Team.
I have been continuing the testing of homemade gas checks using Charlie's “Freechex” system. Here is the latest:
To date the aluminium gas checks have displayed mixed results. I have experimented with:
ALUMINIUM:
1) 2 ply soda can wall (2 x 0.0045) 0.009 2) 3 ply soda can wall (3 x 0.0045) 0.0135 3) 1 ply printing plate 0.011 4) 2 ply printing plate/soda can wall (0.011 + 0.0045) 0.0155
Checks have been formed on two diameter mandrels; 0.284 (standard .30cal GC shank) and 0.290 (CBE .303 Brit GC shank) and in a 0.316 anvil to best match .32-20 and .303 Brit, the calibres I am working with.
The best results have been achieved with singly ply printing plate of 0.011 at low intensity/velocity loads using the 0.290 mandrel. This produces checks that are a loose fit and all results thus far have shown that snug fitting checks generate groups of a greater size. I can not be sure why this is so however my speculation is the loose fitting checks are consistently coming off in flight and the snug fitting checks are not dropping from the bullet 100% of the time.
The following is a typical group shot at 50m with my .32-20 Martini action suppressed rifle pushing a Lyman 311316 in air cooled wheel weight over 3.8gr of Unique for 1000fps with the 0.011 alum. checks inside diameter 0.290.
As I have not more brass shim and the labour of love to recover material from .22 mag brass is labourious to say the least I have not progressed further in this medium.
COPPER:
I particularly generous forum member sent me some 0.010 copper shim and this arrived from the US yesterday. As all tests thus far with 2 ply checks have been 'average' in results I decided to work with the 10 thou copper in single ply only. Checks were formed in the 0.316 anvil using both the 0.284 and 0.290 mandrels.
Today I shot both checks at 50m in my No4 MkII .303 Brit attached to a CBE 313 215 GC bullet in heat treated WW over 20gr of AR2205/H4227.
This target is the 0.284 snug fit gas check:
Again the loose fitting checks came out on top. The accuracy of the 0.290 ID check is close to on par with commercial Hornady checks and I will be retesting tomorrow weather permitting.
In summary the best results to date have been achieved using 0.011 copper shim in a single ply config. loose fit. Checks are best formed with two blows of the hammer on the mandrel. The first blow is soft to start the shaping and the second blow to form the check and push it free. A single hard blow has a tendency to create lop sided checks.
The following is my set up for forming the checks. Charlie's anvil/mandrel sitting in a recease in a slab off wood held in a vice. When the check is formed it passes through the wood via a 3/8 hole into the can for collection.
Cheers from New Zealand