Winchester 244 and erratic ROF in Micro Uzi

[rayjn]

I have 8# of Winchester 244. Loading frontier and berrys 147gr. I am loading at Hodgdon’s recommended max of 3.4gr. COAL 1.145 and kissed with a Lee FCD.

This load runs well in all of my sub guns, cycles well, LRBHO operates. In an MP5 the chrono reads 940fps avg. and Micro Uzi reads 885fps. I have chronographed with the Uzi and Mini Uzi as well and found it to be satisfactory but I am not near my load book to recall the data at the moment.

This load runs well in all but the closed bolt Micro. It runs, however the ROF sounds erratic. Occasionally it fails to fully strip a round, usually with 2-3 rounds remaining in a 25rd star mag loaded to 20-22rds. I believe this to be because of the dual springs of the closed bolt.

My thoughts are to begin working up above the book recommended max load. Looking for advice on how to smooth the Micro out and have it running less erratically.

Shooting this powder under a 115gr load in a FA TEC9 at dusk is producing a large flash, making me wonder if I need a faster powder. It does seem that this sub really prefers tightgroup. Once I finish this 8# off I plan to switch and begin working up new loads.

TLDR; Micro has small feed issue, suspected due to incomplete cycling. All other machine guns ok with this load.


Ray

 

[Slowmo]

It’s not entirely clear to me what you are experiencing, but my fullsize Uzi at times has experienced weird variations in ROF that are sort of like little stutters. It’ll be little sped up double or triples. In an otherwise normal string. I traced that back to the caseheads having swollen oversized. I am sure you have seen what Uzis do to the caseheads. That axial compression causes radial expansion, and it was keeping the rounds from fully seating and causing them to fire a little prematurely. I got a 100rd Shockbottle case gauge that helps me identify the problem children.

 

[rayjn]

It’s not entirely clear to me what you are experiencing, but my fullsize Uzi at times has experienced weird variations in ROF that are sort of like little stutters. It’ll be little sped up double or triples. In an otherwise normal string. I traced that back to the caseheads having swollen oversized. I am sure you have seen what Uzis do to the caseheads. That axial compression causes radial expansion, and it was keeping the rounds from fully seating and causing them to fire a little prematurely. I got a 100rd Shockbottle case gauge that helps me identify the problem children.

I know exactly what you mean. Ever since I have began roll sizing my machine gun fired brass I’ve no longer had that issue.

As far as my initial post, I’ve since loaded 0.3 grains over book max and my issues seem to have resolved.

Ray

 

[Slowmo]

I know exactly what you mean. Ever since I have began roll sizing my machine gun fired brass I’ve no longer had that issue.

As far as my initial post, I’ve since loaded 0.3 grains over book max and my issues seem to have resolved.

Ray

What type of rollsizer do you use? I have the Rollsizer-brand commercial model, and sometimes it still leaves a small lip about 0.030” thick just above the extractor groove. I’ve thought about cutting a plate out of shim stock or sheet metal to make the cases sit slightly higher in the groove to address that lip.

Glad you got to see you got your other issue sorted out with the increased charge weight.