WHY? Because I get .45 firepower in a 9mm package. .45 mags are still an unsolved issue with the .45 conversion. .45 GAP rounds feed out of 9mm mags and are currently factory loaded to .45 +p levels so I loose nothing compared to a regular .45 setup.

Almost done. All I need is a flip up front sight that attaches to the hand guard. I used a Thompson submachinegun, 16" barrel from Gun Parts Corporation. I had a local machine shop shorten the chamber by milling a little off the rear of the barrel and then they made me a new barrel extension that has Thompson barrel threads instead of AR barrel threads. A regular Thompson barrel can be used for an inexpensive, .45, upper build.

Uses 9mm Sten mags and a KKF magwell filler block with an Delton upper I drilled for the Oly Arms spring ejector.

The new barrel extension doesn't have the angled cone shape for the bolt like the Oly extension but it still feeds great.









So what do you guys think?

That is very cool.  While I am not a fan of the GAP round, I am always ready to salute tinkering and do it yourself thinking.  



Cheers

MODS, I meant to put this in the pistol caliber section. Please delete this thread.

Quoted: WHY? Because I get .45 firepower in a 9mm package. .45 mags are still an unsolved issue with the .45 conversion. .45 GAP rounds feed out of 9mm mags and are currently factory loaded to .45 +p levels so I loose nothing compared to a regular .45 setup. Almost done. All I need is a flip up front sight that attaches to the hand guard. I used a Thompson submachinegun, 16" barrel from Gun Parts Corporation. I had a local machine shop shorten the chamber by milling a little off the rear of the barrel and then they made me a new barrel extension that has Thompson barrel threads instead of AR barrel threads. A regular Thompson barrel can be used for an inexpensive, .45, upper build. Uses 9mm Sten mags and a KKF magwell filler block with an Delton upper I drilled for the Oly Arms spring ejector. The new barrel extension doesn't have the angled cone shape for the bolt like the Oly extension but it still feeds great. tangochaser.zoto.com/img/45/86736aa7cbee59bfdeffcae96a73951e-.jpg tangochaser.zoto.com/img/45/6349d4ee017c294ad84a3722df0dc332-.jpg tangochaser.zoto.com/img/45/5cc8ba001a7f6203fe59b24eec3691fc-.jpg tangochaser.zoto.com/img/45/cb3ab6b84b169769da248024e16c5906-.jpg So what do you guys think?

TANGOCHASER:

Though I am 45ACP proponent, give us your rational? I have never like a pistol chambered carbines. There are better subgun formats than the AR. Just asking for an understanding.

Very interesting. Great idea using the tommy gun barrel. Now you need to register it as a SBR, and cut the barrel.

Quoted: I used a Thompson submachinegun, 16" barrel from Gun Parts Corporation. I had a local machine shop shorten the chamber by milling a little off the rear of the barrel and then they made me a new barrel extension that has Thompson barrel threads instead of AR barrel threads.

Did this make it a shorter than 16" barrel?

Posted by pcurtis; TANGOCHASER: Though I am 45ACP proponent, give us your rational? I have never like a pistol chambered carbines. There are better subgun formats than the AR. Just asking for an understanding.

More whack than a 9mm. Bigger holes in bad guys and targets. easier to suppress as the .45 is already a subsonic round. Extends the usable range of the .45 GAP making it more accurate with a longer sight picture. Shoot the same ammo in a pistol and rifle. I used a pre-existing barrel, bolt assembly, and 9mm mag and filler block. Means I didn't have to spend an arm and a leg for specially made parts. The AR platform is more adaptable than any other.

And NOBODY ELSE HAS ONE.

Posted by boltmaster; Did this make it a shorter than 16" barrel?

No. The barrels are actually about 16 1/4" and the amount removed from the rear of the barrel is less than that. I'll measure it tommorrow and get an exact length.

The first, and hopefully the last.  

You're funny.

Quoted: So what do you guys think?

I think it is really cool.
I think that I wish I had the second one!

Dave

Nice going, but I still think I'd want a 45 ACP upper.
You've got a good point with using 9mm Mag though.

Quoted: Quoted: I used a Thompson submachinegun, 16" barrel from Gun Parts Corporation. I had a local machine shop shorten the chamber by milling a little off the rear of the barrel and then they made me a new barrel extension that has Thompson barrel threads instead of AR barrel threads. Did this make it a shorter than 16" barrel?

I think they start at 16.5, but I measured mine a bit quickly.  + the barrel extension, if pinned, would fix that issue.

This is not something I would want for myself, but I have to give you credit for all your hard work.  It looks great and I bet it’s a blast to shoot.

Rob

dude thsat looks like a bad ass piece of kit

Now for my next trick....Gun Parts Corporation sells a 16" Thompson barrel in 10mm. I had 2 additional receiver extensions so all I need is more barrels. I still have to drill the extensions for the indexing pin but that is too easy.

The barrel extensions use the Thompson barrel threads so I can use an unmodified barrel and 10mm feeds good in the M3 mags, so I hear.

OK, now I am lost.  If you have an M3 mag which will fit through a standard AR15 magwell, or a magwell which will accept a standard M3 mag, why not go with the .45 ACP?

I have gone with the Cav Arms MKII lower, and use unmodified M3 mags.  Thus I can't use a CAR style stock.

I like the idea of a 10mm AR15, but I wonder if we are not reaching the limits of a blowback action?

Maybe this will clear up the confusion. Oly Arms makes a 10mm and .45 ACP upper. They are around $594 and are the only manufacturer making uppers in these calibers and in my opinion, are price gouging because of it. They only offer 10 round mags with the 10mm and .45 ACP uppers kits.

Using a Thompson barrel, I can make a 10mm, .45 ACP and a .45 GAP upper for about $400, $200 less than Oly charges.

Justin at CNC and I came up with the AR45 lower that takes GG mags to overcome the lack of a .45 high capacity mag that fits the standard magwell. The AR45 lower can be used to feed a 10mm, .45 ACP or .45 GAP upper using GG mags. The AR45 lower also uses a mag release in the normal location as opposed to the Cav Arms lower that needs an additional filler block from Hahn. The mag release now becomes a paddle out the bottom and you can't use a M4 stock on it.

My .45 GAP upper can be used to shoot .45 bullets at +P velocity using a 9mm Sten mag and a magwell filler block. It can also be used to make a 10mm upper cheaper than Oly is charging using a 10mm Thompson barrel, if you don't mind a low capacity mag and a .45 ACP upper again using a .45 Thompson barrel, but you are limited to mag capacity.

I can use my Thompson barrel uppers with either the AR45, GG mag lower or use it with a regular lower and Oly low capacity mags or the Dalphon type modified GG mags if you can find them.

Can you say "Versatility"?

very nice I like

Very nice!

Now go and shoot something up with it!

Post the picks!!!

Capacity in .45 GAP using the 9mm mags is...???

tsh77769

Do Sten mags need to be modified?

If not how many rounds do they hold, and YOU ARE A FREAKING GENIUS MAN.  

The feed lips need to be opened up a bit. Pliers work fine for this. The Sten mags hold 16-17 rounds and it takes both nuts to load that many in the mag. I highly encourage the use of a Sten mag loader.

Went to the range today to test fire the .45 GAP upper. Feeds great but I found a minor problem. Olympic Arms barrel extensions have a slight taper towards the bore. The barrel extension my local machinest made is straight walled. Some of the rounds would feed into the chamber but would make contact with the end of the barrel first and push the bullet about 1/8" into the brass. The rounds fired fine but were probably over pressure.

I haven't decided if I will pursue making a new barrel extension to fix the problem or break it down for parts and make a regular .45 ACP upper. I originally came up with the idea to see if it could be done. The idea is sound but the barrel extension needs to have a taper similar to Oly Arms extensions.

If I don't fix it, I'll take the barrel to a gunsmith and have him ream the chamber back to .45 ACP and just make another .45 ACP upper or sell the parts for my next project.

This picture is of the target I fired today. 25 meters with an Aimpoint, 17 rounds rapid fire.

Amazing!!!  Personally, I would go ahead and tech out the minor issues and get it running one hundred percent.....just to say you did it.

Great job!!!!