View Full Version : Got my BCM middy upper - ? about fit
Got upper today from the brown santa :D NICE. ............. However, I was a little dissappointed to find that it is a loose fit on all 3 Essential Arms lowers I have and on my Double Star lower. Testing with all of them, the Double Star upper is nice and solid with zero slop on all 4 lowers. I haven't measured the holes yet, but it *seems* that the holes in the BCM upper has play on the take down pins. I searched here and on TOS about this issue. Seen lots of posts over there that a loose fit between uppers and lowers is not uncommon and no reason to worry. Also seen some mention of installing a small o-ring around the front pivot post on the upper to take out the slop, but seems to me that IF that o-ring got cut you could potentially end up with a piece of getting up into the bolt / chamber area. I didn't find much talk here about it. I know you guys are a picky bunch, so what's the feelings on a loose fit with this group of members?
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thopkins22
03-16-09, 22:26
I know you guys are a picky bunch, so what's the feelings on a loose fit with this group of members?
Don't worry another second about it.
From my own experience...I have one LMT upper that does one thing on one LMT lower and another thing on another LMT lower, and something in between on an LCW. Other uppers react differently. There's no difference functionally nor accuracy wise. I got over it pretty quickly.
Though if it truly bothers you...I'll take it off of your hands.
ETA:I'll slap you in person if you put an o-ring on your pivot pin. It might work, but it would be pretty vain. Then again you might be a big dude, in which case I'll keep my hands in my pockets. ;)
I've tried a few BCM uppers on my Mega and LMT lowers. They were looser than my other uppers. Not really a problem, but I hate to hear the upper clack back and forth as I move the rifle. My other uppers don't do that.
spamsammich
03-17-09, 04:31
Doesn't matter, shoot the shit out of it.
You have three choices:
1) Ignore it as it is most likely completely inconsequential.
2) Contact BCM and ask them directly about it and see if there's a chance you can get another one.
3) Start wedging shit into the upper/lower to tighten it up.
Personally, unless it's really flopping around (and I bet it's not) I'd be inclined to pick #1. Also, when trying to figure out if slop is due to one top-shelf part (your upper) or several bottom shelf parts (your lowers), I'd lean towards the issue being in the lowers.
Doesn't matter, shoot the shit out of it.
I 2nd this...
Anyone have a link to a upper print? I'd like to have one for my files and to look at to check the uppers I have.
......
Got upper today from the brown santa :D NICE. ............. However, I was a little dissappointed to find that it is a loose fit on all 3 Essential Arms lowers I have and on my Double Star lower. Testing with all of them, the Double Star upper is nice and solid with zero slop on all 4 lowers. I haven't measured the holes yet, but it *seems* that the holes in the BCM upper has play on the take down pins. I searched here and on TOS about this issue. Seen lots of posts over there that a loose fit between uppers and lowers is not uncommon and no reason to worry. Also seen some mention of installing a small o-ring around the front pivot post on the upper to take out the slop, but seems to me that IF that o-ring got cut you could potentially end up with a piece of getting up into the bolt / chamber area. I didn't find much talk here about it. I know you guys are a picky bunch, so what's the feelings on a loose fit with this group of members?
....
You're not the only one Dude, I posted something also along these lines, and ended up buying another lower from GTS that has the tension screw in the lower.Tactical Innovations makes the lower for them and their own.I will be changing the upper receiver real soon.If you ask me it's the front take down pin on the receiver, it's made different than my other uppers and I THINK that's where the slop is.I put a ruler on both and from the naked eye the BCM's a little narrower.Anyway here are some pics of the O ring fix and the lower I was talking about .Both will work.
the play is normal but I too can get crazy about little things like that. just shoot it , or if you dont, sell it to me :D
I was disappointed with the play in my BCM also. It doesn't feel near as solid as my Sabres.
Max Collins
03-17-09, 13:38
Get a RRA or Sun Devil lower and your problem will be solved.
CMT upper receivers generally fit loosely on most lowers as well (maybe that's what BCM uses on their upper builds?).
so what's the feelings on a loose fit with this group of members?
VERY IMPORTANT!!!!!
Are you testing the fit on lowers WITHOUT the complete BUFFER SYSTEM installed?
I ask this because ALL LOWERS/UPPERS fit sloppy if there's no buffer system in the R.E. to tension up the receivers.
exkc135driver
03-17-09, 14:29
VERY IMPORTANT!!!!!
Are you testing the fit on lowers WITHOUT the complete BUFFER SYSTEM installed?
I ask this because ALL LOWERS/UPPERS fit sloppy if there's no buffer system in the R.E. to tension up the receivers.
I wish that were the case ...
I have an upper from a left-of-chart maker that will not fit on a lower from a right-of-chart maker. The distance between the pivot and takedown pin holes on the upper is shorter than the distance between those holes in the lower. Tolerance stacking, probably. Problem is, I really want to use THAT upper on THAT lower. Yes, I could bodge the holes on the upper to loosen them so they would fit, but I'm not inclined to mess with the gunsmithing from a well-known and highly-respected builder. Hopefully I won't have the same problem with the BCM upper that I will purchase (if I ever get a chance to).
I have a couple of extra pivot and takedown pins and I'm trying to figure out a way to grind one of them so it's a few thousandths smaller in the x-axis but still the same size in the y-axis (basically, make the pin a little bit oval) to see if that will work. Of course I'd have to change the pin anytime I change upper receivers, but I'd rather do that than mess with a pretty pricey upper. If I completely screw up a $5.00 pin, who cares?
Actually, 2 of the lowers are complete and the other 2 are stripped. I was installing the pins in the ones that are stripped when testing fit though. Only reason I was even testing with the stripped lowers was because the fit was loose on the other 2 complete lowers. I first mounted the upper on the lower it was intended to go on, then when I seen it was loose, I tested with the other lowers.
I want to be clear that I am NOT knocking BCM equipment - I understand they are top shelf and have been waiting on a middy upper for a long time and would also snatch up one of their BCG's in a heartbeat if they were in stock. Having said that, I don't believe they actually machine the uppers, right? So they get them from somewhere - maybe same place other manufacturers get them from. My understanding of what makes BCM top shelf is the mil-spec grade barrel steel, HP & MP testing, park under FSB and "F" marked FSB as well as the M4 feed ramps in barrel and upper. These features are highly sought after and rightfully so, but at the same time one would be foolish to think that whoever supplies them, or LMT or Noveske or whoever with uppers are the only vendors of uppers who machine them with CNC machining centers. Most likely the vendor of lowers and uppers who actually do the machining are doing them on CNC machining centers and run the same CNC program to machine them. It would be silly to think that a company would have a "top shelf" CNC program for uppers / lowers that made the parts to the middle of spec tolerances for a few select retailers and then had a "low shelf" CNC program that they ran while machining all other uppers / lowers for other retailers. It is likely that some retailers would submit their own "tighter" than normal specs for items. That would probably demand a higher cost of product due to quality checks to sort out the best ones from all the rest - but all vendors who machine parts to a print SHOULD be making them to be "in spec" as per the part print. That is not to say that all do and one would have to think there are some companies out there who send out of spec parts out the door, most likely those companies with a known reputation for junk.
The take down pin hole locations have a spec for both the upper and lower - I would expect that a combination of a lower with the hole locations on the bottom side of the spec (say lower toward the trigger housing) and an upper with the hole locations on the higher side of the spec (say higher toward the chamber) would result in a tight fitting upper / lower combo and vice verse - all while the individual components being within print spec. Hence why some uppers would fit on some lowers tight and some lowers loose. Tolerance stack-up.
I was just wanting to get your all's (this picky bunch) opinion of fitment between upper / lower on a rifle. I guess I won't worry about it any more and just shoot them :D
I would like to find a print of an upper though for my records. I am building 3 identical rifles for me and my 2 boys and am keeping detailed records that I can hand down to them at some point. I have measured and recorded print details on the lowers and would like to do the same on the uppers if possible.
Thanks guys.
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I wish that were the case ...
I have an upper from a left-of-chart maker that will not fit on a lower from a right-of-chart maker. The distance between the pivot and takedown pin holes on the upper is shorter than the distance between those holes in the lower. Tolerance stacking, probably. Problem is, I really want to use THAT upper on THAT lower. Yes, I could bodge the holes on the upper to loosen them so they would fit, but I'm not inclined to mess with the gunsmithing from a well-known and highly-respected builder. Hopefully I won't have the same problem with the BCM upper that I will purchase (if I ever get a chance to).
I have a couple of extra pivot and takedown pins and I'm trying to figure out a way to grind one of them so it's a few thousandths smaller in the x-axis but still the same size in the y-axis (basically, make the pin a little bit oval) to see if that will work. Of course I'd have to change the pin anytime I change upper receivers, but I'd rather do that than mess with a pretty pricey upper. If I completely screw up a $5.00 pin, who cares?
Wow. Sounds like you're fighting an OLY receiver. Oly's the only one I've heard of that actually won't work with in spec parts. Some receivers fit poorly, but Oly is the only one I've seen that completely WON'T WORK at all.
Medicine Calf
03-17-09, 15:26
I like to grab my BCM/LMT by the pistol grip and make the upper rattle. I like to think of it as my PRY (pitch, roll, yaw) because it is loose in all three axes. It is a solid 2 moa shooter at 100 yd. with XM193, and is my No.1 AR.
exkc135driver
03-17-09, 15:49
Wow. Sounds like you're fighting an OLY receiver. Oly's the only one I've heard of that actually won't work with in spec parts. Some receivers fit poorly, but Oly is the only one I've seen that completely WON'T WORK at all.
Damn, you're good.:D
Yes, it is an Oly (SGW actually, but that's a distinction without a difference). I bought it many years ago and unfortunately cannot replace it. It fits Oly uppers fine, and my Oly uppers fit everything else fine. Guess I need to buy an Oly upper :mad: and make what I want. I'm going to try a modified pin first, though.
I have other this-upper-won't-fit-that-lower problems, but that one is the one that gripes me, because I bought the upper in question specifically so that it could be used with a lower from the same maker as the upper as well as with the SGW lower. Oh well.
I sure as Hell hope the new "grand" BCM middy that is on it's way to me right now does not have a crappy fit as mentioned above.
I pay top dollar for top drawer equipment, not some unit that is sloppy as an old whore!! I don't give a damn if loose rattling is considering "OK" and "cool"......I expect something a bit better out of a "top tier" unit.
Maybe my new upper will be "just enough out of spec. to the norm" to where it fits decently tight. I guess I just expected a bit more.
I will happily give you what you paid for your loose BCM Middy.
I sure as Hell hope the new "grand" BCM middy that is on it's way to me right now does not have a crappy fit as mentioned above.
I pay top dollar for top drawer equipment, not some unit that is sloppy as an old whore!! I don't give a damn if loose rattling is considering "OK" and "cool"......I expect something a bit better out of a "top tier" unit.
Maybe my new upper will be "just enough out of spec. to the norm" to where it fits decently tight. I guess I just expected a bit more.
this all depends on your lower. I put one on a RRA lower and fit was tight, LMT lower not as tight...same goes for my LMT lower with LMT upper, not a tight fit, but not extremely loose either.
quiksilverz71
03-17-09, 20:08
Got my BCM today and tried it on my Bushmaster lower. It fit great and wasnt loose at all
SecretAgentMan
03-17-09, 20:11
The two BCM mid-length uppers that I obtained a couple of months ago fit very tight on my Tactical Innovations billet lower receivers and very loose on my Tactical Innovations forged lower receivers (CMT lower parts kits fit extremely well in both the billet and forged lowers). Seeing as how I've handled Colts that rattled worse but grouped nicely, I'm not too worried about it. Plus the forged lower receivers have a tensioning screw, though I probably won't use it.
I was disappointed with the play in my BCM also. It doesn't feel near as solid as my Sabres.
These are all just tolerence issues. I have a Sabre upper and an LMT lower and I think most people would agree those are good, quality components. They have the loosest fit of any of my 4 AR's.
Another rifle with a Sabre barrel, CMT upper and a RRA lower were so snug I thought I'd never get them apart again.
I'm sure all the parts are in spec (I am assuming) but mate together two at opposite ends of the range, you get slop. Both at the same end of the range, it's tight.
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