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Discussion Starter #1
ACR LWRC XCR M92Also note that the YUGO M92 is only being used for a visual aid.
Center of gravity WITH a full magazine this is by hand and the yellow sticky represents where this would be and how nose heavy it feels.
The controlsThe XCR wins this hands down with the safety and the bolt release is alot smooth but doesn't seem as robust however, the XCR has about 10k through it so that would lend to the smoothness. The ACR has a great charging handle fully ambidextrous and it is the smoothest on "any" rifle I have fondled.ACR
XCRSweetass 45 degree throw
Left sided charging handle
LWRCStandard AR-15 not real user friendly
TriggersACR-crisp but could be lighter, my XCR is lighter.LWRC- timney 3lb single stage (concentrated win)
 

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Discussion Starter #2
The guts. Let's talk about them but first let us cover that's these are piston driven systems but differ in the sense that two are "long" stroke and the other two are "short" stroke systems. Long stroke systems in short have a piston that is connected to the op rod which is attached to the bolt carrier and follows the bolt carrier group through the full length of operation whereas in the short stroke system the piston strikes against an anvil (picture a pneumatic punch like in no country for old men) on the bolt carrier for usually no more than 1 inch of travel and then it is disengaged. Long strokes tend to shoot softer and have faster follow up shots and fixed ejectors.These are long stroke systems (AK actions)
This is the short strokes
At 12 o'clock you can see the ACR's op rod that is driven by the piston.
At 12 o'clock you can see the same setup with the LWRC
Gas adjustability.*The LWRC was said to be self regulating so it is not adjustable for suppress which I had to tweak it to get it to run good (tubbs flat wire spring and a spikes tactical tungsten powder buffer)The ACR has two adjustments suppressed and unsuppressed. This system also vents excess gas out of the port located in the front of the gas block. The top of the piston has a cork screw contour like a prop which causes it to rotate each time the gas hits it cleaning the system.*
The XCR vents under the hand guard and the system has 6 settings S,1,2,3,4 and off.
The bolts, we have two types of bolt design here. The three lug which is typical of AK actions and the seven lug (the ejector which has a lug doesn't truly act as such would make it eight but it could be machined off and not impede function) which is indigenous to the AR system.The ACR and LWRC are AR based*Seven lugs*
ACR bcg
LWRC bcg
Three lug systems
XCR systems
The ACR and XCR are build to be piston systems. What this means is that the engineers or designers already compensated for the carrier tilt which is a side effect of the piston system by incorporating rails for the carrier to ride on. Most AR systems this was a moot after thought because the reliability was of far greater concern.ACR rail system
XCR rail system
LWRC (AR tubular system) you'll find no rails here
The YUGO M92
So in short the these two interchangeable caliber rifles have incorporated what the designers felt were the best operating systems. The ACR is obviously based on the AR-15 using it's bolt design with a plunger type ejector and a short stroke system and AR type barrels. The XCR is based on all the AK's strengths (less the magazine) the three lug bolt, fixed ejector and the long stroke system.*Caliber change.The ACR *is a tool-less quick change that only requires elbow grease.The XCR requires a tool (Allen wrench) I use an inch pound wrench, but is still a quick change system.I'm the beginning most thought that the ACR's system being tool less was the way to go but thoughts have shifted on this. I myself am really indifferent about it meaning I could give a crap either way because once the barrel is removed the zero will shift. Robarms maker of the XCR has found a solution to this with a non adjustable rear sight and a front sight which attached to the gas block and is adjustable for elevation as well as windage but they have yet to incorporate it into the design.
 

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Discussion Starter #3 (Edited)
ACCURACY! that's what we are all here for right?! Please pardon my shaky hands, flinching eyes, poor trigger discipline, failing vision oh and flagellum like arms lol. Ok here's what I did. I used a leupold 3-9x at 9 power with the same one piece mount and I offset the zero from the bullseye for a clear point of aim. I shot six 5 round groups and used a caliper and DID NOT MINUS .224 FROM THE GROUPS, so when you do that you'll have an accurate group. I did not include every group but I did alot for the ACR and averaged some of the others. Note that the LWRC did not have a 55gr post due to extremely poor results.LWRC 10.5 inch CHF 1-7 twist with a "Dutch" chamber more on that here http://forum.lwrci.com/viewtopic.php?f=4&t=6540&view=next68gr hornadys
69gr sierra
It really shot for shit for me :( sorry socomXCR 12 inch button rifled chrome lined 1-9 twist55gr win
68gr hornadys
69gr Sierra*
I tossed most of the 55gr data with the LWRC prints FML. The XCR was not super stunning 1-1.75*moaThe ACR 16 inch CHF melonited treated bore with a "stamped" 1/9 twist... That was the PLEDGENow for the TURN55gr win
68gr hornadys (don't like them)
ACR*69gr Sierra*

The PRESTIGEI saw the same trend in an article and it made me think, why does the ACR group better with heavier pills?Saw this online "shooting times"
So I did some home work.
It is in fact a 1/8 twist. I did this by taking a tipton BB cleaning rod and a patch and jag. I pushed the patch into the rifling and putting a piece of tape on the rod at the rear and marking it at twelve o'clock then I placed another piece of tape right at the beginning of the receiver. I pushed the rod until it rotated 360 degrees and the I market the rod at the beginning of receiver again. I removed the rod and measured between the two points and I got 8 inchs.The clean up
 

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Thanks for sharing your pictures and observations.

I have 2 of the 4 shown, (XCR / ACR) and I like them both. They both bring something different to the table. Both are alot of fun to shoot and accurate enough for what I do. Both are keepers for my tastes.

Again, thanks for the pictures. :cool:
 

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Awesome post. The 1 in 8 Twist is VERY interesting.
+1 on the 1:8 twist

Excellent comparison. I will stop bitching about my front heavy ACR now that I have seen the center of gravity on the LWRC. wow.

I may have to try some heavier bullets
 

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Discussion Starter #8
1/8 twist "is" the best twist rate available and you have it. Gents I'm glad you like the post, I enjoy teaching and raising awareness which furthers "our" sport and right. This barrel loves heavy pills, I shiver at the thought of what those groups would look like with a after market trigger. Btw I did not subtract .223 from the groups for a "true" measurement ie for example the (.869) would actually be .646. That's better than most factory bolt actions. \mm/ too much metal for one hand.
 

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Discussion Starter #9
I don't pretend to know "why" but ideas I have thought of was pre-existing barrel blanks, factory mis communication, lack of appropriate stamp. You guess, I just know what I know. The rifle is dump accurate.
 
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