Looking for opinions of those who reload.. what the issue might be?

I worked up this load for my Scar 20S, 44.5 grains of R15 behind a Scenar 155. Shoots incredibly accurate.

Tried out in my JR / Bula M1A today, and while still very accurate (1.5 moa).. the bolt would not go back far enough to load the next round.

This load has chrono'd out of the scar at 2810 fps.. so while there are no, zero pressure signs, its not a wimp load either.

Thoughts on this?

I load this recipe in large batches, and hate to change whats so "good" in the Scar (less than 1 moa) to bump up power for the M1A.

I will try it...

When I get 2810 FPS in a 308, with stellar accuracy, I called it good. I guess I can look for the next node up.

Gas plug loose?

Paladin

First thing I would do is shoot some M80 ball ammo out of it.

No reason to assume its ammo.

Is the bolt moving at all?

Is the gas turned off?

As little as 40 grains of RL15 is more than enough to cycle that action.  

check the obvious stuff, gas shut off switch and gas cylinder alignment of the barrel gas port.  The holes need to line up.   Screwing the gas cylinder lock all the way back until the gas cylinder is tight against the front band is wrong if it doesn’t time the holes to match.   You screw it in just far enough to make the gas cylinder hole line up with the barrel vent.  Then you install the gas cylinder plug to lock it. You can use shims it you want a tight system if it doesn’t happen on its own.  (I never saw where there wasn’t fore aft shuck on a GI service rifle that wasn’t a match prepped gun). You can flip the lock 180 degrees and start it on the threads through the other face to see if it times better.  

From there I would check to make sure you don’t have burnt crud lube grease on the piston.   It should be dry inside the gas system.

You can check the gas cylinder to barrel vent alignment with a bent copper wire or even paper clip of small enough dia to pass through the barrel gas port.  Bend an L that will fit in the gas cylinder and you will feel the port in the barrel.  

If that is it, don’t feel bad.   BTDT.

The “screwdriver slot” of the shut off should iirc be vertical, one end of the slot pointing at the barrel, the other toward the piston.  Horizontal, is parallel to the bore and off.

I ran ball in it before shooting my load.. to get scope on paper. Box factory ball ran fine, extracted fine, ejected fine.

The 155 Scenar load would extract and eject, just not load the next round.

You could try loading a single scenar round and fire it and see if the bolt locks back on the follower.  If it is then the bolt is going back far enough.  It may be it is coming back too fast, rebounding off the heel and the mag spring isn’t keeping up and the bolt passed over the next round.  

I glanced at my Hornady manual.   For the service rifle loads they max out at 44.6 RL15 with a 155, Amax in their book if I remember from 5 m ago.


I cannot see more powder being the answer.  

Try some at 41 grains.
You could try one of those special bleed off gas cylinder devices
You could also try a NM style gas piston with the groove cut in it that lets some extra gas blow by.
You could try a mag with a fresh spring and a new recoil spring if you have any doubts on yours.

Regarding the load, it is DEFINITELY not in need of more powder.

The M14 is designed around the 7.62 NATO load. Which is definitely a lower-pressure load than being used here.

You can Google the subject of 7.62 NATO pressure. The internet is loaded with conflicting opinions about what is the "correct" pressure for 7.62 NATO.

I do know this for sure: You run hot loads in an M1A or an M1 and the bolt goes back hard and slams against the side of the receiver. This causes the receiver to bulge from the impact, and then crack. We abused the living hell out of real M14 receivers back in the 80's and 90's when we could get replacements literally FOR FREE from DCM. I saw a number of those receivers with the side punched out from heavy loads. If you want your new gun to go that way, keep shooting that hot load in it.

The fact that M80 ammo runs fine in it, and your hot load won't run at all, should tell you all you need to know about what is the remedy.

.308 win spec loads versus M14 rated 7.62 Nato loads.  Some reloading manuals seperate them out.  My last two Hornady manuals do.  The latest Sierra might but my version has .223 rem and seperate mil 5.56 loads but hadn’t yet split the .308 and 7.62 apart in mine.   The sierra tech line was most helpful me in the nineties when I got my Springfield.  

The key difference to consider when comparing .308 and 7.62 load data is H2O case capacity.

7.62 loads tend to assume siginificantly less case capacity than .308 loads.

It is impossible to have an accurate discussion about whether a load is hot/weak/OK until we know the case capacity of the brass actually being used.

Very true!

A winchester commercial case is going to hold more water.  

Also that is a good point on not straying too far away from 2.80”.

2810 fps is HOT from a 24" barrel shooting a 155. Semi-auto rifles don't like hot loads.

Your SCAR has a 16" barrel, correct? That works out to around 3000 fps if fired from a 24".

Brass selection makes a huge difference in .308. Military surplus brass can't safely hold anywhere near the powder of Winchester commercial cases. Average empty unprimed weight for Lake City brass is close to 180 grains. Winchester brand commercial cases can be as light as 155 grains. Other brands fall in between these two extremes.

I would expect 42.5 to 43.5 grains of RE-15 to be close to a good working maximum when using Lake City surplus brass and 155 grain match bullets. M80 ball usually runs between 2730 and 2750 fps through my Springfield Armory M1-A's. 2650 to 2700 fps is plenty fast from a 22".

thanks for the input. SCAR is a 20".. and the velocity was an error on my part. I was reading the recipe sheet, and 2.810 is OAL not velocity. My bad.

Yup.

Remember that an M14/M1A's gas expansion and cut-off system is going to pound the snot out of the end of the op rod, and as WECSOG points out the bolt will be smoking to the rear before ringing off the receiver heel.

The 155 Scenar also has a longer bearing surface than the M80 Ball 147-grain bullet.

OP:

Ok, then what did these loads chrono out of your 20" SCAR if it wasn't 2810fps............  ???
And did you chrono them with the M1A??