i dont know if this was said but try and pinch your shoulder blades together (pulling your shoulders back)it will put more stress on chest. and maybe try a wider grip on the barbell and kick your elbows out(away from the body, if your on a bench)

I would try to not always to try and push the most weight you can and realy focus of your form and controled negatives, count to 3 on your way down and then explode up, most people do not realy control the negatives in there workouts and it can really help with muscle growth.
This is my routine

DECLINE BARBEL
4 SETS 8-12 REPS INCREASING THE WEIGHT EACH SET

INCLINE DUMBELL
4 SETS 8-12 REPS INCREASING THE WEIGHT EACH SET

FLAT/INCLINE DUMBELL FLYS
3 SETS 8-12 REPS

PEC DEC FLYS
3 SETS 8-12 REPS

CABLE CROSS OVERS
3-4 SETS 8-12 REPS

AND SOMETIMES WILL FINISH WITH DIPS OR PUSH UPS TILL FALIURE

AND REMEMBER TO REALY CONTROL YOUR NEGATIVES COUNT TO 3 ON THE WAY DOWN AND EXPLODE UP
TRY THIS AND SEE IF IT HELPS

I had the same problem man, no matter how hard I went on chest days I never saw the results I had hoped for... and then my [little] brother gave me some life-changing advice. Although my brother is 4 years younger than me (19) he is the current record holder for his weight class and age in bench press.
enough about that sh!t bc I'm sure you don't care... the key to building a solid chest IMO is "push&pinch" by this I mean do your flat bench exercise, then move to chest flies-whether it be on a bench with DB's or with cables or whatever you prefer. then after your set of flies move to incline bench and then incline flies. you seem to have mentioned doing something like this previously, but adjust your sets to 4x6 or 4x8. drop sets are mostly for cutting and/or building endurance, you need to focus on EXPLODING through the motion!

When doing flat, incline and decline bench. close up your grip on the bar. This works for me real well. The closer your grip you will notice more focus on the pecs and only come down maybe 3/4 of a way. I also use dumbbell butterflies and cables. Once you feel your pecs filling up stick with that routine.

try switching your work out to start of with
incline dumbbells 3 sets of 8.
incline flys 3 sets of 10
decline dumbbells 3 sets of 8
regular bech with barbell 3 sets of 10
and then do negatives to rip those muscles apart you will get strong as hell and put on size. do this for about 3 weeks then switch it up to high reps!

First off whats your chest workout look like??.......
But yea "MY" advice is, Focus on HEAVY SETS "LOW" REPS BRO LIKE 5x5's or 6x6's but mainly hit that incline n decline, try to do every chest movment with as much weight as u can for that movement, hit those incline flys for about 8-10 reps HEAVY.. Also what i started doing is on any press movement i do i try to do like half reps meaning i never lock out i just try not to keep it too far from my chest so that way my tris and shoulders dont come into play as much, i get way better pumps and more blood in that muscle since im isolating the shit out of it... Also Try flexing your chest between sets to get more blood in ur pecs bro IT WORKS.

(REMEMBER STICK WITH HEAVY SETS LOW REPS) Cuz IMO if your trying to "GROW" your chest or any other muscle i believe you always have to lift that heavy weight brah....... But also keep note that more isnt always better so just keep it simple compound movements and that chest will blow the fuck up. ;)

OR Maybe its just genetics... hahahaha just kidding bro "FUCK GENETICS" thats what i always say. LOL!

For me, alot of hammerstrength, smith machine presses, and dip machines helped me build my chest. Especially benching on the smith machine it allows you to use a really wide grip and have slight cushioning from the way the machine works so you don't injure yourself. Try the decline movement hammer strength with the widest grip you can put on it, and get a deep stretch.

I have the opposite problem, my chest is huge and my arms lag. Have you tried incline or decline? Maybe try some drop sets.

You might be using more of your delts on bench because of your grip.. Weighted dips seem to bring the girth out in the lower pecs for me, cable flies are awesome also. I typically have one week of light weight with high reps then a medium week then heavey and finally max. Make sure your not over training it either

Also..bend your arms in toward your body a little rather that keeping your elbows out parallel to the bar.(if that makes any sense) When your arms are straight out to the sides you are using more shoulder.

Barbell bench press all the way down (touching chest at the nipple line). You are using your chest at the bottom of the movement and getting more fascia stretch. As you go up your tris kick in and take a lot of the load off your chest. So the moral...if you only go to elbows @ 90 degrees...go all the way down.

Pre-exhaust the muscle(Chest) with isolated moves 2 or 3 sets with high reps, then do compounds movements(Bench press or any other compound chest exercise) This would help you to work your chest more, sometimes Triceps over powers chest and chest give up first, and put all the tension on the Triceps. Hope this helps.

Same problem bro. Your tris and shoulders are most likely overpowering the chest on the bench. Maybe try focusing more on different variations of flys. I know it's very frustrating, my chest is very flat but my shoulders and arms look great. Stay consistent my friend.

You and me both. Thats the one thing holding me back from a killer physique

Have you tried incline or decline? Flyes? Cables?