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New 18" American 30 Barrel


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Yours are nice, too.

The first one in my photo is a 358 MGP I just whipped up with my old 357 Herrett dies from my Contender days.

358 MGP in fireforming stage. Must be trimmed for final case.


Edit: No 35s in your lineup?

Edited by bj139
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358mgp website domain has expired as of 2/3/18.

Maybe demand was too low?


More than likely forget to renew it but your thoughts might well be correct. I have had some thoughts on all these at one time or another with the MGP being the center of them. Just thoughts. I never felt the urge to get out the plastic for various reasons.



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I went to the range today and the first round fired but only 3 out of the 10 rounds fired.

After trying them again several times I got 7 out of the 10 to fire.

I even placed the round under the extractor and chambered it gently but the last 3 would not fire.

There was only a VERY small dent in one of these 3 primers.


Unfired length w 357 case 2.631, 2.630, 2.633 2.631-1.285=1.346 average unfired after chambering


2.649-1.285= 1.364 Largest headspace measurement showed an increase in length from unchambered and unfired of 0.013".

2.637 - 1.285= 1.352

(3) 2.641 - 1.285= 1.356

2.624 - 1.285= 1.339 got shorter, I guess due to chambering

2.631 -1.285 = 1.346


It looks like I should have gone up higher in powder charge weight to blow the cases out fully.


I am not sure what my next step will be.


Moving shoulders back seems much easier than moving them forward.



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Now you have a case or two. Measure distance to rifling using your FIRED case. Fix up some cases that you have formed without moving the shoulder. seat bullet about 0.005 into the lands and fire the case make a couple. The COL will be short because as the case blows forward and sucks up COL. Use a 125 Sierra for the job. It isn't optional about jamming the bullet. Do them single shot dropping them in the chamber and drop the bolt manually. A mag can be used but it is not ideal.


You have a chamber that will require fire forming because of the shoulder height. Once the cases are formed you can reuse those just like a normal sized chamber. I would use H 4198/IMR 4198 or RL #7 for the job.


Did you shoot these for group?



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I had to move to 20 yards to get on paper in spite of bore sighting at 50 yards.

I was adjusting the scope during these shots.

Only 7 rounds fired after about 25 trigger pulls so not much opportunity for groups.


I have AA1680 so I will try 25gr of that with a 125gr TNT seating the bullets to hit the lands.

Edited by bj139
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Ifeel your pain. My method is one shot at 25 yards. No bore sight. I got bit too many times by it. Crank in the dope going for 3/4' low and then on to 100. Fine tune as needed. I use 3/4" red dots for my aiming points. On hard core load work I use a 24 or 32X scope unless it's a hard kicker above a 308.



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I reloaded 7 rounds with 25gr of AA1680 and a TNT 125gr bullet at a COAL of 2.400.

I think the bullet is touching the lands. I will have to single load them. I don't have a forward assist yet so I will bring a small screwdriver if needed.

I pulled the bullet out on the 3 which did not fire yesterday to a COAL of 2.400.

I will shoot them today barring an emergency. Wife.

Edited by bj139
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When I seated to 2.410 and chambered a dummy round in a partially resized case the COAL changed to 2.400 so I seated to that.

I just got back from the range.

On the first cycle, chambered gently 2 out of 10 fired. Another fired on a second try.

I decided to remove the bolt and put the round under the extractor and replace the bolt. Some I had to seat the bolt with a 2x4.

I was able to fire all but 2 which resisted several under extractor attempts.

I knew I was in the lands because one of the rounds did not fire and when I ejected it the bullet was left in the bore.

7 shots on target with 3FTF with one of those the bullet was pulled by the lands.

The shot at the bottom was H335. The others were AA1680.

Why move the shoulder forward on this wildcat? It makes it difficult to produce cases.

Here are a few photos.






Edited by bj139
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After work last night a thought popped into my head. Sometimes when I think about things I just let the ideas rest and I have a great idea later. I know I've read about it before so maybe I am just remembering. With our talk about an American 358 and fireforming I remembered about necking up and then necking down to form a false shoulder.

Late last night, I redid the 10 cases I have been using got an increase in headspace of .017, from new brass, when the cartridge justs fits and the bolt can be closed. I primed all of them then loaded 3 with powder (29gr AA1680) and a bullet an could not decide on touching the lands or fit in magazine. I just checked and AA1680 max load for 7.62x39 is 27gr so these may be too hot. 31gr of H335 is listed as max so I may have to switch powders. I will try to get to the range Monday to shoot. Whenever I get problems like this I have this urge to not let the problem beat me. It is a challenge. You did mention in one of your posts that this is a wildcat and chambers may vary. As long as I can get some cases made and the easier the better, I am happy. I will post some pictures later. I do have multistep shoulders now.segrin.gif

Edited by bj139
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