Semi normal problem, since some gas blocks are produced to incorporate the thickness of the hand guard front ring not in play, and your barrel gas port location is doing this already.

Hence standard distance of a gas port on a AR barrel is .300" forward of the barrel shoulder.

Front hand guard rings are about .025" thick, and a standard FSB would be .275" from the back of it to the center line of the gas pasage.


Now,  since JP did not design the barrel for a front hand guard ring use, the barrel gas port was placed at .0275" off the shoulder, which makes the barrel work with a standard FSB/ Gas block that would normaly have a front hand gaurd ring in play.


Now back to the SLR gas block that you have, and here is the glitch, since it was designed to eliminate the space that a hand guard ring would take up (what the barrel is doing already with the gas port moved back isntead) and the problem at hand.  Hence what you are looking for is a gas block that would be used with a front hand guard ring isntead.  So on such a gas block, it distances from back to the center of gas passage, would be .275" instead.

So to resolve the problem, get SLR on the phone, and let them know that you need to swap out the gas block you have now, for one that will incorporate a front hand guard ring instead.  Hence you have a .300 unit now, and need the .275" unit instead.

Your looking at the wrong dimensions.

The dimensions that they list are for the ID of the block, for the OD of the barrel diameter where the gas block will fit the barrel.

So if this is your barrel,

JPSM6.5C-22M8XL
Diameter at Gas Block: .936


Then what is needed is a .936" gas block, and again, one produced to use the standard front hand guard ring on a barrel in play, hence .275" from the  center line of the block gas passage, to the back of the block..


And missing from their drawing is  a side view, to give the needed dimension to see which gas block is .300 to take up the room of a front hand guard not in play, and one that is .275 for a front hand guard ring in play instead (the later the one you need for this barrel, since the relocation of the gas port on the barrel, is taking up the .025 space of the guard ring not being used, to allow this standard distance block to be pulled tight against the barrel shoulder instead).

Since we know what needs to be resolved with the gas block to get a correct alignment with it and the barrel gas port, lets move along to the rig and ammo.



When reloading for the rifle, you are dealing with two actual pressures.


The first pressure is the actual over all working pressure of the round.  
So max working pressure of the round is 62K, but this is not to say that you can just grab any data load, look for a quick check and go by data pressure in your rifle.  You need to work up the load, and watch for signs of over pressure at the spent primers as you are working up the charge ladder from the first reduced loads, to max working loads.  

If we take the below spent primers in the photo, the first two are not showing any signs of over pressure as the spent primer flattened out in the pocket, the third one to the right is starting to show signs of over pressure, and the last one on the right, the round when over pressure since the edge of primer has pressure flowed all the way to the edge of the primer pocket isntead.



Now the second pressure that we have to deal with, is the amount of residual pressure that will reach the gas port once the bullet passes the barrel gas port.
Granted that this is 223, but gives you an ideal of residual pressure down the barrel after the peak dwell spike of the powder burn.


So the way to understand this residual pressure pressure, the faster the powder burns, the lower the pressure to the gas port since it moves the spike dwell more toward the chamber.   With a slower burning powder, the peak spike will be closer to the gas port, which increases the residual gas pressure at the gas port instead.
Also to point out, as you increase the first over all working pressure of the round, you also increase the residual pressure at the gas port as too.  

So starting with a given load, step one is to make sure that the load is not going over working pressure via single shot fired, and the spent primer checked.
Once you know that the load is not going over pressure, than it's time to adjust the gas block for that load to correctly get the rifle to cycle correctly.  Hence single round loaded in a mag, the round charged and the empty mag left in the well and the gas block adjusted more towards the closed positon, the round is fired to see if the bolt will lock back the mag catch.  If it will not, then the block is adjusted slightly more open and another single round mag tried again.   Once you have the gas block adjusted so the bolt will just lock back on the bolt catch, the gas block adjustment is adjusted just a hint more open to allow just a touch more gas though, this was as the rifle starts to foul, will still have the needed amount of gas to correctly cycle the action.  

If the load is changed, then the gas block needs to be readjusted for that new ammo instead.

So not knowing if the photos you listed are all of the same load, lets just say that they are for now.

The spent primer looks fine, so we can weed out over pressure of the round.
The spent case looks fine on the sides of it, so we can weed out a dirty or rough chamber,
But the nasty pull mark on the extractor, the swipe marks on the rim of the case, and even the complelty fouled bolt in only 50 rounds, all of these signs are screaming the the bolt is trying to unlock to soon, with the spent case still too pressure welded to the chamber walls too much during the pull.

So again, if all the photo's shown where of the same load, over all working pressure is fine, but the gas block has been adjusted too far open for that load to allow too much gas through, causing the bolt to unlock too soon instead.  Hence where the B/C does not see enough gas, or sees too much, both will cause short stroking problems.  No enough gas, and the bolt is trying to unlock too late.  To much gas, and the bolt is trying to unlock too soon (residual pressure in the bore has not dropped down far enough to allow a clean pull of the spent case), and too much energy of the bolt lost on trying to pull the over pressure weld spent case from the chamber walls.



Lastly, and this is going to chap your ass, the 6.5 round was designed for a bolt action gun and not an auto loader isntead.  Here, its the powder used for the loads, and instead of say a optimized gun powder that has an ideal burn speed rate to hold some constancy of over all working pressures, and gas port residual pressures amounts as the norm, such is not so.  So with some factory loads, it may be loaded with faster burning power that may not have enough gas port pressure, to loads with much slower burning power, and causing way too high gas port pressures isntead.

So with the auto loader, your going to have find powders to use for the loads that have a more ideal burn rate norm for the system, to achieve both the ideal working pressures and somewhat ideal gas port pressures as well.  The reason that I say somewhat in regards to gas port pressure, is if you do end up with a slower burning powder that does produce slightly higher gas port pressures, you can use the adjustable gas block to solve the problem instead.

So as you are working up loads, start with the gun powder burn rate, how clean the powder is going to burn, and they you dial in on working the charge ladders for these loads.  Hence stop looking that the reloading data like you loading for a bolt actin rifle, and start looking that data for the loads that are going to work in an auto loader isntead.

http://www.reloadersnest.com/burnrates.asp

When you pull the charging handle all the way back, the face of the bolt should be 1/8" to 1/4" in front of the back of the ejection port window.
Knowing this, its easy to make the needed lenght spacer to use a shorter buffer in a longer receiver extension tube.


As for my suggestion, not hard to reduced the weight of the correct buffer for the rig as well.  If you want to lighten a full lenght buffer, then replace a weight or two with something lighter to take up the space instead.  Hell, since your not worried about bolt bounce on a semi auto rig, nothing stopping you from pulling all the weights out if needed to lighten it that much instead.



Simply, the buffers started out as a plastic rod limiter to keep the back of the key from crashing into the lower receiver, and when the Government needed the full auto cycle rate on the rigs slowed down, then is when the plastic spacer rod became a buffer with internal dead blow weights isntead.