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View Full Version : A2 DCM ZERO ISSUES


michael_g927
October 09, 2017, 09:39
I built my A2 at the end of 14. It was a very solid rifle. Threw my 55gr fmj loaded over 25gr of Win748 very respectably. Then about 3 months ago it started having windage issues.when initially zeroed, it was 6L of mechanical zero.
Then i started experiencing windage drifting. So bad that i would nearly run out of sight movement to the left. Then it would be moving the other way. Or i would add 8 clicks and poi would not change, then all of the sudden whammo big change.
Not really elevation, but always windage issues.
Everyone chimed in. Folks blamed the sight. I could clearly see the sight move when i dialed. They pointed at ammo. This phenomenon happened even when using Hornady 68gr match loaded over 25.8gr of 748.
After blaming everything, even my glasses (really had me questioning myself). Last night i took off the handguards and while holding both sights, i could twist the barrel. The index pin would bob back and fourth in the upper index slot.
I have never been so happy! Some how in 7-800 rounds the ole girl settled in and was finger loose.
So after a few minutes of open heart surgery, she is now at 40 foot pounds.
Looking at my notes, the last zero i had was 10 L. So to try to get my zero as close to mechanical zero as possible, i shifted my barrel to the rightside of the index slot.
I will rezero next saturday. Next job will be installing a DCM freefloat tube. Really not looking forward to messing with that front sight.

Mebsuta
October 09, 2017, 10:40
All mine I really needed to crank to get everything lined up. Now I'm glad I did not give in to temptation and buzz off one of the teeth.

michael_g927
October 09, 2017, 15:55
Haha. Now i am tempted to go thru my armory and check every weapon system. The cost to rezero everything makes me not want to mess with it until necessary.

michael_g927
October 10, 2017, 08:15
Ok so i am getting this rifle ready for Camp Perry 2018. I plan to add a DCM free float tube to it.
The official bullet of the Match is the Hornady 68gr match. So i am thinking of swappingvout my A2 upper reciever for a flat top that i can mount a scope on. So basically i am using my barrel and bolt with a scope for load development.
Then once the load is dialed in for that barrel, go back to A2 iron sights.
Any of you guys ever do this?.

MAINER
October 10, 2017, 08:59
Sure, I changed out all my older A1 and A2 uppers to Flattops for scope, red dot or irons as I like.
The only warning here is that the zero changes a bit on the irons and will need to be re-checked after mounting. I don't have a Torque wrench to set the screws, but that would likely be helpful.

I am not a Camp Perry competitor, so it may be that detachable sights are not a great idea, but for gravel pit plinking, it works fine. :smile:

michael_g927
October 10, 2017, 10:57
I just want thrme flattop and scope to dial in my load for that barrel and bolt.after that, i will reassemble the barrel onto the A2 reciever.

hueyville
October 10, 2017, 14:38
Barrel nut at 40 ft/lbs? Your in specs of 30 to 80 ft/lbs according to Gman and his time at LWRC. I was always under the impression supposed to be real close to 50 ft/lbs and most of mine are in the 45 to 55 range as sometimes easier to stop a tad short or go a tad over rather than remove nut and shim to get lined up for gas tube. But his weighing in with god solid specs in a different thread have me thinking more liberally now.

That's from the discussion about barrel extensions where I thought that was a static number of 150 ft/lbs and was again corrected that had a range of 120 to 140 ft/lbs which means most barrel extensions have installed are a whopping 10 ft/lbs over spec. Less than ~2.5% over max is not something going to worry about and go back and loosen any as likely relaxed some over the years and rounds anyway.

15 to 20 ft/lbs on muzzle device rounds out the torque numbers on uppers of which my build data had it a static number of 20 ft/lbs. Its nice to know have some fudge factor in all those values now as making life less complicated on builds.

John Crusher
October 10, 2017, 17:42
I torque 5 times and loosen with torque wrench to 45'lbs.. Then final @ 55'lbs. and never had one shake loose. Build it right once .

Steggo
October 10, 2017, 18:57
Ok so i am getting this rifle ready for Camp Perry 2018. I plan to add a DCM free float tube to it.
The official bullet of the Match is the Hornady 68gr match. So i am thinking of swappingvout my A2 upper reciever for a flat top that i can mount a scope on. So basically i am using my barrel and bolt with a scope for load development.
Then once the load is dialed in for that barrel, go back to A2 iron sights.
Any of you guys ever do this?.

Nope. You are kind of wasting your time and focusing on the wrong thing.

The 223 loads for highpower rifle were developed ~20 years ago and have not changed much. You are not going to discover anything new by doing a load development project. The 68 gr bullet is not optimal but if you want to use it, just drop 24 gr. of WW 748 into the case, call it done and head to the range to practice shooting offhand with your A2 rifle. That will produce more improvement in your scores than gutting the rifle in a quest to re invent the wheel.

nvcdl
October 11, 2017, 19:00
Maybe front site is moving under recoil?

michael_g927
October 15, 2017, 17:03
Steggo. If asking the DCM what bullet is most commonly used at Perry, then calling that bullet manufacturers staff of balisticians for load data is "trying to reinvent the wheel", because there have been no improvements in this millennium, id say inly part of your post is valid.
And another side note. Anyone that just accepts load data as "the holy grail, just because its been used for 20 years" without further testing in THEIR rifle, is someone whos advice is quickly disciunted.