Direct blow back AR head space

[Wolfdog91]

Wanted to see if I can get some help here.
Built a lil .22 TCM direct blow back AR pistol and been playing with it .
Used the reccomended buffer spring and weight from kak And it was work pretty good with factory
ammo cycling wise , but noticed I was getting inconsistent shoulders
From left to right

Thought this was a bit odd

Anyway made my own brass from .223 ( got a whole thread goin in the small caliber section) and tired that. Was shooting way faster getting beautifully formed cases but no ejections. So after going up pretty high j decided to change the buffed deal to make it lighter.... Well started to cycle ...but now I'm getting some weird forming again.

The right case was what the first 15 or so of my converted ones looked like and the left is what all the ones that ejected look like




Was told this might just be a quirk of direct blow back but idk ..anyone delt with this ?

Also, I made this brass from .223/5.56 with crimped primer pockets . Cut out the crimp.liem I always do but I'm using small pistol primers and I'm getting a lot of this


I swear them blow is a good bit but their building out with a bit of cratering is this because pistol primers are a bit too loose for these pockets or ?

Anyhow would appreciate any advice or insight

 

[6MMsteve]

could be the case walls are too thick not letting the brass flow. did you cut the 223 case length, did you turn the necks some, you might need to anneal the case to soften, I really have no clue about it just spoutin but if the case is thick it's prolly not gonna form to well, most other cases are thinner at the shoulder then thicken at midpoint of case

 

[chop house]

This could be one of the more advanced, interesting, and challenging projects you have tackled. Found this on the castboolits site...

". There isn't any information out there on the TCM as far as reloading or dies. 5.7 is a CIP cartridge and has reloading data and dies available-HOWEVER, cases are lacquered to function in the blowback actions and the lacquer is readily scraped off by a size die. Also 5.7 guns allow the shoulder to blow out significantly because they are bottleneck blowback. You will be working the shoulder a lot when you resize a 5.7. ..."

Note, I have not verified this info and have no personal experience

 

[tommeboy]

5.7 is different than 22 tcm. Your shoulder is all over the place as you do not have enough friction to hold the case walls before the case is extracted. What hammer spring are you running? You need a very heavy hammer spring to help delay case extraction. It is not only buffer weight you need to be concerned with.

Every blowback gun i have seen blows out the brass if it is a bottleneck. Some of the Russian 7.62x25 will almost turn the case into a straightwall. That is why no one makes blowback bottle neck guns anymore.

 

[dellet]

Bottom line is the poorly formed cases are cycling too fast. The properly formed shoulders are supported, because the chamber is sealed and bolt is all the way forward. Not cycling.

When it cycles, the bolt moves back and allows the shoulder to move forward. Basically it’s a timing issue. Most likely wrong powder for the application, pressure building too soon, bolt opening too soon. Because you solved the cycling problem by lightening the buffer allowing faster cycling.

The primers being proud of the base is due to the case sticking to the side of the chamber and the bolt pulling back from the case head allowing the primer to pop out. Again pressure and timing.

Blow back systems with a bottle neck, are tough to tune, what you’re seeing is not correct, but not uncommon.

Accurate powders developed the powder for the factory loads and it’s sold oddly enough as “TCM”. Might be worth a try.

Now that Hodgdon owns Accurate, load data for the 22 TCM is on their website, pistol load section. Whether that data will work for a Blow back system or not, would mean a phone call or email.

KAK May also have data that their buffer system was designed around.

 

[searcher]

The only experiences I have had with blowback cases having issues were with a .17 HMR. My rifle would shoot the standard factory ammo just fine - but when I shot the lead-free (lighter bullet) factory ammo of the same manufacturer (both Hornady), the base of the case would bell out as ignition was incomplete when the case was being ejected. Your photo looks to me that you are getting gas blow-by around the neck which is either caused by the bolt coming back way too soon - or possibly due to too slow of a powder being used for the load. As dellet suggested, seems to be a timing issue. I'd try a heavier buffer or spring or a faster powder.

 

[243winxb]

From website - FOR THIS BARREL WE RECOMMEND OUR 10.5 OZ BLUE TIP EXTENDED BUFFER WITH A 308 CARBINE SPRING IN A MIL SPEC CARBINE TUBE. FAILURE TO USE A HEAVY ENOUGH BUFFER CAN LEAD TO PREMATURE BOLT OPENING OVER EXPAND SHOULDERS AND NECKS AND CAN CREATE A DANGEROUS SITUATION..

https://kakindustry.com/oe-spec-22-tcm-ar15-barrel-8-625/

Early ejection has caused some 9mm case heads to rupture, on some direct blowback actions. Hopefully the thick 5.56 brass will hold up better?

 

[wildcat3d]

Wanted to see if I can get some help here.
Built a lil .22 TCM direct blow back AR pistol and been playing with it .
Used the reccomended buffer spring and weight from kak And it was work pretty good with factory
ammo cycling wise , but noticed I was getting inconsistent shoulders
From left to right
View attachment 1582927View attachment 1582928View attachment 1582929View attachment 1582930
Thought this was a bit odd

Anyway made my own brass from .223 ( got a whole thread goin in the small caliber section) and tired that. Was shooting way faster getting beautifully formed cases but no ejections. So after going up pretty high j decided to change the buffed deal to make it lighter.... Well started to cycle ...but now I'm getting some weird forming again.

The right case was what the first 15 or so of my converted ones looked like and the left is what all the ones that ejected look like


View attachment 1582931

Was told this might just be a quirk of direct blow back but idk ..anyone delt with this ?

Also, I made this brass from .223/5.56 with crimped primer pockets . Cut out the crimp.liem I always do but I'm using small pistol primers and I'm getting a lot of this
View attachment 1582932

I swear them blow is a good bit but their building out with a bit of cratering is this because pistol primers are a bit too loose for these pockets or ?

Anyhow would appreciate any advice or insight

It's still a rifle primer pocket, not pistol. IMO I would be using SRP.s Don't think that's all the problem though

 

[tommeboy]

https://kakindustry.com/oe-spec-22-tcm-ar15-barrel-8-625/

Early ejection has caused some 9mm case heads to rupture, on some direct blowback actions. Hopefully the thick 5.56 brass will hold up better?

no that is bolt bounce that causes that

 

[243winxb]

And out of battery firing.

 

[WayneShaw]

So these pistol configuration ARs do not have the gas tube and lockup as a rifle AR?

Sorry for the dumb question, just never looked at one.

 

[Paul's Black Rifles]

So these pistol configuration ARs do not have the gas tube and lockup as a rifle AR?

If I understand you correctly you are right. No locking lugs and no gas system. I have not fired a blowback AR. I do have a 10mm barrel and bolt for a build I plan on completing someday.
The bolt is way heavier, that provides the delay to allow the chamber pressure to reduce before the case extraction.

Paul

 

[ebb]

These blow back ARs are not as simple as we are made to believe. I worked for along time to finally get a 9mm AR to function. Had an empty hung up in the ejection port while stopping a loaded round from chambering. Decided the ejector was too long and shortened several times, finally figured it needed a longer than stock ejector plate. This is the first I am hearing of a 22TCM AR all Ive seen are bolt action. Looks like the Wolf Dog is going to head up the learning curve on this, be patient it will eventually work it self out, maybe!

 

[WayneShaw]

The reason for my question, I would think it difficult to get proper headspace(since forming your own brass) with the stock ejectors. Those things toss a round 10 feet. So to form the shoulder in the right place, removing the ejector would be the first thing I would do. But is spring pressure the only thing that holds the bolt in battery?

 

[Oso]

As others have mentioned, you have a timing issue that needs to be fixed. Things that you can do is change your buffer/buffer spring and also re-evaluate type of powder and charge weight that you need. Have you tried running some of the once-fired cases through the rifle and does the rifle cycle reliably when using these formed cases???

For the initial fireforming (matching the case to the chamber's dimensions) you may want to put back in the heavier buffer spring to ensure the case remains in chamber long enough to full form. Yes, this means an extra step to form cases with manually racking the slide every shot during the initial fireforming. Not the worst thing.... a couple of nice sessions at the range. With that little case you could almost load 750 rounds with #1 powder.

With Direct Blowback there is no gas volume to regulate with the gas block. Instead it is the buffer system that has to be tuned in order to achieve the desired lock-up time and the rate of speed that bolt cycles.

>If the buffer system is too light then the bolt disengages too soon, cycles backwards too fast, and eventually bottoming out at the end of buffer tube, Now, with the buffer spring fully compressed there is additional running room for it to uncoil and slingshot the bolt forward at full speed until it either slams into barrel extension or the bolt stop. This really beats up the equipment and creates a choppy recoil impulse.

> With a heavier buffer system (heavier buffer weight &/or buffer spring) the case remains in the chamber longer and the rearward momentum of the bolt is slowed down. This decreases amount of abuse to the rifle and smooths out the recoil impulse (much less rocking as bolt slams forward and backwards).

My AR9 took a few attempts to tame its blow back. I bet it snapped/sheared off 4-6 bolt stops before I finally found the right combination of buffer weight and buffer spring. I finally went with JP Enterprise's extra power carbine buffer spring and a heavy buffer (7.3oz), and I haven't had a hiccup even when shooting light loads.

 

[tommeboy]

You all have missed one of the most important things I mentioned. The hammer spring functions as a delay. It is actually more important than the buffer weight. That is why you need a NEW propper extra power hammer spring. Buffer weight and spring are secondary.

And you also need a bolt that has the little nub on the bottom of the face. If you don't have that it can fire OOB. If you have a bolt like this and you have a OOB firing it was from bolt bounce. The firing pin can not reach the primer till the extractor slips over the rim. Only way for that to happen is the bolt has to be in full battery. And the solid buffers are one of the worse things you can run in a blow back. I made my own buffer. I made it to act like a standard buffer with the weights inside. This cures bolt bounce. I have 2oz of lead shot inside my buffer.

 

[troupe]

Bolt is opening to soon ! Wrong brass, to thick also.

 

[Wolfdog91]

could be the case walls are too thick not letting the brass flow. did you cut the 223 case length, did you turn the necks some, you might need to anneal the case to soften, I really have no clue about it just spoutin but if the case is thick it's prolly not gonna form to well, most other cases are thinner at the shoulder then thicken at midpoint of case

So sorry I haven't responded been ripping and running and just updated my other post . That being said I think your 100% right. Well at least that it might be why these don't wanna eject.
Long story short I loaded these things up kinda crazy and did a lot with buffer tubes and springs and what not.... replaced the lighter triggers I put in back with the heavy mil spec one and NOTHING would try and eject. I was getting great fire fomings though


Got like one out of the last 40 something to eject / try to

 

[Wolfdog91]

Well finally got towards my wits end and tired som factory ammo ( stuff shoots only like 2200fps) aannnd shot and cycled perfectly! So then j too skem of that brass and loaded it with a mild load and boom boom boom , worked just fine !

Well measured my home made brass then the stuffed front he factory brass aaannnd


Long story short the factory brass works with about everything, buffer wise and all that. Though there definitely is a lil bit of a difference between the heavy and the light springs



Non seem to be as nice as mine though

 

[Wolfdog91]

O and side note ,had my very first case head separation ever