WestKentucky
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Still no word from batfe? Dang sure cool but waiting this long must be killer.
1/2 scale AR-15
- Thread starter MachIVshooter
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MachIVshooter
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I've just gotta order up the reamer and do the barrel. Been busy with other projects, though; ones that actually generate revenue. Having fun making custom muzzle brakes and comps. Some aluminum (far left), carbon steel, stainless steel (2nd from left), but mostly 6/4 ELI titanium:
One on my .308, a 48 port Ti comp:
6 port Ti brake on my featherweight (pinned):
If I fit them here, we do not use crush washers or shims unless that's what the rifle's owner wants. I either put them on to index before profiling, or if the brake is already made, we spin it on to see where it lands, and then pull it off and turn the back end on the lathe until it's timed right.
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horsemen61
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Awesome work on those brakes
Dave Markowitz
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As someone who took up hobby machining a couple of years ago, I am in awe of the talent displayed in this thread.
OP
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MachIVshooter
Member
Finally got my chamber reamer 
Unfortunately, I was not able to test fire it. The force required for primer ignition is still 1:1, so my 1:2 0.020" music wire hammer spring just isn't gonna cut it. 0.039" spring temper wire on order.
Unfortunately, I was not able to test fire it. The force required for primer ignition is still 1:1, so my 1:2 0.020" music wire hammer spring just isn't gonna cut it. 0.039" spring temper wire on order.
horsemen61
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Any update mach can't wait to see it all done
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MachIVshooter
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Well, so far everything I've tried to get enough spring power behind the hammer has failed. Heavier wire, using the trigger spring against the hammer, 2 extra coil springs set up like a Hyperfire trigger-none has worked to achieve ignition. I can get the primer to pop with a de-bulleted .22 short case if I put a punch against the FP and rap it lightly with a 2 oz ballpeen, but not with the actual FCG hammer.
I'm gonna take a trip up to TJ's gunsmithing as soon as I can find time, see if he can recall any firearms that use powerful little hammer spring that might fit in this receiver. I'll get it, but it's an aggravating little snag after all this work.
I'm gonna take a trip up to TJ's gunsmithing as soon as I can find time, see if he can recall any firearms that use powerful little hammer spring that might fit in this receiver. I'll get it, but it's an aggravating little snag after all this work.
Catshooter
Member
Can you increase the hammer weight? That has more effect than spring strength, if you can do it.
Cat
Cat
horsemen61
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I see Mach well I hope you all the best in getting it finished
rcmodel
Member in memoriam
Speed is the key!
Weight is not, unless it is moving at fast enough high speed.
(Witness striker fired guns with low mass strikers moving at very high speed.)
Lighten the hammer, and get it moving as fast as possible.
It might work?
Or not?
But if a Baby Browning, or a Glock can work on speed alone??
Worth a try!!
rc
Weight is not, unless it is moving at fast enough high speed.
(Witness striker fired guns with low mass strikers moving at very high speed.)
Lighten the hammer, and get it moving as fast as possible.
It might work?
Or not?
But if a Baby Browning, or a Glock can work on speed alone??
Worth a try!!
rc
Nature Boy
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Have you looked at companies like Century Springs?
I'll bet they have what you need in their extensive catalog
http://www.centuryspring.com/pdfs/01-04TOC.pdf
I'll bet they have what you need in their extensive catalog
http://www.centuryspring.com/pdfs/01-04TOC.pdf
barnbwt
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And an aluminum hammer, perhaps? The G36 hammer is actually plastic with a steel striking face --very lightweight. I think the AUG and some of the FNH guns have poly hammers as well.
If all else fails...just do a striker conversion. Plenty of room in the FCG box for a disconnected striker sear, and you'd basically be reusing your firing pin hole in the bolt for the striker w/ a second coaxial striker spring/follower.
You could also try playing with your hammer geometry a bit, and see if you can't cut the tail of the bolt or firing pin back, or the strike face of the hammer, so that the hammer gets to swing a bit further than it does now, and pick up a bit more speed. I'll bet it wouldn't take much, but just make sure it still gets knocked back over the sear notch properly
TCB
If all else fails...just do a striker conversion. Plenty of room in the FCG box for a disconnected striker sear, and you'd basically be reusing your firing pin hole in the bolt for the striker w/ a second coaxial striker spring/follower.
You could also try playing with your hammer geometry a bit, and see if you can't cut the tail of the bolt or firing pin back, or the strike face of the hammer, so that the hammer gets to swing a bit further than it does now, and pick up a bit more speed. I'll bet it wouldn't take much, but just make sure it still gets knocked back over the sear notch properly
TCB
I just signed up for this site because this is so interesting. I love what you're doing and what you've done, and I'm just brimming with suggestions! For starters, I was going to suggest a 20mm flare gun for the grenade launcher-ammo would be cheap and easy and you wouldn't have to do even tell the batf(gestapo) anything. Second, the 1/2 half scale is great but just imagine what a 2:1 scale could do! I'm thinking along the lines of a 460 Wetherby Mag rifle which would be awesome, and could have a market with elephant hunters. You might also consider.416 barrette with a double scale. Anyway, keep going and absolute best of luck with getting the firing sequence fixed!
thegunpunch
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Threads like this make me wish I joined THR earlier
swampcrawler
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I can't wait to see video of this thing firing. I'm sure it can be done!!
lysanderxiii
Member
A 2:1 would be much more difficult and require more actual engineering.
A 2:1 would be in the .50 BMG range (the overall length of .50 BMG is almost 5-1/2 inches, .223 is 2-1/4, or 41% smaller), but the loads and material strength do not scale the same....
barnbwt
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"I can get the primer to pop with a de-bulleted .22 short case if I put a punch against the FP and rap it lightly with a 2 oz ballpeen, but not with the actual FCG hammer"
Other things to check would be to make sure the hammer is hitting the pin square-on, that there are no burrs in the pin channel, that the pin can go fully forward as needed, and that the hammer isn't hitting anything in the course of the swing but the firing pin.
"A 2:1 would be in the .50 BMG range (the overall length of .50 BMG is almost 5-1/2 inches, .223 is 2-1/4, or 41% smaller), but the loads and material strength do not scale the same...."
There was a cat doing a 2:1 AK in BMG a while back (had to abandon it due to personal issues, I gather) who found that that particular design was essentially sufficient if suitably scaled. The main worry was things like the firing pin being too heavy to float safely (slam fire), but obviously you can still shrink things when necessary inside a massive design. I believe he got as far as the bolt, carrier, and front trunnion (which were positively massive at 2:1. Think L39 Lahti-sized parts)
TCB
Other things to check would be to make sure the hammer is hitting the pin square-on, that there are no burrs in the pin channel, that the pin can go fully forward as needed, and that the hammer isn't hitting anything in the course of the swing but the firing pin.
"A 2:1 would be in the .50 BMG range (the overall length of .50 BMG is almost 5-1/2 inches, .223 is 2-1/4, or 41% smaller), but the loads and material strength do not scale the same...."
There was a cat doing a 2:1 AK in BMG a while back (had to abandon it due to personal issues, I gather) who found that that particular design was essentially sufficient if suitably scaled. The main worry was things like the firing pin being too heavy to float safely (slam fire), but obviously you can still shrink things when necessary inside a massive design. I believe he got as far as the bolt, carrier, and front trunnion (which were positively massive at 2:1. Think L39 Lahti-sized parts)
TCB
OP
OP
MachIVshooter
Member
I know you mean to be helpful, but honestly, considering the project, it's pretty insulting to imply that I would have missed such things or made such errors.
It's a spring power problem, plain & simple. It dents them, just not enough for ignition.
LoneGoose
Member
MachIV, we're all excited for you. This project is awesome! Please, please get the finished gun appraised by a couple of big-name appraisers. You may find that (this being unique and of a high interest) it will have incredible value. I would love to see an article on the gun in American Rifleman magazine!
I came in late, so forgive me if this has already been covered.
The gun may be half size, but the cartridge is still full size and is going to require the same amount of bolt weight as a full size blowback. The inertia provided by the bolt is critical in a blowback design. If it's too light the bolt will begin to move before the bullet has left the barrel. This will result in the cartridge case being extracted from the chamber while still under pressure, which can rupture the case and spew hot brass and high pressure gasses about. The short barrel will help by reducing the time the bullet spends in the barrel, but you'll still probably have to use some sort of exotic material for the bolt to make it heavy enough.
Again, forgive me if this has been covered, but I wasn't able to read all 15 pages of history at one go.
The gun may be half size, but the cartridge is still full size and is going to require the same amount of bolt weight as a full size blowback. The inertia provided by the bolt is critical in a blowback design. If it's too light the bolt will begin to move before the bullet has left the barrel. This will result in the cartridge case being extracted from the chamber while still under pressure, which can rupture the case and spew hot brass and high pressure gasses about. The short barrel will help by reducing the time the bullet spends in the barrel, but you'll still probably have to use some sort of exotic material for the bolt to make it heavy enough.
Again, forgive me if this has been covered, but I wasn't able to read all 15 pages of history at one go.
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Reopened so OP can add updates.
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