Hard Extractions in a straight pull AR-style rifle.

[topgenorth]

Hello all,

For a bit of background, I'm in Canada, and due to some stupid politics AR's were banned in 2020. This has resulted in a cottage industry of some receiver sets being built to take (most) AR parts. These receiver sets typically take a proprietary bolt carrier but do use a standard AR bolt. Here is one example (and what I currently have): https://mapleridgearmoury.com/produc...-receiver-kit/

I build one of these in .223 and everything just worked. I just swapped out the barrel and bolt and reconfigured the rifle to shoot 6.5 Grendel and I'm running to an issue that I did not notice when I had a .223 barrel on it: The bolt sticks, extractions can be pretty hard (varying from stiff to having to "mortar" the rifle). It matters not if I'm using factory ammo or my own handloads.

Unfired ammo (handloads or factory) seems to cycle just fine - I can load up a mag and cycle the action - works great. There isn't any unusual damage or marks to the fired brass.

I'm 132 rounds through this barrel (mix of factory and handloads from 85gr to 123gr), and the problem still exists.

I've had two pieces of advice:

• Polish the chamber
• Straight pull ARs and 6.5 Grendel (or 7.62x39) rifles on this platform aren't a good mix. You need the force/pressure from the gas system to cycle the action effectively.

Any thoughts/suggestions on what the problem might be and possible fixes?

[Old Bob]

Try the RCBS small base Grendel dies & set back the shoulders on your fired brass .002"/.003". Get a 6.5 Grendel cartridge gauge to verify your resized brass is at its original spec.

Sorry your politicians have their heads up their collective arses. We're seeing a lot of that States-side as well...

[montana]

From what I'm understanding you can load and eject a loaded mag without firing just fine, it is when you fire the rounds they stick..What does your brass look like after firing? Is the brass frosty looking, have you head spaced the chamber with a go or no go gauge or measure the fired brass? Did you contact the barrel manufacturer and tell them your problem??

[topgenorth]

Thanks for the replies. Here's some more details/answers:

I always use a case gauge to check my reloads, so I know they are in spec (I use an LE Wilson case gauge).

The brass looks fine after firing - nothing unusual or weird about it. I have fed a piece of fired brass through the case gauge, and while it does need a bit of trimming, it's not what I would call excessive. I have not checked headspacing with go/no-go gauges (I don't have these gauges in 6.5 Grendel).

Good idea about measuring the headspacing on the fired brass, that I can do pretty easily.

[lazyengineer]

Sounds like a rough chamber to me. FWIW, Grendel has a fairly exaggerated neck diameter cut in the chamber, resulting in considerable brass swelling there, though I don't know if there is issue there.

But yes, the first place I would start is polishing the chamber. Second place is try a bit hotter loads, to see if that speeds up your neck swell and thus sealing out the sticky powder residue. Also, warmer loads tend to burn cleaner, also creating less sticky residue.

Sorry your government is willing to sacrifice your freedom's for ineffectual policy for the votes and Feelz.

[topgenorth]

Just a followup up on this. Gave the chamber a polish and still no luck. Brought it to a trusted gunsmith (former Canadian Forces weapons tech), and he was stumped as well.

It's my guess that, in a straight pull AR, you just don't get the camming force that is required to extract the case from the chamber. It's probably time to put a .223 barrel back on. I've got an orphaned 12.5" barrel looking for a home, so all is not lost with this rifle.

[VASCAR2]

https://cse.google.com/cse?cx=016368947416500061353:paqd_0xcu1o&hl=en