AR Troubles

[Dishonored]

Coming here to gain some insight.
Running this .300blk I was having short stroking issues. I changed out the buffer spring and weight. I corrected that problem.
I then began to have several FTF problems and noticed A LOT of brass shavings within the receiver but not in the chamber area.

Under a closer inspection I’ve found that the upper receiver’s feed ramps and the barrels are not a smooth transition. I can easily hang a toothpick. I can fix this myself. Still didn’t particular answer the question of the brass shavings.

Looking at the bottom of the BCG I’ve noticed what I’d consider heavy brass scoring where it slides across the next round. This gun has roughly 100-120 rounds through it. The brass markings are far more pronounced between wipings on this gun than those on two other guns with way more rounds through them, without even being cleaned.

I swapped lowers thinking the magazine may have been seating too far up, I tried another magazine. Still the same thing.

It’s an Aero upper… has anyone ran into one being out of spec? Allowing the mating of the upper to sit too low on the upper forcing the BCG to ride lower (more pressure on the magazine).

My next step will be to check the dimensions of the BCG but it ran fine in my other gun without any issues or strong markings as it does in this one.

See images provided for feed ramp issue and also a comparison for the bottom of this BCG and 2 others in different guns.

Also providing photos to show the amount of brass shavings throughout the gun after 60ish rounds.

(Apologize for typos I am on my phone).

 

[Bigchillin83]

Under a closer inspection I’ve found that the upper receiver’s feed ramps and the barrels are not a smooth transition. I can easily hang a toothpick. I can fix this myself. Still didn’t particular answer the question of the brass shavings.

id say this is 99% of the problem, what do spent casings look like, also cycle a few live rounds through it, what do they look like? brass is super slick until it meets somthing else that isnt slick and then has reverse effects.. it doesnt take much to slow it down and throw all the timing outta wack.... are you shooting subs or supers? is there good expansion and equal diameter on the neck of casing where it should be expanding to seal off gasses, might be a combo of bad extension, and chamber... aero is usually pretty turn key, what kinda barrel

 

[Bigchillin83]

i know its a pain in the butt but, try loading one round, drop it in the barrel not stripped out of mag, close bolt, insert empty mag, shoot, if it kicks out the brass and locks bolt open, lowering the amount of brass shavings and failures, your prob is likely your barrel or barrel extension and feed ramps...

 

[twinin]

Yes, how does the brass look? Are there signs of pressure? Are you running supers suppressed with pistol length gas?

 

[AdvancedLaser]

Your barrel extension is riding so far back the upper feed ramps are not tilting the round up to clear it. Its acting like a cheese grater. Its the upper.

When your system unlocks the pressure release sends the brass shavings backwards and onto everything.

 

[Dishonored]

id say this is 99% of the problem, what do spent casings look like, also cycle a few live rounds through it, what do they look like? brass is super slick until it meets somthing else that isnt slick and then has reverse effects.. it doesnt take much to slow it down and throw all the timing outta wack.... are you shooting subs or supers? is there good expansion and equal diameter on the neck of casing where it should be expanding to seal off gasses, might be a combo of bad extension, and chamber... aero is usually pretty turn key, what kinda barrel

Shooting 147gr super (FMJ) no hangups. Assuming this is due to the much more forgiving length and nose shape.

Also shooting 200gr Winchester open tip subs. Every hang up was a round on the ejection side.

Bought it from a member here. Not sure on the barrel. Upper is aero.

Yes, how does the brass look? Are there signs of pressure? Are you running supers suppressed with pistol length gas?

Scored. Not sure what signs that would be?
Yes I am mainly subs but I did shoot supers today also. This is a 8” .300 BLK.

 

[twinin]

Pressure signs would be brassed dinged up pretty bad overall, but also look for brass with blown or cratered primers and ejector swipes (circular indention on outside part of brass rim).

Based on what you said, I would lean toward barrel extension or feed ramps though, but still check pressure. I experienced something similar shooting a .22 magnum semi-auto suppressed

 

[Bigchillin83]

Supers have enough thump to keep brass moving… when they are going into the chamber they are more than likely getting scored up on feedramp/ extension and causing a sticky case in the chamber… under supers more than likely won’t see it, but on subs they don’t have the extra thump to break the seal and wasting needed energy in that instead of a complete a cycle , and causing short strokes

 

[Dishonored]

Pressure signs would be brassed dinged up pretty bad overall, but also look for brass with blown or cratered primers and ejector swipes (circular indention on outside part of brass rim).

Based on what you said, I would lean toward barrel extension or feed ramps though, but still check pressure. I experienced something similar shooting a .22 magnum semi-auto suppressed

I wanna say brass looked good other than the scoring marks, maybe a few has a small flat spot at the end of the neck not bad though.

The bolt face looked good.

 

[Dishonored]

Supers have enough thump to keep brass moving… when they are going into the chamber they are more than likely getting scored up on feedramp/ extension and causing a sticky case in the chamber… under supers more than likely won’t see it, but on subs they don’t have the extra thump to break the seal and wasting needed energy in that instead of a complete a cycle , and causing short strokes

I fixed the shirt stroking issue. The SB PDW had a very stiff spring in it. I swapped it for a Nemo .300blk spring but using a H2 buffer instead of a H1.

Gun runs great and ejection angle and distance seems good. It’s just these dang FTF’s now.

 

[Bigchillin83]

Barrel/extension… causing it to sprinkle brass like sand in your upper… barrel should have some kinda marking on it… or it’s the aero upper… but that’s pretty rare with aero quality, not impossible though

 

[Dishonored]

Barrel/extension… causing it to sprinkle brass like sand in your upper… barrel should have some kinda marking on it… or it’s the aero upper… but that’s pretty rare with aero quality, not impossible though

Yeah. I’m just contemplating… sending either off for correction and waiting months or just fixing them myself. I know people hate to hear… but might be dremel time and a polish

Mine are not a smooth transition and they are not equal widths regarding matching bevel lines.

Cause this it what it should look like.

 

[freedive10]

I would take a black permanent marker and completely color a few rounds from tip to primer. Load them up and cycle them through to see where on the round it’s getting the friction. I would do the same live fire and collect the shells to see what’s happening there.

This should help you determine where the rounds are getting caught and shaved.

 

[Bigchillin83]

Agreed!!!

 

[Bmash]

i posted on the same issue a while ago. There are lots of videos and ideas on doing the work. one thing they will tell you is do NOT cut into the aluminum receiver! Take the barrel off to work it.

 

[Dishonored]

I would take a black permanent marker and completely color a few rounds from tip to primer. Load them up and cycle them through to see where on the round it’s getting the friction. I would do the same live fire and collect the shells to see what’s happening there.

This should help you determine where the rounds are getting caught and shaved.

Good idea. I know the tips of the longer sub rounds are hitting the feed ramp and not feeding properly dropped the mag an inspected it from the top (ejection port and bottom from magwell). It also only hangs up on the right side (port side) ramp.

I also really wanna find out why the bottom of the BCG is showing so much brass wear compared to my other rifles.

This is a brand new build, I know it needs to break in but the brass marking on the underside of that BCG seems excessive to what I’ve see before… although I’ve never inspected a new build so closely before as they’ve always ran fine from the jump.

 

[Dishonored]

i posted on the same issue a while ago. There are lots of videos and ideas on doing the work. one thing they will tell you is do NOT cut into the aluminum receiver! Take the barrel off to work it.

Correct. The upper’s ramps seem to look like most I can find online. It’s the barrel extensions ramps that are out of spec; as far as I can tell as of now.

 

[Dishonored]

I think I am going to take the 10.5” barrel off another build and put it into this upper and see what it looks like. As a comparison. The other upper with the 10.5” has proper ramp alignment, I just checked it.

If the 10.5” doesn’t line up on this aero upper then I’ll know it’s the upper. If it does line up then I’ll know it’s the 8” barrel itself.

I’ll also clean the upper and lower then run the 10.5” barrel live and see if I get the same brass shavings or hangup issue.

 

[Bigchillin83]

Good idea. I know the tips of the longer sub rounds are hitting the feed ramp and not feeding properly dropped the mag an inspected it from the top (ejection port and bottom from magwell). It also only hangs up on the right side (port side) ramp.

I also really wanna find out why the bottom of the BCG is showing so much brass wear compared to my other rifles.

This is a brand new build, I know it needs to break in but the brass marking on the underside of that BCG seems excessive to what I’ve see before… although I’ve never inspected a new build so closely before as they’ve always ran fine from the jump.

if i had to guess the majority of the brass on the bottom of the bcg are the flakes you are seeing either being heated up or smashed into the bcg from the next round....

if you are scraping brass going in the debris is landing on the next round in the mag and around the bcg, when you shoot the friction and heat is causing the brass shavins to stick to the bcg, brass is so soft it doesnt take much to smash/smear brass flakes to where ever you want

 

[Dishonored]

if i had to guess the majority of the brass on the bottom of the bcg are the flakes you are seeing either being heated up or smashed into the bcg from the next round....

if you are scraping brass going in the debris is landing on the next round in the mag and around the bcg, when you shoot the friction and heat is causing the brass shavins to stick to the bcg, brass is so soft it doesnt take much to smash/smear brass flakes to where ever you want

I did not think of that. Very likely now that you’ve mentioned it. Thank you for that man.