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concretus
September 27, 2017, 06:32
Hello,
I just recently purchased a Diamondback DB-10 carbine with a 16" barrel, mid length gas tube, 7" carbine buffer tube, 2.5" long 3.8oz buffer, and C Products 20rnd mag.. It is basically stock except for a Magpul MOE grip and Surefire ProComp brake. I placed an Aimpoint PRO on top of it with Magpul BUIS and took it to the range today to run it for functionality and break it in... I started to break it in with some Magtech 168gr match cartridges; they were doing very well shooting about 1.5 moa and throwing them about 6' at 2:00....Then I tried some 7.62x51mm Hirtenberger Austrian and South African Surplus and then things went south. The spent case was being extracted and ejected; but it seemed like it was short stroking? (if that is the correct term)the bolt wasn't picking up the next round. It did it every time with both types of that ammo. It also did it with 165gr handloads; although it shot those 1moa, it wasn't picking up the next round. I went back to the MagTech ammo to check and everything went fine. Switched back to the surplus ammo and the same issues. I have a few thousand rounds of Hirt, Port, S.A each and just recently some of that Malaysian surplus that just hit the market and I was hoping to use them in this rifle (along with my FAL and PTK91). Is the buffer spring is too heavy? That spring is the stock one which came with the rifle. Do the make lighter springs? I didn't really want to consider an adjustable gas block. I have an Alex Pro 18" mid length with a scope on it I use for hunting. It runs with any ammo I put through it. I did install a JP polished buffer spring in that one....Has anybody encountered anything like this? Any input would be greatly appreciated....Thanks

hueyville
September 27, 2017, 07:18
Adjustible gas block won't increase gas pressure. Use for turning down gas and if standard block it's either getting all the gas it can muster, gas block is not properly aligned with gas port or may need to consider a buffer swap as first and easiest option. If lighter buffer or a different spring like a Tubbs Flatwire doesn't clear it up suggest start looking for a gas obstruction.

MAINER
September 27, 2017, 07:20
I have had similar problems, but not with the same components you have. You're using a Carbine buffer with a mid length gas tube so I would agree with you that you may be over-buffered. I think that the rifle will work better as it is after a more thorough "break-in", but I would be thinking of using an adj. Gas-block for any .308 AR.
Too many variables of bullet weights and differences between factory ammo to be fiddling with Buffers and springs.

concretus
September 29, 2017, 19:26
I had a little break in the action so I went to the range this afternoon. After the other day I:
* Took the bolt out, wiped down, oiled it and reinstalled it.
* Removed the stock buffer spring and installed a DPMS LR308 carbine buffer spring.
* I used a 10 Pmag I use for my Alex Pro 18" hunting rifle.

I had a box of Armscorp 308 147gr ball, 1 box of Privi yellow box M80, and 1 box of Portuguese FMN surplus. I ran 1/2 a box of the first two and everything worked fine. BTW the Armscorp shot moa the first five rounds. there was a nice 10 shot wad just under 2". The Privi was not as accurate or consistent. The main thing is that the spent cases were ejecting about 6' away at 3:00....A good sign.... Then I loaded 10 rounds of the Port surplus, crossed my fingers and threw some lead down range...Not one FTF or FTE!!!! Throwing them out in the same location. The point of impact was lower than the other two but grouping like the Armscorp did. I've got some 20rd Pmags ordered and I'll test it again with Hirtenberger, S.A, Austrailian, and Malaysian surplus I have....... Thanks for all your input!!!! How many rounds through it to consider it broken in?

hueyville
September 29, 2017, 23:29
Number of rounds to be broken is is a variable IMO. Many rifles I build shoot till buffer is selected, gas adjusted and shoots reliably with at least three different types of ammo. Also barrel finish and material plays into equation. A button rifled stainless rifle will break in quicker than a hammer forged 4150 or most melonite/deep salt bath finish barrels. Have found that most "average" barrels will stop copper fouling every few shots and settle down into consistency at 80 to 120 rounds. Have over a dozen AR's built as project rifles just to be building that have 20 to 40 rounds which were used to adjust gas, sight in, make sure shot a passing five shot group with one of my "proof" loads.

For 5.56 based on twist my proof loads are either Tubbs DTAC 69 grain SMK's for 1:7 to 1:9 or Black Hills 50 grain for slow twist barrels. For 7.62 NATO barrels use Nosler Trophy Grade 168 or 150 grain and sometimes Federal Premium Gold Medal 175 grain. Like to use closest milspec ammo in appropriate weight for twist to select my buffer and adjust gas. Then shoot a few rounds one step heavier and one step lighter running a damp patch down bore every five rounds. After minimum rounds fired reliably, foul barrel set optic for load most likely used in it. Run a damp patch, foul again and use my premium proof ammo and if is MOA or under then clean and put away. This type "break in" can be done in 30 to 50 rounds usually. If is rifle plan to use regularly will generally shoot 80 rounds and then clean. Shoot two fouling shots followed by five round group of "proof" ammo and push a patch down bore then repeat. When rifle begins to show me groups am pleased with AND no copper fouling on patch it's almost ready. Then go back to range ammo and shoot two fouling shots followed by two five shot groups and a patch. When shoots a dozen rounds without obvious copper deposits its ready for field. Most will pass accuracy minimum requirement before stop fouling. If pressed into service don't want a rifle that will foul and drop off accuracy significantly after a magazine or two is fired.

All are different and 100 to 200 rounds generally knocks enough high spots, burrs and rough areas down to stop majority of copper fouling of areas with micro machining rough areas. If still fouling after 200 rounds will put three lapping rounds down bore and then try again. Have about 16 builds that are broken in and part of my regular use group. All were completely settled by 250 rounds. That said have a safe full of AR's can only tell you they function and are sighted. May pull and wear them out, might neckbeard a few, most may still be in vault for heirs and many of the non adjustible gas, bargain parts builds were cleaned and put up after only 20 rounds. When able to shoot a full magazine through the rifle without it losing accuracy and without a copper/green patch coming out bore am happy enough if going to "work" it.