10mm AR Lightning

[Albroswift]

Haven't shot it yet, maybe next weekend.

 

CMC PCC FCG
Radian Talon short throw ambi
Stern Defense BCG
Sprinco red spring
NFA 16" barrel and NFA receiver set w/ LRBHO
Sightmark M Spec circle dot RDS
MFT minimalist stock
JT Pistol grip
Paired a 7-11/16" SOLGW 9 position buffer tube with an extra long 5 tungsten weight buffer. Length with the BCG came out about 1/8" behind the bolt catch, about right no quarters. Maybe get out to the range next weekend see if it actually works. May need some tuning of the buffer and spring. Should be close.  

 

Cerakote Graphite black over gold

 

[Sisco]

Very nice!👍🏻

[Armed Eye Doc]

Sharp looking carbine Al.

[unforgiven]

That looks like fun brother Al 😁 

[Cunuckgaucho]

[MtnMike]

👍👍

[Rsquared]

Looks good my man.

Dammit. I gotta get around to building me a PCC sometime just for fun.

[Albroswift]

I've done a couple 40's, brothers have done a 40 and a 45, now a 10. Thinking 10mm is about on the edge for blowbacks without delay. 

 

[sketch]

Nice!

[Albroswift]

Over the last few months got this out to the range a few times. Usually never get through more then 5-10 rounds without ripping a case in half. Sometimes a whole mag. Tried a lot of different things. I have downloaded to the point the AR40S&W has a lot more velocity. Always cycles reliably. Doesn't matter if full blow AA#9 powder or downloaded to whimpy titegroup velocities, every 5-10 rips a case in half. Driving me nuts, I should be able to nail this.  Ideas?

14.6 oz buffer

Red spring

What I've tried so far:

EA1095 spring

Wilson AR10 Flatwire

Downloaded ammo

New Starline brass

Factory ammo

Plunk tested ammo -removed barrel, plunk tested, checked BCG, easily grabbed round without jamming it into the bore. Plunk test seems just right. 

Polished chamber

Next range trip, added a collar to the buffer to increase weight (+0.75 oz) and spring tension. Trying a different BCG. 

Ideas?

 

 

[98Z5V]

Albro, blowback, right?  

What are your reloads - from the start, to the downloaded stuff that you're running now.  Have any chrono data on what you've shot, per load?  That's a loooong barrel for a 10mm AR pistol - those velocities are gonna be up there.  What's your .40 SW numbers, compared to these?  

I have some ideas, but want to make sure I'm on the right track.

I don't know how I missed this, until I saw the dates.  Last summer and fall sucked for me, and I dropped off the radar.

[Albroswift]

Don't sweat missing this, kind of a back burner project.  I get it out every once in a while, run some loads, don't fuk with it for months, run some new ammo or spring, repeat. 

Yes. Blowback.

Getting around 1730 fps w/ 15.6gr AA#9 1640fps w/ 6.8gr Titegroup.  I'd scrap it but it's a blast to shoot and accurate, and not very loud. Not much more then the 40.  

I get around the 1430's with the 40. 

Reload ladders, started out  

 

#9 laddered from 14.8 to 15.6. Too compressed at anything over 15.6 

Titegroup did the whole 6.4 to 7.2

 

Getting way over the published velocity as expected, Using 155 XTP's. 

 

The thing is, though, Hot loads or weak loads don't make much of a difference as far as case separation. 

Case goes fully into chamber with extractor under rim so not unsupported blowout.

Separation point about mid case. 

Found a source for 8-1/2" Extensions so adding another 3/4" + 1 more tungsten weight to the buffer. 

14.6 oz buffer

3.6 oz additional weight

14.6 oz BCG

Almost 33 oz reciprocating mass for the next trip to the range. Swapping BCG's with the 40. Think I'm going to back off on the spring go back to an orange or red. 

If this doesn't work, I have a 12" barrel to try. 

 

Also tried some PMC 180's, same. 

 

Edited Tuesday at 10:31 PM by Albroswift

[98Z5V]

On 9/22/2024 at 8:19 AM, Albroswift said:

Sprinco red spring

Paired a 7-11/16" SOLGW 9 position buffer tube with an extra long 5 tungsten weight buffer. Length with the BCG came out about 1/8" behind the bolt catch, about right no quarters.

Alright.  So you get bolt lockback - you have the room, without coil bind on the Sprinco Red.  

6 hours ago, Albroswift said:

Found a source for 8-1/2" Extensions so adding another 3/4" + 1 more tungsten weight to the buffer. 

14.6 oz buffer

Let's go the other way, before you order parts.  Go Rifle Receiver Extension, and a custom buffer from @Slash at HeavyBuffers.com.  Use the same Sprinco Red spring.  Get a Rifle receiver extension, have Slash whip up a Rifle buffer that will work, with the head dimensions that you running on the no-coil-bind buffer head right now, that custom monster...  and it's gonna be WAY heavier than the 14.6oz that you have right now.    Throw massive weight at it, and it'll solve this problem - if it cycles.  Have him load that thing FULL of tungsten weights...  If it doesn't cycle - start looking at why, and you can always start swapping out tungsten weights for steels, and keep the base body mass of the RIfle stainless buffer - with the huge head on it... 

10mm PCCs are a MFer...   

Edited Wednesday at 03:51 AM by 98Z5V

[Albroswift]

Good idea on the rifle length extension. I have everything I need to make a stainless rifle buffer in my shop, and a pile of tungsten weights. Probably have a rifle tube as well. 

full blow 10mm in a carbine is a FUN MFer...

[98Z5V]

18 hours ago, Albroswift said:

Good idea on the rifle length extension. I have everything I need to make a stainless rifle buffer in my shop, and a pile of tungsten weights. Probably have a rifle tube as well. 

full blow 10mm in a carbine is a FUN MFer...

I completely forgot that you are machining all this stuff at home...   

[Albroswift]

While waiting for a few parts to show up took a look at the used brass. A few of them showed bad signs of separation.

 

 

 

 

 

Primers don't look bad

Especially compared to my 1911 10mm primers. 

 

 

 

[Albroswift]

Here is some brass out of the 40 carbine. Starting to show a little flow. 155gr XTP 5.8gr Titegroup, just about max. 

Edited 20 hours ago by Albroswift

[98Z5V]

I'll offer my comments tomorrow sometime - I'm looking over all this, especially the cases.  I've seen this before.  Give me some time to get it all together, brother.