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reccerecon
07-11-11, 15:29
I can't seem to find the info I need so maybe someone here can square me away. I just got a TA31RCO for M4's in a trade and I'm wondering how the BDC will work on a 16" midlength upper? My experience with ACOG's is limited to TA01NSN's on 14.5" M4's. I know if it isn't a good match then I can just record the impacts and adjust for there. Would it just be better to try and get a different model for the uppers I use and if so what do you recommend? All I have now are 16" midlenghts. I've tried the search on multiple site but couldn't find what I needed. Thanks for the help.
ICANHITHIMMAN
07-11-11, 15:51
Middlength or carbine length should have no effect. Its the 1 1/2" more barrel you have that is going to create more speed than the 14.5" barrel on your M4 this making you BDC off but just a bit. I would say its so small you should not worry about it. But if you cant stop thinking on it you can give it to me.
reccerecon
07-11-11, 16:00
That's what I was thinking. I thought it would be a good idea to know for sure before zeroing it. Thanks again for the help.
BooneGA
07-11-11, 19:07
The BDC stadia are simply a guide. Unless you actually shoot the rifle at those ranges there really is no way to be sure. Different rifles, barrel length, ammunition, and enviromental factors (such as elevation) play heavily into the flightpath of the bullet.

If you are going to rely on them, I would reccomend taking the rifle out and verifying the accuracy of the stadia even on a 14.5 inch military M4 shooting M855.

Rick
R0N
07-12-11, 03:36
The BDC is good enough for government work. It is based on standard MV, at sea level and 50 degrees.
Failure2Stop
07-12-11, 10:32
In my experience, 75 and 77 grain loads from 16" barrels shoot very close to the stadia built for M855 from 14.5 barrels if zeroed at 300 meters.
reccerecon
07-12-11, 20:33
That answers my next question, I was planing on trying M855 first but that will save me some ammo. I am going to test dfferent bullet weights so I'll have an idea what to expect.
irish_11
07-27-11, 22:56
I am interested in this as well. I just picked up a TA31RCO for a good price and was going to put in on my Sig556. Any update on the 16" vs 14.5"?
Failure2Stop
07-28-11, 05:32
I am interested in this as well. I just picked up a TA31RCO for a good price and was going to put in on my Sig556. Any update on the 16" vs 14.5"?

Nope, nothing new in the physics department.
irish_11
07-28-11, 10:55
Nope, nothing new in the physics department.

haha, I think I worded that a little wrong. it was more directed at reccerecon and how noticable the difference was.
reccerecon
07-28-11, 20:21
I just got back from the range and I didn't see anything off, the range I used only went out to 300m and I used 55gr ammo. For what I need it to do it works just fine and I'm sure it's more accurate then I am.
mini4m3
07-28-11, 21:10
I'm pretty sure there was a thread/post about having a bunch of Marines with RCOA4 (w/ 20'' M16A4s) and RCOM4 (w/ 14.5'' M4s) shoot a standard test for score. They then swapped the optics so 20'' guns had the RCOM4 and the 14.5'' guns had the RCOA4 and they didn't notice a large change in amount of good hits.

I'll see if I can dig up the thread.