Jump to content
308AR.com Community
  • Visit Aero Precision
  • Visit Brownells
  • Visit EuroOptic
  • Visit Site
  • Visit Beachin Tactical
  • Visit Rainier Arms
  • Visit Ballistic Advantage
  • Visit Palmetto State Armory
  • Visit Cabelas
  • Visit Sportsmans Guide

16" vs 20" HB's


Recommended Posts

As the title reads , I will be putting my 16" against my 20" HB. There will be more to this , the 16 " I just put a 6x18x40 Nikon on it , I ordered the scope for my other build ,but since its a bit off to completion , the 16" is a nice home for now & always wondered how this 16" would shoot with glass on her.


Other things that will go on with the 16" is , the upper to lower fit is not loose its beyond that , its probably the loosest fit I have ever seen . Its not that the disassembly or pivot pins are not tight , they are , as far as pushing them in or out , the upper can slide left or right when assembled . 

I plan on bedding the action on this rifle for two reasons , one , of course to tighten it up ,but also to see how that effects grouping , since I did a base study to day , the rifle as is a good shooter.

The other purpose for bedding is , this rifle will not function right with Magpul P-mags , I want to see if aligning the upper , lower & receiver extension can fix this , as said the set is loose.


I just ordered a Geissele two stage for the 16" to compare to the 20"s SSA . The Spikes enhanced trigger set up is OK but I could not compare the Spikes to a SSA , had to make it fair, as I can.


16" Rifle;


SI Defence Gen. II billet upper receiver


CMMG Billet lower (Early production )


Kreiger Criterion 16" HB with rifle gas system from Fulton Armory ,1 - 10 twist


JP free float hand guard 12"


Tango down pistol grip


Magpul CTR stock with DPMS 308 carbine buffer , Tubbs (Superior Springs) , flat wire spring.


Fulton Armory , Chrome BCG with POF roller cam


Spikes Enhanced trigger system


Nikon 6 x 18 x 40 scope  that I put the target turrets on.


As soon as I get the release agent & trigger we will see how the bedding changes things  & I will post photo's of course , right now they are not cooperating.

Edited by survivalshop
Link to comment
Share on other sites

  • Replies 77
  • Created
  • Last Reply

Top Posters In This Topic



This is how she shot today with Hornady 168 gr. match bullets , my hand loads  & they shoot pretty well out of my 20" @ 200 yards. These are @ 100 yards. . 

The middle grouping is from sighting the scope in @ 25 & 100 yards. 


-top right are two SMK that were loaded to the same specs as the Hornady's


-bottom right are 169 solid copper bullets from questionable origin, I just used them as another base.


- top left is five , yes five, of the Hornady 168 match bullets.


- bottom left is the same as above , five Hornady bullets.


- the one hole top left of center group , is a 150 gr. Barns TTSX bullet loaded with 4064, just shot it for Velocity comparison.


Link to comment
Share on other sites



-DPMS upper(original rail height )


_DPMS lower


-Geissele SSA trigger


_Fulton Armory Chome BCG


_Kreiger Criterian 20" HB, by Fulton Armory , 1-10 twist with PRI, custom cut to barrel dia. ,Compensator 


-Fulton Armory free float hand guard ( only one available for a 308 back then )


_ A2 stock with DPMS 308 spring & buffer.


_Millet 4 x 16 x 50 Tactical scope


There are a couple of things on the 16" that I left out & have edited it 

Edited by survivalshop
Link to comment
Share on other sites

Looking forward to the comparison.  Will you be able to test them side by side beyond 600 yards? 


Some time next summer, 2014 , but for now they will be going at it up to 200 yards.


I set up the shims between the receivers & it locked the receivers up like they were formed together. The instructions that I'm using read , between 0.004_ 0.005 shims should be enough , but this receiver took 0.007 to tighten up the receivers & still be able to push the disassembly pin in/out with out too much force.


Instructions read that a Pea sized portion of epoxy will be enough to bed the receiver ( these instructions are for an M16/AR 15 )& I used Modeling clay to make sure there was enough to bed what I wanted & the Pea size is good even for an AR 308.


I measured the width to the upper receiver lug & the opening in the lower that accepts it & there is a 0.005 difference , of course the lower receivers lug receptacle is wider .


I will also do something I have never done in bedding one of these , besides this method , & I am going to lock the BCG back into the lower receiver extension, during epoxy set up. I want to make sure there is alignment with the upper & lower, hoping this will do it .


Like I said , I have more than one reason to bed this rifle & will be using a P-Mag to hold the BCG back into the extension, not that I think the mag will make a difference , but ya never know.


Yes I'm photographing it all.

Link to comment
Share on other sites

Just waiting for my release agent & Geissele trigger, to complete this test . At least @ 100 yards. Figure to fire same test ammo with same trigger & then change triggers & see what difference it makes .


Just don't tell Van from Mecharmor Defense I put a scope on the 16" & don't have one of his charging handles on it yet . <dontknow>

Edited by survivalshop
Link to comment
Share on other sites

  Release agent & trigger came today . Set up upper & lower with release agent & formed my epoxy to my " pea size & set upper into lower & reset disassembly push pin, let it set a couple of hours & it got rid of 85 % of play , but now the front pivot area is still loose . 
 The gap in the CMMG lower that accepts the SI defense upper pivot block has 0.005 " play, by measurement. I may build this area up ( on the lower ) or make some shims for the pins to take up some of the play. 

 Will shoot tomorrow , just to see if what I did made a difference in shot placement & grouping.Then maybe with front pivot area tightened up. 


I have photo's but they are no different than the ones above , except the epoxy is dark gray.

Link to comment
Share on other sites

  I'm trying to decide to do anything to the pivot pin side play . I may do another fitment with the disassembly pin area of the recoil lug , it may lock it up a little more . I can cut some shim stock to fit the front pivot area , but not sure I want to .If I had a Mill set up , I would build it up with something & Mill it down exactly to center the upper .

  The upper & lower are a good tight fit except for the little side play with the front pivot area. I have a bunch of testing to do with ammo also with this rifle & need the Chrony , but the rain is screwing me .

Link to comment
Share on other sites

Well , the problem is , some jerk ran into my wife's new Mustang & all I got are my Harley's to run any where & have no place to load the hardware for the range . Its about dark thirty when she gets home & i'm lucky to see the truck on weekends , wait, I did redo the rear brakes & rotor's this past weekend , so I guess I did see the truck .


I should have my truck back tomorrow , with luck & get range time Saturday. I have made up some different loadings for some 168 gr. SMK's & IMR 4064.


I can't wait to put this in at the range.


Edited by survivalshop
Link to comment
Share on other sites

Range time was a bit different than the base shoot was , 14 deg. colder , & some gusty winds picked up after I set up , of course .


I thought at first the rifle shot worse than before the action bedding , the rifle shot a couple inches low & to the left as you can see by the bottom left group , the # 6 shot was from a different  batch of same load , just to see if it was the batch that was shooting low , but nope, I had to sight the rifle in again. I'm not sure if the action bedding was the cause ,but pretty sure ,because this rifles upper & lower receivers were loose before hand .

 After getting some trigger time the groups got better , as you can see . I'm sure the wind was a factor . Changing to the Geissele G2S was some fun at the range, the clip that holds the hammer pin in was a little pain in the arse , but worked out OK . Would have been much better if it was installed in my shop .



The shooting of the Geissele two stage was nice , I had to put a lot of effort into the STD FCG ( Spike's Enhanced )to get the results I did , the G2S , I could pop them off rather quickly & get the same results & if you look at the # 4 shot group , I concentrated on that one & with some trigger time am sure I can do better . Can't alwas expect non windy days , but I'm sure it had an effect on all my shooting this day . 



I do not use a lead sled , IMO its good for the load & barrel , but leaves the most important part out , " the nut behind the trigger " .


Now, do I think that an Action Bedding job made this rifle shoot better , no , not really ,  it got rid of the annoying shake & play , but time & longer shots may say more about it . The Geissele Trigger did though. 


So , share some thoughts .

Edited by survivalshop
Link to comment
Share on other sites

  • 3 weeks later...

I took both the 20" & 16 " to the range today & the fog was just lifting & about 72 deg. & no wind . Shooting same batch of Hornady 168 gr. match bullets out of both rifles & I have to say the 16" didn't stand a chance at all . The 20" just flat out puts one hole groups & the 16 " always had flyers that just screwed up the groups in the 16". I even tried my new loads of 168 gr. SMK with 42,5 gr. of IMR 4064 , with out much difference . I have not tested or Chrono'ed  this load yet in ether rifle . 


My glasses fogged up with every shot , but they did it with all the rifles , so can't blame that.


I will post the target photo's as soon as I down load them . Shot @ 100yards.


There could be several factors that make such a difference in groups , the 20" has a PRI brake on it ,the 16" has a VLtor brake /flash suppressor , & there is a deference ( slightly ) in Geissele triggers , but not much , they both are nice .


 I have another brand new DPMS complete lower & new TM. upper & what I think I will do is just rebuild the 16" on the TM upper & use the DPMS lower with the Geissele trigger & see what happens & also order a PRI brake for it , just to make it a little more even. I like that brake any way .

 So let the rebuilding begin , one aspect with changing it to a DPMS lower is I will probably be able to use PMags .


I also took my 308 Mossberg bolt gun to try it out , only has about eight rounds through it be fore this , so not at all broken in . 

Link to comment
Share on other sites

tw, why did you go rifle length on the 16"?  Does it soften the recoil that much?  No cycling problems with such little dwell time?

Rifle length does make for a smoother recoil impulse. There aren't issues with it on a 16" .308 like there are with a 16" 5.56mm barrel. Knight's uses rifle length gas systems for their SR-25 carbines.

I ordered an 18" SS barrel for my MWS that I'm going to have cut down to 16" and dimpled.

Link to comment
Share on other sites

Awesome testing!  I can't wait to see if the 16" rebuild helps!  Btw, why did you go rifle length on the 16"?  Does it soften the recoil that much?  No cycling problems with such little dwell time?

Only cycling problems I have with this rifle is when I use PMags , no kidding . The rifle does have a soft recoil ,like push ,not a shove .


Target photo's , I shot the 20" first , then went to 16" , then back to the 20 " & so forth . I had to shoot the 20" first just to see where it would hit , because I had the scope set for 200 & I put it back to the "0" setting & wasn't sure just turning the knob back to the "0" setting , if it would be on , guess it works .


I like the looks of the early CMMG 308 lower & SI Defense upper , but I have not liked the fit between the two or may be its one or the other . Any way , I'm starting over on this 16 " barrel , just because I can , if for anything else .


I'm also going to take a trigger pull reading on both rifles .





Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...