224 valk revisited

[stagpanther]

Earlier this year H at AR15 performance exposed something of a scandal--that many (most?) manufacturers were using a chamber reamer that resulted in the chamber's freebore length significantly exceeding SAAMI specs (almost double). This had the basic effect that it was nearly impossible to attain near optimal performance given the available selection of bullets/powder.

I managed to get very good results with the 95 SMKs--but that was really only achievable by extensive modifications that basically resulted in "wildcat" development. I'm not one for conspiracies--but this is a classic case of rushing something to market to make a buck before it was really ready; worse than that, it could possibly set back or destroy the future of the valk. I did enough work with it though to see some real brilliance in the performance numbers. Whether or not that can salvage the future of the valk remains to be seen, but I have a SAAMI-compliant chambered valk barrel coming in in the next day or two, so I will take apart one of the other builds and see what the new barrel will do. H tells me the new barrels will also have fluting, so that might help reduce the "am I carrying an AR10?" feel to the build.

[Fla_dogman]

Good information z thanks for sharing

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[stagpanther]

no problem--I look forward to seeing what a "proper" barrel can do.

[stagpanther]

I wonder how many of the barrels and completed uppers being sold as "specials" are really just everyone dumping their out-of-compliance barrels. I suspect a lot--especially if they are in the neighborhood of 20" 1:7 twist.

My personal opinion is if you want any hope of a valk rifle capable of approaching the "hype" numbers of supersonic at 1300 yds, you're going to need at least a 22" barrel with 1:6.5 twist so it can handle the 90+ gr bullets.

[LineStretcher]

Just adds another layer to my "Yeah I'll wait".

[Fla_dogman]

It seems a lot of people want a higher power cartridge in the AR 15 platform but there's so many out there now how do you choose, couple that with the idea of a better round coming out and the one you have now becomes obsolete makes me hesitate to commit to buy anything.

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[stagpanther]

It seems a lot of people want a higher power cartridge in the AR 15 platform but there's so many out there now how do you choose, couple that with the idea of a better round coming out and the one you have now becomes obsolete makes me hesitate to commit to buy anything.

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You have to fire the valk--you'll know why people want it to work when you do.

[ed308]

Looking forward to your results with H's new SAAMI barrel. I

I'll add to Stag's post about the long free bore. H said earlier on that somebody at reamer manufacture is dyslexic since this is not the first time they've screwed up a reamer.

[stagpanther]

I took apart my PSA 224 valk upper this morning in anticipation of the arrival of the new barrel. As long as I had it apart I figured I would do a cast of the chamber to see "once and for all" what their reamer measurement was.

From the case mouth step-down to beginning of lands/ grooves--I measured (as best as I could with the calipers I have) exactly .05"--this matches the actual SAAMI specs as far as I can tell. Where the leade ends and actual groove begins is hard for me to tell from the cast.

Well, there you have it.

[TrueBlue711]

So my barrel is the 24" 1:7"twist from CMMG. Any other reports from them? I noticed some grouping issues with mine (using the 90gr Federal Sierra Match King), but haven't had the energy to chase down the issue yet.

[stagpanther]

So my barrel is the 24" 1:7"twist from CMMG. Any other reports from them? I noticed some grouping issues with mine (using the 90gr Federal Sierra Match King), but haven't had the energy to chase down the issue yet.

I don't know about CMMG--I guess you'll have to call them and ask--but they may or may not know what their freebore is depending who you talk to.

My (again) personal opinion is that another factor hampering the valk is appropriate 224 bullets that are actually optimized for it. Most existing ones seem to be optimized for the sub 90 gr use including full bore applications that may include other cartridges. My impression is that to get the better than 90 gr 224 bullets to give optimal results for the valk (a VERY high SD coefficient) while also optimizing the BC is simply a void at present that needs to be filled with new bullet designs.

But I've been known to be wrong before.

[stagpanther]

90 gr 224 bullets seem to be a bit of a "black hole" in terms of optimally stabilizing in the valk--and nobody I've talked to can really figure out why.

My (again) personal theory (aka WAG) is that the the existing bullet designs--their center of gravities/SD/ and base of ogive and maybe the added curse of the firearm gods-- have combined to make a bullet that for whatever reason fails to optimally stabilize upon exiting the muzzle.

[stagpanther]

OK--I went back and tried to figure out where the throat ended in the leade and the actual engaging of land/groove began. It's a gradual slope and my calipers probably aren't quite accurate enough--sliding it up and down the cast several times I got an approximate position of .096 where the diameter noticeably dropped below .223. I hope I got this right--I assume that's approximately where the "squeezing" of the bullet to engage the lands/grooves begins.



The initial .05 is a "straightwall" of constant width .224

[stagpanther]

Due to my caliper being possibly off by a bit--the actual engagement area might in fact be a bit to the right of where I have the line--but mostly the longish throat I believe is correct.

[ed308]

Stag, if you need a bolt for your 2nd Valk, Brownells has LWRC's Enchanced 6.8 bolts for $55. Great price for the bolt for the price. It does use a proprietary extractor (ie: oversized). I ordered one for my Valk buiild.

https://www.brownells.com/aspx/searc...8992&pid=44813

[Mobuck]

stagpanther,
Was your original barrel accurate with ANY type of factory loaded ammo? By accurate, I mean 1-1.5 MOA.

[stagpanther]

stagpanther,
Was your original barrel accurate with ANY type of factory loaded ammo? By accurate, I mean 1-1.5 MOA.

Yes, it did manage one or two groups with federal's 90 gr fusion in the 1.5" range. I know this is generally viewed as "what an AR should do" but is not acceptable for me for the builds I do; especially when you're talking longer ranges. ARP barrels, in my experience, using the right loads, have all been capable of delivering .5 and under MOA. That's why H has a "cult" following.

What I realized with my freebore measurements is that it really requires very high level and finally tuned instrumentation to get reliable measurements--when you consider the throat slope of less than 1.5 degrees (for the valk, anyway). Basically, what I deduced from this little exercise is that variations in the 10,000Th's of an inch are enough to cause a variation in the taper of that throat slope and bore width--so the point at which the bullet's base of ogive engages the lands/grooves "moves on a sliding scale" toward or away from the case mouth--and that "jump to lands" which can affect the projectile's accuracy.

[stagpanther]

Stag, if you need a bolt for your 2nd Valk, Brownells has LWRC's Enchanced 6.8 bolts for $55. Great price for the bolt for the price. It does use a proprietary extractor (ie: oversized). I ordered one for my Valk buiild.

https://www.brownells.com/aspx/searc...8992&pid=44813

Thanks for that--I like to keep a couple of extra bolts on hand, I might look into that. What is an oversized extractor? An "overzealous" (extra power springs, rubber donuts etc.) extractor and/or ejector can cause it's own issues. I look for extractors made from hardened steel.

[ed308]

The tail (or end) of the extractor is flared out to reduce the potential for breakage. These bolts are similar to JP or ARP 6.8 bolts that are beefed up. Here's photos of the the extractor....

https://lwrci.com/p-90-lwrci-advance...-68-spcii.aspx

https://lwrci.com/p-204-lwrci-acb-extractor.aspx

[stagpanther]

The tail (or end) of the extractor is flared out to reduce the potential for breakage. These bolts are similar to JP or ARP 6.8 bolts that are beefed up. Here's photos of the the extractor....

https://lwrci.com/p-90-lwrci-advance...-68-spcii.aspx

https://lwrci.com/p-204-lwrci-acb-extractor.aspx

Interesting.

Having personally blown up an AR with a 300,000+ psi load--my observation has been the extractor and it's slot in the bolt are a primary conduit for vaporized metal and high-pressure gasses out the bottom of the carrier (which can also fail and blow off) and down the mag well--blowing up your magazine in the process--but otherwise keeping the upper receiver and the shooter intact.

[Model12Win]

Seems a good DMR cart.

[stagpanther]

I have so far failed to come up with a "magic load" that shows exceptional promise using the new barrel--but I've simply exhausted formulas that I found gave me good results in the other barrel.

My impression so far is that the new barrel is a "true" AR chambering--meaning it has the shorter freebore to accommodate shorter overall cartridge lengths. My impression is that you also must use a full-length small base AR die to reload for this different chamber cut (it is tight in the case head area) --whereas the other "long freebore design" strikes me as being "roomier"--my guess the reamer was designed for full-bore/palma style bolt guns.

[constructor]

Hornady dies seem to size the brass without issue.