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Post by HMC710 on Oct 20, 2011 8:55:19 GMT -5
Have been wanting a 7mm AR for a while and looking at the most economical way to get it done. I have built a couple 7 TCU's but both of them were bolt actions to accommodate the longer bullets. Even with the light 7mm bullets, seating depth is excessively deep. I thought about using a shortened 7 TCU, then the thought of using the .221 Fireball case as the parent got my interest back up. Using Quick Design to modify the case and importing that into Quick Load, it predicts 2250 fps with a 120 gr bullet and 19.8 gr of 4227. Let's give it a try... L_R: 300 Fireball, 7mm Fireball (150gr bullet), formed .223 case, .223 The neck of a 7 TCU is .268" and the .221 is .202". I drew up the .221 neck and then overlaid the 7mm expansion to see where it would naturally fall on the shoulder and came up with a .250" neck. This is also the seating depth of the Hornady 120gr SSP bullet so that's what I went with. A set of donor TCU dies were cut down and the brass was formed. I used some 1.400" .223 brass as all my Fireball brass was already "Blackened". The plan is to short chamber a barrel using my stock 7 TCU reamer and see how the brass fits. Stay tuned...
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Post by HMC710 on Oct 22, 2011 7:21:43 GMT -5
Turned and chambered the barrel yesterday and hope to test out this afternoon. Throat might be a bit short for the 150gr pic above by about .050" and need to see where neck tensions are with the Fireball and .223 brass.
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Post by HMC710 on Oct 24, 2011 6:20:53 GMT -5
;D Another day at the shooting bench! Loaded up a couple of the 7mm Fireballs using once fired LC brass cut down to 1.400" One pass through the modified dies, filled with 15 gr of 4227, and a Speer 145gr HPBT. QL predicts just under 1800 fps @ 38ksi with this load. I started my OAL at 2.100" and worked out from there. I put a pistol gas system on based on my notes from the 300 Fireball data. If I wanted to go sub, it had to be pistol length. My gut said Carbine length all the way, but I went with the data. Needless to say, there's plenty of gas in this set up. Function was 100% and the action locked back with authority. I fired two rounds, inspected the brass, and cleaned the barrel. Brass looked good with this load with the shoulders nicely defined. From there I started to seat the 145gr bullets out .025" at a time to see where it wouldn't chamber any more. The dummy 150 gr round at 2.200 I mocked up would not chamber by about .050" so that's why I started short. With the 145's I worked up to 2.195" and gave the barrel a rest. After the first two rounds I put in my 9mm buffer to tone things down a bit. This was a pure function/break in test and did not do any chrono or target work. Next move is to get some lighter bullets for high end testing and work up a sub load with all those 162gr bullets I've got left over from my silhouette days. In hindsight, with the limit of a real heavy bullet, compared to the 300's, I should have went with my gut and did a carbine gas system. But then I would have wondered what a sub would do and would have done a pistol length anyway... The 7mm Fireball is alive and looking forward to see what it will do on the high and low end of the spectrum. The conversion was cheap and easy with minimal mods to existing components. We'll get some rounds on this set up and see what it will do.
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Post by greywuuf on Oct 24, 2011 10:24:38 GMT -5
is it throated long enough for 175's ? or possibly the ultra slick Berger 190's ?
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Post by HMC710 on Oct 24, 2011 17:09:09 GMT -5
I don't know yet. Being a stock TCU die, I would seat my 162's way out there. During chambering I was about .050" shorter on my dummy round with a 150 gr @ 2.200" so I wondered. Testing has the 145s out to 2.195" with some room to go so we'll find out. Just ordered some lighter 7mm and 30 cal's...
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Post by greywuuf on Oct 24, 2011 19:06:03 GMT -5
to my way of thinking the 7mm has always been "magic" for me because of the long slim bullets. ( A.K.A 7x57 mauser ) the 150's out of a 7mm mag just give up mass to anything the 300 Win Mag can do. I realy like your 35 remskie but I dont see a 7mm unless you are chasing BC with the heavy bullets. I dunno seems like the 223 the 30 wtf ever and the 35 have it covered ;-). not saying there is anything wrong with " because I can " I just have not grasped your goal yet I guess. What weight do you want it to shoot well ? is this another deer gun ? a poor mans 6.5 grendle ? a long range chuck gun ? I see it doing any of those things depending on the throat, twist and loading. So where are you headed ?
Dan
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Post by HMC710 on Oct 25, 2011 6:36:53 GMT -5
Goal? Build and shoot guns? All valid points. The 7 TCU has moderate power and designed for the high BC bullets. I can load the <120gr bullets in the TCU and they fit in an AR mag so the 7 Fireball is probably not going to reach those levels. (But I have to find out) That leaves the heavy sub loads. My brl is a 9.5:1, I've got a pile of 162 gr'ers, and MI now allows supperssors. Have you priced 240 SMK's lately?
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Post by greywuuf on Oct 25, 2011 12:02:39 GMT -5
Have I priced bullets at all lately?. Why do you think I just spent nearly 300 bucks on bullet molds.
Sorry about that last post. I have had more random idea's concerning guns and calibers than most so I know better than to question any one else's motives ( .348 winchester cut back to inch and a half and necked down to .223? I have a reamer, never used)
Once a buddy of mine had a contender in 300 whisper and I had one in .256 win mag...... Looking at the two I thought a 7mm version would be awesome...... Never got around to doing it. I love 7mm. So most of my hunting with a 7x57.
But....... For subs. Bullet weight rules. To the point I want to jump over the 338 spectre and do a cross breed using your work with the 35 REM ( the 300 grain .338 smk's are not cheap either) Crap I am rambling........ Anyway I am always interested in 7mm. Watching this one with interest.
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Post by HMC710 on Oct 25, 2011 16:55:48 GMT -5
Got a .338 on the bench. 1st reamer didn't harden that well so will try it again when I stop having fun with the 35. + just found a source of wheel wgts
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Post by greywuuf on Oct 25, 2011 17:39:33 GMT -5
Better make two just in case this time. If the both turn out you could sell me one ;p
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Post by HMC710 on Oct 26, 2011 6:23:32 GMT -5
Usually do - depending on blank size Got .338 and .416 blanks and did some mock up cases a couple yrs ago now , were going to be my first conversions. After talking w/some friends, twist rates are way too slow for any sub work, + the fact I have to do reamers & dies. Have been relegated to spare time projects.
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Post by greywuuf on Oct 26, 2011 10:04:08 GMT -5
.338 Spectre die sets are supposed to be available from hornady. twist that has worked for sub work is reported to be 1 in 7.5" Oh please oh PLEASE do the reamer, i realy want one of these. have some brass and stuff been waiting on this project.
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Post by HMC710 on Oct 26, 2011 11:06:33 GMT -5
Spectre? Did I say Spectre? (Hence the dies and reamer......)
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Post by greywuuf on Oct 26, 2011 11:59:13 GMT -5
Well poop then, if you are going to be that way.....
what the heck am i gonna do with this 10mm mag brass i have?
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Post by HMC710 on Oct 27, 2011 7:01:18 GMT -5
Thought you were doing a 357Sig Mag?
anyway........
New bullets arrived yesterday and cutting brass today to get them formed up. Bullets are Speer 115gr HP and 130gr Flat Nose designed for 30-30 velocities. I'm using LC once fired brass and loading to .223 pressures of 55ksi, not 5.56 pressures. We'll see what the brass has to say.
And as long as I am cutting brass, I was going to do a few at 1.524", but QL did not show any ( just had to stop and unload 5000 lbs of steel....) improvement in performance so we'll leave that one to the 7 ARK guy. I might take a hint from GW tho and do some at 1.29", 7 Sub? 7 Carbine?
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