t use too much. If you need to remove the muzzle device at a later time you will need a LOT of torque.
BARRELS – You get what you pay for. It’s important to know where a barrel came from, so you’ll know who to go to if you need help. Reputable barrel makers do certain things to ensure their barrels are safe to shoot and will be long lasting. MPI and HPT [or Magnetic Particle Inspection and High Pressure Testing] barrel testing as well as headspace checking are normal quality control measures at top notch barrel manufacturers and really ensure that you get something that is going to work and last.
It helps to wipe a thin layer of grease on the outside of the barrel extension to make sure the barrel seats in the receiver smoothly and can be removed easily later on. Not necessary but we like to do it.
Check to see if you have M4 feed cuts in your barrel extension. If you have them, you’ll want an upper receiver with the complementary cuts. If you don’t have them, do NOT use an upper receiver with the complementary cuts. The other way around is okay, but not so great.
Make sure your index pin is in good shape. We’ve seen a few break and more than a few fall out! Do NOT install a barrel without an index pin! Also, check to see if the feed ramps line up. The index pin should fit snug and not allow the barrel to rotate. If the barrel rotates it may cause a catastrophic failure.
Inside the barrel, when looking down the bore, you might see what looks like a small foreign body inside the bore on the top of the barrel. That dark spot is where the gas port was drilled and where a remnant of the drilling remains. The presence of that remnant means the barrel was not test fired. But rest assured that a few rounds fired through the barrel will eliminate it. Before you shoot the barrel, try to run a patch through the barrel and see if it removes the remnant. If it doesn’t, see if the approximate location matches with the location of the gas port.
If there is a dark spot in the same location as the gas port inside the bore, that is just a difference from the lack of reflectivity in that location. Don’t worry if you can’t brush the dark spot out, it’s supposed to be there.
HEADSPACING – This is something that can be easily checked by your gunsmith with a set of headspacing gauges. If you have a good barrel from a reputable company, you shouldn’t have to worry about it. If you have a no-namer from a “who’s that” company, you may want to get it double checked. There are smiths out there who can re-torque or reset your barrel extension to correct headspace, but a specialized tool would be required. Unless you know a capable smith already, it may not be worth the trouble to seek one out and have your barrel fixed. If the extension is reset to correct your headspacing, don’t forget to reset your index pin as well.
GAS BLOCK – The gas block comes in a number of sizes. There is a different gas block for the AR-10 vs the AR-15 and there are different sizes for pencil/lightweight (.625”), standard (.750”), and heavy/bull (.936”). Now this can get confusing. The AR-10 (or Armalite pattern) uses a proprietary gas tube and block, so if you use this pattern, you’ll need to get specific parts for that gun. The AR308 (or DPMS pattern) gun can use a standard AR gas block with a .308 gas tube, or a standard AR gas tube with an AR308 gas block. Reason being: the receiver is taller and the gas key resides at a greater height above the bore, and thus a little more elevation is required to accommodate the additional height. Otherwise the angle of the key end of the gas tube will be elevated and may not make a good contact seal with the gas key. Have guns been built that use standard AR parts in AR308 builds? Absolutely. But for the sake of making sure your gun runs the way it should, make sure that you’re using the right size.
If you are installing a gas block on an upper with free-floating handguards, you might not be installing the standard handguard endcap with it. Remember to use a spacer to give the gas block a little boost forward so the gas hole will align properly. The handguard endcap usually gauges between .02” and .03” thick. For reference, your NRA membership card gauges at .021” and a typical credit card measures at .28”.
Using a spacer isn’t always necessary since the gas hole inside the gas block is considerably larger than the port on top of the barrel (to allow for variations in alignment). But it’s nice to know that the block is installed where the port is measured for. Because of the allowed variation in mounting location, exact placement is not necessary… eyeballing is sufficient. But take your time; it looks better when it’s straight.
Gas blocks can creep if they are not tightened down properly. Use Loc-Tite on the threads of your set screws to keep them in place. Cheap hex wrenches can break when tightening these set screws. Use good quality wrenches or the included wrench that comes with some gas blocks. ONLY use the specified size wrench or risk stripping the screw head. Dimpling the barrel will also help secure the gas block but even dimpled barrels won’t correct issues related to improperly secured set screws.
Because set screw gas blocks are secured from the bottom, tighter screws help seal in the gas that travels between the block and the barrel. When in doubt, these screws should be TIGHT. Vltor recommends between 40 lb/in safe up to 50-60 lb/in. [NOTE: There is an enormous difference between lb/ft and lb/in! Be certain the tool you are using is the correct one!]
Gas blocks and barrels may have differing tolerances and may have an excessively tight fit. It is not abnormal. If you can get the gas block to seat over the gas port, a tighter fit is preferable anyway. Don’t be afraid to go at it with a rubber mallet and a little oil to get it in place. Just remember it will take equal or greater effort to remove it later on: so don’t try too hard either.
Clamp-on gas blocks are an easy way to install and reduce risk of a bolt head or wrench failure. Beware on certain low-profile gas block and free float handguard combinations: clamp-on low-profile blocks are larger in profile and will often not provide enough clearance for certain handguards. You’ll want to dry fit your gas block and make sure there’s no contact between the inside of the handguard and the gas block.
Railed gas blocks come in two basic heights. The ‘standard’ height is actually lower in plane than the rail on the upper receiver. With the standard height railed gas block you cannot mount a front iron sight on the rail unless it is equipped with a longer sight post stem to compensate for the lower height of the gas block. If you use the specially sized front sight, you may have to mount the sight backwards: when folded down, the stem will often be obstructed by the handguard and won’t fold all the way down unless mounted in reverse. The ‘upper height’ or ‘rail height’ gas block is taller and on the same plane as the upper receiver and will allow for the use of standard BUIS. Take note that when mounting the front sight backwards, the release button to fold the sight back down will be on the opposite side from normal. Do not use a riser to compensate for the height difference. It is too small of a difference to correct mechanically, yet too large of a difference to compensate with sight post adjustment.
Be wary of the use of polymer sights on the railed gas block. While Magpul’s MBUS is designed to resist melting, it is probably more prudent to use them on railed handguards only. You’ll want to stick to aluminum or steel when mounting directly to the gas block. I’m aware of the raging debate about MBUS and gas blocks, but for the sake of practicality, metal sights on gas blocks are a safer way to go.
GAS TUBES – These come in four basic lengths for the 5.56mm/.223 caliber. Every once in awhile a gas tube will come in from the manufacturer clogged with some form of grease or other fouling (though very rare). Before installing the tube, stick one end in your mouth and push a small puff of air through. If air doesn’t flow through, clean it out with a gas tube cleaning swab. If it’s packed with grease (and it does happen), you may need to leave it in a tank of solvent or push it out with a swab. Better to find out before installing than after the upper is assembled!
The gas tube can act as a gauge when aligning the barrel nut. Once you’ve installed the barrel nut, slide the gas tube into its hole in the upper receiver and rest the tube upside down onto the slot in the barrel nut. Check that the barrel and gas tube are parallel. If they are not, adjust the alignment of the barrel nut until both are parallel with each other. If everything is installed already, look inside the upper receiver at the key end of the gas tube. It should be straight. If it is cockeyed, the barrel nut is not aligned and the upper may not function properly.
BARREL NUT – Using the correct barrel nut wrench is vital. The wrong wrench can cause functional damage to the nut and make installing the handguard or other hardware especially difficult.
Clean out the inside of the barrel nut before installing. Be sure to apply a small layer of grease to the threads of the barrel nut/receiver before installing. If you don’t, you can cause the barrel nut to seize onto the upper receiver. Over torquing can easily cause catastrophic damage to the upper receiver. The shear tolerance of 7075 T6 aluminum can easily be exceeded with a hand-driven torque wrench.
Torque the barrel nut to 30 lb/ft. Then back it off and repeat two or three times. Unless the manufacturer specifies otherwise, the standard torque range for an AR barrel nut is between 30 and 80 lb/ft. It is a broad range because alignment of the barrel nut is more critical to the build than the actual torque used. After all, on a standard barrel nut, the gas tube will help keep the barrel nut captive. Torque to 30 lb/ft and then increase torque until the barrel nut is aligned, not exceeding 80 lb/ft. On proprietary barrel nuts, follow the manufacturer’s instructions. Not all barrel nuts require alignment, but the ones that do will have a broad torque range.
Do NOT use any kind of thread locker or thread sealant on the barrel nut… EVER.
HANDGUARDS – Midlength and Rifle length handguards often fit into triangular handguard endcaps. Carbine length handguards are meant to be used with round handguard endcaps only. Beware of endcaps that have inward alignment notches (at the 3 o’clock and 9 o’clock positions): if your handguards do not have complementary notches, they will not install easily without modification.
Most standard plastic handguards are tapered. If you install an accessory rail on top of your handguard, it will not serve as a good sight platform because it will be mounted on a downward slope.
Plastic handguards are sensitive to lateral movement. Initially they may lock in tightly and will not roll. But if you install a vertical grip or just through heavy use, the handguards will loosen up over time and will begin to rattle and roll. It does not affect the operation of the gun, but it can be a bit of an annoyance. Once those plastics have worn out, upgrade to aluminum if the user intends to continue using a vertical grip.
Beware of cheap handguard rail covers. Those made for airsoft or sold cheaply online may be of inferior quality. Rail covers made by Ergo/Magpul/Falcon are formulated to resist melting even under considerable shooting stress. Cheap rail covers may melt and burn onto the rail as the gas block heats up.
BACKUP IRON SIGHTS (BUIS) – Some sights can be installed cockeyed. Be sure to seat the bottom of the sight body flat onto the picatinny rail platform before tightening down.
Sights are manufactured with a standard height aperture for the AR-15. Mixing brands is no problem as long as they are built to that standard height.
If you don’t know which direction to mount the rear sight, look at the aperture. The concaved side of the aperture faces the shooter, the flat side faces the target. If there are mounting knobs, they should always be on the left side. If the mount can accommodate, southpaws can mount the knobs on the right side (opposite the ejection port) of their left-handed rifles.
Mount the front sight as far forward as possible. Mount the rear sight such that the rear of the sight when folded does not extend past the end of the upper receiver. With certain brands, the sight may be mounted on notch 2 rather than notch 1.
A2 IRON SIGHTS – I occasionally get customers who complain that the A2’s sight housing wiggles considerably (on the yaw axis). This is normal. As long as the wiggle rotates on the same vertical axis as the center of the aperture, the wiggle will not affect the sight picture/zero.
On A2 carry handle sights, be sure to tighten the mounting knobs well. They come loose pretty easily.
CHARGING HANDLE – A bent (off true) charging handle can cause malfunctions. Lock the bolt back manually and then slide the charging handle back and forth. It should move freely. Check the inside of the charging handle for abnormal off-center wear from contact with the gas key or outside wear on one side. Swap charging handles and see if it ‘feels’ different. This is a rare occurrence but happens on occasion.
BOLT – An AR-15 should briskly eject brass between 3 o’clock and 5 o’clock and will usually land between 5 and 10 feet away when shooting in a seated or standing position. [This can only be measured when actually shooting live. It cannot be simulated by manually ejecting brass or cartridges.] A poor extraction will eject brass to within a few feet and sometimes right next to the shooter. The extractor spring insert has had a few different flavors over the years. If the insert is blue in color, it is of an older variety and should be replaced with the current black insert. The black insert has a higher durometer and will provide the extractor with more force. The black insert can also be supplemented with an O-Ring to further increase the force. Check the ejector and spring as well, but the extractor insert is the most common solution of ejection issues.
Be sure to check the gas rings (3) on the bolt every time the bolt is removed from the carrier. They should not be cracked, worn, or missing. And there should always be three gas rings.
BOLT CARRIER – The carrier can have varying tolerances from brand to brand. Some have a looser fit than others, but the fit of the carrier is not as critical to reliability as the bolt itself. As long as the bolt has a good machined fit (and gas ring seal) to the carrier, it is ‘okay’ to have a carrier that is a little ‘loose’.
Some brands of carriers are very tight and are even a little difficult to draw back with the charging handle. This may or may not affect the operation of the gun. More often than not, these tight fitting carriers are found in guns with excellent performance characteristics.
“Full-auto” or “M16” carriers are not full-auto parts as recognized by ATF. They are legal for use wherever semi-automatic AR-15s are legal. These full-auto carriers are more classic in design than the semi-auto carriers and are approximately 0.8 ounces heavier than a semi-auto carrier (the same increase in weight when moving from a standard carbine buffer to a heavy carbine buffer). The full-auto carrier will be minutely slower than the semi-auto carrier and should reduce ever so slightly the amount of felt recoil.
The gas key should always be staked. Though companies like to use the term “properly staked” the only properly staked gas key screw, is the one where the screws don’t move, regardless of which method is used (and there are quite a few). Loc-tite is not a good alternative as most threadlockers are sensitive to heat and will soften up as the temperature increases. The gas key must endure considerable stress during operation. Nothing but a mechanical staking will do.
EJECTION PORT COVER – Always remember to install the ejection port cover before installing your barrel. The barrel nut is part of what keeps the pin in place. The forward assist keeps the ejection port pin from going the other way. If the upper half is built without the ejection door, it will need to be disassembled again to install it.
As for the ejection door “e-clip” (or hinge pin retaining clip), you’ll want to make sure it is fully seated into the groove of the hinge pin before installing the assembly. If the e-clip comes loose and falls away, you’ll never find it. And by the way, when purchasing ejection port assemblies in prepackaged kits, the e-clip is extremely small and hard to find. It is usually stuck to the face of the door by means of oil. Look carefully and you’ll find it. Don’t just rip the bag open, the e-clip is small enough to look like a shaving and easily mistaken for a machining remnant.
FORWARD ASSIST – I know some of you don’t like the forward assist, but if your receiver has a place for it, you really need to install something there. When driving in the roll pin for the Forward Assist plunger, make sure the plunger assembly is depressed and under spring pressure before driving in the pin. There is a sweet spot between fully depressed and fully relaxed where the roll pin will fit into. Just figure on pushing the plunger in fully and then letting it out about a quarter inch before driving the roll pin in place. Otherwise the back end of the pawl will stop the roll pin from driving in place. The trick is to hold it in place while hammering in the roll pin. I like to hold the plunger in place with my palm while holding the roll pin holder with the fingers of the same hand. That leaves the other hand free to swing the hammer. Remember to oil the roll pin before driving it.
The Lower Half
MAGAZINE WELL – The magwell may be cut with too little space and certain magazines might not fit. Or if the lower was painted, the finish might be too thick to accommodate certain magazines. Some emery cloth or light sanding can open up the magwell (minus some of the finish). This is a rare occurrence but it has happened (Google: Territorial Gunsmiths lower).
PIVOT PIN HOLE – This hole is sometimes drilled improperly. The 0.250” hole may be too small if worn tooling was used to drill the hole in place. Or if the machinist drilled the hole on one side and then flipped the receiver to drill the other, the holes may not be true and centered. Use a .250” manual reamer that can be found in most hardware stores and slowly turn out the holes (all the way across). Make sure to use some cutting oil and be sure to turn the hole open from both sides. Take your time; it takes quite a few turns to open up the hole. Once the hole is the right size, clean out the holes and try reinstalling the pin.
The takedown pin hole in the upper receiver is slightly elongated in shape to allow for variations in the length between it and the pivot pin. This is normal and not a manufacturing defect nor the result of excessive wear.
TRIGGER GUARD – A mounting ear for the trigger guard can easily break off when installing the trigger guard roll pin. Be sure to support the bottom ear with a block of wood or non-marring plastic when installing. Also apply some oil to the roll pin and the holes before driving the pin in.
PISTOL GRIP SCREW – This screw can seize inside their respective hole on the receiver because of improper finishing or a bad screw. If your pistol grip screw is resisting and begins to chatter while turning it in, take it out and use a different screw. If you install your pistol grip and suddenly your trigger doesn’t work, check to see that you installed the pistol grip washer. If the pistol grip screw still interferes with the trigger, you may need to shorten the screw or add another locking washer to act as a shim.
MAGAZINE CATCH – If your mag catch is sticking and not smoothly and reliably going in and out, you may want to try a different mag catch.
If the mag release button is not turned down far enough, the catch may stick out and catch on the outside of the receiver. The threaded end of the mag catch should be flush or near flush with the outside of the mag release button.
BOLT CATCH – You’ll want to check the hole for the bolt catch buffer to make sure it was drilled wide enough for the bolt catch buffer spring. Just drop it in and make sure it falls out on its own. Then do the same with the spring and the bolt catch buffer. Make sure the end of the bolt catch buffer sticks out as it will need to push against the bolt catch.
SAFETY SELECTOR – Install the safety selector after installing the trigger. If you put it in before the trigger, it makes installing the trigger more difficult. If you install it after installing the hammer, you’ll need to lock the hammer back and shimmy the selector into place. It’s easier to just put the hammer in last.
TRIGGER – The trigger is relatively trouble free. It’s a good idea to apply a dab of grease on the front machined surfaces of the trigger before installation. If you are up to it, you can even polish the trigger break surface to get a smoother trigger pull before you install it. Take care not to remove too much material though, else your trigger may fire on its own!
Some brands of drop-in triggers have trigger bodies designed to give a very tight fit into the lower. Because of the low tolerances, the drop-in bodies don’t always fit into the receiver (at least without some gunsmithing). Timney bodies have adjustment set screws that protrude from the bottom. Retract these screws before installing as they will interfere with fitment. Once the body is installed, then tighten those screws per spec.
DISCONNECTOR – The disconnector can fail and cause your gun to fire multiple rounds in a full-auto manner. It will do likewise if it is installed correctly. You may be prosecuted by law enforcement whether you do this intentionally or not, so take care when installing the disconnector.
HAMMER – The most common error with hammer installs is installing the spring backwards. This reduces the amount of spring pressure and can cause walking pins and light strike malfunctions.
The hammer spring is profiled to look like the shoulder end is supposed to hook over the disconnector catch. DO NOT BEND the hammer spring to make it ‘fit’. It is already profiled and bent into the shape it should be to function properly. The shoulder does not need to hook over the disconnector hook and may actually interfere with the safe functioning of your gun.
TRIGGER PIN / HAMMER PIN – These pins are designed to hold in the trigger and hammer as well as provide both with a pivot axis. They are also designed to keep each other captive in the receiver in a non-permanent manner by the use of springs that are already in the system. The trigger pin is held in place by the hammer spring. The hammer pin is held in place by the “J-spring” inside the center axis of the hammer.
If the J-spring is worn out or improperly installed, the hammer pin will walk out of place. If the leg of the hammer spring is not sitting into the groove of the trigger pin, the trigger pin will walk out of place. Low tension or reverse installation can cause the pins to walk as well.
Hammer pins can break along a groove [weak point of the pin], most commonly along the center groove. Once this pin breaks, an otherwise reliable gun may start to have cycling issues. If this happens, check to see if the ends of the pins are flush with the outside of the lower receiver. If not, that may indicate a broken pin.
Anti-walk/anti-rotation pins can be a good solution and are designed to minimize wear on the holes in the lower receiver as well. These are made of a 416 stainless steel which has considerably higher shear strength than 4140.
TAKEDOWN PIN – This pin can get “stuck”. You may need to wear in the pin and its detent by working it back and forth. If the pin locks in place too tightly, knock it free with a punch and a small hammer. The detent needs to be “broken in”. There’s nothing wrong with using a little oil on the shaft of the pin.
BUFFER RETAINER – If you turn your buffer tube in too deep, it can prevent your upper from closing down on the lower receiver. Your buffer tube should only be turned in just enough to hold in the buffer retainer. If the tip of the buffer retainer bends, replace it.
BUFFER TUBE – The buffer tube and the buttstock are the only parts that need to be considered when looking for the difference between ‘milspec’ and ‘commercial’. Commercial tubes are larger in diameter than milspec so be sure to match milspec with milspec and commercial with commercial.
Dirty buffer tube threads or tubes that are not cut or finished properly can interfere with installation. It should not be especially difficult to thread in a buffer tube. In fact, the tube should thread in pretty freely. Both the buffer tube and the receiver are made of aluminum. If you are getting resistance when threading in, STOP. NEVER use threadlocker on the buffer tube threads. If you’re lucky enough to have a tap or die of that size, you can recut or clean out the threads by hand.
You should always stake the endplate against the castle nut when installing a collapsible stock. While it is not common for castle nuts to back out, it is still best to turn that nut down properly and stake it. The tool required for tightening the castle nut is not one often carried in the field.
Buffer tubes should not be lubricated except with a dry film lubricant.
BUFFERS – These should be selected as per their purpose. Carbine buffers with carbine springs go in carbine stocks. Rifle buffers with rifle springs go in rifle stocks and so forth. If you need help with the enormous selection of buffer options, refer to a PREVIOUS ARTICLE.
BUTTSTOCK – The buttstock should be matched with the buffer tube, milspec with milspec and commercial with commercial. Beware of some cheek risers as they may prevent the charging handle from traveling all the way back as necessary.
The number of adjusting positions available for the collapsible buttstock is determined by the number of holes drilled into the buffer tube’s lock channel. It has nothing to do with the stock body itself. However, in certain cases, a tube will not lock down in the full collapsed position. This is sometimes because the buffer tube is slightly longer than spec (more often with commercial spec tubes) and the stock body bottoms out in the tube before reaching the last locking hole.
If the adjusting latch is loose and seems to rattle ever so slightly, the latch pin is either not bottomed out in the adjustment position or the position hole is not milled deep enough.
While this is just a brief sampling, it is a quick head start towards becoming an AR-15 armorer. It doesn’t take much because the AR-15 is such a simple platform, but not doing things “right” can get you into big trouble. Take your time and remember that parts are supposed to fit. If they don’t fit as expected, you may want to take a step back and evaluate why.
As always, if you have any questions or any other things to add, feel free to comment below. Be safe and have fun!