Bolt not fully closed and would not open

[bmash]

Lilja barrel, monster bolt, 129gr ablr, 2.60” OAL (as I remember), Hornady brass.
My grandson killed a deer and my son, while attempted to remover the magazine, wound up letting the bolt close but not slamming home. He then couldn’t pull the bolt open. I tried to pull it open and then pull while tapping the butt on a table top. Didn't budge. So I tapped the forward assist button with a rubber tool and got bolt completely closed. (So there is a good use of a forward assist!) it then opened with no issue. Loads great when letting it close with “gusto”/ slam home.
ALL my other ARs close with very little resistance. This one seems to hang up/ resist closing a little. I was able to replicate the issue by letting it close gently.
I measure distance to lands, it is full length resized, no issue at all when slamming home. Cleaned and lubed and still a little resistance when closing. Anybody else seen this? I have a couple of bolts so I’ll try a different one when I get home. (At daughter’s house for new grandchild birth at the moment…) the bullet may be moving a little but I don’t believe enough to cause this. I think it is something with the bolt but I sure haven’t examined closely yet. (To busy taking grandkids hunting and cleaning deer!!
Btw, the grandkids love the gun! 13 year old killed a doe at 200 yards. Now the 8 yr old wants to use it so he can reach out further than the 300BO!

[Klem]

bmash,

Sounds like headspace.

What is the headspace difference between spent/fired cases from the Lilja, and sized/unfired rounds? Do you know how to measure this?

A related check is to separate the gun and pull out the BCG. Barrel pointing to the floor and drop a loaded round into the chamber. Push on it with your thumb to mimic the bolt slamming it home. Then turn it upright with the barrel pointing at the ceiling and see if it falls out by gravity (it should). If it sticks in the chamber it means there is not enough headspace to guarantee reliable cycling in a semi auto.

Your other guns will all have their unique headspacing so not unusual that reloads work in one gun, but not another. Some chambers are tighter than others but all can still be in spec.

[montana]

Always check head space with any AR rifle and when changing bolts..https://pacifictoolandgauge.com/6-mm-69-...auges.html

Also check the ejector..Remove the bolt and push on the ejector to make sure it will push flush with the bolt face. I have seen bolts that were not machined properly and the ejector will not push flush with the bolt face causing head space issues..

Klem is correct about variances in chambers..The best check is with a function gauge that is machined to the lowest tolerance that meets spec..The negative with function gauges is very few people/ armorers/gun smiths have them..I have mine custom made with long handles so I can easily check chambers mounted to uppers..https://pacifictoolandgauge.com/function...gauge.html

It also could have just been a case that was out of spec..My favorite method to check loaded ammunition is the Sheridan slotted ammunition gauge..There is a viewing slot that allows access to see where the cartridge is out of spec..https://sheridanengineering.com/product/...ion-gauge/

[bmash]

Thanks Klem. I’ll look closer when I get back. It cycles just fine when shot or closed with bolt release and full spring closure. Without my son using it I don’t think I would have ever noticed.
I’ll also check with the “matched” bolt that came with the barrel.

[bmash]

Thanks Montana. I’ll check with factory ammo to see if a difference.
I’ll do ejector check also. I bought this bolt since my other bolt was marking up my brass with ejector and extractor.