GRA Posted June 7, 2015 Report Share Posted June 7, 2015 98 is correct, there is no difference between low and high with regard to triggers, that refers to the rail height (at least I have never seen any indication of there being a difference in triggers in anything I have read or heard). I've most likely had this misunderstood. I guess the high vs low is the measurement from the very top of the rail down to the bottom of the channel for the charging handle. Good point made about the design of the BCG and the new Geissele. I'll keep that in mind. I've never used a Geissele but can't say I won't in the future. I never made it to the gunshot today to check out some BCG(s) and take measurements. Hopefully I'll make it there tomorrow (Sunday). Quote Link to comment Share on other sites More sharing options...
GRA Posted June 7, 2015 Report Share Posted June 7, 2015 (edited) Bob ... I made it to the gun show today. Place was full. Out of everything being sold there I only found 2 JP BCG(s), 1 DPMS .308 buffer and no other buffer parts. I only counted 6 finished rifles there, 1 Armalite DEF10 and the rest were RRA and DPMS .308(s). Nothing else except ammo and plenty of AR15(s) and AR15 parts. One vendor that has actually received some Spike's .308 lowers in actually pulled them from their display because the were absolutely bare and still cannot get the Spike's lower parts kits in and other related parts. Either the .308 is not yet that popular here, or they are extremely popular and nobody can keep parts on the shelf. I took measurements from the JP low-friction BCG with my digital calipers. I hope I hit the same areas you measured previously: Under the gas key: 1.0680 diameter (this is right under the tip of the gas key where it slides over the gas tube, top to bottom) Bolt carrier area / front of carrier (where the bolt enters): 0.9470" Ramp length: 3.2510" All measurements were in inches. I don't know if this did any good, but that's what I got. They were selling nickel-boron bolts in these teflon-coated bolt carriers for $459.00 each. Edited June 7, 2015 by GRA Quote Link to comment Share on other sites More sharing options...
98Z5V Posted June 7, 2015 Report Share Posted June 7, 2015 Ramp length: 3.2510" Bad meaasurement. That's the length of the entire underside of the BCG. Quote Link to comment Share on other sites More sharing options...
geistacwm Posted June 8, 2015 Report Share Posted June 8, 2015 I was under the impression these were rebranded PSA sets. Considering the Shot show tease of seekins designed billet rifles, I was fn bummed. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 8, 2015 Author Report Share Posted June 8, 2015 I will remeasure with pictures (for AIM) when I get a chance, probably the middle of the week. I don't know about rebranded PSA parts. I do know that Seekins did NOT manufacture these (I asked Seekins). None of the parts has shown up on the Spikes Tactical website as yet; however, they did send me the "non-standard" parts (takedown and pivot pins, bolt catch) and the bolt catch is secured by a roll pin rather than a screw (as is typical with DPMS style setups). My upper and lower were pristine, smooth and without any machining marks or other imperfections and they fit together perfectly, without any gaps, even though the upper and lower were purchased from different suppliers. Combined with the Faxon barrel it appears to be a very accurate weapon, even given the lack of fine trigger control I have with my left hand and the stock trigger that is currently installed. At this point I am happy (except for the trigger situation) as this was my first complete build (having just replaced about 75% of my Mossberg MMR (AR-15). My only question is the AIM BCG because of the binding with the Geissele trigger installed. With the stock trigger; however, it ran like a champ. No unusual extractor/ejector marks on the cases and all of the cases ended up within a few feet of each other so it may be that the lower is a few thousandths of an inch less in the dimension from the bottom of the fire control well and the rim - who knows but I am still investigating (an engineer's curse!). Quote Link to comment Share on other sites More sharing options...
GRA Posted June 8, 2015 Report Share Posted June 8, 2015 I am going to the vendor's shop this week to get my buffer spring and this should complete my parts. All I'll need is simple assembly thereafter. I got the impression from them that they have more brands of BCG(s) there than they brought to the gun show. I will bring my calipers again and will be happy to measure whatever they may have then post it on here. I probably will not be able to do photos. From what I can tell at this point, it is obvious there is some difference between our AIM BCG(s) and the JP low-mass BCG I measured today. I'm sure the same goes for others. I am not an engineer so if you want me to take measurements other than what I have taken above please let me know. Quote Link to comment Share on other sites More sharing options...
FaRKle! Posted June 8, 2015 Report Share Posted June 8, 2015 I got the impression from them that they have more brands of BCG(s) there than they brought to the gun show. I will bring my calipers again and will be happy to measure whatever they may have then post it on here. I probably will not be able to do photos. From what I can tell at this point, it is obvious there is some difference between our AIM BCG(s) and the JP low-mass BCG I measured today. I'm sure the same goes for others. I am not an engineer so if you want me to take measurements other than what I have taken above please let me know.Sounds like you'll get some awesome data! That'd be a super nice table to have with what brand of BCGs there are and what the measurements of different areas are! One important measurement is from the front of the carrier to where the shoulder of the carrier ends (the diameter goes down for the tail section), or rather from where the tail/end of the BCG is to the shoulder. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 8, 2015 Author Report Share Posted June 8, 2015 GRA - see the drawing. BCG Measurements.pdf Quote Link to comment Share on other sites More sharing options...
planeflyer21 Posted June 8, 2015 Report Share Posted June 8, 2015 Hunh...all I see are measurements A, B, C, D, Etc with no dimensions given. Quote Link to comment Share on other sites More sharing options...
FaRKle! Posted June 8, 2015 Report Share Posted June 8, 2015 I think it was to mark what to measure. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 8, 2015 Author Report Share Posted June 8, 2015 (edited) Correct FaRKle!. I was rushing out the door to a meeting and was just trying to indicate to GRA where to measure. In fact, if everyone would measure their BCGs to get these 4 measurements we could have a really good idea of how much variance there is in the industry and some idea of which one we might want to use for a particular build based on the other accessories we might want to have. So if you want to join in, list your BCG brand; measurement A (depth of the BCG body at the front of the gas key); B (depth of the BCG body plus the depth of the gas key); C (distance from shoulder of the underside to the firing pin well); and D distance from the front of the BCG body to the shoulder). By shoulder I am referring to the point where the BCG underside begins to slope back to the firing pin well. See the PDF file a couple of posts ago for a picture. Edited June 8, 2015 by EngrBob Quote Link to comment Share on other sites More sharing options...
98Z5V Posted June 9, 2015 Report Share Posted June 9, 2015 Post # 63, 67, 68, and 69 show what we were measuring, during the initial comparisons between his BCG and my Fulton BCG. They're pictures, so it should be pretty clear what we were comparing between the two. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 9, 2015 Author Report Share Posted June 9, 2015 98, assuming front to firing pin well is 3.25"on yours I will put Fulton into the spreadsheet. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted June 9, 2015 Report Share Posted June 9, 2015 Front to firing pin well, along the bottom, was 3.250" on the Fulton. Square area (the flat) on the bottom was 2.00" on the Fulton. I think you measured the flat as 2.250" on yours, which led into the deduction that the ramp angles had to be different. Shorter flat = longer, shallower ramp area. Longer flat = shorter, steeper ramp area. No other way it can be, with those measurements, and 3.250" being the common overall length. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 9, 2015 Author Report Share Posted June 9, 2015 (edited) OK, I think it was 2.019" front to shoulder so that leaves 1.231" shoulder to firing pin well, 0.936" depth forward of gas key and 1.190" depth over gas key base. The Fulton is in the spreadsheet. Edited June 9, 2015 by EngrBob Quote Link to comment Share on other sites More sharing options...
GRA Posted June 9, 2015 Report Share Posted June 9, 2015 Rough weekend carried over today in to what turned out to be a rough day. Hopefully I'll have time to get by there tomorrow and enough time once I get there to take measurements. My job location and the vendor are at opposite ends of Houston which is murder in late afternoon traffic. I'll try the spreadsheet program on this new Apple comp. and print one up before I go so I can organize the measurements. Thanks Bob for the .pdf as it will help out. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 11, 2015 Author Report Share Posted June 11, 2015 OK, an update. Today, quite unexpectedly, my MechArmor trigger arrived. I installed it and.........the rifle cocks perfectly with no hint of binding. Apparently it is just the Geissele setup and the stiffness of the hammer that is the problem. By the way, what a sweet trigger. Very light pull and very clean break. I can't wait to get this out on the range. Quote Link to comment Share on other sites More sharing options...
GRA Posted June 11, 2015 Report Share Posted June 11, 2015 OK, an update. Today, quite unexpectedly, my MechArmor trigger arrived. I installed it and.........the rifle cocks perfectly with no hint of binding. Apparently it is just the Geissele setup and the stiffness of the hammer that is the problem. By the way, what a sweet trigger. Very light pull and very clean break. I can't wait to get this out on the range. Which model of trigger did you buy? Trigger pull weight? Quote Link to comment Share on other sites More sharing options...
GRA Posted June 11, 2015 Report Share Posted June 11, 2015 I'm still getting off work too late to get over to that shop in time. Maybe I'll be able to get there Friday. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 11, 2015 Author Report Share Posted June 11, 2015 They only sell one trigger - 3 lb. pull with no extra travel - very nice. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 12, 2015 Author Report Share Posted June 12, 2015 (edited) After long discussions with AIM and comparisons with the depth of their BCG units that they have on hand, we have agreed that the best thing to do is for me to ship mine back and they will swap it out for a new one. While the MechArmor drop in clears, the 0.015" to 0.020" difference in depth from what they were measuring on in stock units is just too much for comfort and probably why the unit is so tight when putting it in or taking it out of the upper. It certainly looks as if AIM will do the right thing and certainly stay on my list of favorite suppliers. <thumbsup> Edited June 12, 2015 by EngrBob Quote Link to comment Share on other sites More sharing options...
GRA Posted June 12, 2015 Report Share Posted June 12, 2015 Glad to hear this is turning out as needed. Anxious to see the specs on the new BCG when it arrives. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 13, 2015 Author Report Share Posted June 13, 2015 I do have the measurements that the AIM staff gave me, depths of the carrier in front of the gas key ranging from 0.930" to 0.9335" compared to the 0.950" on the one I had. Those measurements are in the same ballpark as 98's Fulton Armory BCG. I just had a call from Van from MechArmor about the trigger I purchased and I can't wait to get the replacement BCG so I can get it out to the range. It is a very nice trigger and should really help with having to work the trigger with my left hand. Quote Link to comment Share on other sites More sharing options...
GRA Posted June 13, 2015 Report Share Posted June 13, 2015 I'm going to look in to that trigger next gun show. Sounds very impressive. If they do a group purchase here I'm most likely going in on it. Quote Link to comment Share on other sites More sharing options...
EngrBob Posted June 17, 2015 Author Report Share Posted June 17, 2015 OK, the swap out BCG should be here tomorrow so I will try to get to the range on Friday (use some of the 26 hours of comp time I will lose this month) to see how it operates as well as fire test the MechArmor trigger. I will do some measuring while headspacing the new bolt to ensure I have a significantly shallower carrier. The ones they had on hand measured roughly the same as 98's Fulton Armory carrier in depth as well as one or two others whose measurements I have seen on other boards. Quote Link to comment Share on other sites More sharing options...
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