My new coyote Whacker .257 Bobcat

B

BIGGDAWG

New member
Thought i would share my latest build the .257 Bobcat. it is my first crack at designing and building my own wildcat.









Intro: The .257 Bobcat is based on the 270AR made by AR15Performance. the 270AR is a 6.5x47 lapua shortened .120 and necked up to .277. It uses AR15performace's 800 series bolt and extension so it can run at 60,000 psi.

I wanted a flat shooting quarter bore so i necked down my 270AR cases to .257

My performance goals are 85gn bullets 3300-3400, 100 grain bullets at 3200 fps and the 115 bergers at 3000 fps that will make it a very flat shooter

.257 Bobcat quickload predicted velocities with 24” barrel

100 sierra pro hunter sp 3050-3200 fps
100 sierra game king bt 3100-3250 fps
100 nosler partition 3050-3200 fps
100 nosler ballistic tip 3100-3250 fps
100 barnes ttsx 3050-3150 fps
110 nosler accubond 2850-3000 fps
115 berger hunting vld 2825-2950 fps
115 nosler partition 2850-2975 fps
117 sierra pro hunter sp 2800-2950 fps
117 hornady sst 2800-2925 fps
117 hornady sp 2850-2975 fps
120 nosler partition 2750-2875 fps
120 hornady interlock sp 2800-2900 fps
120 speer grand slam 2800-2900 fps




here are some dummy rounds for mock up



100gn nosler ballistic tip, sierra 100gn sp bt, 85gn nosler ballistic tip


I have been testing the rifle now for a month and a half and it has reach all the performance goals i had set for it.

here is a little of the data i have collected.

here are the pressure traces and primers, the 8208 didn't lock back with any of the loads with any of the bullets. cfe locked back and cycled fine. gas port seems a little small -- better to start too small.

















and the 100 nbt with cfe





here is velocity from the bergers. neither one is at max but again cfe cycled the action and locked back with 1 fail to feed and the h4895 wouldn't pick up rounds or lock back.I opened up the gas port from .082-.086 and now the guy is cycling better than ever. some slight feed issues but have isolated the problem to the chamfer/blend on the chamber opening -- was the first ar barrel my smith had made. going to take it off and have it messaged a little.




i tested leverevolution to compare to cfe and was pleasantly surprized it pushes the 100 speer spbt faster than cfe here is the chrono data i stopped with 2 shots left because i got a faint ejector swipe.



 
Ok this is cool I been waiting for someone to put this round in an ar15. I want this but in a 6x47 and some 69gr bergers. U might wanna invest in a brass catch for those babies:)
 
yes i have brass catchers, a buck each for the brass then form, trim neck turn and ream. but i have some brass with well over 10 fires still going strong. i anneal every 3-4 fires.

working on a 7mm version and then i may do a 6mm to replace my 6mm grendel.
 
.257 Bobcat
Forming procedure:
start with the modified bushing die with no guts in it.
lube the 6.5x47 lapua cases and run through the press pushing the shoulder back .120
neck ream and trim with forster lathe using the 257 forster reamer in the lathe so you ream and trim at the same time trim to 1.656 at this time, final trim length is 1.646 which will the the last step after final sizing.
now with the trimmed and reamed case you are ready to neck turn. install the forster neck turner on the lathe and install the 6.5 rcbs neck reaming pilot. now set the lathe to just touch at the case mouth and turn to the neck shoulder union. neck should come out at .013 give or take.
now install a 279 bushing in the die with a 257 expander and run the cases through the die. trim to 1.646, now chamfer and anneal the brass, clean and they are load ready.
 
Looks like an awesome round man!

Are you by chance the same BIGGDAWG that has shared a lot of info about SS tumblers over on Brian Enos?
 
Originally Posted By: steve garrettwhat's the case compacity in grains of water on this case??

43.4 grains on my fired lapua cases
 
Originally Posted By: blopez50Looks like an awesome round man!

Are you by chance the same BIGGDAWG that has shared a lot of info about SS tumblers over on Brian Enos?

Thanks

yep the one and only. I still build them too.
 
Originally Posted By: BIGGDAWGOriginally Posted By: blopez50Looks like an awesome round man!

Are you by chance the same BIGGDAWG that has shared a lot of info about SS tumblers over on Brian Enos?

Thanks

yep the one and only. I still build them too.

Don't want to threadjack you here but just wanted to say thanks for some awesome ideas on the tumblers. I spent a lot of time over on BE lookin at different stuff when I built mine:
http://www.predatormastersforums.com/for...360#Post2639360
 
Originally Posted By: BIGGDAWGOriginally Posted By: steve garrettwhat's the case compacity in grains of water on this case??

43.4 grains on my fired lapua cases

that is about the same as the 22-250 case. a big increase without having to go to a WSSM. I think it looks cool. I wish a real viable round like this for the ar 15 would be developed commercially. There are alot of other AR wildcat's out there. the problem is If you load up the 223 as hard as it will run. The other wildcats like the new 6.8 are only running maybe 150 fps faster when loaded to equal pressures. I think this bobcat would be cool in .22 and 6mm variants.
 
Originally Posted By: blopez50
Don't want to threadjack you here but just wanted to say thanks for some awesome ideas on the tumblers. I spent a lot of time over on BE lookin at different stuff when I built mine:
http://www.predatormastersforums.com/for...360#Post2639360


That turned out great. I think the thread there and over on arfcom really helped a lot of guys. glad it did. i learn a lot on the forums and i like to think i help as much as i get helped.
 
Originally Posted By: steve garrettOriginally Posted By: BIGGDAWGOriginally Posted By: steve garrettwhat's the case compacity in grains of water on this case??

43.4 grains on my fired lapua cases

that is about the same as the 22-250 case. a big increase without having to go to a WSSM. I think it looks cool. I wish a real viable round like this for the ar 15 would be developed commercially. There are alot of other AR wildcat's out there. the problem is If you load up the 223 as hard as it will run. The other wildcats like the new 6.8 are only running maybe 150 fps faster when loaded to equal pressures. I think this bobcat would be cool in .22 and 6mm variants.


I have a 6mm drawn up when i recover from this one and the 7mm it will be next on my list.
 
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