And now for something completely different...

[stagpanther]

I usually take on a couple of build projects to help get me through the winter--which can last 5 months up here in the great white north.

Having owned a glock 20 for quite a while now--I've also had a soft spot for 10mm auto, and always wondered how it would perform in an AR type build (actually this is an overture for an eventual 9 x 25 dillon project if this proves viable). Up til now I've always dropped the idea of a blow-back design being sketchy for an AR (and yes I know it has been adapted to DI systems)--but I finally took the bait and ordered Spartan receivers and mostly Kaw parts and am going to give it a go to find out for myself how practical (or impractical) a blow-back AR is or isn't.

[ed308]

A 1911 build would keep you busy the entire winter. One day when brave enough, I'm going to try and build one. Currently eyeballing the .224 Valkyrie as my next build. More barrels should become available in the spring. Not having to form the brass is a big plus too.

[9x19]

MarkCo is working on a DI 10mm build, so now I have two projects to check in on.

Just Right Carbines offers their blowback in 10mm so it shouldn't be too daunting.

[stagpanther]

MarkCo is working on a DI 10mm build, so now I have two projects to check in on.

With luck the parts should be in next week.

A 1911 build would keep you busy the entire winter. One day when brave enough, I'm going to try and build one. Currently eyeballing the .224 Valkyrie as my next build. More barrels should become available in the spring. Not having to form the brass is a big plus too.

Got to make the 1911 jump eventually--probably will do so once I decide to ditch my glock 20 once and for all.

[9x19]

I've done the 10mm 1911 thing with Colt, Kimber and Dan Wesson.

That said, there is a blue-label Glock Model 40 in my future shortly after Jan 1 (already bought my limit (two) for this year).

[ed308]

I bought my first about a year ago. I've only got one, but they are special. Favorite to shoot at the range. Even the wife likes the 1911 and really shoots it well.

[stagpanther]

I bought my first about a year ago. I've only got one, but they are special. Favorite to shoot at the range. Even the wife likes the 1911 and really shoots it well.

The 1911 (and the M1) are the two glaring omissions from my collection that I've always planned on filling--but they are both pricey. I've never liked the grip on my 20SF and have tried a friend's 1911--the only thing that would prevent me from getting one would be seeing how nice SA's new 10mm will be--I've had an 45acp SA XD ever since they came out with it and it remains to this day the most reliable, best built and shooting handgun of all the ones I have or have had (but I don't spend 700 bucks or more on handguns).

The reviews of Kel Tec's new 10mm carbine have been pretty good--I probably would have bought one if it were available. Since pretty much most of the pistol cartridge carbines seem to center on glock style mags, made sense for me to try building one, though the parts are not cheap (unless you go for something in 9mm, seems the market is flooded with them).

[bfoosh006]

https://www.facebook.com/maconarmory/

You might consider talking with the owner... he is a Wizard with the AR platform and various pistol calibers..and is more then helpful over at the AR15.com "Rimfire and Pistol Calibers" sub forum.
https://www.ar15.com/forums/AR-15/Ri...l-Calibers/15/

He just did a DI .460 Rowland AR... using Glock mags.


And his 10MM DI AR...

https://www.youtube.com/watch?v=3MttYVdNwiw

[stagpanther]

Thanks for that bfoosh--I'm sure I'll be checking in with them.

[bamaranger]

Good luck with your project. A 10mm carbine has always had some type of appeal to me too, but if I were to go that route, it would be with a MechTech kit.

Taking the idea a bit further, there is a wildcat .40 cartridge based on the SOCOM case, or at least a case in that ballpark, that REALLY cranks the 10mm family of slugs to exteme velocity. Called the .400 AR (I think)), but it functions on the standard gas impingement system, not blowback, way to hot.

[stagpanther]

Taking the idea a bit further, there is a wildcat .40 cartridge based on the SOCOM case, or at least a case in that ballpark, that REALLY cranks the 10mm family of slugs to exteme velocity. Called the .400 AR (I think)), but it functions on the standard gas impingement system, not blowback, way to hot.

Might you be thinking of the 45 raptor? There's only so fast it makes sense to propel a pistol bullet.

[ed308]

Maybe Bigdawws VRAP...

https://www.youtube.com/watch?v=6k2edmBTzEo

[stagpanther]

Went to pick up my parts today and left the store with more than I bargained for (see bolt and lever gun subforum for that little story).

Having never messed with a blow-back AR I decided to get Spartan's assembled lower so I could study it--I wasn't confident enough to tailor all the separate components in separate purchases--not even sure if that would have saved any money anyway.

I was able to hand-assemble the gun you see in the picture in about 3 minutes--so stupid-easy even a caveman's hamster could do it.



The Kaw components appear to be outstandingly made and finished--the simplicity of the barrel and handguard assembly left me thinking "is that it??" On that note--the simple screw-on screw off of the handguard and barrelnut to receiver BEGS for multiple caliber barrel switchs IMO--but some tuning will likely be needed with the buffer/carrier components I would guess. Called KAW just to see if I could beg for a 9 x 25 dillon barrel--of course no dice since they've "hit the big time" in production runs.

Had a glock 20 mag on hand and it pops in and out just like you would expect on a "regular" AR--even the funky carrier lock-back hook works--at least in manual mode. I'll take everything back apart to clean, true etc and then do a "real" assembly to test fire.

[9x19]

Sweet!

I have a couple of linear comps from Kaw Valley and have always been pleased with their value.

[stagpanther]

I just did a dummy round dry-fire test--as promised by the Kaw engineer I talked to yesterday, the feed angle from the Glock mag is problematic and the cartridge tends to hang on the chamber without going all the way into battery. Looks like I have some grinding and polishing to do.

[stagpanther]

Here she is assembled with a nikon fixed 3x 223 scope on top--I'll probably put a good red dot on eventually.

I took a really close look at the chamber cut--and while KAW did a great job overall with a radius at the chamber face--there still remains a pretty sharp edge where that radius meets the chamber wall itself. Given the angle of the cartridge feed from the magazine I believe that's what's hanging the cartridge up so I polished that edge down a bit on the top and bottom of the chamber face. Even my glock 20 will hang a cartridge every now and then in a similar position if I "limp wrist" it while firing. The factory PMC 10mm still hangs when I try to cycle it--but then I remembered from the last time I loaded cast bullets in 10mm they tend to be a bit wider than a jacketed bullet--and thus can expand the case wall enough that the cartridge becomes problematic for chambering--the 10mm is a "dance" between getting the cartridge narrow enough to chamber reliably while still leaving the necessary width at he case mouth to headspace off of. Testing is a bit hard at the moment with our temperatures in the teens and wind-chills down around zero--but I think a respite is on the way.

[stagpanther]

BTW--that's a minimalist tactical stock--originally bought for an AR 10 build but the spring-loaded pin which locks the stock to the buffer tube is held in place by nothing more than a very thin rim of plastic--and it blew out almost immediately the first time I shot with it. So I epoxied a steel washer onto the handle which is backed up by two metal screws--it looks junky but I didn't have the heart to throw it out (not to mention cost $50). I bought it from High Impact in AZ--and they said they would replace it--but they never did send me a replacement so I just jury-rigged a fix.

Did a test no-fire cycling after the chamber face polish--seems good to go--will tyr to get out and get a few quick shots off before our next snow storm if I can

[stagpanther]

Had to wait for a barrel delivery before heading out the door to test--and by the time I got to the shooting range it started snowing heavily--but I still squeezed off 4 shots fed from the glock mag--and I'm happy to say everything worked--mag feed, cycle, ejection and even empty mag BCG lock-back. Seems the radius edge smoothing did the trick--at least so far.

I have to say I really like the simplicity of this blow-back set-up--the BCG is really just one big bolt. Now it's time to find some good load recipes. : )

[weblance]

If I may ask... whats the total cost?

[stagpanther]

If I may ask... whats the total cost?

No problem--it was pretty much a "one-stop-shopping" at JoeBob Outfitters (much higher quality outfit and parts than the fly-by-night sounding name might suggest ) which ended up totalling about $730.

I bought the Spartan lower already assembled so it has a typical mil-spec trigger (which I'll do some work on) Though the entire gun is much simpler than a conventional DI AR I found out--I just didn't know what the "tolerances" of the parts should be. This is most applicable to matching the weight/velocity of the BCG--which is more like just one big bolt that rides on the charging handle--to the buffer weight and spring. My impression is that this is the most critical aspect to the operation of the gun since it's a blow-back design and thus these components are matched to the cartridge's characteristics (I would assume). The upper is also a Spartan with a last shot bolt lock-back pin dohickey screwed onto the side--it looks alot like a hex key that has been flattened on the ends. You can save some money and "go AK" and get a lower without the lock back if you want. The barrel and rest of the parts are KAW--the linear comp is nice in that it doesn't need any timing (it projects all the exhaust forwards--which also makes it a bit of a challenge for a labradar to lock onto BTW).

My one and only reservation so far is the entire lower schema being designed around Glock magazines--I suppose this is good to the extent it facilitates a quick switch between the rifle and a glock pistol in a fight--sorta like "the good old days" when a lever gun would be designed to shoot common revolver cartridges I guess. But then this also means the functioning of the weapon is subject to the reliability (and foibles) of the glock's mag design. I wonder if a better magazine/lower schema might be more practcal--but that's just my take.

The simplicity of the barrel's "no-gas system" means no timing issues for extension/bolt lock-up--but the thing I'm most impressed with is the speed and ease of barrel swap out--this feature begs for multiple caliber barrels--but that would still require some jiggering of the bolt/buffer/spring to accommodate the different characteristics I would suspect.

Over-all so far I love it and am having fun with it--but now the "serious" part begins in trying to get optimal performance out of a good cartridge formula.

[stagpanther]

OK--so I'm totally new to these blow-back AR's--so I'm learning this stuff as I go along--in my usual style of making mistakes and having things go wrong right from the get-go.

The blow-back is great in it's simplicity, but there are a few "potential gotcha's" along the way, as I'm learning. So, in no particular order, here they are and my thoughts and impressions--and that 's all I'm sayin--my thoughts and impressions--I'm sure that there are thousands of these things out there that operate with zero issues.

The blow back system basically relies on the bolt mass, as well as buffer mass and spring pressure, to cycle a cartridge. It also relies on that system to keep and "hold" the cartridge in battery when it has chambered it, lacking any kind of lug/extension lock-up.

In a final shot bolt lock-back system; the bolt catch will be subjected to slamming of the full inertia of the heavy bolt propelled by the buffer and spring. This can easily and repeatedly break the bolt catch and/or deform it--which in turn can adversely affect cycling.

The glock magazines that I have--given the angle of the round and distance from the chamber--I find is an inherently ineffective way of chambering the round without the cartridge taking some stress/damage on the way into the chamber. I have modified the magazines to reduce the difficuties in chambering--but have not totally eliminated abrasion damage. After successive magazines of firing; enough brass shavings; as well as blown-back powder residue, can easily build on the chamber walls inhibiting proper seating of the cartridge. Because of the "no lock up" design; it appears to me to be rather easy to successfully chamber and fire a cartridge that can be partially out of battery.

I'm starting to have doubts whether this is a fully viable set-up for a powerful little cartridge like the 10mm.

[bfoosh006]

I have a 9MM Colt pattern blowback.

Currently I am running a .308 Tubbs flat wire spring, and a 7.5oz configurable extended 9MM buffer. It is much softer shooting then the OEM configuration.

I used the .308 Tubbs recoil spring because it has more force holding the BCG closed then a normal recoil spring, but the same spring weight for cycling.

If you could post a photo of your buffer... we could see if the same 9MM extended configurable buffer would help your 10MM... you can configure it up to 10oz ( Trust me your 10MM will still run, my 9MM did in that set up, but I changed to the 7.5oz setup )

And it is a deadblow buffer.... not a solid buffer ( Yuck, IMHO )

Here it is from KAK...

https://www.kakindustry.com/ar15-con...-buffer-system


Another bad side effect from your high cyclic speed is .. it can elongate your hammer pin holes from long term high cyclic speeds. All that speed and mass will transmit from the smack on the hammer to your hammer pin.

[stagpanther]

Thanks bfoosh--I've talked to the manufacturers about this and they advised me to stay with the 10oz buffer--might be because of the heavier bolt and more powerful cartridge? I started looking for titanium bolt catches but they are sold out everywhere--what a surprise, right? LOL. I found a couple of high-strength billet catches and I'll see if they fare any better.

I have a 9MM Colt pattern blowback.

Currently I am running a .308 Tubbs flat wire spring, and a 7.5oz configurable extended 9MM buffer. It is much softer shooting then the OEM configuration.

I used the .308 Tubbs recoil spring because it has more force holding the BCG closed then a normal recoil spring, but the same spring weight for cycling.

If you could post a photo of your buffer... we could see if the same 9MM extended configurable buffer would help your 10MM... you can configure it up to 10oz ( Trust me your 10MM will still run, my 9MM did in that set up, but I changed to the 7.5oz setup )

And it is a deadblow buffer.... not a solid buffer ( Yuck, IMHO )

Here it is from KAK...

https://www.kakindustry.com/ar15-con...-buffer-system


Another bad side effect from your high cyclic speed is .. it can elongate your hammer pin holes from long term high cyclic speeds. All that speed and mass will transmit from the smack on the hammer to your hammer pin.

You're right--I'm already seeing signs to the hammer of the heavy strike--I'll take a pic of the buffer later today. I've talked to Kurt at KAK before and may call him if you think he's got some good advice.

[stagpanther]

bfoosh--here are pics of the buffer--probably most of the mass is in the body I would think. Notice deformation on the buffer edge from what I assume are strikes on catch.

[stagpanther]

Pair of Bauer Precision billet catches came in today--noticeably superior in fit and finish to a cast mil-spec catch--I hope these last a while, they're not cheap at about $40.00 a pop. My ultimate goal is to get a titanium one.



BTW--in post #24 I meant to say strikes on the carrier--for some reason I've lost the ability to edit my posts.