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supernachos
06-01-2011, 8:36 AM
Hello All,
I have 7.62x39mm BushMaster 16" upper mated to a standard PlumbCrazy lower.

Just for reference I had *many* misfires with different types of Russian ammo. I read up on another member posting about upgrading to a more powerful hammer spring and modified firing pin for AK ammo. I installed the modifications but I unfortunately haven't had a chance to testfire but I'm sure it'll help.

Now my question is about the trajectory of the spent cartridge. Did the designers of the AR-15 have a optimum trajectory in mind? Was it designed to for the casing to eject 90 degrees perpendicular from the rifle, somewhere in front or somewhere behind? Watching multiple video clips it looks like perpendicular or slightly forward from the shooter?!

With my standard buffer spring on the PlumbCrazy lower the rifle cycles for the next shots ok but I noticed that my spent shells eject all the way back.

Also the recoil is what I consider a bit excessive compared to a Ruger Mini30 and it takes more time to acquire the target after each shot.

For the recoil I will try upgrade to a Wolff extra power buffer spring to see if it reduces the recoil. http://www.midwayusa.com/viewproduct/?productnumber=152626 .

I haven't recieved the part yet to try it out but any advise is appreciated on the 2 questions I have.

Thanks In Advance!

FeuerFrei
06-01-2011, 9:02 AM
Caution. Switching buffer springs can change the timing.
If your empties eject at 5 o'clock where 90 deg. = 3 o'clock then your gas system may need tuning.
On an average AR with a tuned gas system it will eject at 2 - 4 o'clock.
Over gassed usually eject forward of that and under gassed further back.
This too depends on what ammo you are feeding your AR.

supernachos
06-01-2011, 10:25 AM
Hi FeuerFrei,
Yes, I realize that the firing cycle may be affected. I read the review of the buffer spring from a owner of a Colt 7.62x39 version and he said the recoil was reduced to a workable level and the cycling still worked so I figured $12 wasn't a bad choice to try it out.
Hopefully the empty shell trajectory will also be moved forward from the 5:00 to the 3:00 o'clock position. hahaha...
...But thinking about it wouldn't the shooter directly adjacent from you on the right on the range or battlefield be more appreciated that *hot* brass or steel casings are not hitting them in sensitive areas like on the face or in the neck falling inside their shirt...
8-)
Thanks for your input!

PEBKAC
06-01-2011, 10:27 AM
http://img28.imageshack.us/img28/49/20100201092534ejection.jpg

FeuerFrei
06-01-2011, 10:56 AM
Hi FeuerFrei,
Yes, I realize that the firing cycle may be affected. I read the review of the buffer spring from a owner of a Colt 7.62x39 version and he said the recoil was reduced to a workable level and the cycling still worked so I figured $12 wasn't a bad choice to try it out.
Hopefully the empty shell trajectory will also be moved forward from the 5:00 to the 3:00 o'clock position. hahaha...
...But thinking about it wouldn't the shooter directly adjacent from you on the right on the range or battlefield be more appreciated that *hot* brass or steel casings are not hitting them in sensitive areas like on the face or in the neck falling inside their shirt...
8-)
Thanks for your input!

$12 isn't much to spend on experimenting. No prob.
The spring and buffer combo works together and you may also want to try an H/H2-buffer too. No need to make it short stroke.
Is it your objective to "fix" ejection pattern or to lessen recoil?
Both at once?
Let us know your results.

supernachos
06-01-2011, 12:10 PM
..Yes I want to fix the 2 issues of the recoil and ejction pattern at a single go with the buffer spring change....

The reason I am pursuing this calibre for the AR is the average cost of .20-.25 cents per 7.62x39mm round. Easy enough for the pocket and appreciate a higher calibre than the .223 for plinking...

I will update you on my findings...
Regards

supernachos
06-01-2011, 8:03 PM
Sorry for the delay Pebkac. I would have responded to you sooner but it seems my work place blocks the imbedded photos on posted messages and all I saw was your signature block...

Hmmm so it looks like the behavior of my rifle is marginal at around 4:30. I wonder how the stiffer buffer spring will affect the trajectory?! Let me investigate about a lighter buffer...