importance of cam pin fitment

[corey4]

ddm4v7slw 14.5 middie
rifle length RE
tbac ultra9
slr agb
yes, it's a sbr lower, a dd mk18 factory lower
it's 32 right now and i wanted to tune the gas block to cooler weather
223 american eagle 55gr

i bought a chrome bcg and while i was shooting i noticed that the ejection was a little weak. i put the OEM dd back in and noticed the ejection was about 2 feet further, but nearly the same angle. i started to poke around and noticed the cam on the chrome bolt has a lot of slop compared to the dd bolt. both bolts seem to fit nice and tight in each carrier. when i swapped bolts and carries, the brass landed in the same spots as when in their original configuration.

they both eject at 430ish, the dd just throws them further.

could the loose cam pin fitment cause this? is loose cam pin to bolt fitment detrimental?

edit to ad:
does the cam pin being loose allow the bolt to unlock earlier allowing weaker gas drive?

[xFREDx]

i could be wrong but i don't think the cam pin would allow for a weaker gas drive. that would have to do with the gas rings and how the bolt tail rung, gas ring rung fit in with the bolt, as well as fitment of the gas key to the gas tube. I feel like sloppy cam pin fitment could give you premature ware and possibly "possibly" accuracy issues.

[markm]

What kind of BCG is the chrome one? I've never thought about cam pin fitment. There shouldn't be a noticeable variance in fit.

[corey4]

expo arms from primary arms. funnily, the chrome bcg looks like a DD. im thinking its a dd reject. ive been waiting for the microbest chrome bcg from pkfirearms to come back in stock for weeks and saw these expo chromies on primary arms so i figured id give them a whirl. the only reason i want a chrome bcg is because im shooting suppresed 100% of the time.

ill have pics coming later this weekend.

[markm]

Off topic... but for dedicated suppressed, Phosphate hold lube and suspends fouling better. NP3 is very good too... cleans up like a dream.

[georgeib]

This is an interesting topic. OP, is the cam pin equally loose in each bolt, or just in the Expo one? If equally loose, try swapping just the cam pin into the DD BCG and see if changes the ejection compared to the DD cam pin.

[lysander]

The clearance of the cam pin isn't going to make any difference. Look for things that will make substantial changes in bolt velocity.

[markm]

The clearance of the cam pin isn't going to make any difference. Look for things that will make substantial changes in bolt velocity.

Or the spring in the ejector.

[corey4]

Or the spring in the ejector.

this is exactly what it was lol. after all the ****ing around i did, it wasn't til the end i decided to check it with an empty case. oh well.

ill do a write up in a bit on my observations, thoughts, and findings.

[georgeib]

this is exactly what it was lol. after all the ****ing around i did, it wasn't til the end i decided to check it with an empty case. oh well.

ill do a write up in a bit on my observations, thoughts, and findings.Glad you figured it out. Just FYI, a loose cam pin is out of spec, so even though the ejection issue had nothing to do with the cam pin, it will increase bolt wear significantly if loose. According to a SOTAR video.

[Backfire]

I agree, the excess "wobble" may strain the sides of the bolt.
Additionally I know some people mark one side of the pin so they replace it the same direction.

Cheap enough item to swap out

[JoeBobJoe]

[QUOTE=corey4;3016498]this is exactly what it was lol. after all the ****ing around i did, it wasn't til the end i decided to check it with an empty case. oh well.

ill do a write up in a bit on my observations, thoughts, and findings.[/QUOTa loaded round

Slowly pull charging handle to eject a loaded round out of the chamber, & look to see the rotation of the round, a weak ejector spring will rotate a live round slowly & a stronger ejector spring will be rotating loaded round much faster.
That is how I noticed a weak ejector spring before.

[markm]

Additionally I know some people mark one side of the pin so they replace it the same direction.

I pay it no attention any more. But I used to rotate mine so it wouldn't wear on one edge only.... sorta like rotating your tires.

[MistWolf]

The extractor spring also affects ejection. TLDR version- Get Colt extractor springs.