New 6.8; carbine or rifle?

[kentucky_smith]

So I'm about to pull the trigger on getting a 6.8 upper and am curious as to which I should do. It's not so much a matter of gaining fps with the longer barrel, it just seems like the full-length gas system would be less harsh than the carbine.

Ideas? Going with Doublestar/JT 1/10" twist. Purpose is to have a more viable deer cartridge.

 

[ryoushi]

16" midlength gives you the best of both worlds. Good performance and reliability in a compact package.

 

[LakeshoreShooter]

Guess it depends on how long your planning on shooting these poor little innocent creatures....What?!?!? "Kill 'em and Grill 'em" I have not used a crono out that far (2-300 yrads) to see what my 16" is still cruising at...but I got a button buck this last season with the 6.8mm pictured here at about 100 yards with the open A2 sights. Like a sack of potatoes with 130gr. Nosler Partition leaving the barrel at 2710fps on my chrono. No worries mate. The cartridge will put a deer down out to 300 yards without a problem as long as you do your job and put the bullet where it belongs

 

[RockyMtnTactical]

What is the difference in velocity for a 16" vs. a 20" in 6.8?

 

[aspade]

In the vicinity of 100fps. Depends on the load and the barrels.

 

[surfinUSA]

One of the magazines has an article where the writer cleanly took a caribou with a 6.8 bolt gun with a single shot.

I seriously thinking of building an upper for one but barrels, either 16 or 20 seem to be scarce.

Does any one here have the mini 14 in 6.8. I prefer the AR but Ruger may have a real winner with this gun if its accuracy is better than the 223 guns.

 

[Reginhild]

WARNING! Dangerous Pressure Level Loading Mentioned Above.

LakeshoreShooter,

Not sure how safe your handloads are but even with a 110gr bullet 2710fps from a 16" barrel would be a very dangerous hot load. Getting a 130gr to go that fast is likely "blow-up" dangerous.

Here is info from Forest on his pressure signs at 2210fps with a 130gr:

Test #2 - 130gr SST
This is a continuation of my ealier experiments with loading a magazine length 130gr bullet. This load is designed to work in PRI magazines, and the round will not fit in most C-Products magazines.
Powder: H322
Brass: SSA (new)
Primer: Remington 9 1/2
COAL: 2.31"
24.5gr 2136fps sd 13.56 (5 rounds tested) some flattening of the primer
25.0gr 2154fps sd 22.80 (3 rounds tested) primer is flat, some light swipes noticed on the brass. FYI Sierra indicates this is their max loading for their 130gr SP.
25.5gr 2221fps sd 14.28 (5 rounds tested) primer is very flat, swipes more noticable. This is what I'd consider to be the max load - and it just makes what I was looking for. Based on what Hornady indicated in an e-mail that should make the round a decent hunting round out to 125y

Also check the loads herre by AR15barrels (a dealer) where he has multiple "hot load - do not use" listed with 110gr and 115gr bullets. The fastest he gets a 110gr going from a 16" barrel 6.8 SPC is 2528fps. The fastest he gets a 115gr going from a 16" barrel is 2481fps. Both of those fast loads he states "Dangerous Load - Do NOT Use!"
http://www.ar15.com/forums/topic.html?b=3&f=121&t=282708&page=31

In other words: You are pushing a 130 gr bullet 500fps faster than a hot loading listed above for 130gr. You are pushing the 130gr bullet 250fps faster than a hot loaded 115gr bullet. You are pushing a 130gr bullet 200fps faster than a hot loaded 110gr bullet!!!!!!! Hope you don't blind yourself with shrapnel if you keep shooting such a load.

 

[AR15barrels]

I have to call absolute BS on the 2710 velocity from a 16" barrel with a 130gr partition.

Here is a quickload pass to 85,000 PSI in a 24" barrel.

Cartridge          : 6.8 mm Rem SPC
Bullet             : .277, 130, Nosler PART SP 16322
Cartridge O.A.L. L6: 2.283 inch or 57.99 mm
Barrel Length      : 24.0 inch or 609.6 mm

Predicted Data for Indicated Charges of the Following Powders.

Matching Maximum Pressure: 85000 psi, or 586 MPa

or a maximum loading ratio or filling of 110 %

These calculations refer to your specified settings in QuickLOAD 'Cartridge Dimensions' window.
C A U T I O N : any load listed can result in a powder charge that falls below minimum suggested
loads or exceeds maximum suggested loads as presented in current handloading manuals. Understand
that all of the listed powders can be unsuitable for the given combination of cartridge, bullet
and gun. Actual load order can vary, depending upon lot-to-lot powder and component variations.
USE ONLY FOR COMPARISON !

4 loads produced a Loading Ratio below user-defined minimum of 70%. These powders have been skipped.

Powder type          Filling/Loading Ratio  Charge    Charge   Vel. Prop.Burnt P max  P muzz  B_Time
                                      %     Grains    Gramm   fps     %       psi     psi    ms
---------------------------------  -----------------------------------------------------------------
Accurate 2200                      107.5     26.5     1.72    2703    99.8    85000    5477   1.027  !DANGEROUS LOAD-DO NOT USE!
Winchester 296                      91.9     22.9     1.48    2684   100.0    85000    4876   1.044  !DANGEROUS LOAD-DO NOT USE!
Accurate No.1680                   101.2     25.2     1.63    2679   100.0    85000    5089   1.031  !DANGEROUS LOAD-DO NOT USE!
Accurate XMR 5744                   99.0     22.4     1.45    2676   100.0    85000    5015   1.028  !DANGEROUS LOAD-DO NOT USE!
Alliant Reloder-10x                110.0     25.7     1.67    2673   100.0    76460    5239   1.064  !DANGEROUS LOAD-DO NOT USE!

Any of those loads SHOULD send the bolt carrier out through the back end of the buffer tube and empty the mag through the floorplate.

Now, a 270 will easily do what you are saying your 6.8 does, but that's a whole different deal...

Cartridge          : .270 Win.
Bullet             : .277, 130, Nosler PART SP 16322
Cartridge O.A.L. L6: 3.340 inch or 84.84 mm
Barrel Length      : 16.0 inch or 406.4 mm

Predicted Data for Indicated Charges of the Following Powders.

Matching Maximum Pressure: 60000 psi, or 413 MPa

or a maximum loading ratio or filling of 110 %

These calculations refer to your specified settings in QuickLOAD 'Cartridge Dimensions' window.
C A U T I O N : any load listed can result in a powder charge that falls below minimum suggested
loads or exceeds maximum suggested loads as presented in current handloading manuals. Understand
that all of the listed powders can be unsuitable for the given combination of cartridge, bullet
and gun. Actual load order can vary, depending upon lot-to-lot powder and component variations.
USE ONLY FOR COMPARISON !

31 loads produced a Loading Ratio below user-defined minimum of 70%. These powders have been skipped.

Powder type          Filling/Loading Ratio  Charge    Charge   Vel. Prop.Burnt P max  P muzz  B_Time
                                      %     Grains    Gramm   fps     %       psi     psi    ms
---------------------------------  -----------------------------------------------------------------
Vihtavuori N560                    104.3     61.7     4.00    2826    91.1    60000   25029   0.874  ! Near Maximum !
Ramshot Magnum (Big Boy)           108.7     66.0     4.28    2818    91.8    60000   25098   0.867  ! Near Maximum !
Alliant Reloder-22                 106.8     61.2     3.97    2816    93.7    60000   24488   0.878  ! Near Maximum !
IMR 7828                           108.9     61.1     3.96    2815    91.6    60000   24316   0.866  ! Near Maximum !
IMR 7828 SSC                       104.9     61.1     3.96    2815    91.6    60000   24316   0.866  ! Near Maximum !
Winchester WXR                     105.6     61.5     3.99    2813    93.5    60000   24491   0.878  ! Near Maximum !

 

[Reginhild]

....hopefully we'll here back from LakeshoreShooter and he has NOT killed himself shooting a load that is more than double the pressure the gun can take.

...maybe his chrono is broken.