This project started over a year ago and there have been a couple "complications, setbacks and minor inconveniences" along the way, but it's pretty much done and now it's time for the fun part. The initial cartridge design was based off of the 375 Ruger case but after the reamer broke while chambering the barrel, it was necessary to "adapt". What I ended up with essentially a 27 Nosler that's been lengthened by .130" so that it has the base to shoulder measurement of a 338 RUM case but the shoulder diameter and 35° shoulder angle of the 27 Nosler. The idea was to allow the use of ADG's 338 RUM brass (or any other RUM brass properly modified) but still be able to use 27 Nosler dies to neck size and bump the shoulder while waiting for custom dies to be made. Forming brass only requires necking a 338 RUM case down to 270, I used 300 SAUM and 270 WSM dies then annealed the brass before sizing it in a 27 Nosler die until the bolt closed on each case with a slight crush fit. The shoulder diameter and angle are completely formed after the first firing. Here's a 338 RUM case next to a once fired 27 Boondoggle case.
The specs on the build right now:
- ARC Nucleus action
- 28" Broughton 1-8.5" twist heavy varmint barrel
- 25" K&P 1-7" twist #5 heavy sporter
- Timney CE 2.5# trigger
- Stocky's VG2 stock w/Wyatt's bottom metal
The final specs on the build will still change as I decide what scope/trigger/stock I want. I don't hate the VG2 stock that it's in right now but the gun won't stay in there for long. I'm trying to find a sporter style stock that I like for the 25" barrel as well.
Here's a picture with a once fired 27 Boondoggle case next to some other cases for comparison. I couldn't find any 270 Weatherby or 270 WSM brass in my pile so I used a 300 WSM and 7mm Weatherby for comparison since they're both the same basic dimensions as their 270 counterparts.
270 Win, 300 WSM, 7mm Rem Mag, 7mm Weatherby, 27 Boondoggle
These are the expected performance numbers from the 28" barrel. The 25" barrel will likely be 75-100 fps slower.
130gr: 3600 fps
140gr: 3500 fps
150gr: 3400 fps
170gr: 3200 fps
Here are the velocity results from today's testing. This was one shot at each powder charge while looking for max pressure.
Temp: 38°
Bullet: 145gr Hornady ELDx
OAL: 3.530"
Barrel: 28" Broughton 1-8.5"
Powder: Retumbo
Primer: Fed 215
Brass: ADG 338 RUM
90.0gr: 3489 fps
91.0gr: 3489 fps
92.0gr: 3541 fps
93.0gr: 3610 fps
94.0gr: 3626 fps
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Temp: 38°
Bullet: 145gr Hornady ELDx
OAL: 3.530"
Barrel: 28" Broughton 1-8.5"
Powder: IMR 7828
Primer: Fed 215
Brass: ADG 338 RUM
80.0gr: 3318 fps
81.0gr: 3337 fps
82.0gr: 3378 fps
83.0gr: 3411 fps
84.0gr: 3491 fps
85.0gr: 3484 fps
86.0gr: 3536 fps
87.0gr: 3551 fps
88.0gr: 3616 fps
The flat spots you see in the velocity in both the Retumbo (between 90 and 91gr) and IMR 7828 data (between 84 and 85gr) correspond with shots fired from a clean barrel. The barrel was cleaned after the 84.0gr and 88.0gr IMR 7828 charges and then the 90.0gr charge of Retumbo was fired.
I stopped shooting with both powders once I started to feel resistance on the primary extraction when opening the bolt. The 88.0gr charge of IMR 7828 would be a workable max charge. The 93.0gr charge of Retumbo would be a working max and I consider the 94.0gr charge of Retumbo too hot. The velocities I got are consistently 100 fps faster than what Quickload predicted, but the pressures seem to track pretty close. Based on this I feel pretty good about trusting the Quickload predictions.
From a function standpoint, everything worked great. All rounds were fed out of a 300 Win Mag AICS pattern magazine. The more I use the ARC Nucleus action, the more I like it. Feeding is incredibly smooth and ejection is perfect allowing me to either pull the case out of the action by hand or I can cycle the bolt fast and launch the brass 3 feet away.
