yodamer Posted December 19, 2010 Report Share Posted December 19, 2010 Hello all, I have a DPMS LR308 AP4 and I am baffled about my issues using the iron sights. The rifle is very accurate, but it seems that my rear aperature is too high (and yes, I am using the large 0 - 200 hole). I have to bury the front sight into the bottom 1/4th of the sight picture to get point of aim / point of impact close at 50 yards. Aiming like I should be able to, it hits 6 inches high at 50. I have a bushnell holosight (eotech clone) on it and it does great without using irons. I even try using the dot as a reference point for aligning my front and rear, but it seems the rear sight is too high for practical use with the fixed front A2. I could crank the front post way up above the "wings" to make it up, but that is just silly and I would probably catch the post on something and bend it. Anyone had similar problems?By the way, I have also put other rear sights on and they all seem to be the same height. Quote Link to comment Share on other sites More sharing options...
imschur Posted December 19, 2010 Report Share Posted December 19, 2010 man you got me on this one.....maybe something will click after coffee. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted December 20, 2010 Report Share Posted December 20, 2010 Is there an elevation wheel built into that rear sight? If so, what's it set on?Also, don't use the large aperature for zeroing, or any kind of precision work. Use the small peep sight on there for anything with accuracy in mind. Quote Link to comment Share on other sites More sharing options...
yodamer Posted December 20, 2010 Author Report Share Posted December 20, 2010 it is the DPMS A2 style adjustable rear sight (freestanding, not part of a carry handle) and I have it bottomed out. Using the small peep probably wont help me because it is on a different focal plane for distances past 200, and would just make it seem worse. I also have a fancy pants A.R.M.S. flip rear and the results are the same. The newer AP4's come with a carry handle setup, and mine has the older freestanding sight. This makes me wonder if the reciever height is too high and that's why they later changed specs. Would .06" make that much of a difference on my sighting? Can I get a taller gas block A2? Is there any other factors that could weigh in on this? Quote Link to comment Share on other sites More sharing options...
J.Boyette Posted December 20, 2010 Report Share Posted December 20, 2010 Ok, Three things.1. Is the front sight "F" marked?2. Do you use a 6 O'clock hold or center mass at 50yds? 3. Take a picture of the rear and front sight please. I got to see your setup and I might be able to help. Quote Link to comment Share on other sites More sharing options...
yodamer Posted December 21, 2010 Author Report Share Posted December 21, 2010 1. Is the front sight "F" marked?2. Do you use a 6 O'clock hold or center mass at 50yds? 3. Take a picture of the rear and front sight please.1. The sight has markings, but I cant tell what they are.2. I am forced to do a harsh 6 O'clock hold or jack my sight post way up above the "wings" on the front sight.3. Quote Link to comment Share on other sites More sharing options...
J.Boyette Posted December 21, 2010 Report Share Posted December 21, 2010 I could be wrong but I would say you need a F front sight base. The one you have now is not the correct front sight tower. The diff is how deep the front sight post sits. The F marked tower was made to lower the front sight deeper in the body. This gave the shooter the ability to adjust for the height more and still be inside the housing. I would just order one and put it on. Quote Link to comment Share on other sites More sharing options...
yodamer Posted December 21, 2010 Author Report Share Posted December 21, 2010 I could be wrong but I would say you need a F front sight base. The one you have now is not the correct front sight tower. The diff is how deep the front sight post sits. The F marked tower was made to lower the front sight deeper in the body. This gave the shooter the ability to adjust for the height more and still be inside the housing. I would just order one and put it on.thanks, I'll do some research on it. <thumbsup> Quote Link to comment Share on other sites More sharing options...
98Z5V Posted December 21, 2010 Report Share Posted December 21, 2010 There's a 0.040" difference (40-thou) in the F marked front sight base and the standard front sight base. You can make that difference up easily in front sight post adjustment with a standard base. It's not a big deal, and the adjustment is there in a standard base. If it's a concern that can't be lived with, then Bushmaster sells a front sight post that's taller, that you can use in a standard base, just so you don't have the base of the sight post cranked up as far.From what you're describing, I don't think that's the issue here - F marked or standard bases. Something else is going on, besides that. You still don't need to be using the large aperature to zero the weapon. That's a given. The small aperature should definitely not be on a different focal plane, as you're saying. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 1, 2011 Report Share Posted January 1, 2011 It just may be my old eye's , but look at the third photo down . The gap between the charging handle & the lower receiver , where the receiver extension attaches or screws in ,is kinda wide or large. Is the upper receiver & lower mated correctly , meaning , in that photo, is the disassembly pin in its proper place for final assembly ? It looks like it is . Both of mine (charging handles )are just barely clearing the the lower receiver ring where the extension or buffer tube screws into .Could be just me . Quote Link to comment Share on other sites More sharing options...
yodamer Posted January 1, 2011 Author Report Share Posted January 1, 2011 It just may be my old eye's , but look at the third photo down . The gap between the charging handle & the lower receiver , where the receiver extension attaches or screws in ,is kinda wide or large. Is the upper receiver & lower mated correctly , meaning , in that photo, is the disassembly pin in its proper place for final assembly ? It looks like it is . Both of mine (charging handles )are just barely clearing the the lower receiver ring where the extension or buffer tube screws into .Could be just me . It was bought new as a complete rifle, both halfs are DPMS. It does have a slight hairline gap there but the photo shadowing makes it look worse. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 1, 2011 Report Share Posted January 1, 2011 Ya , my bad ,I had my 16" ,with CMMG lower with a SI Defence billet upper , next to me taking measurements and I thought it was the same as the DPMS . Its not ,the DPMS upper & or lower are diff..I'm going to have to take some side by side photo's so you can see why I thought ,what I thought ,I saw. Quote Link to comment Share on other sites More sharing options...
imschur Posted January 1, 2011 Report Share Posted January 1, 2011 How about a picture of the rifle on it's side so we can see the entire weapon. Take the EoTech off and leave the rear site up. Maybe also the same picture with the entire rifle minus the buttstock Quote Link to comment Share on other sites More sharing options...
imschur Posted January 1, 2011 Report Share Posted January 1, 2011 Do you have a front sight to mount on the picatinney to compare heights? Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 2, 2011 Report Share Posted January 2, 2011 Do you have a front sight to mount on the picatinney to compare heights?Ya , see if can barrow some ones BUIS front sight & put it on the rail & try that . I would just get a railed gas block & same manufactures BUIS(one that's made for a railed gas block) & it should work out .Barrow one first ,to make sure there is not something else wrong with the rifle.Actually , this is a common problem when the wrong sights are mix matched . As said M4 flat top upper & std. front sight off and A2 . Quote Link to comment Share on other sites More sharing options...
yodamer Posted January 3, 2011 Author Report Share Posted January 3, 2011 I bought the railed handgaurd and had it put on, you can see that the rail is lower than the one on my receiver. I'm not opposed to a flip front buis and a different gas block if it will solve my problem. I just hope the difference in height between the two rails doesn't affect much. Quote Link to comment Share on other sites More sharing options...
imschur Posted January 3, 2011 Report Share Posted January 3, 2011 I think we can add you to the people pissed at DPMS for changing the rail height on the uppers. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 3, 2011 Report Share Posted January 3, 2011 I think the newer rail height of the DPMS uppers is lower than the std. railed upper . In your photo ,the rail of the hand guard looks lower.Is it just me ? Who made the FF hand guard?This could be ,if , you have a older std. upper & put a newer DPMS FF rail on , that matches the new rail height .You can solve it by using the DPMS BUIS system .They should match up . The railed gas block, front sight & rear sight.Take measurements as stated below & you will know what receiver you have .--------------------------------------------------------------------------------Info straight from DPMS:Our AR15 receivers are all the same height except the High Rider and Tri-Mount. The LR308 Platform has two heights, the A3 and Lo-Pro Raised Rail. The A3 was changed recently to better accommodate our other components. I guess in reality, with the number sold before the change, there are now 3 heights. To find out if you have a newer model or older run, the easiest way to measure is with a caliper from the bottom surface that mates to the lower to the top of the rail. The new versions measure 2.003 and the old versions are 2.063. Any larger receiver rail to handguard rail height difference would be due to the lack of an industry standard in the large frame AR style rifles. Everybody is still pretty much making their own thing and some measurements just don't line up between manufacturers Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 3, 2011 Report Share Posted January 3, 2011 the last statement from them is laughable :Any larger receiver rail to handguard rail height difference would be due to the lack of an industry standard in the large frame AR style rifles. Everybody is still pretty much making their own thing and some measurements just don't line up between manufacturersNo DPMS , its not that there is no industry standard , its you, who changed your rail height differently from industry standard ! Quote Link to comment Share on other sites More sharing options...
yodamer Posted January 4, 2011 Author Report Share Posted January 4, 2011 I need to measure, but I'm positive I have the old receiver height and a newer free float rail. Both are DPMS. I bought the rifle less than a year ago, but I think it was old stock because it had the A2 rear sight instead of a carry handle A2. When I bought the handguard the newer rifles had been out for a while. Quote Link to comment Share on other sites More sharing options...
yodamer Posted January 11, 2011 Author Report Share Posted January 11, 2011 I measured and it is an older height upper for sure. I still can't understand how .05" would make much difference. Not the end of the world. I have the rfile zeroed at 50 with my post higher than the wings. I might buy a new upper to match the handguard rail height, put on a different gas block and put matching front and rear buis on it. I can use the removed upper on that .243 build I have been contemplating. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 11, 2011 Report Share Posted January 11, 2011 You might find some may want to swap out uppers receivers with you or you may find a good intrest if you want to sell your older standard DPMS upper.Not sure which is less expensive ,changing hand guards or upper receivers .Definitely changing hand guards is the easier way to go, as far as what has to be done . You have a larger selection of hand guards that fit the old std. uppers . Quote Link to comment Share on other sites More sharing options...
epilogue Posted October 7, 2011 Report Share Posted October 7, 2011 Just got mine back from DPMS for the same problem (month turn around, not bad). The gunsmith swapped out the Old style A3 upper (high) for their newer low profile A3 and installed an extended front sight post. It does shoot point of aim/impact at 25 yds without having to hold extremely low. Now the front sight post extends higher than the front sight bases protective ears, which I fear could bend. Also, after looking at the new A3 upper, I noticed that its between the listed spec size (top of charging handle opening to the top of the receiver) of the older LR308 AP4 upper and the new low profile Upper. So its anyones guess who makes a rail system that will mate up, but I can't complain ;D Quote Link to comment Share on other sites More sharing options...
yodamer Posted October 7, 2011 Author Report Share Posted October 7, 2011 wow, didn't expect a reply on this one! (old thread)I actually bought a DPMS .243 upper since my last post, and it is the newer (lower) height receiver. I planned on taking off the standard free float tube to put on a vtac tube anyway, so I decided I'm going to swap receivers / barrels around while I'm doing it. Putting the lower height upper receiver mated with the AP4 barrel and lower height handgaurd should work out fine. My .243 setup will be sporting a scope at all times, so the height difference won't matter to me anyway. Thanks! Quote Link to comment Share on other sites More sharing options...
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