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|-+  Bullpup Rifles (Auto & Semi-Auto Centerfire)
| |-+  Desert Tech MDR (Moderators: kfeltenberger, Heathsrow)
| | |-+  State of the MDR today? 6.5 Creedmoor subMOA on the table yet?
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Author Topic: State of the MDR today? 6.5 Creedmoor subMOA on the table yet?  (Read 11280 times)
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« Reply #160 on: October 14, 2021, 03:27:12 PM »

Still not sub-MOA; this gun just can't do that IMHO.  or at least, mine can't reliably do that.  But it's not bad. With the right very carefully tuned loads, it can be sub 1.5 MOA, which to be honest, is pretty "Good-enough" serviceable, if it does that repeatebly. Which... I think it can.

Here's performance from this weekend.  Running 140 gr Nosler basic HPBT with a fast powder (4064).   IMHO, with the MDRx in a heavy power round like 6.5 CM, you have to run a fast powder to get good accuracy.

Not bad.  At 200 yards, POI is within 1 MOA of what was in my record book for my scope settings.  This isn't a precision gun, which is too bad, but it's not a bad general purpose gun.

As to ES Tactical and such to tighten it up; nice guy who knows his stuff - but that's gone nowhere and I've kind of given up on that path.  Not really his fault, 2021 is an odd year!. Thanks for the tip, I enjoyed my conversations with him.  

But to my original thread question - is the 6.5 MDRx a sub MOA gun?  The answer is still mostly no.   But it is a sub 2 MOA gun - WITH CARE in your ammo development.  I've never a had a gun more accuracy sensative to ammo like this one.  But I will say, the reliabilty has been phenominal.
Did you give the supressor/opressor a try to see if that matched my experience of reducing group size? also my experience mirrors yours with 140+gr bullets, but as soon as I go back to 130s, things tighten up considerably.

as far as creedmoor goes, so far I've gotten sub-MoA with the following:
130gr Federal Terminal Ascent (best performance, 0.98" at 200yd, can't say enough nice things about federal's terminal ascent line)
125gr Winchester Deer Season XP
129gr Browning BXR
130gr FGMM Berger Hybrid
and reloads with Hornady 123gr ELD-M over CFE223, winchester large rifle brass

acceptable DMR performance but variable results were had with:
140gr S&B tactical
143gr Hornady Precision Hunter
140gr Hornady ELD Match

It would be nice if I could pinpoint exactly why it behaves this way, but aside from the extra muzzle weight dampening barrel harmonics, I'm kind of stumped.
« Last Edit: October 14, 2021, 03:28:59 PM by WIndstorm » Logged
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« Reply #161 on: October 14, 2021, 06:54:47 PM »

I talked with ES Tactical last week, my 308 barrel is on its way to me as we speak.

He said the issue was the following:

1.  Barrel block fasteners to the chassis loosening
2.  Chassis flex
3.  Gas system hammering the barrel and torquing the the barrel block attachment

He said his barrels do the following to get 25% better accuracy
1.  Straighter bore and more uniform barrel
2.  Stiffer barrel to reduce flex
3.  More mass barrel so the hammer results in lower acceleration

He said that outside of Fabbing a new barrel block and checking screws were tight that is the best we can do.  

This also tracks with the heavier bullet problem being less accurate, more surface contact more energy transfer with friction and bullet deformation in bore.

As far as the suppressor on the end, harmonics aside, the more mass on the barrel means less barrel acceleration from short stroke op rod.
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« Reply #162 on: Yesterday at 12:02:08 AM »

Fired the MDRx at a 500 yard midrange match.  Mentioned some of this in another thread, but repeating here with more details.  The shoot itself was a small affair, so they were fine just letting me run it with the break on, and off of sandbags; so technically I was running "out of competition".

The way a Mid-Range match works is a series of 20 shot for record strings everyone lines up and shoots at their own target in an allotted time.  This one was 4x20, so everyone lines up, and shoots into their target for 25 minutes (1 minute / shot, plus your 2 sighters, plus 3 minutes of preparation time allotted).  And then a stop, and change out rifles, whatever.  So on this day, I brought 4 rifles, and with the MDRx, I used my 25 minutes to just shoot multiple 10-shot strings.  I ran semi-auto (technically you are supposed to single-load), and am naturally a little quick, so getting 36 rounds down-range onto digital targets in 25 minutes was no big deal.
(note, by rule, one must have an Empty Chamber Indicator (the orange flag) in the rifle while not in use.  And so... well, I did the best I could - ha!)

I enjoyed the MDRx, and found it highly reliable, and pleasant to shoot. I built a pile of brass in a hurry:

Thank goodness I reload, otherwise I'd likely have to just take more time bowling or reading more books (very few people will get that reference  Smiley )

One thing about shooting a match, is there's no convenient cherry-picking groups.  Even I do that sometimes, and this was a good reminder of reality.  Here's what my "best tuned" 140 gr match ammo with a fast powder really does, out of a 6.5 CM MDRx.
Ammo Label:

Performance on target at 500 yards:

That's not great.  For comparison, my 6.5 Grendel shot a clean 100-8x, with a tight group.  This rifle, I suspect flexes on recoil, and is just throwing wild random shots off to the left from time to time.  That's not me, and that's not the wind.

I also run some 140 gr softpoints, again with a light load of a fast powder:
Ammo Label:

Performance on target at 500 yards:

These didn't do a lot better, though interesting to see how the first grouping would string horizontal, and this one seems to string more diagonally.

Finally, it's been said that going for a much lighter bullet might help.  So, I launched some 85's, to give that a shot.
Ammo Label:

Performance on target at 500 yards:

The grid is 1 MOA grid, so if you can get that flex under control, it looks like it can crowd 1 MOA.  That's why the common 5.56 guys are able to get 1-1.5 MOA groups pretty good.   But then, that's not the power, distance, and precision of 6.5CM, which is what I was wanting in Bullpup, personally.  

At this stage, would I recomend to a friend to buy an MDRx in 6.5 CM?   Eh, probably not, since it's supposed to be a distance precision round.  It can still be a gong-banger at distances, where wild misses don't really matter, but if you're shooting for precision, it's not that great.   Would I have bought it had I known this is the realiaity of its accuracy?  Probably not.  Would I sell mine, for what I paid for it?  Heh, probably not; as it IS a very cool gun.  But it's more... FG42 cool, then actually capable of delivering my expectations so far. 

If DT beefed up the reciver to control the flexing, and moved the gas system down a few inches, they'd have a much better gun, IMHO.  Even this basic factory barrel, will crowd 1 MOA when it's not flexing - I think.  An HBAR will take me from 1.5 MOA to sub MOA, but I don't know if an HBAR will do a lot to help me with the reciever flexing, other than perhaps offering a higher moment of inertia to that flexing, perhaps.

I suspect if I take those 85's and load those to Grendel speeds, that will tighten things up considerably as well.  Which.. .I might do.  Kinda lame, but then, is that any different than converting the rifle to 6mm ARC?

« Last Edit: Yesterday at 01:17:55 PM by LazyEngineer » Logged
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« Reply #163 on: Yesterday at 04:15:33 PM »

Interesting results, what are you using to generate that 6.5CM ammo label?

I'd still suggest trying a very slightly lighter bullet and some weight on the end of the barrel (flash can or suppressor) before giving up on it.

As of this past weekend, I have two handloads that are giving sub MoA practical results in 10-shot 100% groups:
1) 123gr Hornady ELD-M, Winchester Large Rifle Primer brass (1x fired from deer season XP factory loads), CCI BR2 Primers and 40.5gr of CFE223
2) 130gr Federal Terminal Ascent, Same cases and primer as load 1, still experimenting with powder load but so far best results are with 40gr flat of CFE223

Rifle Details: JARD trigger pack (~2.5lb final break), off a magpul bipod and the reflex handguard, with a SilencerCo Omega 300 direct-thread mounted. Standard 20" conversion kit with no other modifications, Optic is a swampfox arrowhead 1-10 LPVO.

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