I bought a used GDMR upper a couple of months ago. I built a lower using a stripped AA Grendel lower, PRS stock, Timney trigger etc. Threw on a cheaper Leapers 4-16 x 50 scope. Took the build to my range and was not impressed. Windage was good but elevation wandered about 1 1/2" in a 5 shot group. Bought a used Nikon Monarch 8-32 x 50 and went back to the range with 123 Lapua Scenar. Best group was about an inch. I have a 16" Grendel that shoots better groups at 100 yrds. I understand that the GDMR is for MUCH greater distances (twist rate for 200+) but thought that it would perform better at closer range. Thinking maybe the heavier bullets don't stabilize yet at 100? Would the 100 Berger perform better?
Added pictures of the two rifles
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Might require some load workup and / or different factory ammo to learn what a particular barrel shoots well. Even the best of barrels will not shoot to its potential if not fed what it likes, and not all barrels will prefer the same diet.
That being said, have you tried Hornady factory 123gr A-max? It usually does reasonably well in a broad spectrum of barrels.
Drifter
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I've had two GDMR's, and both have shot groups well under 1/2" without issue. Along with the Amax, you might want to try 100 and 120 grain Ballistic Tips and 120 Sierras. At least one of those 4 bullets seem to shoot well in everything.
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I tried the Hornady AMax yesterday after the Lapua scenar. Comparable but the Scenar had slightly tighter groups. My 16" loves the AMax. I don't load my own ammo, but I have a guy that will load for me. He has made me some amazing acurate ammo in other calibers (Black Dog Ammo Tannersville, Pa.). I was going to go to Alexander Arms web site and order a variety. Also I plan on swapping optics between the 16 and GDMR. I have been having reliability issues with Monarch scopes. As a side note; the guy I bought the upper from told me the upper likes Lapua Scenar Varget 27.8 28.4 grains. Not sure how hot Lapua loads their rounds.
Actually; I was just looking at the reloading instructions from the AA web site and the factory 123 Lapua Scenar doesn't show how much powder, but velocity is 220 fps faster than the 28.5 gr Varget. So, I guess it is a hotter load.
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why2dogs Wrote:Threw on a cheaper Leapers 4-16 x 50 scope. Took the build to my range and was not impressed. Windage was good but elevation wandered about 1 1/2" in a 5 shot group. Bought a used Nikon Monarch 8-32 x 50 and went back to the range with 123 Lapua Scenar. Best group was about an inch. I have a 16" Grendel that shoots better groups at 100 yrds. I understand that the GDMR is for MUCH greater distances (twist rate for 200+) but thought that it would perform better at closer range. Thinking maybe the heavier bullets don't stabilize yet at 100? Would the 100 Berger perform better?
W2D:
You mean the Leapers scope didn't work? He, he, he.
As for the Nikon Monarch, it too has problems with durability. Have you checked that it will hold zero? After all, you bought it used.
And, the upper is also used.
Finally, unless you shot four or five each, five shot groups, and are confident in your shot calls, you probably can't claim something is wrong with the upper.
This is the first time I have heard anyone say a twist rate isn't good for distances under a specified number of yards. If you have a twist rate problem, it is because you are using a bullet that is too long for the twist rate. If you have a 1/9 or 1/10 turn twist on the GDMR and you are shooting the long 140's, then maybe. I doubt you have such a twist rate on the GDMR.
So, get some decent optics and shoot a few groups with good calls. Try some 120 Sierra Match Kings with 29 or 30 grains of 2520. If the upper won't shoot a 120 Sierra, most likely the barrel sucks and won't shoot anything well.
LR1955
Yes, imagine my shock that the Leapers didn't hold. Believe me; I didn't buy the scope for this project. I didn't have anything to put on it to try, so I pulled the scope out of the back of my safe. I thought Nikon Monarchs were a really nice scope for the money. I'm finding that they don't care much for recoil. They DO have a no fault lifetime warranty, but what's it worth if you have to keep sending scopes back to California for repair. I have since installed enedyne buffers in all my AR platforms in an effort to keep optics happy. I have a 5-20 x 44 Monarch that holds zero (Holds zero now because it too was sent back to Nikon for repair) on my DPMS SASS. I'll swap them out and head back to the range. If the GDMR checks out, I'll be looking into premium optics. Thanks for the advice.
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When my accuracy shows any hint of falling off, it's usually a simple indication that the barrel needs cleaning. It can vary by barrel, but some powders and bullets don't play well with others. Thus, you might try a good thorough cleaning, removing all copper and carbon, then try the A-max factory again, with the realization that it might take a few shots to find its groove. Just a thought...
Drifter
Hi Drifter. I always clean my guns after each use. I dap a brush in Hoppes 9 run it down the pipe and then dry patch, then wet patches with Hoppes until they come out clean, then dry patches. Would you reccomend another solvent/method? Looking to get a bore snake for this caliber.
why2dogs Wrote:Hi Drifter. I always clean my guns after each use. I dap a brush in Hoppes 9 run it down the pipe and then dry patch, then wet patches with Hoppes until they come out clean, then dry patches. Would you reccomend another solvent/method? Looking to get a bore snake for this caliber.
The bore snakes are great are great for gatting the carbon out. The only thing I would do different is maybe a little oil in bore after solvent and dry patces, just to inhibit any rust.
Question to all. The scope I am using has a 1" tube diameter. The Larue mount is a 30mm bore. I am using GG&G ring adapters. Has anyone had issues with repeatability using ring adapters?
Hello Drifter. I was finally able to return to the range yesterday. Last range session I felt like I was straining a bit for good eye relief. So, last week I moved the mount back and slid the scope back in the mount. Feels much better. Had some " interesting" groups yesterday. After 2 5 round patterns, the grouping started getting tighter and tighter. First group was on a 12" plate. First shot was at least 4" high and left on windage. Each shot walked closer to the center. Going to attach a couple of JPEGS that I took after shooting. I got off the 2 5 round and then had a jam after the 4th round of my next group. Cleared it and shot one round and another jam. Casing in the breech and would not eject. Took her home and found a broken extractor. Not that that would have any impact on accuracy, but kind of odd. Ordered a replacement and spare from AA yesterday. My shot groups used progressively smaller plates. Second JPEG shows the 5, 4 and 1 shot groups respectively. Let me know what you think? Why do the groups tighten as shot count rises? Do you think cold vs. warm barrel shots? Some fouling "seasons" the barrel? ????
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It's not unusual for a clean bore to require a few fouling shots before it settles in with a particular load. It might take 5 to 15 shots (can vary by each individual barrel). Also, consider cleaning only when accuracy falls off, and not after every range trip.
A cracked and eventually broken extractor can have a negative effect on accuracy. A semi-auto weapon that's not functioning properly each shot (regarding feeding, extraction, ejection, etc) can produce inconsistent results.
Any extractor can break, but it can also be an indicator of hot loads. What ammo was used this time?
Drifter
Started with factory AA Lapua Scenar and then Hornady A-Max. (also factory loads).
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One or both of those should shoot reasonably well. When switching between the two, it might take a few shots to settle in with a particular load.
I suggest leaving your barrel fouled, put in the new extractor when it arrives, then return to the range and see what happens. Start with whichever ammo you stopped with on the previous trip.
Drifter
Sounds like a good plan. I was thinking the same thing. Just sent an email to AA asking if the extractors are in stock and when they may ship. Hopefully I can have the part by the weekend. I finished with the Hornady. I have much more of that than the Lapua anyway. I also have a bunch of Wolf that I really don't like. Shoots like crap in both of my Grendels. Do you think it would be a bad idea to use some of that to foul a clean barrel and then switch to the Hornady after 15 rounds or so?
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why2dogs Wrote:Sounds like a good plan. I was thinking the same thing. Just sent an email to AA asking if the extractors are in stock and when they may ship. Hopefully I can have the part by the weekend. I finished with the Hornady. I have much more of that than the Lapua anyway. I also have a bunch of Wolf that I really don't like. Shoots like crap in both of my Grendels. Do you think it would be a bad idea to use some of that to foul a clean barrel and then switch to the Hornady after 15 rounds or so?
W2D:
If the Wolf is the 123 grain soft point ammo, I would not shoot it unless I pulled the bullet and replaced it with a bullet that I trust will shoot well. Like the 120 Sierra Match King. If it is the Wolf MPT, and it is a recent lot, it should shoot a minute relatively consistently.
LR1955
I rarely clean my barrels...don't believe in it, especially a match barrel with a bore snake. The bore snake can accumulate carbon and other hard particulate matter in the fibers of the rope, which are then dragged through your bore, which is a recipe for increased damage to the bore surfaces.
Copper is a great lubricant for the bullet to ride...carbon, not so much.
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why2dogs Wrote:I also have a bunch of Wolf that I really don't like. Shoots like crap in both of my Grendels. Do you think it would be a bad idea to use some of that to foul a clean barrel and then switch to the Hornady after 15 rounds or so?
I prefer to foul the barrel with the load I intend to focus on. Set the Wolf aside for emergencies.
Drifter
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