Ultralight Ultralight Rifles

[Trackselk]

Yes at that angle and wall thickness you would need a machinist/ gunsmith but I wouldn’t think they would charge you to much? I assumed the ball was crimped in there but maybe not. I’m sure a smith could crimp/stake it in place if it’s not.

Yeah, if I get the 2900-2950 79gr loads that I'm looking for, then I'll try my oversized washer/tab idea since i can do it at home in 30 mins. Should work about like southernfrieds method, but keep the bolt and extension meshed 100%. Still might want steel reinforcement so the corner of the slot isn't worn down rapidly.

 

[ACHILLES]

Agreed that’s worth a try first and I think it would work.

 

[Trackselk]

I’ll have to go back to my notes. But I think I filed my carbon lower magwell, upper, and barrel extension to allow 2.4” overall. I think I Loaded a couple TMK’s at 2.39”.


My load testing shows a much bigger increase in velocity than I would’ve expected gaining .1” of case capacity.


I’ll see what I can dig up.


For reference, this is from my wife’s Howa mini with a 16” barrel:

View attachment 849470


I’ll have to find my notes on OAL at that CBTO, but it was measured with hornady comparator.

Bolt was a little heavy at the 27gr load.

Screamin

Do you think you got that 2900 at the 2.39" or considerably shorter?

 

[KyleR1985]

Do you think you got that 2900 at the 2.39" or considerably shorter?

Looks like 2.43” ish.

 

[Thegman]

Hmm, there's no place for it to grab, so he cut the upper to where the bolt rotates further, which affects the bolt 'cog?' Engagement. I'm thinking this will cause excessive wear, especially with hot loads. There isn't a lot of surface area soaking up any rearward travel. What do you all think about that? I think I would be more inclined to put a slightly bigger washer under the screw, and then cut a matching recess so it doesn't affect the bolt engagement.
I'd probably have to flatten 2 sides of the washer to avoid limiting bolt rotation and maybe to fit in the handle recess for the screw. Heck, maybe 3 sides actually. So, make an oval tab basically...

I've not been able to look at one to really know, but it sounds like your idea could work (?).

I could be wrong, but in the video, I didn't think he cut the upper to allow any more rotation (which you wouldn't want to do as that would change the lug engagement with the barrel extension).

I thought he just made a small pocket for the rear bolt retaining screw to engage with. The only thing that happens with that is that the carrier, along with the bolt handle, gets pushed back slightly by the spring behind the bolt, but the bolt itself does not move with respect to its lock-up with the barrel extension, just the bolt carrier.

That does cause a couple of potential issues I can think of:

The first, which you mentioned, is the steel screw gradually wearing the aluminum receiver at the contact point. I haven't been able to mess with one to see if that's going to happen, but I definitely agree that it seems like it could. An idea like that detent ball seems like a better idea from the get go, but would be easier if it the BCA just came that way.

The second possible issue is that with the video modification, the bolt carrier is going to have a tiny bit of play and move forward when hit by the hammer on firing. I don't know how this would affect accuracy, if at all, but seems like it would be better without. I mentioned this before, but the bolt carrier can't be allowed to be pushed too far back by notching the upper too deeply, or then it will cause light strikes, or completely block the hammer from hitting the firing pin.

Looks like there's plenty to look at when I eventually get them in hand! Thanks for getting us started on the beta testing