Review of the Load process thus far:
Firearm:
- KAC 18” LPR Mod 2 upper with a Krieger barrel (1:7 twist)
- Equipped with an AAC M4-2000 suppressor and Ecco conversion, utilizing the Grffin taper mount system
- Rifle buffer system (Tubb spring on order)
- LaRue MBT2S trigger
- NF NX8 2.5-20x50 Tremor 3 scope
- Atlas bipod featuring an Area419 arca attachment and rail
- Utilizing a heavy fill rear bag for stability
- Feeding from a 20-round ASC magazine for long loading
Reload Details:
- Utilizing mixed range brass, which is full-length resized and trimmed using a Dillon RT1200 to a length of 1.7590"
- Cases are chamfered, deburred, and processed with a Dillon superswager tool
- Dry tumbling is performed for cleaning
- CCI450 primers are used
- Employing Sierra 77gr SMK bullets with cannalures, specifically MidwayUSA blems
- Shooters World Precision Rifle powder is chosen for the loads
- Cartridges are loaded to a COAL of approximately 2.290"
Loading Process:
- Dillon 550b is used for reloading
- Brass is run through a Redding full-length die, backed out to merely act as a neck die as its already been FL resized and trimmed
- The Redding die serves to clean media from the flash hole, while the button is left on to slightly open and round the case mouth
- The Dillon trim die may exhibit excessive neck tension and potential impact on the bullet jacket
- Dillon powder dropper is utilized without modifications, throws are consistent with SWP
- Seating is performed with a Redding die, and a light crimp is applied using a Lee die, barely touching the mouth
Load Testing Results:
- Commenced with a starting charge of 22.5gr and increased in increments of 0.5gr up to 25.0gr
- The following results were obtained for the combination of Shooters World Precision Rifle powder and 77gr Sierra MatchKing blems:
22.5gr
- High: 2444
- Low: 2419
- Average: 2428 (still locked back on the mag)
- Standard Deviation: 10.1
- Group size: 1.3moa (0.62moa without cold bore)
23.0gr
- High: 2495 (last shot)
- Low: 2426
- Average: 2468
- Standard Deviation: 29.2
- Group size: 0.53moa
23.5gr
- High: 2556
- Low: 2495
- Average: 2529
- Standard Deviation: 24.4
- Group size: 0.83moa
24.0gr
- High: 2631
- Low: 2532
- Average: 2574
- Standard Deviation: 36.5
- Group size: 0.72moa
24.5gr
- High: 2657
- Low: 2601
- Average: 2638
- Standard Deviation: 23.4
- Group size: 0.51moa (0.7moa second group, chrono off)
25.0gr
- High: 2740
- Low: 2677
- Average: 2717 (21, 25, 25)
- Standard Deviation: 23.8
- Group size: 0.88moa
25.0gr #2
- High: 2751
- Low: 2675
- Average: 2713
- Standard Deviation: 29
- Group size: 0.57moa
Overall Assessment:
- The groups obtained are satisfying, but the standard deviations could be improved, being they were 10-36 SD for the various groups
- At 25.0gr, the velocity was good for the shooter, with the primers showing slight signs of flattening but not at the edges
- No swipes or ejector marks were observed
- Longer loading may have contributed positively to controlling pressure
- Future testing with charges in .2 increments from 24.7gr - 25.5gr is planned, with potential seating depth adjustments, although unlikely
- Regarding the MidwayUSA blems, they have exhibited consistent weight and dimensions, with minor variations in the cannelure placement across different bags
- No significant differences have been noted during testing, although the obvious blems were excluded from the load development
- As a personal consideration, the use of HBN coating on bullets has previously shown lower velocity, lower pressure, and reduced standard deviations
- In upcoming sessions, the shooter plans to sort brass by head stamps, clean primer pockets and flash holes, and apply HBN coating to the bullets for potential benefits
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