Idle thought: 20br in an Accuracy International?

[carbonbased]

I’m bored and see some people have wildcatted a 20br and 22br. I know this is not new news, but it’s new to me.

Since I am a small bore aficionado and own an AIAT, would such a cartridge (fed out of a Grey Ops 6br mag) chamber fine?

Pretend the bullet is a 39gr blitzking or a 40gr vmax.

I don’t reload and know nothing about the tricks of barrel chambering. But if a 20br is a possibility, that might push me into reloading lol

 

[carbonbased]

Oh yeah, here’s a little article on the 20s, including the little 20br.

https://www.6mmbr.com/20caliber.html

 

[Kiba]

22BR with longer 75gr bullets will feed somewhat OK in my AX when I tested it for function, but not as reliably as 6 Dasher which is what I normally run in that rifle.

Because the bolt nose and breech ring is pretty long in the AI it's a bit of a long reach from where the feed lips release the cartridge to the start of the chamber, and sometimes the shorter 22BR will turn a bit sideways in the action and the bullet will hit the breech face. I'm guessing this would be even more of a problem with the 20BR since the 20 caliber bullets and thus cartridge OAL will be even shorter than 22br.

This doesn't happen with the longer 6 dasher in my AX, it feeds fine even with short 55gr varmint bullets.

Best bet would be to whip up a couple 20br dummy rounds and try feeding them into a barrel with a 308ish chamber and see how it does.

On the subject of 20s, I've built 3 20 vartargs just this year and they're awesome... but not really practical in an AI action being they're so short and 223 bolt face. I considered building a 20br but IMO it's too much powder vs bore diameter for high volume varmint blasting (something the vartarg excels at because of the small case capacity and powders used not heating the barrel quickly, but the limited case capacity means it really is best for bullets no heavier than 32gr IMO), but 20br does work very well with the heaviest 20 caliber bullets.

Even with the 40gr+ bullets my feeling is the 20br is a bit too much powder down a .20 bore for high volume varmint blasting; something with a case capacity between the vartarg and BR would be a nice compromise. I've kicked around maybe trying a 20ARC since it would have about 4gr less case capacity than the 20BR, but again, no go in an AI action because of the bolt face requirement.

I saw someone on accurate shooter recently put together a 20GT if you like 20s but also hate barrel life, lol

 

[carbonbased]

Yeah, I didn’t think about barrel life! I don’t hate barrels!

Hmmmmm

I can’t whip anything up to test as I’m not a reloader.

It’d be cool to use my AI for varminting, but keep its stock bolt but use smaller diameter ammo. Just for kicks. Don’t want to futz with the 223 conversion that a bugholes might still provide (they hinted that they were stopping that).

Maybe 22br, like you suggest.

 

[Kiba]

22br is a great round for varmints, can run everything from lightweights to heavies, lots more 22 bullets to choose from than 20s. Not a great round for high volume blasting though, it gets warm pretty quick. Very easy load development, everything I tried made tiny groups.

I use the 6 Dasher barrel on my AX with 55s at 3850ish for ground squirrels... spectacular explosions, but not a high volume cartridge. I had a 223 barrel and bolt for my AX for varmints for a while but sold it, shooting 223 out of my AX was cool and all but it wasn't nearly as smooth or reliable feeding as my R700 based 223 builds.

When it comes to high volume small critter blasting out to 350ish I love the 20 vartarg. Nearly zero recoil and the barrel stays cool for quite a long time. But as mentioned, the limited case capacity means it shines with up to 32gr bullets IMO. Sure you can run 39s or 40s, but you either have to live with lower velocity or hammer the brass with high pressure if you want to keep good velocity with the 39+gr bullets, and with the effort it takes to form 20VT brass I want it to live. Unfortunately, not a real practical option for running in an AI.

If I wanted a 20 and wanted to shoot 39s, 40s, or even the 55 bergers at high velocity but not do high volume fast paced shooting, 20br would probably be my first choice, and there's a good chance it might run OK in your AI from a magazine. I'm 90% sure it would run great from a single shot sled. If I get a chance this weekend I'll stuff some short 40gr bullets in a couple of 22br cases to simulate the length of a 20br with 39/40gr and see if they'll mag feed in my AX.

 

[carbonbased]

Cool man!

Appreciate that you’re humoring me here.

There’s no real need that’s pushing this, except that it’s a pity to see the AT sitting there all lonely crying in the corner.

And I’m bored af haha

 

[Kiba]

OK, have some info.

I loaded 10 22BRs with 50gr bullets and seated them deep (1.950 OAL) to simulate a 20BR with the 39/40gr bullets, then tested feeding them in my AX with a 6 Dasher barrel.

Good news: they feed 100% reliable out of a CNCSWerks AW/AX single shot sled.

Bad news: They feed at best 50% reliably out of 4 AX magazines with HRD Dasher spacer kits. At 1.950 OAL the cartridge leaves the feed lips before the bullet tip is in the chamber, so sometimes they end up pointing into the chamber and sometimes they don't and misfeed and stop the bolt.

If you run the bolt slow, the case pops free of the feed lips then the head of the case falls down into the gap at the front of the mag and the bolt rides over the top of it stopping the bolt.

If you run the bolt faster, sometimes they feed OK, other times the case pops out of the magazine in such a way bullet tip hits the breech face of the barrel and stops the bolt. You then have to back the bolt up and help the tip of the bullet find the chamber with your finger.

Based on the tests, my opinion is that if you're going to want to try a 20BR in an AT/AW/AX with the lighter and shorter 32/39/40gr 204 bullets you're probably going to be limited to single shot sled use only.

If you want to mag feed with any sort of reliability, you're going to need a longer bullet seated long and a longer throated chamber to increase the OAL of the case to increase feeding reliability. The 204 55gr Berger is about the longest 204 bullet out there; it's awesome with a great BC and it blows up critters quite well, but it's a bullet Berger makes only for Graf's and Berger usually does only one run a year of them... so you have to jump on them when they are available. The 55s also need a much faster twist than the 24/30/32/39/40gr 204 bullets; Berger recommends 8 twist for the 55s. So if you get an 8 twist barrel made for the 55s and then for some reason you can't get the 55s and have to step back down to 39/40 gr bullets, not only is the throat going to be long but the 39s and 40s normally run about 4200fps in the 20BR. 4200fps in that 8 twist barrel is going to be spinning the 39s/40s 378k RPM... I can pretty much guarantee they're all going to blow up soon after leaving the muzzle. You would have to use seriously reduced loads down about 3700fps to keep the RPM's out of that 8 twist barrel at about 330k rpm where the bullets should hold together, but reduced loads are often dirtier and have higher ES/SD.

 

[carbonbased]

Wow, thanks man!

I have a couple HRD kits and my Gray Ops 6BR mag kicks their ass. I haven’t really tried to tune the HRD however. Maybe the 20br (or 22br) would be ok in that mag.

About that single shot sled. I found it online but it’s out of stock. Have you heard anything about this one?

Single Shot Magazine Follower

Replaces the magazine in the Accuracy International AW, AE Mk2/3, AX, AT-X rifles and AICS short action chassis systems when used in single shot. Made from aluminium. Can be Cerakoted in other AAI colours at additional cost, please contact us for information. * AICS is for single stack magazines.

www.sportingservices.co.uk

That place is solid and I’ve ordered a number of things from them.

Hmmm I’ve got some thinking to do.

 

[Kiba]

That sled from Sporting Services should work fine. You may want to email CNCSwerks and see if they have any spares sitting around the office.

I was looking to see if Tyler at MKM makes an AT/AW/AX single shot sled since it's a US source and shipping will be faster and cheaper than Sporting Services UK, but oddly enough it looks like he only makes AICS sleds.

And yep, you've got some thinking to do. For the larger case capacity of the 20BR I really like the idea of the 55gr Bergers at 3600ish for the high BC for the long shorts but I don't like that they're single source and typically only 1 manufacturing run per year. The 39s/40s are much more available from multiple manufacturers but they're probably not going to mag feed worth a damn in an AI unfortunately given the shorter OAL of the loaded cartridge.

For years I only mag fed while squirrel blasting, but I ended up treating it somewhat like a single shot as I didn't want my brass ejecting down into the dirt/grass/weeds/alfalfa where I might never find it, so after every shot I'd open the bolt slow, grab the case, and stuff it back in the ammo box. Also, I'd always seem to line up on another great shot right as the mag ran dry and then have to stop and change or reload the mag or toss a single on top of the mag.

This year I switched to single shot sleds and single fed everything for squirrel blasting and honestly I think I liked it more; the rifles feed even smoother off the sled since it's a straight shot to the chamber, I never lost brass, and I always knew there was one on the sled ready to go when I had a target pop up.

All depends what you want to do though. I will say when going for coyotes at night or standing use on the tripod it's easier to feed from a magazine than single load.