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+--- Thread: How to determine if a barrel chamber is a type .125 or .136? (/showthread.php?tid=22726)
How to determine if a barrel chamber is a type .125 or .136? - grendelnubi - 01-20-2021
I purchased, several years back, a 16" Anderson Arms barrel from a local gun show. It was less than $100. I did assemble and shoot it for a short time without any issues that I remember. I am certain I used a .136 bolt because that is all I have. Didn't even know at the time there were different chambers etc.....
The upper I assembled has been sitting for years and I am now questioning if the chamber could be a type 1. Will a type 1 barrel chamber a round using a type 2 bolt? How can I determine which chamber it has?
I heard that Anderson Arms did sale some type 1 barrels but I do not know for sure. I do know there offerings today based on their web site are .136 barrels.
How to determine if a barrel chamber is a type .125 or .136? - Klem - 01-21-2021
GN,
There are no Type 1 and 2 chambers, only bolts. At the shop, the reamer is pushed in as far as the gunsmith thinks is reasonable for the bolt they have at the time. If it's a .125" then the reamer will likely get pushed a little further into the barrel than if they have a .136". But, they can finish a chamber wherever they like within a .01" SAAMI range and still be within spec. The difference in the bolts .011" and the tolerance they are permitted means you can have all sorts of chamber lengths; some in spec, and some not. Plus SAAMI allows a range of tolerance in the ammo Grendels use.
You can determine all this by measuring the headspace of cases with calipers.
More important than knowing the bolt the gunsmith used is how much stretch the cases go through when fired. This is determined by measuring the headspace difference between unfired factory rounds or new cases (which will be on the short/squashed end of the tolerance scale) and their expanded spent cases (your chambers' dimensions).
What is this difference in your cases?
How to determine if a barrel chamber is a type .125 or .136? - grendelnubi - 01-21-2021
Thanks Klem, I just found my 16" notes with the HS measurement before and after. I don't have any factory ammo to verify but my notes indicate Hornady unfired HS of 1.208 and a fired HS of 1.213 using my 16" Anderson barrel. I generally resize to 1.211.
I try not to push the shoulders back on the case to much. I have Hornady brass that has 9 firing cycles and have never had an issue outside of loose primers.
How to determine if a barrel chamber is a type .125 or .136? - Klem - 01-21-2021
That sounds perfect. With that tight tolerance the gunsmith more than likely used a .136" bolt to ream and check headspace.
How to determine if a barrel chamber is a type .125 or .136? - A5BLASTER - 01-21-2021
If it's the AA heavy fluted light weight 16 inch barrel that they stopped making. It will use a grendel bolt with .136 bolt face and has the sammi grendel chamber as designed by bill alexander.
I have several of them. Great barrels, I stocked up on them before they stopped making them.