NEW 7 SHERMAN SHORT TACTICAL (SST)

[SixDemonBag]

Well things are moving along pretty quickly and easily for me. I worked up a ladder test, found 2 nodes and went with the higher node. I loaded up a 5 shot group and got an ES of 11, SD of 4.7, and didn't have to do a thing to the brake or seating depth to get it to group well, see attached, so that will save me a bunch of time and components etc. I'm going to work on getting the rest of my brass cleaned up and sized, then I'll start shooting it at distance to see what happens. Forgive the target, it's what I had. I couldn't be more satisfied with my results.


View attachment 247422

I don't see an attachment. Maybe I am the only one?

 

[archangel485]

I don't see an attachment. Maybe I am the only one?

Interesting, I can see it when I go back and look at my post. In fact even in your post, the portion where you quoted my post there is a link to "view attachment" and when I click that I can see it as well. I'll try sending it to you via PM. If others aren't seeing it and want to, let me know.

 

[SixDemonBag]

I see it now, must have been work computer...

 

[SteelBanger]

Great shooting, and it's great to hear how easy load development went for you! We've pretty well hit the dead of winter so getting out to shoot and break in the rifle hasn't been possible these last few weeks. Shooting in the cold and snow is one thing, but taking the time to clean and break in the barrel in the cold is another thing! lol To pass the time I've been playing with my new Forster Co-Ax press I got this past weekend loading up some .223 and doing a bunch of brass prep. Spring is hopefully right around the corner!

 

[SteelBanger]

@archangel485 have you had the chance to do any more shooting? I couldn't tell you the last time we were above 15 degrees here so I haven't gotten back out yet myself and the long term forecast doesn't put us above freezing until the end of the month ... it's driving me crazy!

 

[archangel485]

I know the feeling, -10 here this morning, been running highs right around zero for about a week now I think. Supposed to stay down there with highs in the negatives for a couple more days then warm up a bit on Monday (of course). But even then highs in the 20s so not exactly awesome shooting conditions. Regardless, I haven't shot it since I posted that target, but primarily due to working in the reloading room, not weather really. I got the remainder of my brass all sized, cleaned and primed, and yesterday I started loading them up. I've got 75 loaded up right now, have 100 more to do over the next few days, then maybe I can sneak out in the evenings during the week this coming week to try some longer shots. I will probably start out with 750yards (just because that's what my range maxes out at), but that should be far enough to get my ballistic model tuned really close. I will let you know how they are grouping when I do that. Later this spring I plan to do some much longer testing, out to 1600.

 

[archangel485]

I did get to shoot at 500 and 750 on Friday. I had to drop my velocity back to get a match so my real velocity is closer to 2900 it seems. I am shooting 180 hybrids, but I am using Hornady 4DOF which does not include custom curves for hybrids, however they do have a curve for the 180 VLD-H (I wish for the target but is what it is). Anyways, from 4DOF the curve and the G7 model are not off by much, pretty much even until 1200 where it's off by a tenth then diverges from there and off by 3 tenths at 1600. Thoughts? Should I stick with the G7 model or go with the custom curve model? I have a feeling neither will work and I'll have to tweak BC in the G7 model, but we'll see, I'm itching to try it out at 1600 to see what happens.

 

[SteelBanger]

Good timing, I was just coming out here with my own update (below). Unfortunately I've never been able to shoot far enough to really have to dial in the BC's. I have gone to strictly using G7's but have only ever played with Hornady's 4DOF, I use the BallisticsARC app for my dope data and have only had to tweak the G7 figure once but that was on the 73gr ELD-M bullets in an AR ... started getting a little off around 500y. I can't remember the guys name who does the custom curves but the G7 he came up with for that 73gr bullet was pretty spot on. Sorry I'm not much help there!

A small update on my 7SST, I still suffer from light primer strikes but think I finally have it narrowed down to a bad trigger, and not the headspace ordeal i detailed above. I spent a good amount of time last night measuring and remeasuring things and the headspace just doesn't make much sense. The only fired case I have (that came from my smith using a different trigger) measures 1.445 to the shoulder and my sized cases are mostly 1.442, so only a 3 thou bump which shouldn't be that big of a deal. A couple sized cases were even 1.443 and at a 2 thou bump those should light up every time without fail. I then sized a case to 1.444 (1 thou bump) primed it and tried to fire it ... barely made a mark on the primer. I talked to my smith for a while tonight and he had me re-prime the fired case (not sized) and try to fire it but it wouldn't go off. A bad trigger is about the only thing that makes sense at this point so he is mailing me a couple different triggers to try out, hopefully will have those this week sometime.

I also have 180 hybrids and 180 VLD-H bullets to try ... once I can finally get this thing to shoot.

 

[archangel485]

I concur, 3 thousandths is not enough to keep firing pin from striking, I've seen cartridges with 10 thousandths that fire fine. Trigger seems by far the more likely problem to me. Or something to do with the trigger/cocking piece interface. That or primer seating like I mentioned before. Have you taken your bolt apart to make sure there's nothing funky with your firing pin and spring?

 

[SteelBanger]

I have pulled the bolt apart a couple times and nothing seems off with it. The main thing that leads me to the trigger is that the rifle fired fine for my smith using my loaded cartridge ... the only different variable was that he used his own trigger. I measured the primer depth on some cases last night and they were around .005 - .007 below the base of the case.

 

[archangel485]

I have pulled the bolt apart a couple times and nothing seems off with it. The main thing that leads me to the trigger is that the rifle fired fine for my smith using my loaded cartridge ... the only different variable was that he used his own trigger. I measured the primer depth on some cases last night and they were around .005 - .007 below the base of the case.

Yeah, well TT are awesome triggers so if it turns out that's the issue then you should be able to get in touch with them and they'll make it right. FWIW I'm running a TT diamond pro-curve on mine, Bighorn Origin action. I just had one more thought come to mind, have you verified the "timing" of the trigger by making sure the cocking piece is getting pulled back far enough when the bolt handle is dropped?

 

[SteelBanger]

A TT pro-curve is one of the triggers my smith is sending me to try, looking forward to that one. At the risk of sounding stupid, how would I check the timing on the trigger?

 

[archangel485]

A TT pro-curve is one of the triggers my smith is sending me to try, looking forward to that one. At the risk of sounding stupid, how would I check the timing on the trigger?

Not stupid at all, I didn't know it was a thing to even look at until just a little while ago, and I've been shooting a long time, haha. Anyways, I used the "stem" end of my calipers (not sure what it's actually called) and measured how far the firing pin indicator was sticking out the back side of the bolt while the bolt handle was lifted. Then I closed the bolt and measured it again. In my case, the indicator was like 10 or 20 thousandths further back when bolt was closed then when the bolt was opened, so it was actually hitting the firing pin harder than necessary. Anyways, I removed that much material from the front side of the cocking piece until the measurement was the same for bolt open and closed. I was just thinking it's possible (though seems fairly unlikely) that your action is actually allowing the firing pin to move forward when the bolt is closed when compared to the bolt open, and if that was the case that would mean the firing pin spring isn't compressed all the way while in the "cocked" position and might not hit the primer hard enough.

I hope my description is good enough to make sense, my apologies for my lack of understanding on all the terms. I can send you pictures later if it's not clear. I bet you can find more info on the forum somewhere too if needed.

 

[SteelBanger]

Thanks, I think that makes sense. The triggers my smith sent out should be here tomorrow so at the very least I'll try to light up a primed case tomorrow night. If these other 2 triggers both touch off the primer then I'll simply go back to TT for a replacement. If the new triggers also fail then I think I'll have to look at the timing piece for sure.