AR Sponsor
Posted: 4/14/2008 9:08:57 AM EDT
|
I have a DPMS AP4 that I have set up as precision rig. This past week I attended a LE marksman observer class with it and it was going well until the 4th day. My groups started going all over. The scope mounts were loose and were retorqued and it still wouldn't hold point of aim. I finished up the class with a Remington 700 LTR. Yesterday I mounted a different scope and confirmed that the scope had let go as the new scope was holding point of aim, but the group size was much bigger than before. A 10 shot group was over 4 inches and up until the 4th day of class I was going head to head with the bolt guns. The barrel has just a tad over 3100 rounds through it. I will give it a very good cleaning before I pass judgement, but shouldn't a barrel last more than 3K rounds? To make sure I wasn't having a bad day, I shot the LTR and my XCR for groups at 100 as well and the LTR was spot on and my XCR shot a tighter group than the DPMS using wolf ammo and a clone magnifier so I don't think it was my shooting. Any thoughts or things to look at? |
|
All Fed 168 match from the same case. It did not get hot as things started going south at night fire. When I rezeroed the next day and checked things out it was 35 and overcast. Both times ammo was around 35 degrees with no sun. Today when I re shot it was 38 so temps were pretty consistent between all tests. |
|
A scope going South on you isn’t any fun. However, several things can cause problems with your opening groups. Some people don’t understand that you can clean a barrel TOO much! Then there is the ammo used that can cause premature barrel ware and lest but not last corrosive primers. I have cycled over 3,000 rds of ammo (1,500 of steel cased Wolf Ammo) without any problems with my AR-7.62x39. I treated my AR just after the 1st 500 rounds with Microlon and have not used any oils or lubes for the remaining 2,500 rounds. Microlon has been known to solve and/or improve on this problem in firearms and I have seen this myself in two weapons treated. You can read more from the Microlon Link about the products available for your weapons and how to use them. Another thing to consider is the weather and the temps you are shooting in. I spent 2 ½ years in the Arctic of Alaska as one of the LE Officers. I have seen weapon failures from the cold temps alone. Years ago a Partner had the chance to shoot the 1st indoor range designed to give “FULL” shooting conditions. My Partner was one of the top 5 shooters taken from the 1st string under normal conditions. The Range Officer then gave them a sunset scenario with the light in their eyes. He was the only one of the 5 that hit his B-27 and that was at the upper edge and a total miss! This got the classes attention and then the real training began. I hope that this info will help! ArticWolf |
|
We punched the bores every 20 to 40 rounds. That's why I am going to give it a real good, detailed cleaning and shoot it again before calling DPMS and seeing what they say. The instructers all thought that 10K should be reasonable for barrel life as well. I am pretty consistent in my cleaning of the rifle. I clean the chamber first and then I run a brush with solvent through it 3 times and then a bore snake 5 times. It gets lubed the same every time and then back in the case. I maintained this practice through the class and all was good. It was in the lower 70's the first day when we zeroed, 50's the next, and then high 30's or 40's. The gun was consistent through all temp ranges and during the problems and troubleshooting between 35 and 40. I've shot it colder so I don't think temp is a huge concern from my records. The only ammo that has been through the gun is wolf 150 grain and Fed GM match, both copper jacketed bullets. The barrel is mounted with a JP free float handguard and there is no sign that the barrel/tube nut has backed off. As I was typing this statement, I figured I would pull the handguard to make sure. There was the problem, the barrel nut was loose as in not even finger tight. At least the problem has been found. I'll have to order a wrench for the nut and re torque it. |
|
When you are finsished with the shoot and are back home. Take off the barrel clean the threads and nut well. Blue Loctite the barrel nut back on. That will take care of any issues in the future but still allow it to be removed without to much difficulty when needed. The normal tighten and loosen a couple of times and tighten down and alight on the 3 rd. did you get to shoot at LR distances? 1K? If so how did the 260 do? |
|
It should be an easy fix. JP hasn't emailed me back yet as to what wrench best fits their nut. I would imagine the nut wasn't properly torqued for most of the class and it was still shooting very well up until the end of the third day, so I am pretty optimistic that it will be a tack driver once I get it reset. The other silver lining was that when switching scopes, my other scope was mounted 1/2 inch lower and I got a much tighter, more consistent cheek weld. The original scope went back on in the lower mounts and should help build my consistency in shooting as well. Hopefully I will hear something from JP in the next day or so. |
| If you want to get your barrel nut to index properly without having to apply excessive torque, use a shim between the barrel extension flange and bbl nut. Stainless steel shims 0.001" thick with 1.25" ID and 1.75"OD can be purchased from McMaster Carr online. Use a pair of sharp scissors to trim the shim to about 1 3/8" OD. |
AR Sponsor