SSK 10.5 AR15 Upper COAL
 

Jus looking to see if there is anyone on ethis forum that has an SSK 10.5 AR15 Upper. I would like to know what there Case Over All Length is with Sierra 220 HPBT.
I was at 2.235 but saw here that some are less COAL and getting good groups.
I am getting verticle stringing 3-4" groups with H110 powder 9.1 and 9.6.
I don't know just reaching as I don't want to start jumping around for a solution when it could be the COAL.
Thank-You

probably your powder more than COAL. I would try 1680 or 4227 I had much better luck with My whisper with them than H110........pretty much COAL is what your magazines will allow sense every chamber can be different.

Good luck :grin:

I had terrible, terrible stringing with H110 powder, spent months trying to figure it out.

Get rid of the H110, problem will probably disappear.

Ok in an attempt ot determine the COAL, I inserted a unprimed empty case with a Sierra 220 HPBT into the chamber and relaesed the bolt to seat the round. Ejected the round and measured the case of which was 2.322.
I understand that it is sitting right against the Lands so it needs to be back off a bit.
Sorry but another question, was this somewhat an accurate way to determine the COAL? If so, how much more should I seat the bullet to obtain the best results?
Once complete I can leave the seating die alone and move on from there.
Thanks again.

You need to buy a bullet comparator to measure off the ogive and not the tip of the bullet.

Otherwise you are just guessing and basing your seating depth on something that varies too much bullet to bullet.

I have a bullet comparator and it measured 2.737

How is your measurement with a bullet comparator larger than your COAL measurement to the bullet tip?

It should be less, unless I am misunderstanding you somehow.

Also try putting one or two cross cuts on a case neck that will be dedicated to checking distance to the lands.

You can then load rounds to test and see if you are getting any scuffing on the bullets from the lands.

If you do, keep backing the OAL down until the bullet is not getting jammed.