Well guys, my RUM is finally finished and some powder has been burnt. Still in the early stages of load development but I should be able to get this thing shooting 1/2MOA or better (at 250yds anyways). Never meant to build a BR rifle.
The weather here has been extremely warm (34 to 36C) so barrel heat is a big problem. Don't think that H870 likes these temps either. Would get a nice group then a wild flyer. Vel definitely increased through the group. I am guessing these are pressure spikes. 240gr MK molied used throughout.
Vel is only at 3000fps at 98gr of H870. The barrel is 35" long (Bevan King) no taper on a Enfield P14 action. Action converted to cock on opening, speedlock, and tuned single stage trigger. Homemade thumbhole BR style stock with 15lbs of detachable ballast. Recoil is quite mild at a total weight of 40lbs. Scope is a 10X super sniper. Have enough elevation to make it out to 2000yds.
Shot at 1km at our 9X9 gong. Lots of close calls and a few hits. Didn't put up wind flag so can blame "some" misses on that. My guess is that the heat was not helping with the grouping of the rifle. More load development and hopefully cooler weather needed.
Those 240grMK are really hitting hard. Where other cals (165gr 30cal, 168gr MK) are just denting the steel, the 240 almost shot through.
After 1 year, the beast is done and with a little effort, should shoot at its potential (goal was 1/2 MOA at shorter ranges and MOA at longer). Will probably get my hands on some WC 872 and IMR 5010 surplus powder to try. There is still lots of room in the case and with a 35" barrel, might like more powder.
Darryl, if you read this would like your thoughts on 5010. I know you use 872 a lot but would want to know if the 5010 shoots well. There is lots of room in that case and I wonder if a slower bulkier powder could help with vel spreads and reduce LR group size.
So my quest to build good shooting, accurate, and economical cannons continue. The cost of this project was reduced greatly by the amount of work I could do myself (stock work, scope shimming, etc). For those looking at an entry level way of getting into LR heavy hitters, this may be a way you can go. The RUM and Tomahawk are definitely the bang for the buck when launching 240gr MK.
I hope to get some pictures of the finished rifle posted in the coming weeks. Let me know if you have any further questions or comments.
Congradulations Jerry , iam on a quest to do the same thing (build my own guns), have bought a lathe and am in the process of getting it hooked up . Will begin with a mauser in a small caliber and work my way up to the bigger ones. Keep us posted and good luck!!! ebb
Boyd, How much Retumbo are you using? How much space is left in the case? I seat my 240's so that the base of the bullet is above the base of the shoulder.
I like the results you are getting. However, I really like the price of the surplus powders with this rather hungry case.
ebb, good luck with building your own rifles. Midway has some good sales on now for different reamers, especially the wildcats that we love so much. I had the barrel install done by a smith. No lathe yet. I figure for the cost of a lathe, I can get a lot of barrels installed. I just focus on the stocks, bedding, scope and trigger work.
Boyd, I would be very interested in how much Retumbo you are using. I ran out of Grizz, and Ramshot will not release any more. 50BMG is giving me to much velocity deviation. I was very happy with my Grizz load and the 240 MK at 3008 to 3030 depending on temp. Any help would be greatly appreciated. Otherwise I will just do what I have done in the past and take an educated guess. I would think that halfway between my RL25 load and 50BMG load would be a starting place, but I will review a few numbers first.
Working to improve hit probability.
I was using 85gr of Retumbo with the 240 in a 30" ten twist barrel....NOTE...THIS WAS SAFE IN MY GUN [img]images/icons/grin.gif[/img] .....There will be room left in the case.Mine was set at 3.700 C.O.L....Work up to that load.
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